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Document No.: 412D 198
CONDITION ASSESSMENT
AND
PRESERVATION PLANNING
PAW PAW TUNNEL
C & O CANAL NHP
January 2004
QUINN EVANS I ARCHITECTS
Washington, DC
McMULLAN & ASSOCIATES STRUCTURAL ENGINEERS
Vienna, VA
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
TABLE OF CONTENTS
Page No.
Title
1.1 - 1.2
CHAPTER 1: INTRODUCTION
Study Purpose
Study Team
1.3
Figure
2.1 - 2.11
CHAPTER 2: BACKGROUND INFORMATION
Brief History of Construction
History: 1850 to 1924
Recent History: Ca. 1956
Recent History: 1960's
Recent History: 1970's to Present
1997 Photographic Documentation by NPS
2002 Survey Monuments
2.12 - 2.19
Figures
3.1 - 3.10
CHAPTER 3: EXISTING CONDITIONS SUMMARY
DESCRIPTION
Field Survey Methods
Test Pit #1
Test Pit #2
General Findings
Vault
Towpath, Railing and East Wall
Prism Wall - East Side
Prism Wall - West Side
Portals
Mountain Top
3.11 - 3.23
Figures
3.24 - 3.25
Paw Paw Tunnel Survey Form
4.1 - 4.5
CHAPTER 4: STRUCTURAL ISSUES
Towpath Railing
Prism Wall - East (below towpath)
Vault
Final: Jan 2004
TOC -1
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & 0 CANAL NHP
TABLE OF CONTENTS
4.6 - 4.7
Figures
4.8 - 4.9
Structural Calculations
5.1 - 5.6
CHAPTER 5: LONG TERM MONITORING
PROGRAM
Goals
Expand Survey Markers
Periodic Inspection Protocol
Mountain Top - Drainage Issues
Future Research and Investigation
5.7
Figure
6.1 - 6.6
CHAPTER 6: PROBLEMS REQUIRING
IMMEDIATE SOLUTIONS, COSTS
Purpose
Cost Estimate
Cross Timbers, Posts
Selected Brick Liner Repairs
Selected Prism Wall Repairs
6.8 - 6.9
Figures
7.1 - 7.4
CHAPTER 7: FIELD SURVEY DOCUMENTATION
Survey Methodology
Survey Keynotes
Field Survey Documentation Forms (278 sheets)
Biblio 1 - Biblio 5
BIBLIOGRAPHY
Prepared by Dr. Robert Kapsch
Appendix 1 - Appendix 5
APPENDIX: Determining Shaft Locations
Prepared by the NPS: 8/27/03
Back Sleeve
DRAWING SHEET: Current Dampness Condition
and Vertical Shafts Data
Prepared by QUINN EVANS | ARCHITECTS
Final: Jan 2004
TOC -2
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 1:
INTRODUCTION
Study Purpose
This report is the result of a consultation by QUINN
EVANS I ARCHITECTS and McMULLAN &
ASSOCIATES, STRUCTURAL ENGINEERS to survey
the condition of the Paw Paw Tunnel and recommend
corrective actions. The tunnel is an important historic
feature of the Chesapeake & Ohio Canal National
Historical Park.
In the A/E scope of work, the National Park Service (NPS)
provided the following five specific objectives for this
project:
1. "To develop a repair/preservation document that would
assist Park managers in specifying work needing to be
done in the Paw Paw tunnel.
2. To assist National Park Service and contractor
employees to orient themselves inside the 3100 foot
long tunnel.
3. To develop a document that would provide Park
managers with specific information on existing
conditions within the tunnel.
4. To develop a long range plan for monitoring conditions
within the tunnel and to recommend special features,
such as monitoring hatches, that would facilitate
inspection.
5. To identify problems which need to be remedied
immediately, to identify conceptual design solutions for
those problems and to provide a Class C cost estimate
(i.e. conceptual for those identified problems)."
These are addressed in Chapters 2 through 6 that follow.
In Chapter 7 is found the field survey documentation for
the tunnel elements.
Final: Jan / 2004
Page 1.1
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 1: INTRODUCTION
Study Team
The consulting team is lead by QUINN EVANS
ARCHITECTS. Baird M. Smith, AIA is the project
director and senior historical architect. Mr. Smith is the
primary author of this report. James Thompson, historical
architect, assisted in the field survey work and evaluation
of the data. McMULLAN & ASSOCIATES provided the
structural engineering analysis of the conditions and
participated in the field survey effort. Denis McMullan,
PE, President was the senior structural investigator,
assisted by Doug Bond, PE. The structural analysis is
presented in Chapter 4.
Many NPS personnel assisted at various points with this
effort as follows:
National Park Service, National Capital Region
Dr. Robert Kapsch, Special Assistant to Deputy Director
National Park Service, C & O Canal NHP
Douglas D. Faris, Superintendent
Kevin Brandt, Assistant Superintendent
Robert Hartman, Chief of Maintenance
Mike Seibert, Exhibit Specialist
Glen Gossert, Paw Paw District Maintenance Supervisor
Project Site
The Paw Paw Tunnel is accessible by automobile from
Maryland State Route 51, approximately 20 miles south of
Cumberland, MD. The town of Paw Paw, West Virginia
is less than 1 mile south. Lock 67 of the C & O Canal is
upstream while locks 66 to 62 are immediately
downstream from the tunnel. The 3100 foot long tunnel
runs more or less north and south, with the south portal
being upstream (see Figure 1.1). The south portal is
nearest the visitor parking area and is the most common
entry point. The towpath is open year around and many
visitors pass through the tunnel each year on foot or on
bicycles.
Final: Jan / 2004
Page 1.2
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 1: INTRODUCTION
Hollow
BALTTE
TIMORE
Cherry Orchard
Cam
Gross
BM
Hollow
524
OIHO
CANAL
R
Hollo
BM
Tunn
528
ALLEGA
961
North Portal
908
Tunnel Course
ROAD
BM
JUNNEL
946
South Portal
ROAD
AND
(ABANDONED)
BM
548
end
Maryland State
Gaging
Route 51
RIVER
819
un
Paw Paw
(BM 572)
Figure 1.1
Regional topographic map showing the location of the Paw
Paw Tunnel (see arrow). At this location, the Potomac
River is flowing in a northerly direction, toward the top of
this map.
Final: Jan / 2004
Page 1.3
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2:
BACKGROUND INFORMATION
Brief History of
There are many secondary articles about the construction
Construction
of the Chesapeake & Ohio Canal in general, and several
about the Paw Paw tunnel. These draw from a very large
quantity of original documents that include daily
construction correspondence and many reports to the Canal
Company and investors. These documents are found in the
National Archives in various record groups. Dr. Robert
Kapsch, National Park Service, has spent time researching
the canal and has made file copies of selected documents.
The following is not intended to be a thorough, or even
summary, history of construction. We try here to record
the key historical data that has a bearing on the decisions
that will need to be made regarding preservation and repair
of the tunnel elements.
The tunnel was begun by the Chesapeake and Ohio Canal
Company in 1836 to avoid a longer route along the
Potomac River that would traverse a double loop. The
principal design engineer was Ellwood Morris. The tunnel
would not be completed until 1850 and, upon completion,
permitted the Chesapeake and Ohio Canal to open
operations between Cumberland, Maryland and
Georgetown, DC. Construction of the tunnel not only
involved the excavation of the tunnel itself, over 3100 feet,
but also deep cuts at both ends, 200 feet at the Southern
(upstream) end and 890 feet at the Northern end
(downstream - also known as Anthony's, or alternatively
Athey's Hollow). The tunnel excavation was
approximately 27 feet wide and 26 feet high, with a
vaulted ceiling.
Excavation:
Excavation proceeded from both North and South portals
and from vertical shafts driven from above. A total of four
vertical shafts were driven down from ravines located
above the line of the tunnel. These vertical shafts were
Final: Jan / 2004
Page 2.1
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
labeled A, B, C and D in engineer Morris' drawings. They
provided both additional access so that the tunnel
excavation could be accelerated, as well as fresh air
ventilation. The shafts were eight (8) feet in diameter and
paired for ventilation. The first pair of shafts was located
370 feet inside the North (downstream) portal and the
second pair was located at 900 feet from the portal. An
1839 article in the Journal of the Franklin Institute
(pages 24-27) documents the status of work to that point in
time and provides critical information about the approach
to the excavation. When written, the excavation was about
15% complete. Figures 1, 2 and 3 from that article are
very important to this project (see Figure 2.1). These
provide critical design dimensions and a cross section of
the proposed tunnel design, including the location for the
vertical shafts. The article describes the excavation
method. In the first excavation, the top half (i.e.,
hemisphere of the vault shape) was taken out. A
temporary railroad bed was then laid along one side to
accommodate removal of the spoils. Once this excavation
had progressed, a second excavation followed behind to
take out the lower half of the tunnel section. A second
temporary railroad bed was laid in the floor of the tunnel.
From figure 2 of this article, the final geometry of the
tunnel section is illustrated. Shown in these diagrams is a
wooden towpath assembly along the side of the tunnel.
Since the current towpath has a brick wall and there is no
timber of this sort now present, we do not believe the
timber towpath was actually constructed. We know from
records that the excavation proved difficult and time
consuming, so we speculate that the towpath was
constructed on top of a rock shelf that was purposely left
unexcavated.
Proper alignment of the tunnel excavation began with six
survey alignment stones, located on top of the mountain
along the line of the canal. Chief engineer C.B. Fisk is
credited with tunnel survey and layout. Most of these
alignment stones still exist.
Brick Tunnel Liner:
According to Dr. Kapsch, the documents reviewed to date
do not provide a clear record of the placement of the brick
Final: Jan / 2004
Page 2.2
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
tunnel liner. A tunnel liner was envisioned from the
beginning. In the canal company's Ninth Annual Report
(1837), the company reported,
"The material through which the excavation is to be made
consists of blue slate, in elliptical strata, with very slight,
if any, admixture of earth or other substance.
It is
believed that no danger from caving in will attend the
operations on this work, as the stone lies in strata
representing the segment of a circle and forming in some
degree a natural arch."
Although the slate was resistant to cave-ins, it was also
extremely friable and crumbled when exposed to air.
Engineer Ellwood Morris writes of this problem in his
article on the Paw Paw Tunnel for Journal of the Franklin
Institute, (1839), page 27,
"The material through which this work is carried, is of a
consistency, in general, quite equal to sustaining itself and
carrying all the weight above it; yet in all probability from
its slaty nature, it would, if exposed and unprotected, yield
in the course of time to the destructive action of
atmospheric changes. It is therefore contemplated to
protect the interior by a lining of brick in the arch form,
either one or two bricks in thickness.
The brick liner was apparently constructed in two separate
phases. In the first, the vertical wall was brought up from
the canal bottom to the line of the spring point of the vault
ceiling. This lower portion of the brick wall was laid using
a " English Bond," that is, alternating courses of headers
and stretchers. The number of wythes, or thickness, of this
wall is not known. The wall is vertical.
From the spring line up, the brick ceiling was placed after
wooden "centering" was erected. There remain "putlog"
holes at regular points along the spring line where this
"centering" was anchored to the lower brick wall (see
Figure 2.2) The brick of the ceiling arch was laid in a
continuous running bond. There are no header bricks
visible in this work. Dr. Kapsch has also found reference
to filling the cavity between the liner and the rock
excavation with "packing." Whether this happened at all,
and/or what the "packing" consists of, is not known.
Final: Jan / 2004
Page 2.3
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
Of the many documents that were reviewed by Dr. Kapsch,
there are a series of drawings by Ellwood Morris, perhaps
completed in 1840, that are cross sections (profiles) of the
tunnel (see Figure 2.3). They are consecutively numbered,
beginning at 3 at the South end, and continuing to number
51 at the North. The spacing is not uniform. These
profiles appear to record the extent of excavation
completed at the time of the drawing. We believe these are
a form of measurement that may have been used to
determine payments to the contractor. It is clear from
these sections that there could be a considerable cavity
between the brick liner and the excavation. Figure 2.3 was
included here as it illustrates one of these extreme
conditions.
The tunnel was terminated with portals, constructed of cut
stone, at both the North and South ends (see Figure 2.4).
Water infiltration has been a problem since construction.
In 1838, for example, H.W. Dungin reported to Assistant
Engineer Ellwood Morris that:
"We have struck a vein of water in (Vertical Construction)
Shaft D, with a drill hole which drove the workmen out and
filled the Shaft to the depth of eight feet & (Contractor)
Montgomery tells me one bucket plied 24 hours with only
such interruption as the blasting in the shaft occasioned has
failed to reduce it more than two feet..." (Letter, H.W.
Dungin to Assistant Engineer Ellwood Morris, May 26,
1838. National Archives, Record Group 79, Entry 214.)
Towpath and Railing:
Although there have been repairs over time, the current
configuration of the towpath retains historic integrity and
probably closely resembles the appearance from the early
construction period. Figure 2.5 illustrates the basic
assembly of the towpath wall and the railing as it appears
today.
