| With the rapid development of subway construction,various subway lines have appeared in urban construction.It is sometimes seen that newly built lines cross under and side tunnels.Proximity shield construction of a new tunnel will inevitably disturb the soil layer,causing deformation of the existing tunnel and soil,which is not conducive to the safe operation of the subway.Therefore,research on the shield construction of new tunnels is very important for the disturbance of existing tunnels.In addition,the previous research on shield construction tended to intersect new tunnels with existing tunnels,and the specific process of shield construction did not involve much research on new tunnels.These are also one of the key factors for shield construction.Therefore,it is valuable to study the influence of specific construction parameters on existing tunnels in numerical simulation.In this paper,based on C-W shield tunnel passing through the entrance line tunnel as a research background,through numerical simulation and calculation of FLAC3 D software,the palm face during shield excavation was studied.The influence of thrust,grouting pressure and grouting amount on existing tunnels,and summarize the most reliable shield parameters in this project.In addition,the numerical calculations of the different excavation sequences of the left and right lines are compared with the monitored values.The main research results are as follows:(1)During the construction of the left-line tunnel shield,the existing tunnel subsidence decreases with the thrust of the palm face below 100 kp,while the existing tunnel subsidence does not change when the thrust increases above 100 kp.When the thrust of the right-line tunnel is below 135 kp,the existing tunnel subsidence decreases with the increase of thrust.When the thrust is above 135 kp,a small uplift occurs on the ground surface.The earth pressure at the buried depth of the new tunnel is about110 kp,which means that the optimal palm surface thrust of the left line tunnel is 0.9times the earth pressure at this depth,and the optimal palm surface thrust of the right line is 1.2 times the earth pressure.(2)The empirical grouting pressure is 0.2Mpa.In this paper,numerical calculations are performed with different times of grouting pressure.The optimal grouting pressure of the left line shield tunnel is 0.15 Mpa,and the right line shield tunnel is0.2Mpa.In addition,the amount of grouting is mainly reflected by the thickness of the grouting layer.In the numerical calculation,different thicknesses are given to the grouting layer.The optimal grouting layer thickness for the left line tunnel is 0.175 m,and the optimal 0.225 m.(3)The excavation of the left line mainly results in the vertical settlement of the existing tunnel,and the excavation of the right line mainly results in the lateral deformation of the existing tunnel.When the excavation of both lines is completed,the existing tunnel behaves as an "increase in vertical radius." Greater than the transverse radius ",the tunnel develops in the direction of the ellipse.The shield excavation sequence adopted in the actual project is left line first and then right line.In this study,the actual excavation order is compared with the right line first and then left line order,and the following conclusions are drawn: first left line then right line The order has a greater impact on the existing tunnel and has a smaller impact on the ground surface;the order of the first right line and then the left line has a greater impact on the ground surface and less impact on the existing tunnel.In actual excavation,an appropriate excavation sequence should be selected according to thespecific surrounding environment. |
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