PASSIVE ICING SHIELDS FOR RAILROAD TUNNEL … to locomotive exhaust blast to the underside and rusting of the rock bolt ... structural support to the tunnel ... of the shotcrete tunnel

PASSIVE ICING SHIELDS FOR RAILROAD TUNNEL IN GALLITZIN, PA

Authors’ Names and Contact Information:

Phaidra Campbell Jacobs Associates 1109 First Ave, Suite 501 Seattle WA 98101 206.588.8112 Ruth Brown Norfolk Southern Railway 1200 Peachtree St NE Atlanta GA 30309 404.529.1225 Joseph Schrank, PE, PEng Jacobs Associates 1109 First Ave, Suite 501 Seattle WA 98101 206.588.8125

© 2012 AREMA

Word Count This manuscript has 3,374 words, 10 figures and 1 table.

© 2012 AREMA

ABSTRACT

Severe seepage and resultant winter icing restricted clearances in the Allegheny Tunnel

lining and covered the track structure for hundreds of feet, interfering with traffic and requiring

significant maintenance. The tunnel was enlarged to a double track/double stack structure in the

mid-1990s by CONRAIL, predecessor to Norfolk Southern Railway (NSR) in central

Pennsylvania. At that time, passive icing shields (no heat added) were installed for about 335

linear feet (102 m) as part of the enlargement project. These shields consisted of interlocking

panels fabricated from a layer of closed-cell polyethylene sandwiched between galvanized steel

sheets. The back of the panels was covered with a sprayed waterproof sealant; however, the

underside was not. After 15 years of use, many of the panels were seriously deteriorated, mostly

due to locomotive exhaust blast to the underside and rusting of the rock bolt hangers that

connected the panels to the adjacent rock.

In 2010, NSR requested Jacobs Associates design a retrofit or replacement for the

existing icing shields that would fit in the clearance envelope and could be implemented in work

windows of 2 to 6 hours duration. Jacobs Associates, working with NSR’s Engineering

Department, designed a self-supporting structure consisting of steel sets lagged between the

webs with closed-cell polyethylene insulation, a thick drainage mat over the back of the structure

for seepage control, and shotcrete covering the underside to protect the structure from

locomotive blast. Additionally, individual small seeps in other areas of the tunnel were captured

using bladders encased in shotcrete.

© 2012 AREMA

INTRODUCTION

Allegheny Tunnel is located at the summit of the Allegheny Mountains in Gallitzin,

Pennsylvania, and crosses Cambria and Blair counties (Figure 1). Allegheny Tunnel is one of

three Gallitzin tunnels that were constructed to allow train passage running east to west through

the mountain range. The tunnel was constructed between 1851 and 1854 by the Pennsylvania

Railroad Corporation using steam shovels and drill-and-blast operations to a length of 3,600

linear feet (1,097 m) (Station 0+00 to 36+00) at an elevation of 2,167 feet (661 m). The lining

consisted of a brick arch and masonry sidewalls, with ashlar sandstone masonry at the east and

west portals.

Ownership of Allegheny Tunnel was transferred to Consolidated Rail Corporation

(CONRAIL) in 1976. From 1994 to 1996, excavation was completed to expand the tunnel from a

single track/single stack to a double track/double stack structure. The approximate cost for this

construction was $27.7 million. Work included removal of approximately 90,000 cubic yards of

original masonry and brick lining, and approximately 12 feet of lining and rock per foot of tunnel

for the second track. The entire tunnel was relined with a combination of shotcrete and rock bolts

for most of its length, while the east end had 550 feet of steel sets installed, and the west portal

was cast-in-place concrete (Figure 2). The original ashlar masonry portal headwalls and portal

facade were reconstructed with salvaged masonry blocks in order to replicate the original historic

composition of the structure (1). In addition, premanufactured icing shields were installed at

several sections of the tunnel that were experiencing significant seepage and freezing. To control

drainage, through-tunnel drain lines were installed at the north and south inverts along with two

steel pipes to carry water transiting from one portal to the other and to catch in-tunnel seepage.