Dr. Kapsch has discovered three sketches by Ellwood
Morris during 1839 that provide an interesting view of the
evolution of the design for the towpath railing during the
construction period (see Figures 2.6, 2.7 and 2.8). The first
Final: Jan / 2004
Page 2.4
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
is dated March 1, 1839. This illustrates a timber
construction that cantilevers out from the rock base. If we
understand the notations correctly, the "rub" rail is
incorporated at the base of the timber railing assembly.
This proposed rub rail was a very heavy element: 10" x
12" by 22 ft. long. The two subsequent sketches, dated in
October of 1839, substitute a masonry wall and railing.
The later one, dated October 15, is the closest to the
towpath railing assembly in place today. In this sketch, if
one substitutes a wooden railing assembly for the masonry
one that is indicated, the current assembly results.
History: 1850 to 1924
The tunnel was operational from its completion in 1850 to
the canal's demise in 1924. During normal operation, the
water levels were dropped during the winter and the canal
was not used. The canal was then flooded each spring
back to normal operating levels. This annual cycling
between wet and dry conditions, including the possibility
of freezing temperatures, would clearly impact the lower
portions of the brick tunnel liner over time.
There were many severe storms and hurricanes over this
time that caused considerable damage at many locations
along the canal. The flood waters often carried massive
trees and debris that would rip through canal features and
adjacent structures. Further research could establish how
these storms affected the tunnel features.
From 1924 when the canal ceased operation, through to the
first National Park Service project undertaken on the tunnel
in the summer of 1956 as part of Mission 66, there was no
maintenance on the canal or tunnel elements. Based on
photographs of other portions of the canal, it is clear that
overall conditions deteriorated badly. The canal was
dewatered, trees and brush were growing everywhere, and
the canal prism filled with debris. We assume the
conditions in the tunnel were no better.
Recent History:
There is limited documentation that has come to light
Ca. 1956
regarding the condition of the canal and repair efforts in
the 1956. There is a good collection of black & white
photographs on file at the Park that document the repair
efforts (see Figure 2.9). Dr. Kapsch's research reports that
in 1956, a National Park Service inspection discovered
Final: Jan / 2004
Page 2.5
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
fallen brick, cavities in the towpath, gaps in the handrail, a
rotten timber-framed towpath in Athey's Hollow and a
rock slide that obliterated the towpath North of the Hollow.
National Park Service Director Wirth allocated $30,000 to
fix these conditions and the work was undertaken in the
summer of 1956 by National Park Service maintenance
personnel. These efforts are reported in an article that
appeared in December of 2000 (C & O Canal Association,
"Paw Paw Tunnel During 1956 Restoration - Hahn
Collection," Along The Towpath, Vol. XXXII, No. 4,
December 2000, p.1. A photograph shows four workers
alongside a pile of bricks and adjacent to a tractor and cart
in front of South portal, Paw Paw Tunnel.)
Our current field survey of conditions in the canal (see
Chapter 7), cite at least 30 locations where the brick walls
were repaired. These repairs range in size from 5 feet long
by 5 feet high to over 40 feet long and 10 feet high. There
is a uniformity of technique and brick color (middle to
dark-red) among these repairs. Generally, the brick
coursing of the repair utilizes a continuous running bond,
even though the adjacent brickwork utilizes the modified
English bond (see Figure 2.9). Also, the repairs tend to be
in the area below the spring line and virtually all of the
repairs are on the west side of the tunnel (the side opposite
from the towpath). We attribute these repairs to this early
time frame, but this cannot be confirmed at this time.
Recent History:
There are several documents that shed some light on the
1960's
conditions and repairs contemplated in this period,
however, there remains considerable lack of clarity on the
extent and type of repairs that were actually completed in
this decade. The following summarizes this information:
A tunnel cross section drawing was prepared at the
beginning of this period by C. H. Blake, Park Engineer (C.
H. Blake, Park Engineer and W.E. McGarvey, Student
Assistant, Study Sketch of Conditions Causing Failure
at Paw Paw Tunnel, C & O Canal National Monument,
September 1963, Scale 1" = 100'; Sheet 1 of 1. No
drawing number. Pencil on vellum. Original drawing filed
at C & O Canal Headquarters, Sharpsburg, Maryland).
The drawing shows profile (1" = 100') with existing
Final: Jan / 2004
Page 2.6
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
conditions indicated; topography above the tunnel (1" =
100'); elevation of North Portal (1/8" = 1') and typical
tunnel; section (1" = 100'). The primary focus of the
drawing appears to be an effort by Blake to document the
location of the four vertical shafts. The drawing does not
give any comment regarding the condition of the tunnel or
canal. Bear in mind that the shafts were not visible on the
interior nor on the top of the mountain. The only evidence
was the severe watering staining over a general area on the
interior. Blake included his calculation methods to locate
and size the shafts on the drawing. He attempted to use
the total quantity of brick as a method of estimating the
diameter of the brick-lined shafts. His methods had good
intentions, but his findings do not agree with other
documentation.
A Historic Structure Report was prepared by the Park
Service and was issued in two volumes:
Architectural Data Section by Archie Franzen,
Architect, March 1965
Historical Data Section by John F. Luzader, undated
manuscript, assumed to be 1965.
We conclude that the tunnel was in relatively good
condition by the time these reports were written, based on
the following comment:
Franzen, page 6,
"The outer widths of the lining have become loose in large
sections in several places, and that this is a recurring
condition can be seen by the number of patches that have
been made over the years."
Based on the total number of brick patches now evident,
we believe only a handful of areas needed repair when
Franzen prepared his report.
Franzen continues to describe needed repairs. There
actually is no mention of repair to the brick walls, but
rather, he lists needed work as "correct seepage" (page 8);
"drain and clear canal bed" (page 9); "check wooden rub
Final: Jan / 2004
Page 2.7
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
rails" (page 9); "repair railing posts and timbers" (page
10); "provide lighting" (page 10), and lastly, Franzen
recommends replacement of the timber towpath at the
North end of the tunnel (page 12).
Franzen provides a tunnel profile and plan drawing that are
marked with his notations regarding the condition of the
tunnel. There are two items of interest: he illustrated
wooden planking for short sections of the towpath in the
immediate vicinity of the vertical shafts, and there is
notation of missing rub rail in many locations. The first
issue, wooden planking, is very interesting because this has
been removed and replaced with the towpath gravel
material. We speculate that the planking would have
allowed the large quantities of water seeping into the
tunnel at these locations to pass on into the canal without
impacting the towpath area.
Luzader concludes his documentary history of the
construction period of the canal (i.e., 1836 to 1850) with
the sentences,
"Thus ends the story of the construction of the Paw Paw
Tunnel, the most remarkable structure on the C & O Canal.
It is, today, in remarkably good state of preservation,
requiring only to be re-watered in order to provide an
excellent interpretive medium." (page 58).
Recent History:
Several of the current Park Maintenance staff have worked
1970's to Present
on the canal for at least 20 years, including Robert
Hartman, Glen Gossert, Joe Smith, and Ray Fishel. They
have given accounts of the repairs that they have
undertaken and given their recollections of repairs made
prior to their time. From this, we can document two types
of repairs during this period. These are described below.
Repairs to Brick Liner:
Damaged areas of the tunnel walls were repaired from time
to time. According to Joe Smith, the brick that were used
are slightly darker red in color than the existing, and the
same darker red brick was used repeatedly over the years.
The repairs were well done, but the slight difference in
Final: Jan / 2004
Page 2.8
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 2: BACKGROUND INFORMATION
color now helps to distinguish these repairs from those
undertaken previously. There are less than 10 areas
repaired using these darker red bricks. A stockpile of these
brick remains for future repairs.
Repairs to Railing and Cross-timbers:
Over the years, the maintenance staff has replaced 40 to 60
of the cross timbers that support the railing. They have
used pressure treated timber, and the timbers are a close
match to the historic timbers. The staff has also replaced
the entire length of the standing 2 x 12 kick board, again
using pressure treated lumber. Lastly, they removed the
existing middle rail of the assembly and installed a new, 4
x 4 inch pressure treated middle rail. A few individual
sections of the top wooden rail have been replaced. When
these were replaced, the replacement timbers were beveled
to make their appearance blend with the adjacent original
elements.
There is documentation for repairs to the entry portals in
1979 in the form of architectural drawings for proposed
work. However, it is not immediately clear how much of
this work was actually accomplished. (Drawings
developed by this project included: John Milner Associates
for Denver Service Center, National Park, Paw Paw
Tunnel Complex, Chesapeake and Ohio Canal National
Historical Park, Drawing No. 412/25045-A, 8 Sheets,
May 15, 1979. Half size Xerox copies available from
Denver Service Center Technical Information Center
(TIC). Drawings Marked, "IFB No. 3100-78A."
Sheet 1. (Cover Sheet: Project Title and Location).
Sheet 2. (Project Site Identification: Access Plan)
Sheet 3. (North Portals: Paw Paw Tunnel Portals)
Sheet 4. (South Portals: Paw Paw Tunnel Portals)
Sheet 5. (Structural Details: Portal Parapet Repairs)
Sheet 6. (Structural Details: Tunnel Portal Drainage
System)
Sheet 7. (Structural Details: Tailings Pile, Wing Wall
Repairs)
Sheet 8. (Structural Details: Slope Scaling, Towpath
Repairs, Tunnel Shafts)
Final: Jan / 2004
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CONDITION ASSESSMENT AND PRESERVATION PLANNING
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These repair design efforts by Milner were preceded by a
"study" report in 1978. In this report, there is
recommendation to install stainless steel pans and piping to
help catch and direct the water seepage between the brick
liner and the rock walls. Although this type of work was
reported in the "study," there is no evidence that these type
of repairs were ever undertaken. (see John Milner
Associates and Edward H. Richardson Associates, Paw
Paw Tunnel Portals, Chesapeake and Ohio Canal
National Historical Park, Allegany County, Maryland:
STABILIZATION STUDY, Preliminary Design,
(Denver, Colorado: National Park Service Center,
September 1978). Drawings developed by this project
included: John Milner Associates for Denver Service
Center, National Park, Paw Paw Tunnel Portals,
Chesapeake and Ohio Canal National Historical Park,
Drawing No. 412/25063, 6 Sheets, October 4, 1978. Half
size Xerox copies located at C & O Canal Headquarters,
Sharpsburg, Maryland. Marked, "Preliminary Working
Drawings."
Sheet 1. Location and Vicinity Maps.
Sheet 2. Paw Paw Tunnel Portals - South Portal
Sheet 3. Paw Paw Tunnel Portals - North Portal
Sheet 4. Paw Paw Tunnel Portals - Portal Drainage
Systems
Sheet 5. Paw Paw Tunnel Shaft Collection Works
Sheet 6. Paw Paw Tunnel Closure)
Top of the Mountain:
There exists today a series of concrete lined troughs and
other drainage diversion ditches that were placed to control
(i.e., divert) storm water from collecting in natural basins
over the tunnel (see Figure 2.10). The date that these were
installed is unclear, but they have proven over time to be
hard to maintain due to logistics. Debris, such as leaves
and dirt, accumulates within the troughs and impacts
positive drainage within them.
1997 Photographic
The park sponsored the preparation of large-format
Documentation by NPS
photographic documentation of the east side of the tunnel
(i.e., the towpath side). This was a very systematic
documentation effort that began by subdividing the tunnel
Final: Jan / 2004
Page 2.10
CONDITION ASSESSMENT AND PRESERVATION PLANNING
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CHAPTER 2: BACKGROUND INFORMATION
into segments, 25 feet long (plus/minus 6 inches). An
example of a typical record photograph is provided in
Figure 2.11. Each segment was physically marked by
attaching an aluminum marker plate to the underside of the
top wooden rail. These remain today. The photos include
a small numbered sign attached to the front of the middle
railing to record the segment number. The numbering
began at the South portal, and moved to the North. There
are 137 segments in all. The black and white photos are
scalable and rectified (vertically plumb). These photos
have been scanned and are available as digital images.
2002 Survey Monuments
A task of this study effort was the installation of permanent
survey markers at 100 foot intervals along the towpath side
of the tunnel walls. These were surveyed and installed by
a land survey sub-contractor, Alpha Corporation of
Sterling, VA. These were placed approximately 24 inches
above the towpath (see Figure 2.12). The wall markers
were anchored into the joints between the brick courses
using an epoxy adhesive. The zero, or starting point, for
these wall markers is 2 inches South of the vertical face of
the South Portal stonework.
After this study had commenced, the study team found a
bronze station point that was set in the stone work of the
towpath just outside the South Portal. This may have been
placed by the NPS to be the zero point for tunnel
measurements and documentation in the 1960's. There is a
44.5 inch differential between this NPS station point and
the zero point used for the wall markers installed by this
study team. The NPS marker is to the South of the zero
point used by this study team.
