ABSTRACT
Several mega transit projects are currently under design or construction in soft rock of Montreal. An innovative design method to reduce the excavation and concrete volume and carbon footprint of the construction has been adopted for these projects resulting in significant cost and time saving and a more sustainable infrastructure. The main principle of this method is to only use permanent structural elements in the design of initial excavation support. The mechanical and hydraulic properties of local rock allow for a drained design concept, and this was successfully implemented in the existing underground transit structures in Montreal. Rock mass grouting is used to bring down the water infiltration to an acceptable level; this is combined with applying drainage strips over the rock leaking fractures to relief the hydrostatic pressure. An additional drainage grid is sandwiched between the layers of shotcrete to make sure the final liner surface remains dry.
