The Wairau Aquifer sits barely two metres below ground across much of Blenheim, feeding the region's vineyards but complicating any subsurface work. When a tunnel alignment cuts through the unconsolidated alluvial silts and gravels of the Wairau Plain, you are not dealing with rock mechanics — you are dealing with saturated, low-cohesion materials that collapse the moment pore pressure shifts. We run the advanced triaxial and consolidation suites that feed into NZGS Guideline-compliant numerical models, because standard SPT blow counts alone will not capture the undrained behaviour that governs face stability here. For shallower investigation stages we often pair test pits with continuous sampling to map the gravel lenses that dominate the Rapaura formation, giving the design team a stratigraphic picture that boreholes alone can miss.
Face stability in Blenheim soft ground is controlled by pore pressure, not total stress — undrained testing is not optional, it is the baseline.
