Blenheim sits on the broad floodplain of the Wairau River, where the soil profile tells a story of shifting river channels and gravel deposition over thousands of years. When the town expanded eastward into areas like Redwoodtown and Riverlands, builders started hitting pockets of loose silty sand sitting right over dense alluvial gravels, sometimes at less than two metres depth. That variability makes shallow foundation design here less about textbook assumptions and more about reading the ground correctly on every single site. A standard rib-raft floor might work perfectly on one section and need significant ground improvement on the plot next door. Before any concrete goes in, we pair the investigation with targeted test pits to confirm the gravel refusal depth and assess the moisture conditions that govern settlement behaviour under load.
Blenheim's Rapaura gravels can handle 300 kPa, but the metre of liquefiable silt sitting on top is what dictates your foundation depth.
