A study of the triaxial shear behaviour of some artificially cemented sand specimens

The thesis describes an experimental study in the behaviour of cemented sand at small strain levels considering type of cementing material, sample preparation method, curing conditions, biocementation technique, and waste tire inclusion. In this study, the experiments were carried out using triaxial apparatus modified for local strain measurements for observation of the response of cemented sand at small strain levels. The influences of five different sample preparation methods, and four different cement types (gypsum, lime, calcite, and Portland cement) on the cemented sand behaviour were studied. It was observed that cement type has a significant effect on stress-strain and stiffness of cemented sand. Sample preparation techniques slightly affected the triaxial shear behaviour of cement stabilized sand; whereas specimens stabilized using other agents were significantly affected from sample preparation technique. A new method for the ground improvement, the biocementation of sand by induced formation of calcite from the bacterial activity was also investigated. The efficiency of the biocementation for improvement of the shear strength and the small strain stiffness in comparison with other cementation methods was investigated. The biocemented sand specimens were prepared under confining pressure at three levels of the cementation corresponding to the amount of the urea-calcium chloride flushes. Significant increases in the strength and stiffness of biocemented sand were observed due to the precipitated calcite. Response of the biocemented sand specimens was found to be similar to that of calcite and lime cemented specimens. Microscopic study was conducted to verify the formation of cementing material at three different concentrations. Furthermore, the effect of tire crumbs and cement addition on the response of clean and cemented sand was investigated.