| As the density of urban underground rail transportation network increases year by year,cable tunnel construction will inevitably encounter the situation of up-down close overlapping crossing.In order to reduce the risk of close connection construction,this paper will study the construction mechanics of pipe jacking method and the stress release rate of surrounding rock,and use finite element simulation and on-site monitoring means.The change characteristics of surface settlement and existing structure deformation law in the construction process are studied.In order to reduce the influence of proximity construction disturbance,construction control measures are proposed.Specific research conclusions are as follows:1.The mechanical effects and disturbance zones generated during the construction of pipe jacking method are studied,and the representative formulas for calculating the positive thrust and tube-soil contact pressure are summarized.It is concluded that the reasonable value range of the positive thrust is 0.1 MPa ～ 0.4 MPa.The average friction resistance distributed on pipe jacking lining ranges from 14.72 k Pa to 128.88 k Pa.The friction resistance of different parts of pipe jacking varies,and the friction resistance of pipe jacking machine is about 13.5% less than that of lining.At the same time,the range of stress release zone caused by the excavation of pipe jacking tunnel is defined,and the variation of stress release in each section is calculated.The research shows that: The excavation has a constraint effect on the cavity within 10 m behind the tunnel.The stress in this range is gradually released along with the tunneling process,and the maximum stress release amplitude is found near the excavation face.The maximum difference between the maximum stress release rate and the minimum stress release rate is 41%.2.Finite element analysis results show that: The surface settlement increases significantly with the increase of the initial stress release rate.The positive thrust is an important factor to maintain the stability of excavation face and control the surface settlement.The surface settlement increases with the increase of the positive thrust.Under the same friction resistance,the surface uplift deformation above the excavation face caused by the side friction resistance of pipe jacking machine is greater than the influence of the lining side friction resistance.Under the same stress release rate,the cumulative superposition effect of the lining friction resistance will cause the settlement behind the excavation face to increase slowly,and the maximum settlement increases by about 20%.3.In the process of close construction of pipe jacking,due to the effect of stress release,the existing structure will float upward in the vertical direction as a whole,translate backward along the jacking in the horizontal direction,and uplift deformation will occur at the intersection of the structure.The construction mechanics will further aggravate the disturbance in the vertical direction and control the disturbance in the horizontal direction to a certain extent.Based on the blocking of disturbance media,a micro-disturbance control measure based on the formation reinforcement is proposed.Based on the disturbance source,a disturbance control measure based on the adjustment of mechanical parameters of pipe jacking construction is proposed.The maximum structure floating value after reinforcement is reduced by 46%,the maximum vertical deformation is reduced by 54%,and the maximum horizontal displacement of the structure is reduced by 13%.Horizontal deformation was reduced by 21%.By comparing the numerical simulation results with the field measured data,it can be seen that the construction disturbance laws obtained by the two research methods are basically consistent. |
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