SEM Tunnelling in Toronto Construction
A portion of the recently constructed Toronto-York Spadina Subway Extension (TYSSE) Northern Tunnels includes the first tunnels in Toronto to be mined in soft ground using the Sequential Excavation Method (SEM). This portion of the extension is a 381-meter long special trackwork tunnel with crossovers and is referred to as the Double-Ended Pocket Track Housing Structure (DEPTHS). The DEPTHS includes a 221-meter long triple-cell tunnel, referred to as the SEM Tunnels, which was excavated and supported using SEM. A unique excavation and support sequence was developed and employed during construction to avoid surface constraints and address the narrow pillar widths necessary for the triple-cell configuration. This paper summarizes the results of the construction of the DEPTHS SEM Tunnels including comparisons of ground response to design predictions.