Ownership of the Allegheny Tunnel was transferred to Norfolk Southern Railway (NSR) in

© 2012 AREMA

1999. Currently, 40 to 50 freight trains and Amtrak passenger service operate through this tunnel

each day at a speed of 50 mph.

ICING ISSUES

The 1996 icing shields were designed to be a passive system that would control ice

formation in the tunnel (Figure 3). The icing shields were manufactured off site and consisted of

3-inch-thick (75 mm) panels constructed of two thin galvanized steel sheets with a core of

polyurethane insulation planks between them. The steel sheets acted as protection to the

polyurethane insulation planks while also providing structural rigidity to the system. Individual

steel sheets were connected to adjacent steel sheets with camlock devices. The entire shield

structure was suspended from the irregular shotcrete perimeter liner with hangers attached to the

shield panels with screws, and was founded on formed concrete footings. The ends of the icing

shield were bulkheaded with marine grade plywood that trapped air between the icing panels and

the shotcrete tunnel liner surface. All of the attachment hardware was either stainless steel or

otherwise protected from the corrosive effects of the seepage. In addition, a layer of heavy

mastic protection was later painted on the field side of the sheets to protect against corrosion.

The steel shields were not meant to offer structural support to the tunnel ground or ice

loads, but rather to inhibit the formation of ice by maintaining the temperature of the seepage

above freezing until the seepage entered the tunnel drainage system. This system seemed to work

well because no signs of ice loads on the shields or puncture damage from impact loads were

observed.

However, after 15 years of operation, the existing icing shields were deteriorating and the

track side of the sheets and the hanger screws were intensely rusted (Figure 4). The deterioration

reached a point at which individual panels started falling off and the track side steel sheet

© 2012 AREMA

completely delaminated from the polyurethane insulation plank. This deterioration of the track

side appeared to result from seepage into the polyurethane core from the joints in the panels and

possibly from the locomotive exhaust gas. Existing shields were located at the following

locations within the tunnel (Figure 5): Station 24+32 to 25+00, Station 32+04 to 34+71, and

Station 35+50 to 35+53. In 2009, the existing shields at Stations 24+32 to 25+00 and 35+50 to

35+53 were removed because of their deteriorated condition.

With extreme winter conditions and record freezing temperatures in 2009 and 2010, large

icicles developed within Station 24+32 to 25+00 from existing seeps within the tunnel (Figure

6). The icicles were large enough that NSR personnel were required to remove them every other

day to limit hazards to rail traffic. Such hazards consist of penetrating or damaging of rail cars,

including possibly the windshield of a passing engine; reduction of clearances leading to speed

restrictions; and possible derailment if ice built up over the track structure because of poor

drainage. Because of the high volume of rail traffic in the Allegheny Tunnel, derailment was less

of an issue. Of bigger concern was damage to rail cars, clearance restrictions, the time required

to remove the icicles, and hazards that NSR personnel faced during ice removal.

Icicles also have a long-term impact on structure components within tunnels. Such impact

includes the loss of integrity of the shotcrete tunnel lining, ballast contamination, and unplanned

additional weight on utility lines. Over time, freezing and thawing of water in the shotcrete lining

can cause consequent cracking in the shotcrete, especially if the shotcrete was applied

improperly with subsequent voids or had a poor mix design. Additional cracking in the shotcrete

allows not only for more water to seep through the liner, but reduces the structural integrity

allowing for a greater chance of rock fall. Icicles can also introduce waterlogging and clogging

of the track ballast, which can lead to difficulties with track maintenance. Utilities within the

© 2012 AREMA

tunnel may experience heavier loads than expected and could be damaged or collapse from the

weight.

A site visit was conducted in January 2010 by NSR and Jacobs Associates to address the

replacement of the existing icing shields. The site visit confirmed that the existing tunnel

shotcrete lining was still in good condition. However, in addition to the presence of large icicles,

additional observations revealed six ruptured drainage bladders within the shotcrete liner, little to

no shotcrete present on the existing steel sets at the east portal, and missing bulkheads on

existing icing shields.

