Experimental Study On Transparent Model Of Deformation Mode Of Excavation Face Of Shield Tunnel In Sand-clay Composite Stratum

With the rapid development of China’s economy,the urban population is gradually increasing and urban construction is constantly speeding up.In order to further improve the urban operation efficiency,the amount of subway construction is gradually increasing.In subway construction,shield tunneling,as a safe and efficient tunnel construction method,has been widely used.In the construction of shield tunnel.Shield tunnels are faced with the risks of excavation surface instability and surface collapse in the construction of complex stratum,among which the sand-clay composite stratum is a common formation of soil-soil composite.In different areas and under different engineering conditions,it is difficult to predict and control the stability of excavation face because of the different soil mechanical properties of sand and clay layers.Therefore,it is of great significance for tunnel construction to study the deformation and failure mode of the excavation face of shield tunnel in sand-clay composite stratum.However,And the model test study used more common similar material cannot be observed deformation inside,inside the soil to the observed deformation,this paper adopts the transparent physical model test study on soil similar materials and supplemented by the numerical simulation analysis,the sand adhesive compound formation on the surface of the shield tunnel excavation deformation failure mode in-depth research,the main research results are as follows:(1)Summarizes the transparent soil preparation method,compares the similar material,the preparation of all kinds of transparent soil chose fused quartz sand,precipitated silica,dodecanoic and shortening on the fifteenth day of the mixed liquid synthetic transparent transparent clay and sandy soils,and has carried out two transparent soil physical and mechanical properties of experimental research,proved the feasibility of the simulation of natural soil.(2)A transparent model test system for shield tunneling is designed,which is composed of consolidation device,vacuum degassing device,shield tunneling model device,data acquisition system and image testing system.The whole model is transparent,the soil internal deformation is observed without contact,the shield model device is receding automatically,and the data and images are collected automatically.(3)Based on the transparent model test system of shield tunnel,the deformation and failure rules of excavated soil under different buried depth conditions are studied,and the relationship between soil displacement and support force at the center of excavated surface of sand-clay composite stratum and the failure modes of local and global instability of excavated surface are obtained.(4)The stability analysis of the excavation face of the shield tunnel with the composite formation of sand sticking up and down is introduced with the concept of composite ratio to describe the soil distribution of the excavation face,which reflects the soil difference of the composite formation.The influence of factors such as different buried depth,spatial distribution of different soils and different composite ratio on excavation surface deformation,ultimate support force,surface deformation and failure mode of excavation surface is studied by using finite difference numerical simulation.(5)The deformation failure mode of the excavation face of shield tunnel obtained by model test and numerical simulation is compared and analyzed,and compared with the classic deformation failure mode of the excavation face,which indicates the rationality of the deformation failure mode of the excavation face obtained in the sand-clay composite stratum.The thesis includes 90 figures,10 tables and 98 references.