Instrumented Hybrid Shoring System for a Deep Temporary Excavation Incorporating Cutter Soil Mixing in Vancouver, BC, Canada-Paper

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The paper describes a hybrid temporary shoring system built for a 19.8 m-deep, five-level basement excavation in downtown Vancouver. It combined 880 mm-diameter reinforced soldier piles, spaced about 3 m apart, with Cutter Soil Mixing (CSM) infill panels to support weak fill, peat, wood waste and overburden. Soldier piles extended into dense till and were supported by three rows of tie-back anchors; shotcrete lagging was used below the CSM panels.<br /><br />Two trial panels and adjacent drill holes helped establish CSM termination criteria. During production, Bauer B-tronic data—particularly penetration rate and cutter-wheel pressure—were interpreted alongside geotechnical information to identify dense till and guide panel embedment. Obstructions caused five of 57 panels to terminate short of the intended depth; grouted columns behind these panels controlled seepage. Strength testing confirmed the target CSM compressive strength of 2.0 MPa at 56 days.<br /><br />Inclinometers in two panels and two soldier piles, together with survey targets, tracked wall movements throughout staged excavation and anchor installation. The system generally met the project’s 20 mm displacement limit: measured movement at final excavation was about 19 mm on one wall and 16 mm on another. Local over-excavation increased movement to 27 mm, but no additional supports were required. CSM panels moved 2–4 mm less than adjacent soldier piles.<br /><br />The authors conclude that the hybrid system provided effective support and faster construction than traditional secant piling in variable ground. Real-time mixing data aided construction decisions and quality control, though interpretation remained experience-dependent. They recommend developing clearer graphical tools and validating them with data from more sites.

Keywords

temporary shoring

hybrid support system

basement excavation

Cutter Soil Mixing

soldier piles

tie-back anchors

shotcrete lagging

geotechnical monitoring

inclinometers

Vancouver excavation