Elastic-Plastic FEM Analysis Of Pile-Anchor Protection In Deep Foundation Pit

In the recent years, along with the high-speed development of city construction, a great number of high-rises are constructed together with the exploitation of the underground structure, which surely brings large-scale excavation and support of the foundation pit project. In this dissertation, a large quantity of the fundamental theories about the earth pressure calculation and the traditional design methods applied to the protection of the foundation pit are comprehensively analyzed and evaluated. Aiming at a deep foundation pit in Changsha, the author has written a elastic-plastic finite element program, in which a constitutive model of "Druck-Prager" is used for soil. A method employing the "Goodman" joint element to describe the frictional behavior between soil and pile which are divided into 4-noded plane strain isoparametric elements, is proposed. The anchor is divided into bar element. In this program, the modified "void element" method is adopted to simulate the excavation of the foundation pit. The results from the comparison between calculated values and field results show that the method of elastic-plastic finite element analysis is practical.The calculated results of the numerical model show that the horizontal displacement of the lower pile is larger than that of the upper. Because the embedded depth of the pile is only 1.2 meter, the "kick foot" phenomenon should be emphasized in the practice. The blowups of the pit bottom increases with the longer distance from the wall, reaching its maximum value in the middle of the pit. The most dramatic settlement happens in the upmost edge of the pit, decreasing with the increasing distance from the edge of the pit. The anchor tension increases with the excavation depth, and the peak value of the tension tends to move towards the end of the anchor. The allowable anchor capacity of 330 kN is larger than the maximum load of 197 kN.The soil condition, construction method and the surrounding are considered synthetically for compare and selection of the plan. The selected plan assures the deep foundation pit is safe and reliable. Obvious social and economical benefits have been obtained.