In addition to these wall markers at every 100 lineal feet,
four additional wall markers were placed at the
approximate locations of the centers of the four vertical
shafts. These bronze markers are designated "Shaft A, B C
and D." The 1963 drawing by Blake was used to
establish these locations. It should be emphasized that the
locations of the bronze shaft markers are approximate since
there are conflicts in the historical data. Locating the
actual centers of each shaft can only be finalized with some
form of physical investigation and visual confirmation.
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98
LONGITUDINAL SECTION OF THE TUNNEL, JANUARY 1st, 1839.
Magnetic Course of the Tunnel in 1836, N6t° E.
Fig. 1
shaft DO
South Portal
352
345
252
Shaft
North Portal
Civil Engineering.
142
State Rock
426ft
Heading level
487
Canal Bottom
1974
ix
441
South
3118ft
Scales.
Horizontal 500 A. to the inch. , Heading driven = 1274 ft. lineal. The shaded parts show what has been exervated:
Vertical 200 do.
do.
$
Do. to be done = 1844
do.
The blank parts that which remains to be done.
Note-The whole course of the Tunnel consists of state rock (in inclined strata sometimes contorted) of a bluish gray
colour, containing considerable lime and occasional veins of shell limestone.
Fig. 2.
Fig. S.
Transverse Sections.
TowPath
Heading
27 ft
872
Canal
Bottoming
18ft
zift
Scale 15 feet to the inch.
Figure 2.1
These 3 diagrams are taken from the 1839 article about the Canal
in the Journal of the Franklin Institute. Figure 2 is a
transverse section of the intended final tunnel design, however,
the wooden towpath indicated was apparently not constructed.
Figure 3 indicates the two excavation sections: "heading" - the
upper portion of the transverse section, and "bottoming" - the
lower portion.
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Figure 2.2
The spring line is noted with the last row of header course bricks
and the occasional "putlog hole" (shown with the arrow). Below
the spring line, the brick courses are in an English Bond pattern,
that is, alternating courses of headers and stretchers.
W
24
6.0
Paw Paw Tunnel Sections
Chesapeake & Ohio Canal
78% Reduction From Originals
National Archives RG79 # 222
Believed to have been drawn by
Ellwood Morris, Asst. Engineer C. 1840
Robert Kapsch
October 1, 2001
Figure 2.3
Cross-section profile. Drawings prepared by Ellwood Morris,
probably in 1840, showing the extent of excavation at each of 51
points along the length of the tunnel. The section pictured is
number 24.
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Figure 2.4
South Portal, current condition. Towpath on the right. This is the
upstream end of the canal and is the portal closest to the visitor
parking area and Maryland State Route 51.
PUT LOG /
SCAFFOLD HOLE
DIRT / GRAVEL
TOWPATH
5"x5" RAILING
3"x3" RAIL
ROCK
2x10 BOARD
SPRING
LINE
RUB RAIL, ON
BOTH SIDES
1'-10"
OF PRISM
O.C.
BRICK LINER
*
(THICKNESS
UNKNOWN)
11"x11"
TOP OR RUB RAIL
TIMBER
TO LEVELING BED
PRISM
BED
UNDER TOWPATH
± 5'-10":
PRISM BED TO
TOP OF RUB RAIL
DASHED LINE
INDICATES
ROCK
PROFILE OF
BRICK LINER
Figure 2.5
Isometric diagram of the towpath and tunnel transverse section
showing current conditions. The pattern of brick coursing in this
illustration should not be taken literally. Drawing by Quinn Evans
I
Architects.
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RG79 ENTRY 214-
RACORDS OF Europe Malla
Box I Folore 4
12 or 00
MARCH 1835
Four
wall
from
East
speet
le
Canal
20/-
of ament +
Rock
resign for a Propeting How Path for the
Leugth of the You Path = 4050 feet or 405 Pannels of 10 fleach:
Figure 2.6
Construction sketch by Ellwood Morris, March 1, 1839, from Record
Group 79, Entry 214, Box 1, Folder 4. Note the use of heavy
wooden timbers for the railing assembly. The "rub" rail was
incorporated into the railing assembly. This was about 12 inches
above the assumed water line.
Design In a Inn Path In the Junnee
to Lane a Buck Paratet with
RG79 ENTRY 214
a Ime Crhing
RECORDS or FLLWOD Misers
Box I (OF 1)FOLDER5
12.06.00
OCTOBER 7, 1839
etone
coping
X
6
to he let in June Cement)
Figure 2.7
Construction sketch by Ellwood Morris, October 7, 1839, from
Record Group 79, Entry 214, Box 1, Folder 5. Timber is no longer
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indicated. A brick wall with stone coping is proposed. Note that the
rock wall below was to be battered and that no rub rail is indicated.
Figure 2.8
Construction sketch by Ellwood Morris, October 15, 1839, from
Record Group 79, Entry 214, Box 1, Folder 5. This sketch indicates
a vertical masonry wall to form the prism wall and a continuous wall
for the towpath, topped with a stone coping.
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Figure 2.9
Copy of a 1956 photo from the NPS archive in Park Headquarters
showing the repair work within the tunnel.
Figure 2.10
Brick patch, using the dark red bricks. Note the brick coursing is
running bond. We believe these-type repairs were made in the
1960's.
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Figure 2.11
Existing drainage trough on the top of the mountain, over the tunnel.
The date when these were constructed needs to be confirmed.
Figure 2.12
Sample of the typical photographic record of the towpath side of the
tunnel prepared by the NPS in 1997. This image is for segment no.
006. Vertical scale posts were temporarily mounted at the edge of
each segment for the purposes of the photographic documentation.
Segment number appears on the white card at the left edge of the
image.
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Figure 2.13
The bronze markers are placed every 100 feet along the towpath side
of the tunnel. They are 3 inches in diameter and include the
inscription "Chesapeake & Ohio Canal National Historical Park, Paw
Paw Tunnel, Survey Station Mark, March, 2002."
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EXISTING CONDITIONS SUMMARY
DESCRIPTION
Field Survey Methods
One of the primary tasks of this study effort was the visual
survey of all elements of the tunnel, including the portals
and mountain top. The survey effort was broken into two
parts: an initial survey of one day (held 22 May 2002), and
a 3-day full survey (held 29-31 October 2002).
One goal of the survey was to utilize the 1997
photographic documentation prepared by the NPS. Each
photo records a wall segment approximately 25 feet long.
There are 137 segments in total. In the initial survey, basic
methods and survey forms were tested. Typical conditions
of deterioration were evaluated and language to describe
these common conditions was established. This survey
was accomplished primarily from a vehicle provided by the
NPS that was driven up the canal prism. The survey form
used in the initial test was found to be less than optimum,
so a new form was adopted which used the 1997 photos at
a larger size. The large size assured that the resolution and
detail of the photograph could be utilized in the survey. A
two-page survey form, using standard letter paper, was
finalized (a sample form is found at the end of this
chapter).
During the full survey, the two-page survey document was
completed for each of the 137 survey segments. The
condition of the east and west walls and the ceilings were
noted, using 20 standard keynote notations. These
repetitive notations, with definitions, are included in the
beginning of Chapter 7 as are the completed survey forms.
The term survey segment refers to each survey area.
These correspond exactly with the segments established by
the 1997 NPS photographic survey. As an aid to this
analysis, the following segments are referenced:
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Segment 000 - Beginning point at South Portal (upstream)
Segments 097 to 099 - Approximate location of vertical
shafts C and D.
Segments 119 to 121 - Approximate location of vertical
shafts A and B.
Segment 137 - Final segment at North Portal (down
stream)
During each survey period, test pits were opened up by the
Park staff for evaluation and recordation (see results
below). These two excavation sites explored the
condition of the cross-timbers and masonry/stone below
the gravel towpath materials.
The full survey was conducted over 3 days and was
conducted in two parts due in part to physical access and
lighting issues. In part 1, a portable electric generator and
lights were moved along the towpath (see Figure 3.1),
enabling visual survey of the towpath zone and the vault
ceiling. The high level of light output provided very
satisfactory conditions for the visual analysis. This
accounted for about 75% of the total survey area. In part 2,
a vehicle provided by the NPS was used in the canal prism.
This enabled visual survey of the lower portions of the east
and west walls and the prism. This last part was
accomplished in a half-day time period.
Test Pit #1
For test pit #1, the gravel and rock towpath materials
around a single cross-timber were removed, exposing the
top and one side of a timber, and the base of the brick wall
(see Figure 3.2). This investigation occurred during the
initial site visit on May 22, 2002 and it was viewed by the
entire team. The candidate timber was selected because
the area appeared to be relatively dry and the timber had a
satisfactory appearance (i.e., the end that is normally
exposed to view was dry and in good condition - see
Figure 3.15). This timber was opposite a survey station
mark noting that it was 100 feet from the South Portal
entrance, in survey segment 005. The candidate cross-
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timber appeared to be an "original" timber, not a
replacement.
Findings:
1.
The cross-timber did not penetrate into a pocket or
recess of the adjacent brick wall (see figure 3.3).
2.
There was an iron bolt that anchored the timber to
the masonry base material (see Figure 3.3).
3.
The masonry base under the timber provided a flat
and level surface to support the timber. This flat surface
appeared to be continuous under the towpath gravel
material. This masonry appeared to be a mortar and rock
composite material, similar to modern concrete.
4.
The towpath gravel material was a composite of
larger and small stones, crushed rock and a soil binder. It
had an overall depth between 22 and 24 inches. The upper
layer was much lighter in color and was composed of
smaller gravel and soil. It was about 3 inches deep. This
upper layer had been placed by the NPS in recent times.
5.
The cross-timber was thoroughly rotten and punky
(see Figure 3.4). A drill bit was used to penetrate at
various points and there was virtually no firm wood at any
point along the timber.
6.
The timber and surrounding towpath gravel were
damp, even though the top surface of the towpath gravel
appeared dry.
The condition of this timber was very poor and it should be
a candidate for early replacement.
Test Pit #2
As a follow-up to test pit #1, a second investigation was
undertaken during the full survey on October 30, 2002.
The general goal was to examine two additional cross-
timbers, and to try to investigate the masonry base under
the timbers to determine composition and depth. A site
was chosen where the towpath materials were clearly damp
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in appearance. Test pit #2 was at a distance of
approximately 120 ft. from the entrance, in survey segment
006.
Findings:
1.
Both cross-timbers were severely deteriorated.
The surrounding towpath gravel material was damp (see
Figure 3.6). Only one of the cross-timbers had an anchor
bolt. The timbers were installed at a uniform spacing of
5'-0" plus/minus 1". As in test pit #1, these timbers did
not penetrate into the adjacent brick wall.
2.
The towpath gravel fill material was the same as in
test pit #1, a combination of large and small stones with a
soil binder. The towpath material was very porous and
apparently had the capacity to both hold moisture and
spread the moisture through capillary action (see Figure
3.6).
3.
The masonry base was uniform and flat between
the timbers. A masonry saw was used to cut through the
material and it was found to be a composite of mortar, rock
and broken bricks (see Figure 3.7). Impact with a heavy
iron bar had no effect on the base material (i.e., there was
no sense of hollow or soft materials below). It appeared
that this masonry fill material may have been placed over
bed rock. We concluded the purpose was to provide a
sound and flat surface to receive the cross-timbers and
railing assembly.
General Findings
Based on the field survey work and the findings of the two
test pits, the following general findings can be provided.
We have broken the discussion into four analysis zones
that correspond to four components of the tunnel when
viewed in transverse section (see Figure 3.8). The analysis
zones are:
Vault
Towpath, Railing and East Wall
Prism Wall - East Side
Prism Wall - West Side
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Following discussion of these zones are comments on the
two portals and the drainage issues of the mountain top.
Vault
This zone includes all brick work of the vault above the
spring line. In the upper portion of the vault, there have
been few brick patches and, by and large, the overall
condition of the vault ceiling is good. There is substantial
staining, both dark black and white in color, and water
staining and active water droplets in the areas near the
vertical shafts (i.e., segments 097 to 099 and 119 to 121).
No physical probe was undertaken of this area at this time.
An NPS maintenance team did open two small access
holes into the ceiling vault about 20 years ago. Robert
Hartman was part of this team. He recalls the following:
1.
There was a 2 to 3 foot air space/cavity above the
brick vault and below the rock excavation of the tunnel.
2.
There were brick piers extending up from the vault
to connect with the rock excavation. It is believed that the
brick vault is thus providing some support to unstable rock
of the tunnel roof.
The locations of these two probes cannot be confirmed, but
there appears to be visual evidence in segments 96 and
121, immediately above the towpath, in the form of
rectilinear brick patches about 2 feet square.
In the region of the spring line on the west side, there are
numerous brick patches. Based on the different bricks
used and workmanship, these appear to have been
undertaken over a long time period. See below under
"Prism Wall - West Side" for additional discussion.
Brick Condition:
The face brick units appear in good condition in general.
In the areas of the vertical shafts, there are active water
leaks and evidence of long standing water intrusion. This
has caused mortar to erode away in the areas of the most
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severe water intrusion (see segments 97, 98, 120, 121, and
122). Severe loss of mortar could eventually cause brick
units of the vault to slip or bulge. Collapse is unlikely due
to the arching effect of the brickwork.
