The initial, primary and secondary consolidation response of soft clay reinforced with a granular column under isolated loading

This paper presents the measurement and assessment of initial, consolidation and creep settlements of an isolated circular footing supported on soft clay samples reinforced with a single granular column. Clay samples (300mm diameter, 400 mm high) were formed from reconstituted kaolin and remoulded sleech which is an active material, exhibiting significant creep. These samples were tested in two identical testing chambers with various features to capture the settlement under constant foundation loading and dissipation of pore water pressure.

The behaviour of a circular footing (70 mm in diameter) on a clay bed was observed. In one model, the footing was supported by a 40mm diameter granular column formed by compacting crushed basalt in a preformed cavity. The model footings, with and without a granular column, were subjected to five vertical loading increments: 60 kPa, 120 kPa, 180 kPa, 240 kPa and 300 kPa in the case of kaolin. Similar tests were conducted in sleech, in this case with vertical loadings of 60 kPa, 120 kPa and 180 kPa. Each test lasted approximately 10 months. In the case of kaolin, the settlement reduction factor was marginal, although it was considerably better for sleech. Kaolin exhibited marginal creep settlement under low-moderate bearing pressure, which increased substantially under high bearing pressures. Creep settlement was more prominent in sleech at all levels of bearing pressures. The very interesting finding from the investigation is that the settlement reduction factors due to consolidation and creep are similar in order under low to moderate loadings.