Theoretical Study On Soil Deformation Caused By Shield Tunneling In Saturated Soil

In recent years,as a new symbol of urban underground space development,subway construction has been accelerating.However,the city is full of tall buildings,the underground pipe network is criss-crossed,and the existing structures such as building pile foundations,municipal pipelines,and existing tunnels will impose greater restrictions on the route and form of crossing of the new subway.Therefore,more and more subway constructions are showing double-line overlapping and multi-line overlapping construction conditions,and the frequency of shield tunnels passing through large buildings and dense building groups is increasing.The shield construction will inevitably cause disturbances to the surrounding soil,especially in the lowpermeability saturated soil area.Due to its high compressibility and high sensitivity,the disturbance and deformation of the soil are more obvious.Therefore,for saturated soil areas,under the influence of existing buildings,the study of the influence of construction of single and double-line shields on soil deformation at different positions has important engineering significance and academic value.Based on the initial value solution of the semi-infinite saturated soil,this paper fully considers the influence of multiple factors,secondary disturbances and existing buildings,and modifies the soil deformation formula caused by the saturated soil shield.Combined with the typical London saturated hard clay engineering case and the Hangzhou Bay saturated soft clay engineering case,through comparative analysis with Mindlin solution and Ding Zhi solution,the conclusions are as follows:(1)Taking into account construction factors such as soil squeezing effect,grout spreading,soil softening,grout weight,unevenly distributed grouting pressure in the circumferential direction,and grout filling shield gaps,and the different positions and construction intervals of the first and subsequent shields.Compared with the Mindlin solution and Ding Zhi solution,the calculated results of the soil deformation caused by single-line and double-track shield construction are closer to the measured curve,which can more accurately reflect the characteristics of vertical and horizontal surface deformation during shield tunneling.(2)The secondary disturbance effect is mainly reflected in that the structural strength of the soil body will be drastically reduced after being disturbed,but as the shield advances,the structure and strength of the soil body will gradually recover over time.Therefore,the surface settlement caused by the simultaneous construction of twoline shields is the largest.With the gradual lengthening of the interval between the construction of the first and subsequent tunnels,the strength of the soil gradually recovered,the disturbance effect of the first tunnel construction on the soil gradually weakened,and the surface deformation caused by the subsequent shield construction gradually decreased,so the total surface subsidence has gradually become smaller.(3)When the shield is adjacent to an existing building,the ground settlement on the outside of the building will undergo abrupt changes.This is because the rigidity of existing buildings and the existence of pile foundations will restrain the deformation of the soil near the structure.In order to compensate for the ground loss caused by the shield construction,this part of the soil loss will be transferred to the outside of the building.As a result,the amount of ground settlement outside the building is greater,and the impact range of the settlement trough is also wider.The influence of the stiffness of the existing building on the soil can be roughly divided into the influence of overall stiffness and the influence of local stiffness.The overall stiffness can be equivalently achieved by transforming the existing building into the overlying soil layer.The local stiffness cannot be accurately predicted for the time being,but its existence will only speed up or slow down the trend of the settlement curve,and the final settlement mainly depends on the overall stiffness.