Swelling behaviour of unsaturated fine grained soils

The aim of this research was to investigate the swelling behaviour of unsaturated fine grained soils by means of various laboratory tests such as a 100 mm stress path triaxial cell and a computer controlled oedometer. Centrifuge modelling was used as a link between the laboratory tests performed and an existing prototype experimental wall. Three types of soils with different plasticity have been tested simulating the boundary conditions that act on a soil element behind a stiff wall. Therefore the laboratory equipment was designed or modified to enable the measurement of the swelling pressure of the soil under conditions of lateral confinement. The results show that the swelling behaviour of these soils is controlled by the testing conditions imposed on the soil as well as the initial state of the soil as described by dry density and water content. Suction measurements made using the filter paper method, showed that dry density and water content can be used instead of specific volume and suction when defining the state of an unsaturated soil. The results from the centrifuge model tests, in which soil was compacted behind a stiff instrumented wall, showed that measurements of lateral stress change on the model wall were consistent with the swelling behaviour observed in the laboratory tests as well as in a previous full scale prototype test. Analysis of the experimental data indicated a possible method of extending the current specification set in the United Kingdom (Manual of Contract Documents for Highway Works, 1991) for the use of fine grained soils as backfill material near to structures