Outside of the areas where there is water damage and the
horizontal zone along the spring line, the brick of the vault
is dry and in good condition. There is evidence that the
brickwork was coated with a cementitious coating, less
than 1/8 inch in thickness (see Figure 3.9). Whether this
coating was from the original construction or was a
subsequent maintenance coating is unknown. At this point
in time, it covers less than 25% of the brickwork surface
over the whole vault. It has eroded or peeled away from
the majority of the surface area.
Mortar / Efflorescence:
With the exception of the areas that are impacted by water
intrusion, the mortar of the vault is in good condition.
There is little surface erosion and the joints appear sound.
A considerable quantity of efflorescence was discovered
during the full survey (October 29-30) that had the
appearance of fine hair and spun wool, emanating only
from the mortar joints (see Figure 3.10). The efflorescence
was not tested, but since it is comes only from the mortar,
it could be assumed to be the soluble salts and lime that are
leaching from the mortar. This condition was viewed
between segments 048 and 070, see keynote 15. It
occurred in disconnected areas, ranging in size from 1 to
20 square yards. In low light conditions, this efflorescence
would be difficult to detect. It had not been observed in
any of the previous site investigations. Also, it was only
viewed on the east side, but this may be a product of the
viewing distance and low light conditions on the west side.
The efflorescence did not seem to be damaging the mortar
as it remained sound.
Towpath, Railing and
For the purposes of this report, this zone includes the
East Wall
towpath materials, the railing assembly (see Figure 3.11),
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and a segment of wall opposite the towpath. The current
condition of each is described below.
Top Railing and Iron Post:
The top railing is a wooden 5 x 5 in very sound condition.
Most of this element is original, or at least very old, but
there are a few segments that appear to be modern. The
railing is supported on 5 foot centers with wrought iron
posts (stanchion) that have a special yoke fitting to carry
the 4 X 4 railing (see Figure 3.12). When a lateral force is
applied to the railing, the railing is very stiff and there is
little deflection. The iron posts are basically a 2 inch
square, solid iron bar. These show some degree of
corrosion, but this has have been occurring at a very slow
rate over the proceeding 175 years. There are 625 iron
posts all together and most are in good condition. There
are 5 to 10 where the corrosion has proceeded at a more
rapid rate and caused the iron to separate, or delaminate,
along the seams of the iron. The posts showing the
greatest corrosion have lost about 25% of their cross-
sectional area (see Figure 3.13).
The iron post is anchored into the wooden cross-timber
using an iron strap and pin (see Figure 3.14). The
condition of these parts varies from good to very poor.
Also, the connection to the cross-timber is obviously
dependent on the condition of the wooden timber. If any
one of these elements is in poor or very poor condition, the
stability of the iron post and railing is in question.
See Chapter 4 for more discussion of the structural
conditions.
Wooden Cross-timbers:
In general, these timbers are about 11 x 11 inches and 6
feet long. They are spaced every 5 feet. From our field
survey, we have concluded there are three different
generations of these cross-timbers: original, pre-NPS and
NPS (or recent). The differences, based on visual
characteristics, are illustrated in Figures 3.15, 3.16 and
3.17.
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From the early documentation, and interviews with the
maintenance staff, it appears that all timbers are oak.
Based on the end grain that is visible, most are
"heartwood." Unfortunately, given the findings from the
two test pits where three severely deteriorated timbers were
discovered, and coupled with the fact that NPS has found it
necessary to replace over 60 of these timbers over the last
few years due to deterioration, it can only be concluded
that the general condition of the remaining timbers is poor,
perhaps very poor.
We believe that the towpath fill material, which is a
composite of large and small stones with a soil binder, has
proven to be a medium which holds moisture and permits
the moisture to migrate over large distances through
capillary action. Thus, water leaks in a localized area
impact a large quantity of cross-timbers. The timbers
apparently never dry out, but rather, are continuously
impacted by excess moisture.
Brick Wall:
The brick wall adjacent to the towpath is in generally good
condition. Few problems were noted in general, except for
the area in the vicinity of the vertical shafts where there are
moisture and water related problems.
Prism Wall - East Side
Upper Segment:
This area is discussed separately because it is exhibiting a
unique problem due to the apparent inability to support the
adjacent towpath fill material. In addition, the water
leakage and high moisture content of the adjacent towpath
material has caused the brick work to deteriorate (see
Figure 3.18). There is a high degree of mortar erosion and
some areas of brick are out of alignment with the adjacent
surfaces.
There is evidence that this zone has been repaired and the
brick replaced in many locations. This has clearly been an
ongoing problem zone for many years. If this wall
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segment collapses, the towpath fill material caves into the
prism, creating a sink hole in the towpath. This is an unsafe
condition to the visitor.
Lower Segment:
This is the lower segment of wall discussed above It
forms the canal prism. The problems here are not so
pronounced as above, partly because this portion of the
wall may be built directly against rock (see Figure 3.19).
The moisture from above may not be getting behind this
brickwork as it is above. There is a "tide mark" of
uniform joint erosion along the high level of the canal
water. This is to be expected and is reflected on both sides
of the prism.
Prism Wall -- West Side
There are certain conditions along the west wall that differ
markedly from the east. The most notable is the absence of
the towpath and its associated problems. However, there
have been many brick related problems over the years
because most of the brick patches occur on the west side.
Further, most of these patches occur below the spring line,
often just above the rub rail. There is apparently a strong
force or stress within the brickwork in this location
because it has been strong enough to shear off the header
bricks, causing a collapse of the outer course of brick
work, the face bricks (see Figure 3.20). We believe there
has been severe mortar erosion in these locations that has
contributed to the collapse.
See structural discussion in Chapter 4 for more information
on this condition.
Portals
The South and North Portal are constructed of coursed
ashlar, quarry faced stone (see Figures 3.21 and 3.22).
There is vegetation and mold growth in many locations,
and problems from water and drainage. The overall
condition of both portals appears to be fair, but routine
cleaning and repointing is needed. Up to 25% of the
mortar joints are in poor condition and should be repointed.
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Mountain Top
The mountain top is not easily accessed by Park staff, nor
is it seen by many visitors. There is significant tailings
piles that remain from the excavation of the ventilation
shafts. Unfortunately, these create some areas where
surface water is retained (see Figure 3.23). In addition,
there appears to be settlement in the immediate vicinity of
the shafts so that water and debris can collect in these
locations.
To address this water ponding, the NPS erected
bituminous drainage troughs. The date of this work is not
known, but it is believed to have been associated with the
planned work of the late 1970's. The troughs themselves
are in fair condition, but it is not clear if water is finding its
way into them do to negative drainage and erosion around
and under the troughs. The effectiveness is lessened when
the troughs fill with leaves and debris (see Figure 3.24).
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Figure 3.1
Field Surveyor with portable electric generator and lights.
Figure 3.2
General view of test pit #1 in survey segment 005. Note
that the towpath material near the wall appears dry, while it
is damp near the railing. 100 ft. station mark appears on
the east wall.
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Figure 3.3
One of the purposes of the excavation was to examine the
physical connection of the timber to the wall. It was
confirmed that there was no connection to the wall, nor
does the timber extend into the wall. The top of the
anchor bolt and nut is noted with the arrow.
Figure 3.4
The timber was probed at many points and no firm wood
was found, but rather, the entire length of the timber was
rotten and punky, although the exposed end appeared in
fair condition (see Figure 3.15).
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Figure 3.5
General view of test pit #2. Two timbers were uncovered, in survey
segment 006.
Figure 3.6
View of the cross section of the typical towpath fill material. Note the
variety of rock and small stones, bound together with soil. This
composite material apparently absorbs moisture and has great capacity to
spread this moisture through capillary action.
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Figure 3.7
The timbers are installed upon a relatively flat table of mortar and brick.
A probe was attempted to try to penetrate this flat masonry base using a
masonry saw (see arrow). This masonry base is very firm and does not
have any flex under impact blows.
ROCK
A
BRICK LINER
R12-0"
±3'-0"
DIRT / GRAVEL
TOWPATH
B
24'-0"
+1'-8"
D
+7'-6"
BRICK PRISM
LINER
ROCK
«
WEST
EAST
ANALYSIS ZONES
A
VAULT
B
TOWPATH, RAILING, AND EAST WALL
C
PRISM WALL EAST SIDE
D
PRISM WALL WEST SIDE
Figure 3.8
Diagram of "Analysis Zones."
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Figure 3.9
The survey determined that the brickwork of the tunnel had previously
been coated with a cementitious coating. Whether this coating is
original, or some subsequent maintenance coating, could not be
determined.
Figure 3.10
Efflorescence was observed, associated with the mortar joints only, in
disconnected areas ranging in size from 1 to 20 square yards. This
seemed to be only present on the east wall, between survey segments 048
to 070. The cementitious coating is also visible in this image.
Final: Jan 2004
Page 3.15
CONDITION ASSESSMENT AND PRESERVATION PLANNING
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CHAPTER 3: EXISTING CONDITIONS
G
5'-1"
5x5 TOP RAIL
BRICK LINER, EXACT CONDITION
AND THICKNESS UNKNOWN
IRON STANCHION
3x3 MIDDLE RAIL
±3'-0"
4
2x12 BOARD
DIRT / GRAVEL
TOWPATH
IRON BAND
<
11x11 CROSS
TIMBER
CONCRETE
4
LEVELING BED
BRICK PRISM
s
LINER
4
4
2
4
RUB RAIL
ROCK; EXACT
CONDITION
UNKNOWN
Figure 3.11
Detail of the Railing Assembly - Current Conditions
Figure 3.12
Iron posts (stanchion). Note that numerals "23" appear on the top side
face of the post. These may be left from the original time of fabrication.
The numbers are in chalk and were sequential for a group of posts
together in this location. The upper rail pictured here is believed to be an
original. The stainless steel bolt between the iron rail and the top rail is a
replacement, by the NPS. The amount of corrosion illustrated here is
typical for the wrought iron.
Final: Jan 2004
Page 3.16
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.13
Note that the lower portion of the post appears to be tapered (see arrow).
This is a result of corrosion which may have been accelerated due to the
contact with the soil and rock of the towpath. The loss of cross section
may be more than 50% for this post.
Final: Jan 2004
Page 3.17
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.14
The iron post is anchored to the wooden cross-timber with this strap and
plate assembly. There are locations where the iron strap is completely
deteriorated.
Figure 3.15
This photo illustrates the "original" type of the three types of cross-
timbers that were identified through the field survey. This is based
only on visual characteristics - the actual age is unknown. It can be
identified because there are two steps of size reduction associated with
the iron strap. The final face of the end of the timber is about 9 inches
square, down from the 11 inch cross section. This is the timber
excavated in Test Pit #1. See also Figures 3.2, 3.3 and 3.4.
Final: Jan 2004
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CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.16
We believe this is the pre-NPS replacement timber. We do not have
any confirmation of when these timbers would have been placed.
They could be toward the end of canal operation in the 1910's. They
are characterized by a single step down in cross section, with the top
and bottom iron plates recessed as they were in the "original" timbers.
Figure 3.17
This is the final replacement timber type. These have been replaced by
the NPS on an as needed basis over the last 15 years. Heartwood oak
is used. There is a single step down to receive a replacement steel
strap. There are no top and bottom iron plates as used in the first two
types. We understand that the anchor bolts found in the earlier
timbers were generally cut off because they could not be loosened.
Hence, these type of timbers do not have an anchor bolt (see above
under test pit #2 for a view of one of these type).
Final: Jan 2004
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CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.18
Photo of the top of the east wall, showing the extreme levels of
deterioration and brick displacement that occurs, primarily due to the high
levels of moisture in the towpath fill materials and the ongoing water
leaks. The excess moisture impacts the mortar, causing it to lose strength
and bonding. Once it is weakened, it is displaced by the lateral loads from
the towpath. There is evidence that this zone has been repaired on many
occasions.
KICK BOARD
Figure 3.19
View of a portion of the lower east wall analysis zone. The piles of dirt
and debris on top of the rub rail (see arrow) come from two sources. The
greatest quantify of this comes from the towpath fill materials that either
are kicked over the top of the kick board, or that slip through the gap
between the rub rail and the top of the brickwork. However, many of
the mortar joints above the rub rail are eroded back at least ½ inch, so
this spalled mortar also collects on top of the rub rail. Some of this
spalling can be attributed to the tide mark erosion from the canal when it
was "watered." Below the rub rail, the brick work is in fair condition.
Final: Jan 2004
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CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.20
Existing wall patch, west side. At the time of this photo, water was
actually cascading down the face of this brickwork.
Figure 3.21
South Portal. After the vines and vegetation are removed, about 1/3 of
the mortar joints in the stonework will need to be repointed. Cleaning
with low-pressure water would be useful.
Final: Jan 2004
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.22
Detail at North Portal. Note that the granite is heavily stained with
lichens and moss growth. The vertical slot cut in the prism wall held a
"stop gate" which was lowered into place when flood waters were
expected.
