Inspection, Maintenance, and Repair of PaCT Canadian Pacific Rogers Pass Tunnels British Columbia, Canada

Transcription

1 Inspection, Maintenance, and Repair of PaCT Canadian Pacific Rogers Pass Tunnels British Columbia, Canada by David N. Bilow, P.E., S.E., Director, Engineered Structures Portland Cement Association 5420 Old Orchard Road Skokie, IL Phone and Scott J. Paradise, PE Service Area Manager Engineering BC Interior Service Area Canadian Pacific PO Box 50 Revelstoke, BC V0E 2S0 Phone:

2 Title: Inspection, Maintenance, and Repair of PaCT Canadian Pacific Rogers Pass Tunnels British Columbia, Canada Abstract A 9.4 mile long tunnel through Mount Macdonald and 1 mile long Mount Shaughnessy tunnel were placed into service by the Canadian Pacific (CP) in Paved concrete track (PaCT), a type of concrete slab track, was used in both tunnels to minimize track maintenance. PaCT consists of an 8-inch thick reinforced concrete slab anchored to the tunnel concrete invert floor slab. Each 136 pound rail is supported on a 5/8" thick continuous rubber rail pad which retards rail seat abrasion forces on the PaCT and provides resilience to the track system. Pandrol shoulders and rail clips are spaced at 12- inch (curves) to 24 inch (tangent) intervals. Train speed though the Mt. Macdonald tunnel is 30 mph and from 16 to 20 westbound trains operate through the tunnel on a daily basis. Broken shoulders and cracked PaCT concrete were first observed in isolated locations in both the Mt. Macdonald and Shaughnessy tunnels during Subsequently, a detailed cleaning and inspection of PaCT resulted in the identification and prioritization of failure locations. An imperical correlation was initially found between PaCT failures and high hydrostatic pressure between the PaCT and the tunnel invert floor slab. To reduce the hydrostatic pressure and improve drainage in local areas, drain holes were cored down to a longitudinal collector drain under the tunnel. This paper describes the methods and materials developed by CP to inspect and then efficiently and effectively repair 50 to 200 feet of PaCT each year within an approved track block schedule.

3 Inspection, Maintenance, and Repair of PaCT Canadian Pacific Rogers Pass Tunnels British Columbia, Canada Introduction The Canadian Pacific (CP) completed the single track tunnel projects through Rogers Pass, British Columbia, Canada in The tunnel projects through Mount Macdonald (9.4 miles long) and Mount Shaughnessy (1 mile long) were designed to minimize the track grade and accommodate multilevel auto carriers. Due to the heavy volume of traffic through the two tunnels, closures for maintenance must be kept to a minimum. To reduce the need for closures due to maintenance of the track, CP constructed Paved Concrete Track (PaCT), a type of concrete slab track. Prior to construction of the Macdonald tunnel construction, CP constructed a test section of slab track at Albert Canyon near Rogers Pass in British Columbia. The Albert Canyon test section was 930 feet long and built during late 1984 using the patented PACT- TRACK system developed by British Rail and McGregor Paving Limited in the United Kingdom. The track test section simulated the proposed tunnel track conditions. Based on the overall satisfactory performance of the Albert Canyon slab track, 9.4 miles of the PaCT system was constructed in Macdonald Tunnel during This paper discusses the background, inspection, and repair of the PaCT in the Mount Macdonald and Mount Shaughnessy Tunnels. BACKGROUND Tunnel Construction The tunnels are 25 feet, 10 inches high and 17 feet wide. The Mount Macdonald tunnel is concrete lined to keep water infiltration to a minimum and to provide a smooth interior surface which can be washed. The invert of the tunnel consists of a 12-inch thick reinforced concrete base slab which is supported on solid rock except for a few locations which are supported on overburden or a mud sill. Two longitudinal collector drain pipes from 200 mm to 300 mm in diameter are located under the cast-in-place concrete tunnel invert to carry groundwater to the ends of the tunnel. The grade of the track in the tunnel does not exceed 1%. Track Design and Construction The PaCT slab is 9 inches thick at its maximum and 7 feet, 10 inches wide. For the Rogers Pass projects, Pandrol clips with insulators are spaced at about 24 in tangent track to 12 inch intervals in curve track and were used with 136RE rails.

