Surrey sits on a complex glacial and post-glacial landscape where the Fraser River has deposited deep sequences of compressible silts and clays over the past ten thousand years. The city’s population, now exceeding 600,000, drives continuous residential and commercial development onto soils that can settle unevenly under heavy structural loads. A raft or mat foundation becomes the practical choice when isolated footings would be too large or would experience excessive differential movement. The 2020 National Building Code of Canada places Surrey in seismic zone 4, meaning every foundation design must account for significant lateral shaking. MASW testing helps map shear wave velocities across a site, giving our engineers the data needed to model soil-structure interaction accurately. In areas near the Serpentine and Nicomekl rivers, where soft organic silts extend ten to twenty metres deep, we often recommend crossing site data with a CPT test to resolve thin drainage layers that affect consolidation time. These combined approaches let us tailor the mat geometry and reinforcement to Surrey’s actual subsurface, not just textbook assumptions.
In Surrey’s Fraser River floodplain, a properly designed mat foundation bridges soft compressible silts and reduces differential settlement to levels that isolated footings simply cannot achieve.
