Analysis Of Equivalent Ground Settlement And Excavation Surface Stability Based On Discrete Element Method

In the past ten years,metro construction in major cities has developed rapidly.Shield tunneling is widely used in the construction of metro tunnels with its unique advantages.However,the shield machine will cause soil disturbance and ground settlement around the excavation surface in the course of crossing the stratum,which will not only increase the risk of tunnel construction,but also have a great impact on the surrounding environment.Starting from the analysis of ground settlement and excavation surface stability,the effective methods to maintain excavation surface stability and control settlement are sought to reduce construction risks and improve the safety of the surrounding environment,which is of great practical significance for the excavation of shield tunnels.At present,many related research methods based on continuum theory,such as finite element method and finite difference method,have some limitations.Because of the discreteness of rock and soil,the discrete element method based on discontinuous medium theory is also more suitable for the study of stratum settlement and excavation surface stability in tunnel construction.Based on practical engineering,this paper simplifies complex strata,carries out parameter calibration tests,and introduces grey correlation analysis method to explore the relationship between macro-mechanical parameters and micro-parameters.Finally,the paper carries out discrete element analysis of stratum subsidence and excavation surface stability.The main research results are as follows:(1)The parameter calibration of discrete element biaxial test meets the requirement and can be used to establish the target soil model.The influence degree of each meso-parameter on the macro-parameter is obtained by using grey relational theory analysis method,and the meso-parameter is graded accordingly,which provides a reference for the fast calibration of the parameters of the discrete element model in the future.(2)As with the surface condition,the settlement curves of strata at different depths show the distribution law similar to Peck curve;in different strata depths,the settlement at the surface has the greatest influence on the surrounding area,so the control of surface settlement is very important;when the depth of tunnel increases,the maximum value of surface settlement gradually decreases,while the width of settlement trough gradually increases,and the scope of lateral influence enlarges.Increasing reasonable burial depth in tunnel design can reduce ground settlement.(3)With the decrease of supporting force,the redistribution of soil stress in front of excavation will form arch effect,which has a great protective effect on the stability of excavation face;when the supporting force keeps decreasing or even less than the ultimate supporting force,the soil in front of the excavation will be destroyed;therefore,in the actual tunnel excavation project,the rational selection of supporting force is very important,which is of great significance to the safe construction of the tunnel.(4)The sliding failure modes of excavation face are as follows: the sliding failure of front soil body is wedge shape,and the sliding area above is irregular prism shape;the improved theoretical calculation model of wedge body is in agreement with the numerical model results,which shows that the discrete element analysis method is suitable for further study of the stability of excavation face of shield tunnel.(5)Comparing the simulated settlement prediction curve with the modified Peck formula prediction curve and the measured data settlement curve,the validity of the discrete element analysis method prediction is verified.Finally,according to the in-depth analysis of the stratum settlement law in this paper,effective measures to control the surface settlement are put forward,which can provide reference for the safe construction in the actual project.