Study On Deformation And Collapse Of Soil Stratum Above Underground Cavities Based On The Double-Arch Effect

In recent years,a lot of underground engineering such as metro subway and underground complex have been constructed.It poses a risk to the formation and destruction of underground caverns,or eventual surface collapse.More and more attention is paid to the research on urban ground collapse.To solve this problem,this paper mainly uses numerical simulation and theoretical analysis to study the ground subsidence mechanism of soil stratum which contains underground cavities.The paper’s main research contents and results are as follows:(1)With the numerical modeling analysis software GDEM which combines finite element with discrete element,a simulation model is established.The numerical results show that there are three kinds of sinkhole failure modes in soil stratum:global failure;arch failure at first,global failure at last;arch failure.The former two kinds will develop to the ground and cause surface collapse.The latter maybe develop to a stable arch.(2)According to the results calculated by GDEM,double-arch effect is proposed to analysis the deformation and destruction of the soil layers above the cavities.The collapse arch which is adjacent to the cavity controls the stability of the soil in the damaged area above the cavity.The compressive stress arch above the collapse arch controls the stability of the soil in the deformation zone.The overall stability of the overlying strata is determined by the joint action of collapse arch and compressive stress arch.(3)Based on double arch effect containing formation and stability analysis of a void,the ground subsidence development process is divided into the gradual collapsing arch phase and overall slippage collapsing phase.The gradual collapsing arch stage corresponds to the destruction and development process of the caving arch,which contains a critical cave arch.When the critical collapse arch is reached,the formation damage enters the overall slippage collapsing phase,which corresponds to the instability and failure of the compressive stress arch.(4)Through the plastic limit analysis of soil,and combining with the associated flow rule and nonlinear M-C code,geometric equations of ultimate collapse arch of long strip cavity and cylindrical cavity are deduced corresponding to the gradual collapsing arch stage.The influence of each parameter is analyzed,and the comparison with the existing theoretical formula is reasonable.(5)The calculation formula of the critical buried depth ratio of the overall slippage collapsing phase is derived by using the method of soil plasticity limit equilibrium.The theoretical value range of the critical buried depth ratio is 1-3.29,which is comparable with the current norm and the result is reasonable.