Laboratory Study of Loosely Compacted Unsaturated Volcanic Fill in Hong Kong

A laboratory investigation was carried out to primarily study the unsaturated shear behaviour of loosely compacted fills. The soil used was a colluvial fill of volcanic nature and the soil samples were initially compacted to a dry density of 70 % of the maximum dry density obtained from the standard Proctor compaction test. Two series of triaxial tests were conducted. The first series were consolidated undrained shear tests on saturated samples and the second series were constant water content tests on unsaturated samples. From the test results, a nonlinear shear strength-matric suction relationship is observed for the loosely compacted unsaturated volcanic fill. The frictional characteristic of the fill is independent of matric suction while the extent of the increase in the shear strength with matric suction is influenced by the degree of saturation.