Moss St Sink Hole - Repair of Collapsed 12 m deep EggShaped Brick Storm Sewer in Victoria, BC

Abstract

This paper is a case study outlining the complexity of addressing a sink hole caused by the collapse of a 12 m deep, 1275 mm x 850 mm (H x W) egg-shaped brick storm sewer on a narrow residential street in the City of Victoria. This storm drain is part of the City of Victoria’s 150-Year-Old Brick Sewer Storm Drain system. AECOM has provided engineering services for inspection and renewal of storm drain assets since 2009. In May 2024, the failure of a storm sewer that was installed by tunnelling 100+ years ago created a sink hole on a residential road. This pipe failure endangered the travelling public and damaged adjacent underground infrastructure. AECOM was retained by the City of Victoria to provide engineering services to design and oversee construction of a solution to repair the failure and put this piece of critical infrastructure back into service. The project team had to contend with numerous site constraints including overhead hydro and telecommunications lines, adjacent underground infrastructure, unknown geotechnical conditions, bypass of stormwater flows, risk of additional voids, known archaeological zones and potentially contaminated soil. Various reinstatement options were explored including open-cut dig & replace, pipe jacking, and slip-lining. This paper outlines the risk-based approach to design decision making along with future considerations for full trenchless renewal of the system upstream & downstream of the collapse. Initial planning for the repair commenced immediately after the discovery of the sink hole in May 2024. Field investigations, design and tender preparation occurred during the latter half of 2024. Construction commenced in May 2025, and the storm drain was successfully returned to service by August 2025.