Final: Jan 2004
Page 3.22
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
Figure 3.23
Mountain top tailings from vertical shaft excavation. As these cross
a natural ravine, surface water is trapped above the tailings piles.
Figure 3.24
Drainage troughs. There are times when considerable water ponds
in the low points of the ravines. These troughs were installed to
alleviate the ponding problem, but they have proved less than
effective over time. In some locations, erosion has undercut the
troughs so that water is not carried away as intended.
Final: Jan 2004
Page 3.23
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 3: EXISTING CONDITIONS
EAST CEILING TO CENTER LINE
218
8
of
3
046
SEGMENT 046-EAST WALL
045
4
2
0
4
8
Survey Form
1/4"=1'-0" SCALE OF FEET
Page 1
SEGMENT
PAW PAW TUNNEL SURVEY
046
C&O CANAL. MARYLAND
QUINN EVANSIARCHITECTS
PROJECT NO. 01225
+ 202 298 6700
Oct.2002
Final: Jan 2004
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CHAPTER 3: EXISTING CONDITIONS
WEST CEILING TO CENTER LINE
011 -
73
- 18
SEGMENT 046 - WEST WALL
8
4
0
8
1/8"=1'-0" SCALE OF FEET
KEYNOTE LEGEND:
1
Brick patch in wall, darker red brick, presumed to be 20th-century repair area
2
Spalled face of brick, severe spall, at least 1 Inch in depth, could be 2 inches
3
Deep mortor erosion, at least 1 Inch, could be several inches deep. Mortar is also soft
4
Loose bricks, appear to be dislodged and/or out of alignment
5
Dark black water/mold stains to brick area
6
Severe water stains, includes lime and calcium build-up
7
Wet face of brick; could include active water flows
8
Original
cross timber SECOND GENERATION CROSS TIMBER
9
Replacement cross timber, approximately 11x11
10
Comment on railing, iron post, or cross timber
11
PUTLOG/ SCAFFOLD HOLE, APPROX. 2 1/2, 5 INCHES
12
MISC.
18 MISSING BRICKS
Survey Form
Page 2
SEGMENT
PAW PAW TUNNEL SURVEY
046
C&O CANAL, MARYLAND
QUINN EVANSIARCHITECTS
PROJECT NO. 01225
v 202 298 6700
Oct.2002
Final: Jan 2004
Page 3.25
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4:
STRUCTURAL ISSUES
Towpath Railing
The towpath railing consists of a wood handrail, iron post
(stanchion), intermediate wood rail, and cross-timber. The
configuration of the railing is illustrated in Figure 3.11.
The posts are spaced at 5 feet on center and extend through
the cross-timber.
Existing Conditions:
The handrail is 5 inches square and appears to be in good
condition. The intermediate rail is 3 ½" square and
appears to be in good condition.
The iron post is 2" square and several of them have
deteriorated significantly from rust. Where the post is
inserted into the cross-timber, the post is 1 ½" square.
The posts are spaced at 5 feet on center and extend through
the cross-timber. There is a 3/8"x 2" strap around the
timber just outside the post, and a 3/8"x 4" plate let into
the top and bottom surface of the timber. At several posts,
the strap and plates are rusted completely through.
The cross-timbers are 11"x11". All three cross-timbers
exposed in the test pits were found to be soft when drilled
with a small bit. The ends of many of the timbers are
rotten. Two of the three timbers in the test pits are bolted
to a brick lining below the timber with a 7/8" diameter bolt
of unknown length.
Analysis:
The railing components were checked for compliance with
1996 BOCA code loading requirements that refer to ASCE
7. The computations are included at the end of this
chapter. These requirements are as follows:
1. Handrails and posts - 50plf in any direction or a
200lb load in any direction.
Final: Jan 2004
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CHAPTER 4: STRUCTURAL ISSUES
2. Intermediate rails - 50lb load in any direction
For analysis of the railing components, material properties
similar to southern pine were assumed with an allowable
bending stress of 1200 psi. For the iron posts, values for
steel manufactured prior to 1900, with an allowable
bending stress of 16,000 psi, were used.
The bending stresses in the wood railing and wood
intermediate railing are within the assumed allowable
bending stresses.
The bending stress produced in the 1 ½" square post base
is 21,429 psi. A one-third increase in the allowable stress
for temporary loadings should be applied for this
condition, resulting in an allowable stress is 21,333 psi.
This condition is considered adequate. However, if the
cross section of the post inside the timber were reduced
25% to 1 1/8" square, the bending stress would be 50,600
psi. Therefore any small decrease in cross section due to
corrosion causes a significant overstress in the posts.
The strength of the railing is enough that there is a
significant load distribution among posts for a single
concentrated load such as might be applied by a single
person. However, the uniform load requirement is not
reduced as was used to determine the maximum stresses in
the post.
The weight of the towpath material and the cross-timber
itself was determined to be sufficient to resist the
overturning force of the railing load with a Factor of safety
of 1.5.
The railing components are adequate to resist the loadings
if the materials are in good condition. However, the
deterioration of many of the ends of the cross-timbers does
not allow transfer of the railing post stresses to the timber,
and the deteriorated condition of a given timber itself may
not be adequate to hold down an overturning load applied
to the railing.
Final: Jan 2004
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
Recommendations:
The posts and timbers that are deteriorated need to be
replaced since they are likely to be inadequate to support
railing loads. Unsafe areas of railing should be cordoned
off until repairs are made.
Prism Wall - East
The top of the prism wall that supports the towpath railing
(below towpath)
and cross-timber was determined to be 9" thick in Test Pit
#1. The amount of fill material behind the wall depends on
the profile of the remaining rock after the original
excavation (See Figure 3.11).
The condition of this wall is poor in some locations along
the towpath, particularly the upper 12 to 18 inches of the
wall in areas where there is a lot of water seepage. In some
areas this portion of the wall has partially collapsed. In
many areas, the mortar joints appear to be eroded back
several inches. In one location, this erosion was measured
to be 5 inches. The joints may have deteriorated as a result
of water in the canal during canal operations and water
seeping through the wall from the fill behind the wall.
Recommendations:
Unstable areas of the wall should be repaired. Joints
missing several inches of mortar should be pointed. The
remainder of the wall should be monitored on a regular
basis.
Vault
Existing Conditions:
The brick arch tunnel liner spans approximately 25 feet
between brick walls at the edges of the tunnel. We have
received conflicting information regarding the thickness of
the liner, but believe it may be 3 courses or about 13 inches
thick. The thickness may or may not be constant
throughout. The thicknesses of the walls supporting the
tunnel liner are assumed to match the thickness of the liner.
The bricks are sound when scraped with a knife.
Final: Jan 2004
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CHAPTER 4: STRUCTURAL ISSUES
There are alternating header and stretcher courses in the
walls supporting the liner. There does not appear to be
header courses between wythes in the arch itself.
The only information we have regarding what the liner
may support comes from the report by NPS personnel that
brick piers were observed in one test hole several years
ago. These piers were reported to extend from the tunnel
liner to the surface of the original rock excavation above.
A report by Ellwood Morris, Assistant Engineer,
completed around 1840, indicates that the surface of the
rock excavation is a jagged line in cross section and the
cross sections varied along the tunnel length.
There is one bulged area above the towpath in segment 117
that is a few feet in diameter. There is evidence of brick
repair in several areas, particularly on the prism wall
opposite the towpath. Water was observed to be dripping
from the arches in several areas near the north of the
tunnel.
Analysis:
There is not enough information to perform an analysis of
the stress conditions in the tunnel liner, but there are
several conditions that could affect the strength of liner
that can be discussed.
It is unclear where the arch is supported horizontally. At
the juncture of the arch and the wall (arch springline) the
arch may derive vertical support from the brick wall if it is
contact with the rock or some other solid infill material
directly behind the wall. If there were a gap between the
wall and the rock, the stresses in the arch would be
increased since the horizontal arch reaction would be
carried to the wall base. Generally, the stresses in the
tunnel liner will be less if the arch can transmit a horizontal
thrust to the surrounding rock above the spring line.
Where there are areas of missing mortar, or those few areas
where the brick appears to be bulging, it would be
important to determine if there is a void above the face
Final: Jan 2004
Page 4.4
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
brick. A probe up through the mortar joint using a drill
could identify voids.
There are several factors that could affect the stresses in
the tunnel liner (Fig. 4.3) including the following:
1. The thickness of the tunnel liner
2. The location of the horizontal arch thrust reaction.
3. The bedding planes in the rock above the surface of
the original excavation. Loose rock may be
supported by the tunnel liner.
4. The location and spacing of brick piers above the
liner. If the piers were built to support potentially
loose rock, there may be unsymmetrical
concentrated loading on the arch.
The internal strength of the tunnel liner will be reduced
where mortar erosion has occurred.
There appears to be no obvious condition in the tunnel
lining requiring immediate repair other than the small area
described above. However, the number of patches on the
prism wall that supports the arch is an indication that there
have been problems in the past. These patches could be
related to damage from canal boats or mortar erosion. The
stresses in the walls that support the tunnel liner may vary
along the length of the tunnel and could also be a factor.
Recommendations:
The tunnel liner should be monitored on a regular basis for
signs of bulges or other problems. Since there is water
continuing to seep through the tunnel liner, the condition of
the mortar joints and bricks should also be monitored. The
area with bulged bricks should be repaired. If the repairs
extend through the tunnel liner, we recommend that the
opening be photographed, measured, and documented.
Should there be a need to investigate the tunnel liner
further, test pits at the arch spring line would provide
information on how the arch is supported and its thickness
and test pits in the ceiling would provide information on
what loads the liner may support.
Final: Jan 2004
Page 4.5
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C&O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
45"x44" TIMBER MAILING
INTERMEDIA TE RAILING
2-24"X 2. 4% BOARDS BACK
TO BACK THEY REST ON IRON
PINS AND ARE NOTCHED
AROUND THE POSTS.
PROJECTS * EACH SIDE AND is LOCATED
17" DOWN PROM THE TOP RAILING
TOWPATH FLOOR is
GRAVEL. AT LEAKING
PLACES in 15 WOOD
DECKED
SQUARE IRON POSTS TOTAL of
625 SPACED 510 ON
POSTS REDUCE TO 18 SQUARE
THROUGH TIMBER CROSS BEAMS.
3"x12"
E"WIDE THICK IRON STRARS
NAILED IN PLACE THROUGH 31065
THICK IRON
LAT INTO TIMBER
ENDS TIMBER CROSS
BEAMS SQUARE
JOUARE TIMBER
CAOSS DRAMS
RAILING POSTS INSIDE TUNNEL
Figure 4.1
Sketch of railing configuration from Archie Franzen report.
Final: Jan 2004
Page 4.6
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
Figure 4.2
Rotten cross-timber end and iron post size reduction from 2" to
1 1/2" square at the top of the timber.
PAW PAW TUNNEL
McMullan is Associates, INC.
PROJECT NAME
FROM
NO
CONSULTING ENGINEERS
8381 Old Courtbouse Road, Suite
DB
DATE
JAN 2003
Vienna, Virginia 22182
(703) 556-0651
DATE
BRICK PIERS
BEDDING PLANES
As REPORTED
IN ROCK (ASSUMED
BY BOB HARTMAN,
SIM. TO THOSE
NPS. SPACING
OUTSIDE NORTH
AND SIZE
FORTAL)
UNKNOWN
SURFACE OF ROCK
BRICK TUNNEL
EXCAVATION VARIES
LINER, THICKNESS
ACCORDING TO ELLWOOD
UNKNOWN.
MORRISREPORT, 1840
HORAZONTAL
HORZ.
THRUST REACTION
REACTION
SPRINGLINE
III
FROM ARCH
(LOGATION
GAP TWEEN
UNKNOWN
BACK FACE
OF TUNNEL
LINER AND
VERTICAL
SURFACE OF
REACTION
ORIGINAL
EXCAVATION
ROCK
FILLED IN?
VERTICAL
REACTION
FROM WEIGHT
OF LINER, POSSIBLY
LOOSE Rock
SECTION THROUGH TUNNEL
3"=1'-0"
I
Figure 4.3
Cross Section Through Tunnel indicating potential factors
affecting the stresses within the tunnel liner.
Final: Jan 2004
Page 4.7
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
McMullan & Associates, Inc.
PROJECT NAME Pan Paw
PROJ. NO
CONSULTING ENGINEERS
SHEET NO
OF
8381 Old Courthouse Road, Suite 350
CALCULATED BY
DB DATE 10-21-02
Vienna, Virginia 22182
(703) 556-0651
CHECKED BY
DATE
Paw Paw Guardrail
Posts 5'-0"0.c.
