Research On Surface Subsidence Caused By Shield Construction Of Two Parallel Tunnels

With the rapid development of the city,the land resource becomes more and more precious.As a consequence,people pay more attention to the development of underground space,one efficient way of which is tunnelig.In the design of tunnels,two parallel holes arrangement is often adopted.However,Two holes tunnel construction will influence each other to a certain degree,and the interaction not only affects the stress and displacement of surrounding rock,but also has an influence on the surface displacement and supporting loads.Therefore,it is necessary.to study the mutual influence of parallel tunnel construction systematicallyIn this article,the research status of parallel tunnel is reviewed firstly,then shield tunneling method and the measurement for the settlement of the tunnel between Shahekou station and Xianggong street in Dalian are introduced briefly.And the mechanism of ground settlement caused by shield tunneling construction are studied and analyzed.Finally,the numerical simulation software FLAC3D and how to simulate shield tunneling in this software are illustrated.After conducting geological parameter sensitivity back-analysis and shield tunnel construction back-analysis,a three-dimensional calculation model of double hole parallel tunnel is built,combining with the practical situation of construction.By comparing different models,four factors influencing the surface subsidence are obtained,the spacing of the tunnel,the condition of surrounding rock,excavating method and buried depth of tunnel.The following main conclusions are obtained:(1)When other conditions are same,as the thickness of overlying soil increases,lateral subsidence range of surface becomes larger and the maximum settlement decreases instead.(2)Other things being equal,as the spacing of two tunnels increases,bimodal curve of surface subsidence gets more obvious.When the spacing is greater than 3D,surface settlement curveis almost the same with the superposition of two tunnel construction respectively.(3)The soil layer which the tunnel passes through is mainly composed of sandy silt and silty clay.When there is not water or little water in sandy silt,it has a great stability.Therefore,when tunneling through this kind of soil,the ground settlement caused by shield construction is often very small.In contrast,the stability of the silty clay is worse,and the ground settlement is bigger.As a result,when making route planning,it is required to avoid the silty clay strata.(4)The surface subsidence varies with construction methods.Tunneling in the same direction simultaneously caused the maximum subsidence,and the subsidence of reverse excavation simultaneously is smaller than the former.In contrast,tunneling in the same direction unsimultaneously causes the minimum subsidence.When the situation permits,tunneling in the same direction unsimultaneously is preferred.