ICING SHIELD DESIGN

After reviewing the condition of the existing icing shields and alternatives to replace it, a

similar passive system was designed to control the icing condition at the same locations as the

existing icing shields (Figure 5). The new passive icing system design (Figure 7) consisted of

steel sets spaced evenly on center anchored into the existing concrete footings; between the steel

sets was a layered arrangement of components. This arrangement, going from the field side to

the track side, consisted of a drainage mat and two layers of insulation planks (Ethafoam 220 - a

closed-cell polyethylene). The track side of the steel sets and the insulation planks were covered

with galvanized metal Stay Form and a 2-inch (50 mm) layer of fiber-reinforced microsilica

shotcrete.

This shotcrete layer allowed not only protection of the insulation planks from locomotive

exhaust gas, but also helped form an airtight system to help contribute to the effectiveness of the

icing shield system. This airtight system can be compared to the insulation of an attic or

basement of a house - air does not circulate but maintains heat and acts as an insulator. The

shotcrete was limited to a 2-inch thickness because of clearance concerns. Along with the icing

© 2012 AREMA

shield, a drainage system was included in the design to collect the water seeping from the tunnel

liner and direct it into the existing invert drains that would eventually take it out of the tunnel.

Although the icing shield system was designed to inhibit ice formation, the steel sets

were designed for varying loading conditions, including ice formation located universally along

the entire span of the icing shield, along half of the icing shield, and along one-third of the icing

shield. The geometry of the steel sets was determined based on typical steel set geometry used in

tunnels while also complying with the tunnel clearance requirements: two column sections and

two arch sections with a single radius of curvature. The connections were typical steel set

connections with steel plates and threaded bolts at the spring line and crown. All of the steel

elements were required to be corrosion protected.

In order for the icing shields to be successful at inhibiting ice formation, adequate

thermal resistance (R-value) and an adequate drainage system were needed. The R-value is a

measure used to determine the required insulation parameters for specific structures in a climate

location. For our icing shield design, the required R-value came from the 2009 International

Energy Conservation Code (IEEE) (2) for Cambria County, Pennsylvania, which is identified as

Climate Zones 4 and 5. The required R-value range was determined to be a minimum of

19 ft2·F°·h/Btu to a conservative value of 38 ft2·F°·h/Btu for ceilings. The R-value for our system

was determined by the Colorado Energy Organization values for material properties (3), shown

in Table 1.

The total R-value of 34 ft2·F°·h/Btu was adequate because it is within the required range

stated above and some of the materials that may be contributing to the thermal resistance were

not used in determining the design value, such as the drainage mat and galvanized steel.

© 2012 AREMA

The drainage system is extremely important for the icing shields to be effective since

blocked drainage could impose hydraulic loads on the shields. The drainage system ensures that

no water gets through the icing shields and over to the track side of the tunnel. Therefore, the

design drainage path allowed for water to seep from the tunnel liner to the back of the drainage

mat, down to the concrete footing, through the PVC piping, and to the existing drains.

Additional design work included in the icing shield replacement project included

applying fiber-reinforced shotcrete over the exposed steel sets near the east portal and replacing

the ruptured drainage bladders (as shown in the locations in Figure 5). The drainage bladder

replacement design consisted of a dimple board drainage mat pinned to the existing tunnel wall,

covered with a single 2-inch insulation plank, then a layer of Stay Form, and finally a 2-inch

layer of fiber-reinforced shotcrete.

CONSTRUCTION

The design work was completed in June 2010 and put out to bid by NSR. LRL

Construction Company of Tillamook, Oregon, was the winning bidder, and construction of the

new icing shields began in late September 2010. LRL’s construction plan included assembling

partial sections of the icing shields (up to five vertical posts of the steel sets with insulation

planks and drainage mat [Figure 8]) in the staging area and then moving the partial section into

the tunnel for installation.

