The Capital Line project - Microtunneling Construction

Abstract

The Capital Line project is part of the early works for the Capital Line South LRT Extension. Managing stormwater runoff from 23 Avenue and the future 111 Street underpass is critical to keeping the extension on schedule. The project includes a storage tunnel for groundwater and surface drainage, along with a lift station that pumps stormwater to the existing trunk along 23 Avenue. The tunnel extends from the southwest side of the 111 Street/23 Avenue intersection to the northeast, continuing east along 23 Avenue and ending at 109 Street. The scope includes microtunnelling two storm sewers: a 125 m, 1350 mm ID tunnel; and a 400 m, 1800 mm ID tunnel, which is constructed at the transition between the Edmonton Formation bedrock and the Empress Formation sand. Additionally, 51 m of 1350 mm reinforced concrete casing pipe, housing a 375 mm PVC SDR35 storm sewer, was installed via trenchless hand tunnelling. The project also includes four manhole structures (2400–3000 mm diameter, 14–18 m deep), one with a 450 mm slide gate and another with an air vent pipe. One of the primary construction challenges was completing three tunnel drives from a single launch shaft. To address this, a two-level working platform was designed and constructed to accommodate the simultaneous installation of two micro tunnels while avoiding interference with subsequent hand tunneling and manhole construction. Another challenge was tunnelling through an unexpected gravel layer beneath a busy intersection, requiring a geotechnical investigation, MTBM front cleaning, and additional grouting.