Abstract:
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ABSTRACT This experimental work was performed to study the effect of some parameters on the behaviour of a soil under monotonic and cyclic loading. It includes four parts: The first part includes a bibliographical analysis of the previous works dealing with the influence of certain parameters on the liquefaction resistance of soils such as the grain size distribution, the global void ratio, the inter-granular void ratio, the relative density, the presence of fines, saturation, the overconsolidation and the sample preparation methods. The second part presents the apparatus, the experimental procedure and the materials used in the testing program. The repeatability tests were carried out to check the reliability of the testing devices and the experimental procedure. The third part presents the results of the monotonic tests and discusses the influence of some parameters on the behaviour of the studied soil. The results of different triaxial tests on loose, medium dense and dense silty sands show clearly that there is a correlation between the undrained shear strength measured at the phase transition point (Sus) and the inter-granular void ratio (es), which is the void ratio of the sand-grain matrix. It is shown that for the range 0-50% of the fines content, the undrained shear strength at the phase transition state decreases linearly with an increase of the inter-granular void ratio. In fact, when we increase the fines content in the range of 0-40%, all the fine-grained soil fills most of the voids in the sand-grain matrix and the contact between sand grains decreases and thus the inter-granular void ratio increases. As the fines content increases the undrained shear strength at the phase transition state decreases until a fines content of 40% is reached. After that a strong decline in the undrained shear strength at the phase transition point was observed.
The fourth chapter discusses the undrained cyclic triaxial tests and discusses influence of the fines content, the global void ratio, the inter-granular void ratio and the relative density on the liquefaction resistance of the Chlef sand-silt mixtures. Cyclic tests results show that the liquefaction potential of the sand-silt mixture decreases with the increase in the inter-granular void ratio (fines content) and the samples sheared with higher level loading (CSR= 0.25) are more vulnerable to liquefaction than those sheared with a lower loading level (CSR = 0.15). They also show that the liquefaction resistance increases with the relative density but it decreases with the increase in the inter-granular void ratio and the loading amplitude. The reduction in the liquefaction resistance of the Chlef sand-silt mixture becomes very marked for the smaller cyclic stress ratios CSR = 0.15 and 0.25.
