Christchurch sits on a complex alluvial plain where the 2010-2011 Canterbury earthquake sequence permanently altered shallow ground behavior. Over 400,000 tonnes of silt erupted through liquefaction across the eastern suburbs alone, burying streets and gardens under a new sedimentary layer that now complicates every shallow foundation decision. An exploratory test pit cuts through that recent history in hours. The excavation exposes the contact between post-quake anthropogenic fill, pre-2010 topsoil, and the underlying Riccarton Gravel or Christchurch Formation sands, giving geotechnical engineers a direct view of what actually lies beneath the grass. Unlike borehole logs that rely on discrete samples, a properly logged test pit reveals lateral continuity, moisture regime, and the presence of organics or uncontrolled fill that borehole drilling can miss. Our laboratory integrates the field descriptions with grain size analysis and Atterberg limits to classify the exposed strata according to the NZGS soil classification system, building a defensible ground model for TC1, TC2, or TC3 foundation zones.
A test pit shows what a borehole log can only infer: the true lateral continuity of Christchurch's post-liquefaction fill layers.