Some excavation of the shotcrete liner and bedrock was required to obtain adequate

clearance to place the steel sets. Unfortunately, the rock excavation was slow and time

consuming, and track time was limited. A large part of the construction work was performed

over one track at a time while traffic was maintained on the second track. Because of the increase

in train traffic for Christmas (NSR’s UPS season), no construction could be conducted between

© 2012 AREMA

November 15 to January 1 since UPS trains are guaranteed to be on time during this period and

cannot be held up for construction. Therefore, the 2010 construction season consisted of

installation of icing shields between Stations 24+32 to 25+00 and 35+50 to 35+53 (Figure 8), but

there was not enough time to replace the icing shields between Stations 32+04 and 34+71 or to

complete the drainage bladder replacements and strip drain installations. These items were left

for the 2011 construction season (Figure 10).

Before construction restarted in 2011, several modifications of the icing shield design

were made to improve constructability and performance. These modifications were based on

observations during the 2010 construction season and the winter of 2010. During the winter of

2010, a solitary leak was observed in the crown of a new ice shield. This leak was likely because

the plastic used for the drainage mat on the field side of the icing shields was often blown into

the rock above it when a train passed. This created pinholes in the mat. Therefore, thicker pond

liner was required for the drainage mat, to make it heavier and much less susceptible to damage.

Other design modifications included:

• Altering the shape of the steel sets to reduce /minimize the amount of rock

excavation required

• Increasing the thickness of the shotcrete in the crown of the icing shields between

the centerlines of the two tracks for both the 2010 and 2011 icing shield

installations

• Adding a waterproofing additive to the shotcrete

• Replacing the drainage pipes installed in 2010 that had shattered over the winter

because of ice buildup and insulating the new drainage pipes

© 2012 AREMA

• Limiting the drainage bladder replacements to only the portions of the bladders

that were ripped and deteriorating

Construction continued in early April 2011 with the contractor removing the old icing

shields between Stations 32+04 and 34+71. The design modifications were effective, and

construction proceeded smoothly with the only major issue being track time availability. Since

traffic was heavy and track time limited, the construction schedule had to be extended.

Construction of the icing shields and repair to the bladders were completed in late August 2011.

However, because of extensive seepage and icing concerns at the east end of the tunnel, the

contractor was remobilized to the tunnel in late October to implement additional leak repairs.

The worst leaks were diverted into PVC pipes by concentrating the flow at one location using a

hydrophilic cement. The pipes were then insulated with insulating foam sealant and an insulation

plank, which was secured in place with metal flashing. Minor leaks were plugged with

hydrophilic cement.

Final shotcrete application is scheduled for June 2012.

CONCLUSION

The final inspection of the 2011 work in Allegheny Tunnel was performed by the railroad

on November 16, 2011, after a week of rain. The seepage control measures were working

effectively. NSR personnel checked the tunnel periodically over the winter, and the icing shields

were found to be performing satisfactorily.

Key lessons learned during this project included:

• The importance of good survey data. A clearance survey was not performed

during the design phase in 2010 because of time and budget constraints. The rock

© 2012 AREMA

excavation during the 2010 construction season was at least partially due to the

combination of a lack of good survey data and the irregular tunnel perimeter.

• Understanding the effects of material substitutions. At the start of construction in

2010, the contractor requested substitution of the thinner plastic for the pond liner

drainage mat because it was more readily available and easier to work with.

Unfortunately, the plastic was easily torn and, with the limited track time

available, was often placed behind the steel sets but left unprotected, causing it to

be blown against the rock surface. The pond liner used in 2011 was far more

successful.

• The benefits of good coordination between the contractor and the flaggers. Since

track time was always limited, a great deal of the work was performed on one

track at a time.

