Compaction behaviour of clay

Abstract

This paper presents an experimental study of the compaction behaviour of non-active clay. One-dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using Trento high-capacity tensiometers. At lower water contents, a transistor psychrometer was used to measure post-compaction suction. Samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses. Three water content regions were identified in the compaction plane depending on whether post-compaction suction increased, decreased or remained constant as the degree of saturation was increased at constant water content. Hydraulic paths of specimens subjected to loading–unloading cycles at constant water content have clearly shown that post-compaction suction may increase as the degree of saturation increases. This non-intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour. To this end, a coupled mechanical water retention model was formulated. Irreversible one-dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress, modified suction and void ratio. Irreversible hydraulic ‘wetting’ paths were modelled by a boundary surface in the space suction, degree of saturation, and void ratio. This study was completed by investigating the pore size distribution of compacted samples through MIP tests. This paper presents an experimental study of the compaction behaviour of non-active clay. One-dimensional static compaction tests were carried out at high and medium water content with matric suction monitoring using Trento high-capacity tensiometers. At lower water contents, a transistor psychrometer was used to measure post-compaction suction. Samples were compacted on the dry side of optimum to cover a wide range of compaction water contents and vertical stresses. Three water content regions were identified in the compaction plane depending on whether post-compaction suction increased, decreased or remained constant as the degree of saturation was increased at constant water content. Hydraulic paths of specimens subjected to loading–unloading cycles at constant water content have clearly shown that post-compaction suction may increase as the degree of saturation increases. This non-intuitive behaviour was demonstrated to be associated with the coupling between mechanical and water retention behaviour. To this end, a coupled mechanical water retention model was formulated. Irreversible one-dimensional mechanical paths were modelled by a boundary surface in the space average skeleton vertical stress, modified suction and void ratio. Irreversible hydraulic ‘wetting’ paths were modelled by a boundary surface in the space suction, degree of saturation, and void ratio. This study was completed by investigating the pore size distribution of compacted samples through MIP tests.