Matric suction and shear strength of dynamically compacted soils

Abstract

Dynamically compacted soils are used in many civil engineering projects. It is perhaps the only soil in classical soil mechanics treated as unsaturated. The characteristics of the compacted soils are presented as a compaction curve of dry unit weight versus water content. The fabric of the compacted soil is described as flocculated on the dry side of optimum and dispersed on the wet side of optimum. The objective of this study was to investigate the role of fabric on shear strength and matric suction of dynamically compacted soils. A residual soil in Singapore was compacted using the standard proctor compaction effort. The shear strength of the compacted soil was determined using unconfined compression test and the matric suction of the compacted soil was determined using the filter paper method, high suction tensiometer and the chilled-mirror dew-point apparatus. A series of compacted soils were prepared at 98% and 99.3% relative compaction. For the compacted soils prepared on the wet side of optimum, the soils were dried in a constant relative humidity environment to approach the corresponding water content on the dry side of optimum. The shear strength and matric suction of these compacted soils were measured to investigate the role of soil fabric. The test results showed that the relationship of shear strength with water content for the compacted soils on the compaction curve showed similar trend as the compaction curve but matric suction showed a decreasing trend with water content. For the compacted soils dried from the wet side of optimum, the shear strength and matric suction increased as the water content was reduced. At the water content on the dry side of optimum, the shear strength and matric suction of the compacted soils showed higher values especially for the soils at a lower level of relative compaction.