4 The PaCT slab is cast-in-place continuously reinforced concrete. U shaped dowel bars anchor the PaCT slab to the tunnel base slab. The transverse reinforcement in the PaCT is #10M at 20 spacing. The longitudinal reinforcement in the PaCT is 17 #15M with variable spacing of 4, 5, and 8 spacing for control of shrinkage cracks. The amount of longitudinal reinforcing is equal to 0.7% of the cross sectional area of the PaCT. (Figure 1) Concrete for the PaCT was placed using a customized slip form paving machine, which rides on two rails (which are later used for the track) and which feed the concrete into the front of the paving machine using a conveyer system. After the concrete is cured, the continuously welded rail was installed.. Each 136-pound continuous welded rail is mounted on a continuous 10 mm (3/8 ) thick rubber pad on top of the PaCT slab and the rail is attached to the slab with Pandrol direct fixation e clip fasteners (#4267) set in cored holes with epoxy resin and spaced at 24 to 12 inch centers. The top of the PaCT slab is sloped from the rail to the center of the slab and drains are provided along the centerline of the track. The PaCT was constructed at the rate of approximately 1000 per day. CP initially used ballasted track with concrete ties in the transition between the tunnel PaCT and the exterior ballasted track at each portal. Retaining walls two feet deep below grade on each side of the track run parallel to the track for 20 feet in the transition. Also, a concrete slab runs for 20 feet under the ballast between the two retaining walls. Operation The tunnel handles general freight trains, multilevel auto carriers, coal trains and passenger trains. Loaded coal trains typically move at 9 to13 mph depending on power configuration and the maximum authorized speed of any train through the tunnel is 30 mph. The slow speeds through the tunnel give rise to low frequency vibrations that do not amplify because of the high natural frequency of the track structure. It is reported that there are no noticeable vibrations from a train moving through the tunnel. CP Rail Traffic Controllers (i.e., RTC or dispatcher) monitor train locations via a centralized train control system which is based on transmission of a low voltage signal through the running rails. There is no special electrical insulation at the Pandrol clips. Snow, moisture, and coal dust has the potential to accumulate in the tunnel and when combined with infiltrating water can sometimes mix to cause isolated shorts in the signal system which result in false indications of track occupancy (TOLs). However, after drainage is re-established in the TOO area, the signal system works well for the CP. Because the tunnel through Mount Macdonald is very long, a very sophisticated computer controlled ventilation system is used to provide fresh combustion air for operation of locomotives and it also evacuates locomotive exhaust from the tunnel. Large overhead doors located at the east portal and mid tunnel are opened and closed automatically in coordination with operation of up to 5 tunnel ventilation fans at various times so that tunnel sections are isolated for proper operation of the ventilation system.

5 Maintenance Water enters the tunnel sometimes ponding along the PaCT. The ponding is mainly caused by coal dust accumulation which clogs the drains. Also, in some ponding areas plants grow from small amounts of grain. As a result, the tunnel is thoroughly cleaned by CP on an annual basis. In the past CP has cored holes through the base slab into the drainage pipes under the slab to drain the ponding water. Track surfacing and alignment have not been required. INSPECTIONS After five years of use, in 1993, the following four primary areas of PaCT started to develop cracks or evidence of failure: 1. At the ends of the tunnel PaCT slab 2. At the joints between the tunnel section and the cut and cover portal section; 3. At a sixty foot section where excessive seepage water partially submerged the PaCT slab; and 4. At one end of day construction joint where there was seepage water. Subsequent inspections showed that the areas which fail are sometimes at locations of broken rails repaired by installation of new rail and joints, end of day joints in the PaCT, and within 1.5 miles of the ends of the tunnel. The ends of the tunnel are subject to freezing temperatures. Away from the ends, the tunnel stays at a constant temperature. CP typically repairs from 50 and 200 feet of PaCT each year. Since the initial detailed inspection in 1993, subsequent inspections include mapping of cracks which is done by walking inspections performed each year and preparing plan drawings of the cracks (Figure 3). The areas with cracks are then prioritized for repair based on rates of changes from year to year and comparison to results of track geometry testing for cross level and track gage. CAUSE OF FAILURES One cause of the PaCT failure is the excessive water in the tunnel, sometimes ponding along the PaCT. CP conducted an extensive investigation with piezometers, extensometers and strain gages and determined that very high pore pressures occurred between the PaCT and tunnel invert slab when a train traveled over the PaCT. One solution was to core 3.5 into the longitudinal drainage pipes below the tunnel. This allowed water to be drained off by the drainage pipes which generally flow half full under normal conditions.. Another cause of the PaCT failures is insufficient lateral and longitudinal reinforcing in the PaCT slab and the poor condition of the U shaped reinforcement attaching the PaCT slab to the base slab. It is believed that the U reinforcement was flattened during the initial construction and then bent back into place. When PaCT concrete is removed during repair, often the U bars are found broken or badly bent.

