Study On Earth Pressure Of Limited Soil In Foundation Pit Engineering

With the vigorous development of China's economy,various industries have been developing in full swing in recent decades,and various buildings have sprung up on Chinese land.However,all kinds of buildings cannot be separated from foundation pit engineering.Foundation pit has always been one of the most basic topics in geotechnical engineering.Due to the numerous constraints on foundation pit engineering,it is not only affected by the soil geology and hydrogeology where the project is located,but also restricted by the surrounding environment.There are also deficiencies in the theoretical principles of foundation pit engineering,such as geotechnical pressure,geotechnical constitutive relation and so on.Generally,foundation pit works are temporary works with small safety reserves and relatively large risks.Therefore,it is inevitable to have various problems or hidden dangers in foundation pit works.The research on foundation pit in China started late.Although many years of development in the construction industry have made a lot of progress in the field of foundation pit engineering,the research on the foundation pit of limited soil mass has been little or not thorough enough.In this paper,the formula of soil pressure of unsaturated soil is derived,the test of soil pressure of finite soil is carried out in laboratory,the process of soil pressure test of finite soil in laboratory is simulated numerically,the theoretical data,numerical simulation data and test results are compared and analyzed,and the rationality of the formula and simulation is verified.The conclusions of this paper are as follows:(1)This paper deduces the theoretical calculation formula of unsaturated soil pressure of finite soil mass,including the active soil pressure of finite soil under the building behind the retaining wall,the active soil pressure of finite soil under the slope condition behind the retaining wall and the passive soil pressure of finite soil in the pit.When B/H is greater than 0.6,it can be regarded as the active soil pressure of infinite soil.When B/H is greater than 2,passive soil pressure of infinite soil can be considered.(2)The soil pressure tests of retaining walls with different widths at the top of finite soil slope were carried out,and the soil pressure tests under the excavation process of infinite and finite soil under the outside of the pit were carried out,and the corresponding soil pressure variation rules were obtained.(3)Numerical analysis software was used to simulate three kinds of soil pressure in laboratory tests,and the simulation results were in good agreement with the test data.The influence of different displacement of retaining wall on soil pressure of limited soil mass is studied.For limited soil mass,the horizontal displacement of the top of retaining wall is about 0.05‰ of the height of retaining wall to reach the limit equilibrium state of active earth pressure,while the displacement to reach the limit equilibrium state of passive earth pressure is about 1.2‰ of the height of retaining wall.(4)By simulating and analyzing the excavation process of the basement foundation pit in Liantai Block A-19-2,the paper obtained the maximum horizontal displacement and bending moment distribution of the front and rear piles,and analyzed them with the straightening software.It can be seen from the calculation results of finite element and Lizheng deep foundation pit software that the calculated displacement of lizheng deep foundation pit software is slightly smaller than that of finite element calculation,which is unsafe.The bending moment of the front pile is larger than that of the straightening software,while the bending moment of the back pile is smaller than that of the straightening software.(5)The influence of the spacing between front and rear piles on the horizontal displacement of pile top in the basement foundation pit support pile of Liantai Block A-19-2 is further studied.The results show that the horizontal displacement generated by front and rear piles is inversely linear with the spacing between front and rear piles.The current width of the back of soil between piles at the back 2 times the depth of the pile embedded in solid,front row pile top horizontal displacement produced by gradually tends to be stable,that reason is assumed in the calculation of pile soil body get smaller displacement of pile top,unsafe,and finite element method considering the influence of front row piles and front row limited the effect of soil between piles,conforms to the actual situation,the conclusion has the guiding significance for the project.