The replacement of the icing shields, repair of the drainage bladders and installation of

additional seepage control measures have successfully reduced icing issues in Allegheny Tunnel,

which is subject to harsh winter conditions. Observing construction issues during the 2010

construction season and the performance of the icing shields during the winter of 2010 allowed

the designers to make design modifications for the 2011 construction season that improved

constructability and overall performance of the icing shields.

ACKNOWLEDGMENTS

The authors thank Norfolk Southern Railway for its assistance in preparing this article. In

addition, thanks are also due to the members of the design and construction team: Jacobs

Associates, LRL Construction, and NSR Division Engineer Craig Webb, Retired Assistant Division

© 2012 AREMA

Engineer Jim Rockney, Bridge Supervisor Dwayne Meadows, and the NSR flagmen for their

contribution to the project.

REFERENCES

1. Historic American Engineering Record. 1993. Pennsylvania Historic Railroad Bridges Recording Project, HAER No. PA-515.

2. International Energy Conservation Code (IECC). 2009. http://energycode.pnl.gov/

EnergyCodeReqs.

3. Colorado Energy Organization, http://coloradoenergy.org/procorner/stuff/r-values.htm.

4. Gallitzin Tunnels Park & Museum, http://www.gallitzin.info/tunnels.php. LISTING OF TABLE AND FIGURE CAPTIONS

Table 1. Material R-value Properties for the Allegheny Tunnel icing shields

Figure 1. Map of Pennsylvania showing location of Allegheny Tunnel in Gallitzin.

Figure 2. Construction at the west portal of Allegheny Tunnel for the double stack/double track project (4). Figure 3. Existing icing shields near the west portal, including the plywood bulkhead and the adjacent shotcrete tunnel liner. Figure 4. Deterioration of existing icing shields.

Figure 5. Allegheny Tunnel stationing and locations of icing shields.

Figure 6. Icicles observed within tunnel lining where icing shields deteriorated in January 2010.

Figure 7. Layered passive icing system design.

Figure 8. Installation of icing shields between Stations 24+32 and 25+00.

Figure 9. Installation of drainage mats in areas of heavy seepage.

Figure 10. Applying shotcrete to the newly installed icing shields between Stations 32+04 to 34+71.

© 2012 AREMA

TABLES

© 2012 AREMA

TABLE 1. Material R-value Properties for the Allegheny Tunnel Icing Shields

Material R-Value

(ft2·F°·h/Btu) / thickness (3)

Thickness in Allegheny Design

Total R-Value (ft2·F°·h/Btu)

Insulation planks 2.3 / inch 3 inches 6.9

Shotcrete 0.08 / inch 2 inches 0.16

Air Space (air space between the tunnel sidewall and icing shields) 1.0 / 0.5 to 4 inches Approx. 24 inches

Ranges 48 to 6 (Average 27)

TOTAL 34

© 2012 AREMA

FIGURES

© 2012 AREMA

Figure 1. Map of Pennsylvania showing location of Allegheny Tunnel in Gallitzin.

Figure 2. Construction at the west portal of Allegheny Tunnel

for the double stack/double track project (4).

© 2012 AREMA

Figure 3. Existing icing shields near the west portal, including the

plywood bulkhead and the adjacent shotcrete tunnel liner.

© 2012 AREMA

Figure 4. Deterioration of existing icing shields.

© 2012 AREMA

Figure 5. Allegheny Tunnel stationing and locations of icing shields.

© 2012 AREMA

Figure 6. Icicles observed within tunnel lining where icing shields deteriorated in January 2010.

© 2012 AREMA

Figure 7. Layered passive icing system design.

Figure 8. Installation of icing shields between Stations 24+32 and 25+00.

© 2012 AREMA

Figure 9. Installation of drainage mats in areas of heavy seepage.

Figure 10. Applying shotcrete to the newly installed icing shields

between Stations 32+04 to 34+71.

