Experimental Research On Tensile And Compressive Strength Of Cement Stabilized Soil And Numerical Simulation

According to"Technical Specification for Retaining and Protection of Building Foundation Excavations", the allowable tension-compression strength ratio is only 6% when designing cement-soil walls, which causes cement mixing ratio to be larger and wall thicker, thus generates waste. In fact, to different soils, the tension-compression strength ratio varies greatly. Therefore, the research on tension-compression strength ratio is of great practical significance.The thesis describes the relationship of compressive strength and tensile strength. By the methods of laboratory test, numerical simulation and engineering example, the change law of compressive strength and tensile strength and the tension-compression strength ratio are studied in this paper. Consequently the reasonable tension-compression strength ratio is obtained. The main achievement and conclusions can be given as follows:(1) A comprehensive review is conducted on the available literatures on compressive strength and tensile strength of cement stabilized soil, pointing out deficiencies to be improved and problems to be solved in existing studies.(2) The change law of compressive strength with different curing ages, cement mixing ratio and water content is researched by the experiment of compressive strength. The results show that the relationship between compressive strength at different curing ages and the growth of cement mixing ratio is generally linear. And the relationship of compressive strength with different cement ratio can be fitted with logarithmic function. Compared among three cement stabilized soils, the early strength growth of silty clay cement stabilized soil is relatively slower while middle and later strength faster. The optimum water content of cement soil is around 25%~30%.(3) The change law of tensile strength with different curing ages, cement mixing ratio and water content is researched by the experiment of tensile strength. The results show that the tensile strength grows with the increase of cement mixing ratio. The change law of tensile strength decided by curing age and water content is similar to that of compressive strength.(4) Tensile test compared with compressive test, the minimum tension-compression strength ratio of silt and silty sand cement stabilized soil is 12% or so while that of silty caly cement stabilized soil may reach 16%. Results are much larger than 6% which is stipulated by standard.(5) The electron microscope scanning shows that the increase of cement mixing ratio provides a large number of Calcium for generation of hydrate, thus improves the strength of cement soil. With increasing of the curing age, the quantity of hydrate becomes more and more. The framework structure of silt and silty sand cement stabilized soil is mainly particle shape while that of silty clay cement stabilized soil is mainly prothallial and floc. It is the framework structure that makes the strength of silt and silty sand cement stabilized soil greater than that of silty clay cement stabilized soil.(6) Numerical simulation software is used to simulate compressive strength and tensile strength tests. Tensile strength of cement stabilized soil is calculated using different test methods based on changing boundary condition and loading condition. It is shown that Axial Tension is closest to the test result with Radial Splitting and Axial Splitting the second closest.(7) The result of cement-soil wall analysis shows that the tension-compression strength ratio gained from laboratory test can be used in practice. Under the soil condition in Yang Zhou, it is over conservative to use 6% as the tension-compression strength ratio while adopting"Technical Specification for Retaining and Protection of Building Foundation Excavations"to calculate the tensile stress. Consequently a reasonable ratio fitting Yangzhou area is obtained.