A recent mid-rise project on Columbia Street hit refusal at 2.4 m—classic Fraser River sand, loose and saturated. The structural engineer had specified a shallow footing, but the geotech report flagged liquefaction potential under the NBCC 2020 seismic hazard for New Westminster. We redesigned the ground improvement using vibrocompaction, targeting a relative density above 70% to eliminate the risk. In this part of Metro Vancouver, the subsurface is a post-glacial delta; you are almost always dealing with clean to silty sand that densifies well under vibration. Knowing when vibrocompaction works—and when it does not—comes down to the fines content. Before mobilizing, we often run a CPT test to map the profile continuously, because the transition from sand to silt can be sharp and shallow across the Queensborough reach.
In New Westminster’s deltaic sand, getting the grid spacing right is more important than the vibrator power—miss it by half a metre and you leave untreated lenses.
