Christchurch still lives with the memory of the 2010-2011 Canterbury earthquake sequence, a period that reshaped the city’s relationship with its own ground. Much of the urban area sits on alluvial plains where silts and fine sands dominate the subsurface, making particle size distribution more than a routine index test. For developers and geotechnical engineers, a reliable grain size analysis (sieve + hydrometer) determines how water moves through the soil, how the ground might behave under cyclic loading, and whether a fill material meets compaction specifications. At our ISO 17025-accredited laboratory, we process hundreds of Christchurch samples each year, from Riccarton gravels to the silty fines of the eastern suburbs. A complete gradation curve, covering the full range from coarse sand down to the clay fraction, often pairs with liquefaction screening when the water table is high and the fines content becomes critical.
A 5% error in fines content can flip a Christchurch soil from 'non-liquefiable' to 'liquefiable' — the hydrometer step is not optional here.
