NZS 3404 and the NZGS soil description guidelines form the backbone of any site investigation in Blenheim. The Wairau Plains present a complex alluvial puzzle. What you see at the surface rarely matches what lies below. Exploratory test pit excavation cuts through the guesswork. It lets the engineering team stand inside the profile. They can see the gravel lenses. They can touch the silt layers. They can measure groundwater seepage directly. This is not a remote sensor reading. This is direct, tactile verification. In a region where the Wairau River has shifted course for millennia, the soil can change from clean gravel to soft clay within the length of a single section. A CPT test provides a continuous resistance profile, which is useful for tracking these sudden transitions. But nothing replaces the visual certainty of an open excavation for confirming bearing stratum continuity before a concrete pour.
An open test pit turns a one-dimensional borehole log into a three-dimensional understanding of the ground formation.
