Plane Strain Experiment Research Of Simulating Stress Path Of Excavation Pit By The True Triaxial Cell

Exploitation of underground space becomes more and more common in modern city construction. Amounts of foundation pit projects are increasing rapidly. What's more, foundation pits nowadays tend to become much bigger and deeper. Since the surrounding conditions have higher and higher demands over the displacement caused by foundation pit construction, foundation pit designing, which was previously controlled by pressure, has now gradually become controlled by deformation.In actual construction, the three major stresses that a point under the ground bears are different. In geotechnical engineering projects, many problems belong to problems of plane deformation. In order to study the pressure features and deformation features of soil under three different major stresses, complicated truly triaxial test are needed. The main contents can be summarized as follows:(1)By way of analyzing the stress path of soil during the process of digging foundation pits , and doing simulative test on the special stress path surrounding the foundation pit and then analyzing the results of truly triaxial test, this thesis tries to recognize the pressure and deformation features of soil when the surrounding area of foundation pits are under load.(2) Applying the 3-parameter model on the potential energy dissipating principle from the essay , the relationship of stress and strain is prescribed . On the base of the truly trixial test, a non-linear q~ ε_s constitutive model ,which can reflect the influence of middle main stress ,is established . Also the parameters of model are deduced and fitted .(3) A formula which reflects the relation of earth pressure and displacement is deduced. Using this formula , the earth pressure can be calculated by the structural deformation ,which is useful for deformation control design.(4) On the basis of the nonlinear finite element consolidation program (BCF) , a modified program fitting to this article's model is attained . From the calculation result of 3-parameter model and Duncan-Chang model , we can see that the displacement of guard post, and the displacement of the back of guard post increase are a little lager, compared with the calculation result of Duncan-Chang model , but the calculation result passive pressure and passive pressure is much similar , and the result is according with practical situation better . By way of analyzing the stress path of soil during the process of digging foundation pits.the design of Foundation Pit is much safer using the calculation result of 3-parameter model.