| With the construction of a large number of urban subway lines,new tunnels are emerging to cross existing tunnels in short distance.The construction of the new tunnel inevitably disturbs the surrounding soil mass,which causes the stress redistribution in the surrounding strata in a certain range,resulting in the uneven settlement or uplift of the existing tunnel.Therefore,it is necessary to study the deformation of the existing tunnel structure caused by the construction of the upper span of the existing tunnel,and explore the control measures to limit the deformation of the existing tunnel.In this paper,based on the background of a new metro double track short-distance up crossing existing metro line project,the deformation law,unloading factor influence,construction factor influence and reinforcement measures of the existing tunnel in the construction of shield short-distance up crossing existing tunnel are studied by using the research method of theoretical analysis and numerical simulation.The main contents include:(1)In this paper,a two-stage analysis method is used to study the mechanism of the influence of the unloading effect of the construction of the upper span of the new tunnel on the existing tunnel,and the relationship among the shield,the soil and the existing tunnel,as well as the main parameters affecting the construction of the upper span of the existing tunnel.(2)In this paper,14 typical working conditions in the process of shield double line construction are selected as the research focus,and the variation laws of surface displacement,subway tunnel deformation and tunnel structural stress caused by the construction of the upper span existing tunnel are obtained.The results show that: the surface displacement sinks within the range of 1.3 times the outer diameter of the shield along both sides of the metro tunnel axis,and the surface uplift within the range of 1.3-5 times the outer diameter of the shield along both sides of the metro tunnel axis;the surface displacement changes significantly within 20 m before and after the shield machine reaches the monitoring section,and the final settlement value of the ground caused by the double line construction is less than that of the single line construction;the influence of the shield up crossing the existing tunnel construction is concentrated in the new and old Within the range of 3 times of the outer diameter of the shield before and 4 times of the outer diameter of the shield after the intersection of the horizontal projection of the tunnel;the small angle crossing of the new tunnel causes the displacement of the deformation peak position of the existing tunnel;the vertical deformation of the existing tunnel has a "lag effect",and the influence of the second crossing of the shield on the construction of the existing tunnel is less than that of the first crossing;the stress change of the existing tunnel lags behind the displacement change,and the soil disturbance occurs The redistribution of stress after moving is the main reason for the change of tunnel stress.(3)Increasing the vertical clear distance between the new and old tunnels,increasing the angle of horizontal projection between the new and old tunnels and increasing the clear distance between the new and old tunnels can effectively reduce the impact of shield construction on the existing tunnels below.During the actual construction,the angle between the horizontal projection of the new and old tunnels shall be greater than 60° as far as possible;the clear distance between the new and new double line tunnels shall be greater than 2 times of the opening diameter as far as possible;the vertical clear distance between the new and old tunnels shall be greater than 1.5 times of the opening diameter as far as possible.(4)At the end of the construction of the upper span of the existing tunnel,the floating value of the existing tunnel does not change with the change of the earth bin pressure,but the deformation of the tunnel decreases with the increase of the grouting pressure.The influence of construction parameters on the deformation of existing tunnel is far less than the unloading effect of tunnel excavation.(5)For reducing the vertical deformation of the existing tunnel,the reinforcement effect of high-pressure jet grouting pile is more significant;for reducing the horizontal deformation of the existing tunnel,the reinforcement effect of radial annular grouting is more significant.The comprehensive reinforcement can improve the reinforcement effect of the two reinforcement methods when they are used alone and produce a "synergistic effect",thus reducing the deformation value of the existing tunnel. |
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