50 plf (5') = 25016 > 20018 min. use 250 45
Mase 250'b (36" 12") = 12000 in-lb
Check timber 11/2x/1/2 S= 25 3in3
fb= = 250(36+1215) 53ps, ps, < 1200 psi ok
253
Check Post 12"x12" solid Sy. = 0.56 in3
Assumed
Fb Fb = - 12,000 = 121,429 psi 4 16,0,000 psi IF 1.33 short term load
0.56
factor applied,
Check Railing 5** 5x=20.8 is
Fbc15,000x1.33c 21,333ps
OK
M= = 50(5)², x 12 = 1875 in-lb or 156 FElb
8
Assumed
fb= = 90 psi ≤ Fo = 1200psi ok
Check stability
132plf
1120ft.16
Timber 112x112 : x Assumed 3516 = 32 plf
144
Ft3
A
5'-0"
D
Soil 1ftx 100pstx11 = 100plf
Structural
FS= 132 ÷ 1120 =1:47 = : OK
-
N
Calculations
Handrail o.m- resisted by timber soil weight
Final: Jan 2004
Page 4.8
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PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 4: STRUCTURAL ISSUES
McMullan & Associates, Inc.
PROJECT NAME. Paw Paw
PROJ. NO
CONSULTING ENGINEERS
SHEET NO.
OF_
)
8381 Old Courthouse Road, Suite 350
Vienna, Virginia 22182
CALCULATED BY
DB
DATE -10-03
(703) 556-0651
CHECKED BY.
DATE
Check reduced cross section of past
25 . less 1'2" = 1½" 5x= .24
M= (36" +12* ) 250 1b 12,00 into
F6=50,600 psi Assumed psi X x1.33 = 2 2 ,' No good
Intermediate Rail
P=50(5) = 62'5in-1b
4
Fb= = 8.3 psi <1200 psi OK
Structural
Calculations
Final: Jan 2004
Page 4.9
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
CHAPTER 5: LONG TERM MONITORING
2.
There are bronze station points at 100 foot
intervals that were mounted as part of this project
along the towpath, about 24 inches above the walking
surface.
The survey of this study utilized, and built upon the 25 ft.
segments of the 1997 NPS photo documentation project, so
we propose to build upon that marker system. The
existing tags are difficult to read underneath the railing, so
we propose to have a second set of tags made that would
be clearly visible on top of the railing. These tags would
need to be strong enough to withstand vandalism and
permanent enough to last many years. The most
straightforward method may be to have plastic straps made
that would band around the railing at each marker location.
A prototype is illustrated in Figure 5.1
Any marker system that incorporates the elements of the
one systems proposed above will be acceptable. The point
is that one needs to be able to determine your position
within the tunnel quickly, and accurately, for any
monitoring and inspection system to be successful.
Periodic Inspection
The frequency and methods of periodic inspection are
Protocol
challenging for this project. It may not be fully
recognized, but many historic sites essentially rely on the
visiting public as the first line of inspection. There is
either a complaint, or someone notices something that is
out of place, something dangerous, or something needing
repair (i.e., a broken water pipe). Relying on visitors
would be imperfect because: 1) the visitor frequency is
relatively low, perhaps a few dozen each day in the
summer and then seldom in the winter; and 2) the tunnel is
dark and a visitor flashlight does not provide any range of
view for even the most cursory of inspections.
Potentially Dangerous Conditions:
The issues at the tunnel are greatly compounded because
there are serious structural and safety conditions that could
occur on a given day due to the age and deteriorated
condition of the tunnel. The two most likely dangerous
conditions would be:
Final: Jan 2004
Page 5.2
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CHAPTER 5: LONG TERM MONITORING
A sink hole in the towpath creating a tripping
hazard to the visitor. Where the towpath fill
material can funnel under the kick board, a small
sink hole is created. This already happens with
some frequency from year to year.
Part of the brick tunnel lining collapses. There are
a couple of areas over the towpath with the
potential for collapse. If there were a small
collapse of the brick liner out over the canal, or on
the west wall, this would not likely affect the
visitors. Collapses have occurred in the past and
will occur in the future. These are preceded by
bulging and dislocation of brick courses.
Inspection Protocol:
To address these conditions, we suggest that the following
criteria will need to be met in a periodic monitoring
program:
Frequency. We recommend at least a weekly
inspection of the full length of the tunnel. We
recognize that this will be dependent on human
resources and funding. A greater frequency would
be better, but less frequent does not seem prudent.
Expertise. The inspector must be trained and have
time dedicated to make these inspections. Anyone
with basic construction and maintenance
experience could be trained in the inspection
protocol and provide satisfactory reports. This
could include a combination of Park staff and/or
volunteers.
Lighting: We strongly recommend that some form
of wheeled cart be provided to carry a portable
generator and lights. This could be as simple as a
wheel barrow or cart. The lights will be most
useful if they are hand held and can be directed
from side to side for maximum viewing angle. If
funding were available, some form of permanent
electric lighting along the towpath would obviously
facilitate these inspections.
Reporting Uniformity: A field report must be
prepared and filed after each inspection. We
Final: Jan 2004
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CHAPTER 5:
LONG TERM MONITORING PROGRAM
Goals
As with any building or structure, especially historic
structures, there is an ongoing requirement for periodic
inspections and monitoring of conditions. This is
particularly true when the historic resource has aged and
the deterioration process is underway as is the case with
the tunnel. With a building that is visited daily, there is an
ongoing informal inspection. However, for the Paw Paw
Tunnel, since visitation is light, there is an even greater
challenge especially given the immense size and scale of
the resource and the unlighted conditions inside. For these
reasons, formal inspections on a cyclical basis are strongly
recommended.
The following steps are recommendations of activities that
can be implemented by the Park in the future. These are
intended to supplement current monitoring by the Park
maintenance staff.
Expand Survey Markers
With the tunnel, it is difficult to inspect and monitor
conditions because the appearance is so homogenous.
Inspections that do not indicate precise locations within the
tunnel are meaningless. To address this, we propose an
expansion of the survey marker locators so that anyone on
the towpath can determine his/her location immediately.
We believe this is the first and critical step, to improving
annual monitoring in the tunnel. Several methods could
accomplish this, but the following seems practical and
inexpensive.
There are currently two marker systems within the tunnel:
1.
There are aluminum tags on the underside of the
wooden railing at approximately 25 foot intervals that
were placed as part of the 1997 NPS photo
documentation project, and
Final: Jan 2004
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CONDITION ASSESSMENT AND PRESERVATION PLANNING
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CHAPTER 5: LONG TERM MONITORING
believe there are current NPS inspection and
reporting methods that can be readily adapted for
this purpose.
Mountain Top -
Virtually all the same issues and criteria noted above apply
Drainage Issues
to the drainage problems along the mountain top.
However, the frequency of inspection can be greatly
reduced. Since the problems to the drainage come from
the accumulation of leaves and tree debris in the drainage
troughs, it would seem prudent to have a focused
inspection about 4 times a year. Maintenance work could
then be requested to deal with whatever conditions were
encountered in the quarterly inspections.
Future Research and
Physical Probes of the Brick Liner:
Investigation
There remain at least two unknown conditions where
confirmation of the actual conditions through physical
probes would be very beneficial. The methods used for
the probe could be a core drill, extracting a 2 inch or 4 inch
diameter core of masonry, or the selective dismantling of a
small area of brick work. Funding and human resources
would probably dictate the method. The areas to be
investigated would be:
Vault Ceiling. Confirming the thickness of the
brickwork, as well the conditions between the brick
vault and the rock excavation, would be very
beneficial. The greater the number of probes, the
greater the information developed. We recommend
a minimum of 3 probe locations, but also feel that 6
to 10 would be much more beneficial. Taking two
inch diameter vertical cores may be the most
practical. We believe a truck mounted core drill
machine could accomplish this effort. Once the
cores are complete, then a lighted video recording
through each core can be made to examine the area
above the vault. It would be prudent to leave the
probes open so that future inspections could occur.
Based on recollections of the two vault probes
undertaken 20 years ago by the NPS, we believe
there is 2 to 5 feet of space above the vault and that
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CHAPTER 5: LONG TERM MONITORING
this is filled with isolated brick piers to support the
rock elements. If there is also packing in the form
of soil or loose rock, this would be extremely
important to investigate.
West Prism Wall: During the full survey of
October, 2002, the quantity of water leaking
through the tunnel walls into the canal was very
great. Clearly this water is accumulating behind
the brick liner and then finding pathways through
the liner into the tunnel. We are fearful that water
is ponding between the liner and the rock
excavation. Secondly, we now feel there could be a
significant structural weakness in the vault and wall
connection if the wall is not fully braced against the
lateral thrust of the vault. To investigate these two
factors, we propose to have two inch diameter
horizontal cores made along the west wall, in the
general vicinity of the vertical shafts. If these cores
are on 10 foot enters, we believe 10 cores in total
would be sufficient. The cores would be
investigated using the video device and the cores
would be left open and water flow, if any,
monitored over time. If there is packing material
present, this would be documented.
Physical Probes of the Towpath Wall:
The amount of fill behind the brick towpath wall is
unknown. If there is a significant quantity of loose fill, it
may exert lateral pressure on the brick wall. We
recommend that cores be taken through the wall at several
locations to determine the amount of and condition of the
fill between the back of the wall and the surface of the
original excavation. If a gap is found, then a video device
should be used to explore the conditions behind the wall.
Alternately, if repairs are performed on the walls in several
locations, then the areas to be repaired could first be
extended to create test pits through the walls. We
recommend examining the wall conditions in several
locations because the original rock excavation surface may
vary.
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CHAPTER 5: LONG TERM MONITORING
Analysis of the Vertical Shafts:
It is generally assumed that the vertical shafts are mostly
open, free of fill or debris. If access can be gained from
above, then a video camera investigation could be
undertaken of the full length of the shaft. This type
equipment is used to examine storm water systems under
streets, but it is mounted on rather large truck rigs.
Vehicular access to the mountain top locations above the
shafts may preclude this type of examination. Other video
equipment may be available that would not require truck
access.
Final: Jan 2004
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CHAPTER 5: LONG TERM MONITORING
006
Figure 5.1
Prototype marker on railing. These would be placed at 25
foot intervals at the same locations used by the 1997 NPS
photo documentation project. Having these in place will
greatly facilitate monitoring and inspection of tunnel
conditions.
Final: Jan 2004
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CHAPTER 6:
PROBLEMS REQUIRING IMMEDIATE
SOLUTIONS, COSTS
Purpose
When this study was envisioned, the poor condition of the
tunnel features and the long history of repairs were well
understood. Further, there was an early assumption that
urgent conditions could be identified that needed
immediate solutions. The following is a listing of three
urgent work elements that can be identified. This should
not be viewed as a comprehensive list of needed work, but
rather, a short list of the high priority work needed to
maintain the status quo regarding visitor safety and access.
Since the Park has undertaken many of the repairs with
Park maintenance staff in the past, the following repair
recommendations lend themselves to continuing this
practice, however, the cost estimate assumes competitive
bid contracting.
Cost Estimate
The cost estimation effort provided below is intended to
support budgeting and decision exercises that will follow
to implement recommendations of this report. These cover
the net construction costs and do not include the costs for
architectural and engineering work, nor services to
administer construction contracts. Also, if this project
were to stretch over many years, then a price escalation
factor should be added. We have added a 20%
contingency to the construction to cover unforeseen
developments during the design or construction phases.
Cross-timbers, Posts
Based on the survey and analysis presented in Chapters 3
and 4, we have concluded that many, perhaps most, of the
625 cross-timbers may have sufficient rot and deterioration
to warrant replacement. Unfortunately, visual analysis
would not be conclusive to make this determination. A
physical probe or core section taken from the exposed end,
at least 18 inches deep, could be most useful. Since the
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CHAPTER 6: IMMEDIATE REPAIRS
greatest risk of danger to visitors comes if the iron post
does not have sufficient support from the timber, this probe
of the outer 18 inches may be sufficient in making a
determination regarding replacement.
The iron post and the wooden railing elements can be
reused once the timber is replaced.
Timber Replacement - General:
The previous practice of using heart oak for the
replacement timbers is logical. Generally this species is
quite resistive to rot from moisture and insects. However,
it would appear based on the test pits in the tunnel that
even the oak is only lasting 20 years or less. Having
replacement cycles for the timbers of 20 years would be
very costly over time, and probably cause interruption to
visitation by the public.
Over the last few years, new hybrid wood products have
come into the market place that utilize re-cycled wood
products, bound together with re-cycled polyesters, to form
wooden decking and timbers for exterior use. These
products also have the programmatic benefit of being
"sustainable or green" and they have proven to have very
good service life. Some manufacturers are offering 40 year
warranties on the materials, even if submerged in water.
We would strongly encourage the Park to consider some of
these products for these timbers. They are available in the
needed sizes and can be worked and cut with typical wood
working tools. The appearance and texture will nearly
match the oak timbers.
These materials can be found by searching for "structural
plastic lumber." There are a growing number of
manufacturers and suppliers and two regional
manufacturers are:
Polywood
125 National Road
Edison, NJ 08817
Phone: 800-915-0043
www.polywood.com
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CHAPTER 6: IMMEDIATE REPAIRS
Phoenix Plastic Lumber Yard
220 Washington Street
Norristown, PA 19401
Phone: 610-277-3900
www.plasticlumberyard.com
Pressure treated lumber would not be recommended where
high moisture levels are a frequent occurrence. Such
timbers might last less than 10 years in such an
environment.
