Research On Settlement Mechanism And Prediction Of Shield Tunnel Underpassing Existing Buildings In Shalao Section Of Qingdao

As an important part of urban rail transit,the subway plays an increasingly important role in daily public transportation.In the actual construction of shield tunnels,it is inevitable that it will pass through the commercial and residential areas of the city.The buildings in this area are relatively dense,and the dense building group will bring a lot of challenges to the construction of subway tunnels,how to reduce the disturbance of the construction to the stratum and ensure the safe and rapid passage of the shield is an urgent problem to be solved when the existing building is constructed.This article is based on the shield tunnel section of Qingdao Metro Shazikou Station ～ Laoshan No.6 Middle Station as the project support,through the analysis of measured data,numerical simulation calculation,and orthogonal test analysis,the stratum and building settlement laws caused by shield tunneling through existing buildings are studied,finally,the settlement prediction model under successive excavation conditions is established through the BP neural network,and the settlement of the surface and buildings is predicted accordingly.The specific research results are as follows:(1)By analyzing the measured data of the ground surface and buildings,the results show that: The closer it is to the surface directly above the tunnel on the excavation side,the greater the disturbance effect of the shield excavation on that side,and the greater the resulting settlement value,in addition,the construction of the trailing line tunnel will cause secondary disturbance to the leading line tunnel,which will increase the settlement to a certain extent.The measurement points near the central axis of the two tunnels are most affected by the superposition of the excavation of the two tunnels,resulting in the largest final surface settlement.(2)MIDAS GTS finite element analysis software was used to establish a numerical model of shield tunnels passing through existing buildings,and the settlement laws of the ground surface and buildings under successive excavation conditions and simultaneous excavation conditions were studied.The simulation results show that: 1)The influence of shield construction on the tunnel is mainly manifested in a certain settlement of the soil at the top of the tunnel vault,and a certain uplift at the bottom of the tunnel vault.2)Under the condition of successive excavation,the ground surface has been disturbed by construction before the arrival of the shield,resulting in corresponding settlement,and the ground surface is most affected by the construction of the first line tunnel.The maximum subsidence position of the ground surface is offset from the axis position of the two tunnels after the shield tunnel of the backward line passes through.The influence of shield tunnel construction on surface settlement varies with the position of the section,that is to say,the surface under the building is more affected by the construction of the shield tunnel than the surface under the non-building.The closer each measuring point of the building is to the surface directly above the tunnel,the greater the disturbance affected by the tunnel excavation,and the measuring points near the central axis of the two tunnels are most affected by the superposition of the two tunnel excavations.By calculating the settlement of the measuring point,it is known that the construction of the trailing line tunnel has little influence on the leading line tunnel.The building tilts in the direction of the tunnel of the leading line when the leading line is penetrated,and inclines along the excavation direction when the tunnel of the trailing line is penetrated.3)Under the condition of simultaneous excavation,the impact of shield construction on the surface and buildings is greater,and the main impact range of the surface settlement tank is also greater.The maximum subsidence value of the ground surface not under the building always occurs at the central axis of the two tunnels,and the position of the maximum subsidence value of the ground surface under the building is constantly changing with the excavation.When the shield approaches the building,the building tilts in the opposite direction of the excavation,and when the shield leaves the building,the building tilts along the excavation direction.The building sank as a whole at all stages.(3)Through the orthogonal test analysis of the three factors affecting the surface settlement,the driving pressure,the elastic modulus of the segment and the elastic modulus of the grouting material,the results show that the sensitivity of the three factors to the formation subsidence is not the same,and the sensitivity to the formation subsidence is specifically expressed as follows: The elastic modulus of the grouting material>the elastic modulus of the segment>the excavation pressure,and the influence of the elastic modulus of the grouting material on the surface settlement is highly significant,and the other two are significant effects.Using the optimal combination scheme obtained from the orthogonal test,the correctness of the combination results was calculated and verified by numerical simulation software,that is to say,the optimal combination is: the excavation pressure is 200 k Pa,the elastic modulus of the segment is45 GPa,and the elastic modulus of the grouting material is 18 MPa.(4)Using the prediction model of ground surface and building settlement under successive excavation conditions established by BP neural network,14 groups of test samples are predicted,and the results show that: The error between the prediction results and the numerical simulation results is very small,and the agreement is very high,that is to say,the model has a good effect on the prediction of ground surface and building settlement under successive excavation conditions,and can provide a certain reference for similar projects.