Abstract
This thesis investigates the utilisation of wet cohesive materials as embankment fill. An attempt is made to formulate a rational approach to assessing the suitability of such materials through standard laboratory and field measurements and tests. Consequently a method of establishing critical moisture content limits of these soils is proposed. The three factors which influence the use of such fill are traffickability, embankment stability and self-settlement of embankments. Primarily these factors depend on the remoulded undrained shear strength of a soil. The first part of this thesis therefore concentrates on the remoulded properties of cohesive soils and finds that there is a general relationship which summarises the undrained shear strength moisture content behaviour of these soils. It is shown that the principal influence on this behaviour is that of Liquid Limit. In the second part of the thesis the three primary influences on soils suitability are examined. The restrictions on usage imposed by stability and self-settlement can be determined by calculation, and these are also shown to be related to Liquid Limit. Field observations show that, in a general way, the depth of rut caused by trafficking plant can be related to the remoulded undrained shear strength. Equivalent strengths can therefore be obtained for the observed practical limits of plant operation. Tyre pressures and vehicle size are found to influence these limits. Since the suitability of a cohesive soil is shown to be related to remoulded undrained shear strength, moisture content. Liquid Limit and depth of rutting, it is possible to propose a rational method of assessing, the suitability of such soils in embankment. As a consequence it is shown that the common practice of employing a factor times the Plastic Limit as an earthworks control specification, is inappropriate and highly inaccurate when compared with a Liquid Limit control.