Experimental Research On Shear Strength Growth And Constitutive Model Of Soft Clay In Consolidation Process

In the south-eastern coastal regions of China,there exists a large areas of modern sedimentary layer that consist of soft clay with high moisture content.The foundation need to be reinforced before building construction.Vacuum-surcharge preloading method is widely applied in the soft foundation owing to its great advantages in the foundation stabilization engineering.The foundation is compressed by vacuum stress before the surcharge is loaded.In fact,the soft clay can not consolidate completely,because the increment of consolidation degrees is getting smaller in this process.Therefore,the details of the way of the surcharge load appling is not given in the Code for Design of Building Foundation.It is necessary to direct the corresponding test to do the further research on principle the shear strength growth and constitutive model in the consolidation process.The settlement value can be predicted by using the method combined the layerwise summation and Duncan-Chang model,but the change of the modulus of deformation under volume stress can only be calculated by complicated iterative method.In the Duncan-Chang model,the parameter n and k,determined by the experimental data fitting,are assumed to be constant,that can appear error.The constitutive relationship of volume stress should be studied.This thesis is based on the triaxial test by the GDSTTS.The specific content includes:?1?According to the result of undrained triaxial test under different confining stress and consolidation degrees,the change rule of shear strength index with consolidation degree is obtained;The corresponding triaxial test data of different areas are collected,and the growth law of internal friction angle with the consolidation degree is explored by the normalization method.The cumulative frequency of consolidation volume strain and shear strength is analyzed,and a reasonable surcharge loading method is proposed.?2?Based on the experimental results,the modified Duncan-Chang model,considering different initial consolidation degrees is established,and the relationship between the model parameters and the consolidation degree and confining stress is obtained and the reliability is verified.?3?The experimental results of CD test with different initial moisture content are analyzed,and the hyperbolic relationship between the effective stress and the strain is summarized.The physical meaning of the parameters of the new model is clarified by theoretical derivation and the tangent modulus expression in the process of isotropic consolidation is obtained.?4?The comparison of the initial tangent modulus value calculated by using different method shows that the new formula is reasonable.Moreover,it shows that there is not a strict linear relationship between ?E_i/p_a? and lg??₃/p_a? It is shown that the new method is reasonable for predicting the initial tangent modulus under small stress.