Repeated load triaxial testing of soils

Samples of an over-consolidated saturated silty clay, Keuper marl, and a partially saturated granular material, Breedon gravel, have been used in a triaxial test programme, with a view to characterising certain aspects of the material behaviour for use in a flexible pavement design procedure. Samples of over-consolidated Keuper marl were subjected to repeated axial sinusoidal loads. In addition, further samples were tested under creep loads and standard slow rate of strain triaxial tests. The results from these tests are used to relate the plastic deformation under repeated loads to simple creep tests and to the standard undrained soil strength test. In addition, the resilient behaviour is shown to be a function of the stresses applied to the soil. The samples of granular material were tested drained and were subjected to cyclic vertical and horizontal stresses. The development of a method of lateral strain measurement allowed a fundamental analysis of the behaviour of this material under a cyclic lateral stress. The resilient and permanent deformations occurring under a cyclic horizontal stress have been related to those occurring under the simpler situation of a static horizontal stress. A review of previous work considers research carried out on flexible pavement design with special reference to the role of unbound materials. In addition, an outline is given of studies carried out on creep of clays and repeated behaviour of clays and granular materials. The behaviours of the silty clay and the granular material are analysed in the context of a theoretical pavement structure. The basic testing apparatus is outlined briefly, while developments to the apparatus including an automated computer based data collection system are described in the form of appendices. A summary of the test results is given in the conclusions together with suggestions for further work