© 2012 AREMA

September 16-19, 2012 l Chicago, IL

2012 Annual Conference & Exposition

Passive Icing Shields for Railroad Tunnel in Gallitzin, PA

R. Brown, Norfolk Southern Railway P. Campbell, J. Schrank, Jacobs Associates

AREMA 2012 Annual Conference & Exposition Chicago, IL September 16–19, 2012



OUTLINE   Overview   Project Background   Icing Issues   Icing Shield Design   Construction   Conclusion

Permission to use photos by Gallitzin Tunnels Park & Museum



OVERVIEW   Allegheny Tunnel – Gallitzin, PA

Photos by Google Earth Professional, 2012

ALTOONA

GALLITZIN

ALLEGHENY TUNNEL

ALIGNMENT



PROJECT BACKGROUND   Train traffic – 40 to 50 freight trains and Amtrak each day



PROJECT BACKGROUND   Constructed in 1851 & 1854 (Penn RR) – 3,600 feet long, single track – Brick arch & masonry sidewalls, sandstone

portals



PROJECT BACKGROUND   Double track/double stack construction from 1994 to 1996 (CONRAIL) – Removal of existing lining, relined with rock

bolts and shotcrete lining – Cast-in-place concrete portals



ICING ISSUES   Condition of the tunnel – Significant seepage and

freezing



ICING ISSUES

2011 Construc�on

267 �

2010 Construc�on

4 �

2010 Construc�on

68 �



ICING ISSUES   Icing Shields originally installed1996   Drainage ditches on either side of tunnel



ICING ISSUES   Deterioration of icing shields from freight exhaust and corrosion



ICING SHIELD DESIGN   Passive system – Free-standing structure – Steel sets, insulation sheets, drainage mat – Shotcrete layer



ICING SHIELD DESIGN

  Insulation Thermal Resistance (R-value)

Rairspace Rinsula�on Rshotcrete

𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅= 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅+ 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅+ 𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅𝑅

Material R-‐Value

(�2·∙F°·∙h/Btu) / thickness

Thickness in Allegheny Design

Total R-‐Value

(�2·∙F°·∙h/Btu)

Insula�on planks 2.3 / inch 3 inches 6.9 Shotcrete 0.08 / inch 2 inches 0.16 Air Space (air space between the tunnel sidewall and icing shields)

1.0 / 0.5 to 4 inches

Approx. 24 inches

Ranges 6 to 48

(Avg. 27) TOTAL 34

Tunnel sidewall

Track side

Air Space

Rtotal = 34 >19 (IEEE for Cambria County,

PA Climate 4&5)



ICING SHIELD DESIGN

  Drainage System – Pond liner – PVC piping – Cold-weather

insulation

Photo by Firestone Pond Liner, 2012



CONSTRUCTION - 2010

  Construction between Sept – Nov 2010 – Station 24+32 to 25+00 = 68 feet – Station 35+50 to 35+54 = 4 feet – Replacing drainage bladders



CONSTRUCTION – 2010

  Chipping shotcrete liner for clearance   Slow progress, track time issues, etc.




  Shotcrete applied to Icing Shield and Bladders



CONSTRUCTION – 2011   Construction restart in May 11 – Aug 11 – Design Alterations:

  Redesign of steel set geometry   Drainage mat material substitution   Drainage pipe insulation plan

–  Station 32+04 to 34+71 = 267 feet

– Replacing drainage bladders







  Other work – Applying

shotcrete to existing steel sets



CONCLUSION

  Inspected November 16, 2011   Performed satisfactory throughout winter 2011   Key lessons learned: – Survey information – Understanding effects of materials –  Importance of good coordination and

communication



CONCLUSION

NSR, Jacobs Associates, LRL Construction, NSR Division Engineer Craig Webb, Retired Assistant Division Engineer Jim Rockney, Bridge Supervisor Dwayne Meadows, NSR Flagmen, and the Gallitzin Tunnels Park & Museum

Thank you to the following:



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PASSIVE ICING SHIELDS FOR RAILROAD TUNNEL … to locomotive exhaust blast to the underside and rusting of the rock bolt ... structural support to the tunnel ... of the shotcrete tunnel