Suction of compacted residual soils

Abstract

Compacted soils are used in many civil engineering works such as pavement, backfills and soil covers. Though it is understood that compacted soils have degrees of saturation less than 100%, the unsaturated soil properties of compacted soils are seldom determined. Matric suction, the difference between pore-air and pore-water pressures, is an important stress-state variable of unsaturated soil and is a function of soil structure and soil moisture content. In this paper, the matric suctions of two residual soils (mudstone and sandstone) from Singapore, compacted at three compaction efforts and at various placement conditions (viz. dry density and water content), are presented. Matric suctions of the soil specimens were determined using two methods: (a) null-type axis translation technique and (b) high suction probe. The soil-water characteristic curves of the compacted soils were also established from compacted soil specimens via pressure plate tests and salt solution tests. In the determination of the soil-water characteristic curves, the compacted soil specimens were saturated prior to the pressure plate tests. The matric suctions of the soils at the as-compacted condition can also be obtained from the soil-water characteristic curve. The matric suctions of the compacted soils from the null-type axis translation technique, high suction probe and soil-water characteristic curve are compared and discussed with respect to the dry density, degree of saturation and compaction effort.