Spatial Variability during Shrinkage Testing of Expansive Clays

Civil infrastructure constructed with, buried in, or underlain by expansive clays is affected by high volumetric changes, especially because large-scale facilities are spatially distributed. This research focused on determining spatial variability during the shrinkage testing of expansive clays. An initially saturated sample (600 mm in diameter) of a high-plasticity clay was exposed to desiccation and thoroughly monitored over five months. The results indicated an expansive clay (30% smectite and 14% illite) in alkaline-pore water (695 mg/L Na⁺ and 1150 mg/L SO₄²⁻) for developing a dispersive soil fabric. The vertical shrinkage in the intact-soil portion was unchanged (remaining at 114 × 10⁶ mm³) in the first 10 days, sharply decreased the initial volume by 30% (up to 280 mm or 80 × 10⁶ mm³) in 68 days, and slowly decreased the initial volume by 40% (up to 240 mm or 68 × 10⁶ mm³) in 145 days. Furthermore, the soil temperature was found to be 10% lower than the air temperature, whereas the relative humidity within the cell was found to be 30% higher than that outside the cell. The soil showed an initial prominent central ridge with a few cracks that gradually evolved into a distinct crack pattern with equal-sized and irregular soil chunks. The average soil surface showed no volume reduction up to 18 days and a subsequent linear reduction, reaching 25% of the initial soil volume by the end of the test.