The Impact Of Shield Excavation On Existing Foundation Pits

Shield tunneling is one of the most important methods in the construction of urban subway tunnel.Its influence on the existing buildings has become the necessary research content and important research direction of urban construction.In this paper,the research of shield excavation on adjacent supporting structure includes theoretical calculation and analysis method,indoor model test method and numerical analysis method of finite element software.The additional stress of shield excavation is calculated by the formula of additional stress,and the influence of ground displacement caused by soil loss on anchor and soil nail is studied by indoor model test and numerical simulation.The research work of this paper mainly includes:(1)Based on Mindlin's solution and sagaseta's solution,the calculation formula of additional stress is derived by theoretical calculation method,and the calculation and analysis of engineering examples are carried out.This paper analyzes the additional stress on the supporting structure,the law of supporting lateral displacement and the trend of change;points out the most dangerous and unfavorable position of this working condition;obtains the additional stress and the law of supporting lateral displacement after the increase of horizontal spacing and embedment depth;obtains that the maximum value of the calculated additional stress is not different from the measured maximum value,and can check the supporting structure according to the maximum value of the calculated additional stress.In this paper,the model test is not designed according to the law of similarity,only to verify the law.(2)Through laboratory test and numerical analysis,the influence of soil loss on anchor and soil nail is analyzed.Analyze the law of soil nail axial force change,the law of sheet pile moment increment,the law of soil pressure increment,and analyze the reasons with numerical simulation;analyze the influence of different soil loss on the existing support structure;the influence of different tunnel buried depth on the support structure;analyze the reasons for the difference between the indoor test and the numerical analysis: the numerical simulation is ideal,while the indoor test,due to the soil's Because of the uneven compaction,excavation disturbance,boundary effect and other reasons,the moment increment value of the final measured plate is larger than the measured value,but the two laws are the same,so it is feasible to use numerical simulation software for example analysis.(3)The theoretical analysis algorithm and numerical simulation method are used to analyze the engineering examples.Taking the pile anchor support engineering as an example,the calculation results show that the lateral displacement of pile body calculated by theoretical analysis is smaller than that measured,but the law is the same;the lateral displacement of pile body obtained by numerical simulation is quite different from the measured value,but the difference between the axial force and the loss of axial force of anchor rod is not big;the lateral displacement obtained by adding the two values is similar to the measured value in the law and value;according to the previous paper Research and analysis put forward suggestions for the actual project.