Replacement of a Timber Trestle with an MSE Retaining Wall System CN Rail, Yale Mile 118.93 Trestle Replacement Innovative use of MSE and Staged Construction Techniques

This timber trestle caught fire in the early 1990’s. The structure required replacement due to subsequent deterioration over time, coupled with ever increasing rail demands. Canadian National (CN) had to ensure minimal rail disruptions during replacement of this section of mainline, with upwards of 40 trains per day. This paper will discuss the innovative approach adopted by CN using Mechanically Stabilised Earth (MSE) to replace the ageing structure, and support the overhead rail. The project was challenging from the construction and staging perspectives. Canadian Pacific (CP) and Front Street were located immediately parallel to each side of the trestle. Construction was further complicated by limited headroom as MSE panel placement proceeded directly below the existing trestle deck. The MSE system selected was Reinforced Earth®, designed and supplied by the Reinforced Earth Company Ltd., and consisted of precast facing panels, inextensible steel reinforcement, and precast coping. Precast MSE panels were placed around the timber bent structure. MSE panel placement then proceeded upward, and as close to underside of deck as practical. CN opted to finish panel placement/backfill at the top of wall during two separate track closures work blocks. The first was for 12 hours and the second was for 18 hours. The timber pile cap, deck, and rail were removed by crane. The removal of the deck enabled CN to complete the top of wall placement, and resume backfilling by more conventional backfill techniques. The rail was reinstalled by use of jointed rail sections. The precast coping was placed atop the wall and handrails completed. The mainline was back in service being fully supported atop the MSE wall. Construction commenced in January of 2004, and was substantially completed in May of 2004. MSE provided a successful staged construction solution, while allowing CN to maintain safe rail traffic throughout the construction corridor, during the entire course of structure replacement. This paper will illustrate the technical considerations of using MSE, along with the various construction stages, and safety considerations associated with this project.