Study On The Interaction Between Support Pile And Berms Earth By Numerical Simulation And Model Slot Test

Due to the rapid development of the economy and the development of urban construction in the direction of high-level development,this has also promoted the progress in the field of foundation pit engineering.As a relatively practical foundation pit support technology,the supporting method of retaining the berms earth on the base has the advantages of safety,economy,convenient material selection and short construction period.The berms earth is widely used in engineering,but theoretical research is still relatively lagging.Through the model slot test,theoretical analysis,ABAQUS simulation,engineering case and other methods,the influence of the action mechanism of the berms earth and the cross-section size of the berms earth on the earth pressure distribution of the supporting structure,the bending moment distribution of the pile and the horizontal displacement of the pile top are studied.The other issues have been studied,and the main work is as follows:(1)Compare the berms earth and direct excavation through the model slot test;analyze the soil pressure distribution of the retaining structure,the bending moment distribution of the pile body and the displacement of the pile top by retaining the berms earth with different height and top width influences.The test results show that compared with direct excavation,the presence of the berms earth makes the earth pressure distribution of the pile body similar to the static earth pressure,which can effectively reduce the displacement of the pile top and restrain the deformation of the pile body.(2)As the height increases:the earth pressure becomes smaller and closes to the static earth pressure;the displacement of the pile top decreases,but the decrease rate decreases with the increase of height,indicating that the height of the berms earth reaches a certain value.The effect is reduced;the bending moment of the pile body is gradually reduced.When the height of the berms earth reaches 25cm,the reverse bending point occurs.At this time,the berms earth can achieve the effect of internal support;when h=20cm,the kh is the largest.That is,when the ratio of the height h to the depth H is 0.50,the comprehensive benefit is the best.(3)As the width increases:the earth pressure gradually decreases and approaches the static earth pressure;the pile top displacement decreases continuously,and when the bi approaches the bottom width bd,the pile top displacement no longer decreases;The bending moment decreases continuously,but the decreasing trend gradually decreases.When b_l=15cm,the kb is the largest.that is,b_l=0.75h,the comprehensive benefit is the best.(4)Based on the elastic foundation beam method,the spring stiffness coefficient is modified.The lateral and vertical actions of the back pressure soil are regarded as the back pressure spring and the bottom of the pit are overloaded respectively.The simplified calculation method of the back pressure soil is proposed and compared with the model test results.Verify the accuracy and feasibility of the method.(5)Based on the finite element software ABAQUS,the model test is carried out to simulate the influence of the shape of the back pressure soil on the supporting structure,the mutual verification of the simulation and model test results is carried out for the model test.(6)Based on a three-dimensional model of a foundation pit project in Yangzhou,two kinds of support methods for direct excavation and retaining the berms earth excavation are predicted.Through soil pressure distribution,horizontal displacement of steel sheet pile,vertical displacement of steel sheet pile,foundation pit uplift,three aspects of comparative analysis of the advantages of the berms earth.The results show that berms earth can effectively limit the vertical displacement of the steel sheet pile and the foundation pit uplift,and the displacement of the top of the steel sheet pile can be greatly reduced.(7)Combining with a project example in Yangzhou,using two types of support:the berms earth+steel sheet pile and steel sheet pile,and use the LIZHENG deep foundation pit software to calculate the two supporting structures,and finally obtain universality from the actual monitoring data.The conclusion proves that the support of steel sheet piles is greatly affected by time.When the support of the berms earth+steel sheet piles is used,it will not cause large fluctuations with time.It proves that the support form of the berms earth+steel sheet piles is safer economical and reliab_le,and provide theoretical basis for future engineering practice.