6 A third cause of failure is potentially associated with differential settlement of the base slab where the base slab subgrade transitions from overburden at the tunnel portal section to solid rock for the rest of the tunnel. REPAIRS After several months of study, CP issued formal drawings for repair to the PaCT. The types of repair included in this paper are as follows: 1. Improved surface drainage 2. Removal and replacement of PaCT slab concrete 3. Epoxy injection to restore structural integrity Improved Surface Drainage Surface drainage is improved primarily by cleaning of existing clogged drains and in some cases using coring methods to provide vertical drainage pathways through the center of the PaCT in conjunction with cutting a horizontal grove in the bottom slab as shown in Figure 2. In very wet areas holes are cored through the tunnel base to below the base slab. This drainage allows for pressure equalization and up-flow of groundwater flowing under pressure below the tunnel down to the horizontal drain pipes. During times of low groundwater pressure, this allows water to be drained off by the longitudinal pipes which flow half full most of the time. Also, if walls exhibit characteristics of groundwater infiltration or effervescence, drainage pipes are installed through the walls to direct the water to drains in the tunnel floor. Improved drainage has helped in reducing damage to the PaCT. (Figure 2) Epoxy Injection Injection of epoxy into small cracks was attempted to retard the growth of the cracks. 22 feet of cracks were repaired in 2007 and 90 feet of cracks were repaired in 2008 using this method. The Concresive 1380 structural concrete bonding injection resin as manufactured by BASF was used for the crack repair. During epoxy injection the crack is first cleaned and then injection ports are placed into the crack at an appropriate spacing. A surface seal is then applied over the crack between the ports and the epoxy is then pumped under pressure through the injection port into the crack. The long term effectiveness of the epoxy repair is not known at this time however initial results indicate that epoxy injection will retard crack growth at a minimum. PaCT Slab Removal and Replacement Where the cracks in PaCT are less than.02 wide and spacing is greater than one foot (minor cracking), epoxy injection is considered and complete PaCT repairs are not made. Where the cracks are larger than 0.5 mm.02 but less than.06 and the spacing of cracks is less than one foot (significant cracking), the area is monitored. Where cracks are larger than.06 or there is breakup of the PaCT concrete or loose pieces of concrete, the distressed concrete is removed and replaced as described below. Two five foot sections of PaCT are repaired in a single repair event and this repair was observed at a location within 100 feet of the west entrance to the tunnel and performed on

