Study On Design Parameters For Deep Foundation Based On CPTU Test

With the development of urbanization,different kinds of complex deep pits are coming.And determining the geotechnical parameters is one of the key issues in deep foundation design.This article relies on National Science and Technology Support Program (2012BAJ01B02) and Suzhou rail research projects.Based on Suzhou Metro Line No.1,4 deep excavation,the Yangtze River Tunnel pit and other projects.The theoretical analysis, laboratory soil test, field pumping test, in situ testing, numerical simulation and other means were used to determine the parameters of the inversion analysis, And then the parameters based on CPTU were applied to the design of foundation excavations. There are the main conclusions as following:1.According to the existing methods, combining multiple excavation sites’test data,the approach to determine the internal friction, cohesive,undrained shear strength based on the CPTU test in Yangtze River Delta is issued.Based on the bearing capacity of soil damage theory, a method to calculate the joint friction angle and cohesion is given.The test site CPTU test results are analyzed, and laboratory tests were compared, the results are close, and the accuracy and feasibility of the proposed method is verified.The strength parameters determined based CPTU are applied to the calculation and stability analysis, engineering calculation shows that the strength parameters determined based CPTU can be applied to the stability analysis.2. The SCPTU test datas from different clay test sites at home and abroad were counted. A relationship with the compression modulus of shear wave velocity of soil is established,and the method to determine the compression modulus basing on the shear wave velocity.Combined with experimental data, and existing methods abroad were compared, the results show that this method can reliably determine the compression modulus of soft soil.3.The relationship between soil permeability and soil type index were analyzed, the method to determine soil permeability coefficient based on soil type index method is amended. The test method to determine the permeability coefficient based on the pore pressure dissipation are discussed.The method are applied in Suzhou subway excavation site. The results show that the method to determine soil permeability coefficient based on the CPTU can be used as preliminary design reference for engineering.Analyzing the shortcomings of consolidation in situ permeability testing,improving the method to determine the permeability coefficient of partially drained soil.Basing on the examples of engineering test data, the new method to determine the permeability coefficient of partially drained soil is issued.4.The average permeability of Suzhou pastry-like soil equivalent was determined using the weighted average method with the CPTU test,which was compared with results coming from laboratory test and field pumping test.Conclusions show the silt sandwich has a great impact on the overall permeability of the whole soil,and the average method based on CPTU is fitting for the the value of the pumping test, the method has some applicability.5.Based on the principles of flow stress coupling analysis,using finite element software Midas GTS,analyze Suzhou Hongzhuang subway station deep excavation numerical analysis.The reliability of permeability coefficient and the compression modulus from in situ tests was verified. The deformation characteristics of foundation pit excavation with considering and without considering the influence of dewatering were simulated,containing the horizontal displacement of diaphragm wall,the ground subsidence,the vertical deformation values of the wall,and the values of rebound deformation in the pit bottom.The values of the horizontal displacement of diaphragm wall and the ground subsidence values with considering fluid-structure coupling were larger than that without considering fluid-structure coupling.The values of the vertical deformation values and rebound deformation values in the pit bottom.with considering fluid-structure coupling were less than that without considering fluid-structure coupling,and the former was more closer to the measured data.