Cost Estimate - Single Cross-timber Replacement:
We believe the cost to excavate and replace a cross-timber
using the hybrid wood product, and refit the existing iron
post and railing, will be about $ 1,500 each. This is a two
day job for 3 persons.
There will be economies of scale of more than one cross-
timber in a given area can be replaced at the same time. If
$50,000 could allocated for each fiscal year, then at least
35 timbers could be replaced each year, perhaps up to 45.
This work could be accomplished during the winter when
towpath use is minimal. This could take 15 years to
replace all of the timbers.
Special Case - Areas Near Vertical Shafts:
Since the excess water in the vicinity of the vertical shafts
is such a problem, and there is little hope of really curbing
this condition, we would propose a dramatically different
solution for the towpath and railings in these areas.
Actually, the proposal is to return to the treatment that was
apparently in place when Archie Franzen undertook his
study in 1965, namely, to use timber planking and decking
where there is excess water and eliminate the towpath fill
material. It seems clear in the analysis in Chapter 3, that
encasing the oak timbers in moist soil material is a recipe
for wood rot and deterioration. Where we have high
quantities of water, it makes sense to eliminate the soil and
rock so that water can flow below the timbers and there is a
good chance that the timbers will dry out from time to
time. This new replacement assembly is illustrated in
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
Figure 6.1. Further, we propose to use the new hybrid
wood products that have such a long service life. The
decking planks using this hybrid wood have a non-slip
texture so the constant wetting should not be a concern.
These wooden deck assemblies could actually be
fabricated off site and brought to the tunnel. They could be
fabricated in modular section of say 15 feet in length (i.e.,
4 timbers and 4 post units). These would have a good deal
of rigidity because the timbers and planking would be tied
together to form an integral structural unit. We suggest
two 45 foot long assemblies, one at each vertical shaft
location.
Cost Estimate: New Timber Decking Module
This cost estimate is based on the proposal above to
remove the towpath fill material and install a new timber
decking assembly in 15 foot long module. This
replacement module is illustrated in Figure 6.1.
Estimate Calculation ( One 15 foot long module):
ITEM
UNIT
UNIT COST
TOTAL
Excavation
LS
$ 2,000
$ 2,000
Disassemble
LS
$ 600
$ 600
Railing
Fabricate and
LS
$ 6,000
$ 6,000
install 15 LF of
towpath decking,
with cross-
timbers. Re-use
railing and iron
posts.
Final
LS
$600
$ 600
adjustments
SUBTOTAL
$ 9,200
Contingency @
$ 1,800
20%
TOTAL - 15 LF
$ 11,000
To replace two 45 foot long segments at the vertical shafts
as discussed above, the estimated costs would be about
$66,000 (i.e., 6 modules @ $ 11,000 each). Since these
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
elements can be fabricated off site, the disruption to the
tunnel visitor could be shortened to only a few days. This
work can be undertaken during the winter months, when
towpath traffic is minimal.
Historic Precedence:
There is some reason to believe that the current towpath
configuration of crushed rock may not have been the case
for portions of the towpath. In the 1960's when Archie
Franzen undertook his assessment, his drawings clearly
indicate that here was wooden decking for short segments
of the towpath in the immediate vicinity of the ventilation
shafts. The proposal above would return the towpath to
those conditions. We assume that the wet conditions
near the ventilation shafts have existed since the tunnel
was opened. These wooden decks would have been a more
satisfactory way of maintaining towpath continuity through
that long period of time since the excess water would have
flowed under the decking rather than remaining within the
towpath soil.
Replacement of Damaged Wrought Iron:
Although a few of the existing iron posts have deteriorated,
the wrought iron overall has proven a very good material
for use in this environment. For the damaged ones, it
would be logical to replace with wrought iron,
unfortunately, wrought iron is very hard to find in any
quantity as it was long since replaced by steel in the market
place. Substitutions using mild steel, or galvanized steel,
could be considered, but these would have a service life in
the range of 20 to 40 years. This would not be long
enough for this project. Stainless steel could also be
considered. It would have a very long service life, but its
appearance might be an issue. It could be made to have the
same size and shape as the existing, but it would have a
shiny surface. Also, stainless can not be "wrought." It
would need to be bent and welded to obtain the yoke shape
at the top. Given the low light levels in the tunnel,
appearance issues may be less of a factor than service life.
Cost Estimate - Iron Post Replacement:
Estimating the costs for replacement of the iron posts is
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
compounded by two issues: 1) the very low supply of
historic wrought iron and, 2) the relative short supply of
craftsman able to undertake wrought iron work of this size
and type. We estimate more than 40 hours for the
craftsman to fabricate a single post, so these will cost a
minimum of $2,000 each. To be conservative, this price
should be doubled. There are between 5 and 10 posts
that should be considered for replacement, so as much as
$40,000 should be allocated to iron post replacement.
Selected Brick Liner
At the time of the survey, there was one small area on the
Repairs
west wall, in segment 024, which had actually collapsed.
Approximately 6 square feet is involved. There are other
areas where the brick liner appears to be bulging, which is
believed to be the first symptom of a collapse. These areas
will be identified for ongoing monitoring and then repair
work should be scheduled if the conditions worsen.
Cost Estimate - Brick Liner Replacement:
For the purposes of this estimate, a work area 4 ft. high by
8 ft. long is priced. This should be taken to be the
minimum area that can be repaired.
ITEM
UNIT
UNIT COST
TOTAL
Selective
LS
$ 600
$ 600
Demolition
Place brick in
LS
$ 1,200
$ 1,200
patch - 2 days
Clean up
LS
$ 600
$ 600
SUBTOTAL
$ 2,400
Contingency @
$ 480
20%
TOTAL
$ 2,880
Thus, about $3,000 could be assumed for each 32 sq. ft. of
brick liner repair. However, this cost may be difficult to
extend to multiple work areas. The extra costs for a
general contractor to mobilize for only one or two repair
areas, VS. many more, is hard to estimate. Small projects
will always cost more, perhaps twice as much, as larger
projects.
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
Selected Prism Wall
Urgent repairs are needed to the segment of brick wall at
Repairs
the top of the east prism along the towpath. This is
immediately below the wooden kick board where there is
serve erosion of the mortar joints and in the worse case, the
brick courses are actually out of alignment (see Figure
6.2). If these were to fail, as they have in one small
location, the towpath material would collapse, creating a
sink hole. A very unsafe condition results on the towpath
itself.
Cost Estimate: Top of East Wall:
The worst cases are in the area of the vertical shafts, in
survey segments 097 to 099 and 119 to 121. Approxi-
mately 40 lineal feet of repair area is involved.
ITEM
UNIT
UNIT COST
TOTAL
Selective
LS
$2,700
2,700
Demolition,
layback towpath
material, 3 days
Clean brick,
LS
$ 4,200
$ 4,200
replace wall
segments, 5 days
Clean up, replace
LS
$ 600
$ 600
towpath fill
material, 2 days
SUBTOTAL
$ 7,500
Contingency @
$ 1,500
20%
TOTAL
$ 9,000
This assumes all work is done at the same time in
contiguous work areas. This does not include the cost to
re-route visitors. The towpath would be closed during this
work effort. Mortar and brick work should not be
undertaken when temperatures are below 40 degrees.
Luckily, the interior temperature in the tunnel remains
above this level, even when the outside temperatures are
lower. Therefore, this work can probably be undertaken in
the winter months when tunnel traffic is reduced.
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
FILL MATERIAL
NEW DECKING
Figure 6.1
Some of the timbers in the worst condition will most likely
be those in the vicinity of the vertical shafts because of the
excess moisture conditions. We propose to remove the
towpath fill material in these locations and then install
several sections of wooden deck and planking as illustrated
here. These units could be fabricated off site in 15 foot
lengths, and then installed in a short period of time. The
hybrid wood products that utilize recycled wood and
polyethylene will be used. The iron posts and railing
would be re-used from the existing assemblies. The pattern
of brick coursing in this illustration should not be taken literally.
Final: Jan 2004
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CHAPTER 6: IMMEDIATE REPAIRS
Figure 6.2
Many of the horizontal sections of brick between the
wooden timbers need to be rebuilt. This is especially true
in the areas near the vertical shafts. The mortar appears to
be in such poor condition that these existing assemblies
could probably be disassembled and re-installed relatively
easily.
Final: Jan 2004
Page 6.9
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
CHAPTER 7:
FIELD SURVEY DOCUMENTATION
Survey Methodology
The methodology is described above in Chapter 3. The
following are the actual field survey data sheets, two for
each of the 137 survey segments, including the South and
North Portals.
The notations use numbers, which in turn refer to standard
notations, or keynotes. Along with the keynote numeral on
the survey sheet, there may be additional information that
is unique to that note, in that location. For example,
keynote 5 refers to water / mold stains. The words
"DAMP" or "WET" may be added to the notation. See
below for a definition of these terms.
Survey Keynotes
These are the keynotes used for the field survey work.
Comments in brackets [], provide the reader with
additional information.
1.
Brick patch in wall, darker red brick, presumed to
be 20th -century repair area.
[This notation was indicated for any obvious brick
patch, whether it was the dark red or medium red
brick type].
2.
Spalled face of brick, severe spall, at least 1 inch in
depth, could be 2 inches.
[This condition was rather rare.]
3.
Deep mortar erosion, at least ½ inch, could be
several inches deep. Mortar is also soft.
[The word "deep" should be ignored in this note.
During the survey, conditions much more severe
were discovered and a new keynote, # 17, was
developed for the "deep" erosion.]
Final: Jan 2004
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CHAPTER 7: FIELD SURVEY DOCUMENTATION
4.
Loose bricks, appear to be dislodged and / or out
of alignment.
5.
Dark black water / mold stains to brick area.
[Words were sometimes added to this note.
"Damp" meant visibly moist, while "wet" meant
that water was clearly flowing across the area of
the stain.]
6.
Severe water stains, includes lime and calcium
build-up.
[This could include stains from active conditions
(currently moist) or stains from previously damp
conditions.]
7.
Wet face of brick, could include active water
flows.
[This condition was similar to that noted in 6, but
differs in that the brick was definitely wet.]
8.
Second generation cross-timber.
[See Figure 3.16, noted as pre-NPS timber.]
9.
Recent replacement cross-timber, approximately
11 X 11.
[See Figure 3.17, noted as NPS timber.]
10.
Comment on railing, iron post, or cross-timber.
[Additional information would be placed directly
on the survey form with this notation.]
11.
Putlog / scaffold hole, approx. 2 2/1 inches x 5
inches.
[These holes always occur at a uniform height, in
the same course of brick, just below the spring line
of the vault. See figure 2.2. They are irregularly
spaced, but often they were 10 to 14 feet apart.
These occur on both the east and west sides of the
Final: Jan 2004
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PAW PAW TUNNEL
REPORT OF FINDINGS
C&OCANALNHP
CHAPTER 7: FIELD SURVEY DOCUMENTATION
tunnel, but they do not occur immediately opposite
each other. The holes are 5 to 8 inches in depth]
12.
Weep hole, approx. 5 inches x 5 inches.
[We have characterized these as "weep" holes
because they occur only in the immediate vicinity
of the vertical shafts. They are spaced close
together (i.e., 3 to 5 feet) and at differing vertical
heights. Water actively runs out of many of them,
and they appear to be very deep, some more than
20 inches in depth. The 5 x 5 inch dimension was
quite uniform.]
13.
Rowlock course at spring line.
[This is an all-header course at the top of the
vertical walls.]
14.
Stalactite-like formation.
[This note used only where there was visible build-
up of the lime/calcium deposit, forming a
distinctive drip or icicle. White colored stains
would not have been given this notation.]
15.
Efflorescence
[By and large, this note was used where the
crystallized salts were visible at the mortar joints.
Other general white stains across the face of the
brick were probably noted with keynote 6.]
16.
Brick powder on tow path at base of east wall
[There were only a few areas where the face of the
brick work above is actually spalling, or scaling,
sufficient to leave a pile of brick dust on the tow
path.]
17.
Severe mortar loss.
[This notation was used where the erosion was
deeper than ½ inch (where keynote 3 would have
been used). Where this note is used, the erosion
Final: Jan 2004
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REPORT OF FINDINGS
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CHAPTER 7: FIELD SURVEY DOCUMENTATION
was often over 2 inches in depth.]
18.
Missing Bricks
[This notation used where brick had actually
collapsed. The "missing" brick were often at the
base of the wall in the canal prism.]
19.
Misaligned brick courses
[This note used where one course had shifted and
was no longer flush with the adjacent course(s).]
20.
Moss growth on the base of the east wall, near tow
path.
The survey sheets for each segment follow.
Final: Jan 2004
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BIBLIOGRAPHY
This bibliography was prepared by Dr. Robert Kapsch of
the National Park Service based on his research efforts that
preceded this study. It is reproduced here to record his
documentary research.