7 August 14, CP has repaired from 50 feet to 200 feet of PaCT each year since 2003 using this procedure. CP Structures personnel perform the work and focus on short 5 foot long sections to ensure repairs can be completed within approved track blocks. Repair sections are also limited to 5 foot because of the heat generated from the fast setting high early strength concrete used in the repair. The CP Structure crew which performs the work consists of 6 workers and one foreman. Equipment is lined up on the track to make it easy to move different pieces of equipment in and out of the work space. (Figure 4). Work starts at 1:00 am and concrete placing is completed by 7:00 am. The PaCT concrete 5 foot section to be removed is first saw cut. One section of PaCT 5 feet long is removed across the entire PaCT width with hydraulic breaker techniques that include braking up by the use of a large jack hammer mounted on the end of the hydraulic arm of a Kubota compact excavator (Figure 5). Another 5 foot section was previously removed the day before and temporary steel pedestals with shoulders were used to support the rail for train traffic at 10 mph as shown in Figure 6. After breaking up the PaCT concrete with the large hydraulic hammer, concrete around the rebar is removed by smaller jack hammers. Care is taken to minimize damage to the rebar and base slab. A vacuum truck is used to vacuum the loose concrete pieces. Additional longitudinal and transverse galvanized rebar is added and tied to the existing rebar (Figure 7). Also, holes are drilled into the base slab in which L bars are inserted and then epoxy adhesive is injected into the hole around the rebar (Figure 8). The L bars supplement the U bars in the original PaCT construction and tie down the PaCT slab to the base slab. After the rebar is installed, sand blasting is used to clean the concrete surfaces and rebar. Imperfections in the galvanizing on the rebar are then touched up and a compressed air lance is then used to remove the sand from the blasting operation. A new piece of 3/8 thick rubber pad is attached to the underside of the rail using adhesive tape as shown in Figure 7. Pandrol shoulders and concrete anchors shop welded to a 6 x ¾ x 1-3 ½ horizontal plate are attached to the rails by e clips at the appropriate spacing. Forms are then placed on the sides of the PaCT and expansion anchored to the adjacent sound concrete. Master Builders Set 45 mix (also sold as BASF Emaco Set-45) with 3/8 aggregate is used for the concrete repair. The concrete mix is prepackaged in measured large totes which are lifted by a crane and then opened over the concrete mixer which is mounted on a rail cart. Precise amounts of water are added to the mixer. The concrete mixer is then tilted down (Figure 9) so that the concrete falls through a hole in the rail cart into the space of the removed concrete. The concrete is distributed by the use of shovels and a steel trowel is used to finish the sloped edge of the PaCT. Another form board is placed on the sloped edge and anchored into the adjacent sound concrete.

8 Since the concrete is self consolidating, no vibration is required. About five concrete batches are required to fill the 5 foot space of the removed concrete. After additional concrete is placed, a form board is then placed on top of the fresh concrete and depressed in a concave shape (Figure 10) to provide a shallow drainage trough in the concrete which will carry water longitudinally to a vertical drain that is installed with each repair. The concrete strength increases to 5,800 psi in two hours after the concrete is poured. Trains are allowed over the track at 10 mph by 9:00 am. At 28 days the repair concrete has a strength of 7,000 psi. The removal and replacement of PaCT has been very effective and only one repair patch has had to be replaced since Other repairs which have been done or which are being considered are listed below. Pandrol clip and shoulder replacement along with replacement of rubber rail base pads were made after a 2007 derailment which damaged the shoulders. Approximately 1000 broken rail clips are replaced each year after visual inspections. Polyurethane was injected in cracks in the ventilation shaft to reduce seepage through cracks into the tunnel. Sealing the joint between the base slab and the PaCT to keep surface water from penetrating under the PaCT may be attempted in the future. Using post-tensioned Dywdag threadbar anchors to improve the attachment of the PaCT to the base slab may be attempted in the future. Summary of Results Since the start of repairs in 1993, a total of 378 feet of PaCT have been replaced in the 9.4 mile long Macdonald tunnel and the 1.4 mile long Shaugnessy Tunnel. The repairs amount to 0.66% of the total length of PaCT. Most of the PaCT sections failed because of a combination of excessive water in the tunnel and construction deficiencies. The repairs to PaCT have been successful and improvements in surface drainage in the tunnel have resulted in less water in the tunnel in the repaired areas. Acknowledgement The authors wish to acknowledge the leadership and work of John Creighton, CP Structures Supervisor, in the execution of the repairs.

9 List of Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Typical Cross Section Lower Part of Tunnel Drainage through PaCT and Base Slab Inspection Drawing Showing cracks Line-up of Equipment at Tunnel Entrance Kutoba Excavator with Jack Hammer After Removal of Concrete Showing Rail Support Addition of Galvanized Reinforcement Epoxy Grouting Dowel Bars into Base Slab Placing Concrete Showing Mixer & Totes Completed Repair with Forms in-place

10 Figure 1 Typical Cross Section Lower Part of Tunnel Figure 2 Drainage through PaCT and Base Slab

11 Figure 3 Inspection Drawing Showing cracks Figure 4 Line-up of Equipment at Tunnel Entrance

12 Figure 5 Kutoba Excavator with Jack Hammer Figure 6 After Removal of Concrete Showing Rail Support

13 Figure 7 Addition of Galvanized Reinforcement Figure 8 Epoxy Grouting Dowel Bars into Base Slab

14 Figure 9 Placing Concrete Showing Mixer & Totes Figure 10 Completed Repair with Forms in-place