PEDESTRIAN TUNNEL INSTALLATION UNDER CN MAINLINES IN 44 HOURS - COLLABORATION BETWEEN CN AND METROLINX Authors: Dario Flammini Edward Wu, P.Eng., P.E. Birju Bhavsar, P.Eng. Manager of Structure (Retired) Project Manager Manager Metrolinx Canadian National Railway Metrolinx [email protected] Design & Construction – 20 Bay Street, 20th Floor Eastern Canada Toronto, Ontario M5J 2W3 1 Administration Road [email protected] Concord, Ontario L4K 1B9 [email protected] ABSTRACT Canadian National Railway (CN) and Metrolinx completed a pedestrian tunnel installation under two (2) mainline tracks with no injury and ahead of schedule in a 48-hour workblock in 2018. The pedestrian tunnel is a cast-in-place concrete structure and it was casted within an excavated launch pit area. A horizontal jacking methodology was implemented to advance the tunnel installation in order to mitigate impacts on train operations. The cast in place tunnel section was advanced into final position by utilizing two – 100 ton telescopic cylindrical jacks acting in tandem mounted on a specialized sled jacking assembly. The jacking assembly was positioned on 1” (25mm) steel jacking plates. The tunnel section was advanced a total distance of 57’ (17.5m) until it reached its final destination underneath the two (2) mainline tracks. This paper will discuss planning, design and construction of the tunnel installation under two (2) CN mainline tracks during a consecutive 44-hr weekend work block. PROJECT BACKGROUND Metrolinx is an extension of the Ontario government which involved itself with public transportation. Currently, Metrolinx is undertaking the Regional Express Rail (RER) project in the Greater Toronto and Hamilton Area. As part of the RER project, infrastructure improvements at the Bramalea GO Station were proposed. One of the improvement is to extend the existing west pedestrian tunnel under CN mainline track 1 and 2 and tie into the future bus loop canopy at the north side of the station as shown in Figure 1 below. The tunnel extension is located at CN Halton Subdivision which accommodates both freight and passenger trains. Proposed West Tunnel Extension Figure 1 – Bramalea GO Station layout PLANNING AND DESIGN OF TUNNEL EXTENSION The project site situates on bedrock at a relatively high elevation in relation to the railway tracks. The proposed tunnel extension length is approximately 55’ under the tracks. Metrolinx evaluated a few tunnel installation options such as hoisting/craning and post-tensioning pre-cast concrete segments. After analysing several methodologies, it was concluded that the tunnel would be cast in place followed by an open-cut excavation and jacked into final position. The tunnel was cast north of Track 1 inside a launching pit approximately 8m (26’) wide by 30m (98’) long. The roof of the tunnel sits 800mm (2.6’) below existing base of rail elevation. Since there is no passenger train services on weekends, a continuous weekend work block was chosen. The 16.5m (54’) long cast-in-place concrete tunnel weights approximately 3,216 kN (722,986 lbs). See the tunnel cross section details below: Figure 2 – Jacking general assembly in launching pit Figure 3 – Jack set up prior to pushing Figure 4 – Jack general arrangement Figure 5 – Tunnel loading diagram and calculations CONSTRUCTION METHODOLOGY AND SEQUENCY In order to minimize the amount of work during the scheduled 48-hr work block, the following construction activities were performed prior to the work block: - Excavated a 30m L x 8m W x 6.5m D (100’ L x 26’ W x 20’ D) tunnel launch pit to allow for tunnel cast - Prepared subgrade for temporary 1” steel plate installation to be placed under the tunnel - Placed 6” of screening material over the subgrade and compacted to support the plate system - Installed eight 1” thick x 8’ wide x 20’ long plates welded together to form one system - Position 5 individual row of 1” thick x 16” wide Ultra High Molecular Weight Polyethylene (UHMW) to be casted - UHMW sits in pre-determined pathway on the 1” steel plate - On the top of UHMW, ¼” steel plates are interconnected with the underside of the concrete tunnel base. These plates are cast into the concrete via studs. UHMW will serve as the riding surface between the tunnel and the steel plates and will ensure the push is straight as it is position in predetermined pathways for the entire length of the push - Used EFCO steel forms to form and pour tunnel structure - Cured concrete to 50 MPA and stripped forms - Installed temporary shoring wall on the island platform to facilitate tie in between the existing and new tunnel extension - Installed temporary overhead structure to support Bell 360Network fiber cable - Relocated fiber cable onto the temporary overhead structure - Waterproofed the tunnel structure - Installed ballast mat over tunnel structure - Installed hydraulic jacks required to push tunnel into place - Test push approximately 2’ of the tunnel structure - Imported and stockpiled all granular materials required for backfill - Mobilized all equipment required to site - Constructed two access ramps from the north parking lot to tracks to facilitate excavation and backfilling operations during work block Construction sequences are illustrated in the figures below. Figure 6 – Existing site condition Figure 7 – Install shoring wall, excavate pit and install jacking plates Figure 8 – Cast tunnel Figure 9 – Install hydraulic jack and prepare for tunnel installation Figure 10 – Remove track panels, excavate, jack and slide tunnel into final position Figure 11 – Backfill and reinstate track panels CONSTRUCTION DURING WORKBLOCK The 48-hr work block started at 2000 on September 21, 2018. Rails were saw cut on both tracks to remove two 90’ long track panels. CN utilized two hi-rail excavators to pick up the panels and carried them in the westward direction away from the construction zone. The track panel removal was completed in 30 minutes. Two excavators with multiple trucks and loaders carried out excavation of ballast, subballast and subgrade. Bedrock was encountered between 2m to 3m (6’ to 10’) below base of rail. Pneumatic hammers were used to fracture and breakup relatively soft shale. After excavation was completed, granular/screening base was placed, levelled and compacted. Jacking plates were hoisted into the launching pit by a 90-ton crane and jacking plates were welded. Once the jacking plates were welded and the steel floor assembly completed, the tunnel was jacked into place by utilizing a jacking assembly attached to the front portal of the tunnel and sitting on 1” steel plates. Figure 12 – Jacking runway The plate have pre-assembled jacking plates welded on top to provide a jacking surface for the Hydraulic jacking system. UHMW was placed between the jacking plates to provide a smooth surface for the tunnel to slide on. Two 153-ton capacity Hydraulic jacks working in tandem were used for the jacking operation. In addition to reduce friction during jacking operation, all steel plates where UHMW travelled had a heavy application of Shell SRS Grease 2000 Extreme to assist with friction reduction. The tunnel jacking was done in 5’ increments. The jacks were retracted once the 5’ stroke was completed, reset in predesignated holes in the 1” plate system and then jacking proceeds again. The tunnel was jacked into final position approximately 24 hrs after workblock commenced. Waterproofing was applied and a 24” CSP culvert was installed vertically to close gaps between the tunnel and the south shoring wall. The CSP was held in position during backfill operation and filled with granular fill. Approximately 12” of subballast was backfilled around and over the tunnel. This was a preferred over tradition lagging methods. Ballast was placed after the subballast layer was compacted. Finally, track panels were reinstated and surfacing was performed. Please refer to the construction schedule in Appendix A. Figure 13 - Jack set up in the pit Figure 14 – Tunnel push into final position Figure 15 – Track panels reinstated Figure 16 – Prepared tracks to resume train operations at end of work block CONCLUSION The Bramalea GO Station west pedestrian tunnel installation was completed in 44 hours and 4 hours ahead of the schedule without any injuries. The Metrolinx and CN teams undertook all the tasks per the work plan. Fortunately, none of the contingency plans needed to be executed. However, it was worth investing extensive time and effort in preparing contingency plans ahead of the work block to prepare for sudden and unexpected change of site conditions. Construction progress was communicated to the operation team regarding resuming train operations ahead of schedule. In conclusion, the chosen construction method, jack and push, was ideal for the tunnel installation based on the site conditions. ACKNOWLEDGEMENTS - CN - Earthline Foundations and Shoring Ltd. - GeoTerre - Kenaidan Contracting Ltd. - Metrolinx - Terraprobe - Veresk Inc. - Western Mechanical Electrical Millwright Services Ltd. - Roc.ca Rail Consultants Inc. LIST OF FIGURES Figure 1 – Bramalea GO Station layout Figure 2 – Jacking general assembly in launching pit Figure 3 – Jack set up prior to pushing Figure 4 – Jack general arrangement Figure 5 – Tunnel loading diagram and calculations Figure 6 – Existing site condition Figure 7 – Install shoring wall, excavate pit and install jacking plates Figure 8 – Cast tunnel Figure 9 – Install hydraulic jack and prepare for tunnel installation Figure 10 – Remove track panels, excavate, jack and slide tunnel into final position Figure 11 – Backfill and reinstate track panels Figure 12 – Jacking runway Figure 13 - Jack set up in the pit Figure 14 – Tunnel push into final position Figure 15 – Track panels reinstated Figure 16 – Prepared tracks to resume train operations at end of work block Appendix A Pedestrian Tunnel Installation under CN Mainlines in 44 hours - Collaboration between CN and Metrolinx Birju Bhavsar, P.Eng. – Metrolinx Edward Wu, P.Eng., P.E. – CN Orlando Gutierrez, P.Eng.