Historic Drawings
Ellwood Morris, Paw Paw Tunnel Profile, 1836.
National Archives, Record Group 79, Entry 222,
Volume 1 of 1. Scale: 1" = 100'.
This is the original tunnel profile submitted by
Ellwood Morris to Chief Engineer Charles Fisk.
It is essentially a design document and differs in
some details from the completed tunnel. For
example, the length of the tunnel is indicated at
3120 feet (vs. 3118 feet) and only two vertical
construction access tunnels are indicated
(instead of four), labeled "A" and "B."
Nonetheless the drawing is probably very close
to "As-built." This drawing was the base
drawing used by Archie Franzen in his "Sketch
2," 1965 Historic Structures Report.
Ellwood Morris, Design for a Projecting Tow Path for
the Tunnel (including a quantity take-off), March
1, 1839, National Archives, Record Group 79, Entry
214.
This may be the closest design drawing to what
was actually constructed. The towpath is
supported by unexcavated rock. Above the
unexcavated rock are horizontal white oak
members that cantilever 2 feet over the
unexcavated rock to support the railing assembly
above. A small cavity is shown between the
brick lining and the rock excavation.
Ellwood Morris, Design for a Iron Path for the
Tunnel to have a Brick Parapet with a Stone Coping
(including a quantity take-off), October 7, 1839,
National Archives, Record Group 79, Entry 214.
This later sketch indicates a brick wall with stone
coping as the towpath wall. This construction was
obviously rejected and was never constructed. A
Final: Jan 2004
Biblio 1
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
BIBLIOGRAPHY
similar drawing by Ellwood Morris, dated January
4, 1840, is attached to Steve Kline memorandum of
November 1, 1994.
Ellwood Morris, (Sketch: Section of Tunnel, including
liner and towpath), October 15, 1839, National
Archives, Record Group 79, Entry 214.
This sketch indicates a circular brick lining (27'
O.D.; 24 - 10/12' I.D.) rising on vertical walls.
This is contrasted to the horseshoe shaped tunnel
section shown in the 1839 issue of Journal of the
Franklin Institute. The towpath in this sketch is
shown on unexcavated rock (while the towpath
shown in the section appearing in the 1839 issue of
the Journal of the Franklin Institute is open to the
water below). This cross section indicates what
appears to be a masonry railing.
Contemporary Drawings
C. H. Blake, Park Engineer and W.E. McGarvey,
Student Assistant, Study Sketch of Conditions
Causing Failure at Paw Paw Tunnel, C & O Canal
National Monument, September 1963, Scale 1" = 100';
Sheet 1 of 1. No drawing number. Pencil on vellum.
Original drawing filed at C & O Canal Headquarters,
1850 Dual Highway, Hagerstown, Maryland.
Drawings shows profile (1" = 100') with
existing conditions indicated; topo above the
tunnel (1" = 100'); elevation of North Portal
(1/8" = 1 ft.) and typical tunnel; section (1" =
100 ft.).
(No Title: Remove Rock Slide at North Portal),
No Date (late 1970s?). Three sheets: (Sheet 1: Location
Plan); (Sheet 2: Topography); (Sheet 3: Detail of Rock
Slide to be Removed at North Portal). No drawing
number. Blue line drawing filed at C & O Canal
Headquarters, 1850 Dual Highway, Hagerstown,
Maryland.
Not much information depicted on drawings -
included to show the extent of the rock slide,
and the temporary wood cribbing installed at the
North Portal during its removal. This may have
been removed late 1970s/early 1980s.
Final: Jan 2004
Biblio 2
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
BIBLIOGRAPHY
John Milner Associates for Denver Service Center,
National Park, Paw Paw Tunnel Portals, Chesapeake
and Ohio Canal National Historical Park, Drawing
No. 412/25063, 6 Sheets, October 4, 1978. Half size
Xerox copies located at C&O Canal Headquarters,
1850 Dual Highway, Hagerstown, Maryland. Marked,
"Preliminary Working Drawings."
Sheet 1. Location and Vicinity Maps.
Sheet 2. Paw Paw Tunnel Portals - South
Portal
Sheet 3. Paw Paw Tunnel Portals - North
Portal
Sheet 4. Paw Paw Tunnel Portals - Portal
Drainage Systems
Sheet 5. Paw Paw Shaft Collection Works
Partial copy of: C. H. Blake, Park
Engineer and W.E. McGarvey, Student
Assistant, Study Sketch of Conditions
Causing Failure at Paw Paw Tunnel,
C & O Canal National Monument,
September 1963, Scale 1" = 100'; Sheet
1 of 1. No drawing number. Pencil on
vellum. Original drawing filed at C &
O Canal Headquarters, 1850 Dual
Highway, Hagerston, Maryland. (Listed
above).
Note: This drawing shows stainless
steel pipes installed, stainless steel
drips pan and other details related to
water entering the tunnel.
Sheet 6. Paw Paw Tunnel Closure
John Milner Associates for Denver Service Center,
National Park, Paw Paw Tunnel Complex,
Chesapeake and Ohio Canal National Historical
Park, Drawing No. 412/25045-A, 8 Sheets, May 15,
1979. Half size Xerox copies available from Denver
Service Center Technical Information Center (TIC).
Drawings Marked, "IFB No. 3100-78A." [Copies of
these drawings are not available at C & O Canal
Headquarters]
Sheet 1. (Cover Sheet: Project Title and
Location).
Sheet 2. (Project Site Identification: Access
Plan)
Sheet 3. (North Portals: Paw Paw Tunnel
Portals)
Final: Jan 2004
Biblio 3
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
BIBLIOGRAPHY
Sheet 4. (South Portals: Paw Paw Tunnel
Portals)
Sheet 5. (Structural Details: Portal Parapet
Repairs)
Sheet 6. (Structural Details: Tunnel Portal
Drainage System)
Sheet 7. (Structural Details: Tailings Pile, Wing
Wall Repairs)
Sheet 8. Structural Details: Slope Scaling,
Towpath Repairs, Tunnel Shafts
, (No Title: Field Survey of Existing
Conditions, Sheet 1 of 1, "Field Survey 7/25/63,"
Scales are not given but appear to be 1" = 100' for the
tunnel profile and 1/4" = 1 foot for the North Portal
(South Portal not drawn); Sheet 1 of 1. No drawing
number. Pencil on vellum. Original drawing filed at C
& O Canal Headquarters, 1850 Dual Highway,
Hagerstown, Maryland.
This drawing does show existing conditions in
tunnel profile, such as seepage points, stains,
wall conditions, etc.
Reports
Luzader, John F., Historic Structure Report: Paw
Paw Tunnel, Chesapeake and Ohio Canal, undated
typescript.
National Heritage Corporation, Archeological Survey
of Paw Paw Tunnel Hollow, (Denver, Colorado:
Denver Service Center, February 1, 1976).
John Milner Associates and Edward H. Richardson
Associates, Paw Paw Tunnel Portals, Chesapeake
and Ohio Canal National Historical Park, Allegany
County, Maryland: STABILIZATION STUDY,
Preliminary Design, (Denver, Colorado: National Park
Service Center, September 1978).
Franzen, Archie W., Historic Structures Report, Part
I, Architectural Data Section on The Paw Paw
Tunnel, C & O Canal National Monument,
Typescript. (Philadelphia: National Park Service
Eastern Office of Design and Construction, March
1965).
Denver Service Center, Assessment of Alternatives,
Stabilize Paw Paw Tunnel Portals, Package No. 153,
(Denver, National Park Service, January, 1979)
Final: Jan 2004
Biblio 4
CONDITION ASSESSMENT AND PRESERVATION PLANNING
PAW PAW TUNNEL, C & O CANAL NHP
BIBLIOGRAPHY
Articles
Morris, Ellwood, Prin. Assis. Eng., C & O Canal
Company, "Sketch of the Tunnel now under
construction upon the Chesapeake and Ohio Canal, at
the Paw-paw bend of the Potomac River," Journal of
the Franklin Institute of the State of Pennsylvania
and Mechanics' Register, Vol. XXIII (1839), pp. 24-
27.
Luzader, John F., "The Paw Paw Tunnel on the
Chesapeake and Ohio Canal has been called the
Engineering Marvel of 1850," The Baltimore Sun, no
date, (1960s?), pp. 7-13.
Other
, "Paw Paw Tunnel, C & O Canal NHP Segment
Files 000-138, Scale Elevations of Towpath Wall at
Scale 1/4" = l' - 0" (Compact Disk of photographs taken
within Paw Paw Tunnel under contract to the
Chesapeake and Ohio Canal NHP of towpath wall,
October 17, 2000).
Final: Jan 2004
Biblio - 5
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
APPENDIX: Determining Shaft Locations
The attached materials were prepared by the NPS in an
effort to determine the locations of the former ventilation
shafts on the top of the mountain. The terrain and
vegetation make identification of the top of the shafts very
difficult, so this calculation effort narrows the variables so
that future physical probes could be undertaken with
greater certainty. Locating these shafts has been the
subject of several previous investigations and these results
are documented on the drawing prepared by QUINN
EVANS | ARCHITECTS that is bound with this report.
The following description for the shafts is provided by
Archie Franzen on page 1 of his 1965 report;
"The shafts were employed to increase the working
surfaces and were bored in pairs, with one shaft
presumably used for ventilation, while the other
was used for hoisting men, tolls and rock spoil.
These paired shafts were located, a pair in each of
two ravines, near the North portal. Their locations
were selected to minimize the hoisting height and
to provide suitable spoil area for the material
removed from the bore. From the record it appears
that they were eight feet in diameter, and a pair
were spaced twenty-three feet a part
Final: Jan 2004
Appendix 1
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
APPENDIX
Paw Paw Tunnel: Determining Shaft Locations
CHOH GIS Lab 08/27/2003
NATIONAL
Objective:
The question arose regarding the determination and location of four ventilation/access shafts and six
historic survey markers above the Paw Paw Tunnel. In order to document and make the best
possible judgment of these locations, GPS technology was utilized to map the locations of the
potential shaft locations and the path of the tunnel with which the shafts and survey markers are
aligned.
Methods:
Data Collection
Data was collected using a Trimble Pro-XR with real-time differential correction, allowing for sub-
meter accuracy of point locations. GPS point locations were first collected approximately above the
keystone of both the North and South portals. These points were used as navigation waypoints, as
well as reference marks for locating survey markers and shaft locations. All markers and potential
shaft locations were also collected via GPS.
Data Analysis
Data of portal keystones were utilized in a GIS to develop a line file representing the centerline of
the tunnel, which was then used to verify shaft locations (figure 1). Features thought most likely to
be shaft openings were designated shafta, shaftb, shaftc, and shftd. Other potential locations were
also collected for purposes of eliminating alternative features as the shaft openings. These features
were designated x1, x2, x3, y1 and y2. All GPS data was converted to GIS point layers for
visualization and shaft location verification.. In order to determine which features were actual shaft
locations, GIS point layers were compared to the developed tunnel centerline.
Conclusion:
This analysis illustrates that features designated as shafta, shaftb, shaftc and shaftd either fell on the
line or were within a proximity of 3.5 feet (figure 2 & 3). From this analysis, the locations and
designation of the shaft openings is conclusive. Distances between GPS locations of shafts were
also approximated. These locations were neither recorded in the center of the cap, or the shaft. The
distances did not correspond with schematic diagrams. However, error of standing location, as well
as an error of up to one meter associated with the GPS, may explain this discrepancy.
Note:
Maps were created on 08/27/03 by CHOH GIS Lab. Base data for map is 1:24000 DOQQ. Point features were
collected using Trimble Pro XR GPS. Line file for tunnel centerline was created from GPS keystone locations, using X
Tools extension in ArcView 3.3. Data is suitable for planning purposes only.
Final: Jan 2004
Appendix 2
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
APPENDIX
Tunnel Centerline (GPS)
640
660
680
y1
shafta
700
720
9
y2
shaftb
N
20
0
20
40
60
80
100
120
140
160
180
200 Feet
Figure 2
Final: Jan 2004
Appendix 3
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
APPENDIX
Tunnel Centerline (GPS)
780
760
740
720
x3
x2
x1
b
shaftc
shaftd
N
20
0
20
40
60
*80
100
120
140
160
180
200 Feet
Figure 3
Final: Jan 2004
Appendix 4
PAW PAW TUNNEL
REPORT OF FINDINGS
C & O CANAL NHP
APPENDIX
Paw Paw Tunnel
Shaft Locations
Figure I
+
Portal Keystone
Survey Marker 2
Survey Marker 3
Survey Marker 4
North Portal
Survey Marker 5
mark 6
A
Survey Marker 6
shafta
o
Shaft A
shaftb
Shaft B
Shaft C
mark 5
Shaft D
o
x1
x2
shafte
x3
shaftd
.
y1
o
y2
mark 4
Paw Paw Tunnel
see attached document for project details
mark 3
mark 2
south portal
500
1000
Final: Jan 2004
Appendix 5