Study On Land Settlement Law And Control Technology Of Shield Tunneling Crossing Water-Rich Stratum In Qingdao Area

When the shield construction method encounters soft,loose,poor self-stability and high permeability coefficient in the water-rich stratum,it is easy to cause common geological hazard such as segment seepage,spewing of the face,and ground collapse.Previous research on the water-rich stratum only focus on a single stratum.Therefore,it is necessary to research the ground deformation law and settlement control when shield passing through different water-rich stratum.The research results have important theoretical significance and practical engineering value.This paper relies on the shield construction method of a section of Qingdao Metro Line 1 to pass through different water-rich stratum as an engineering example,and comprehensively application the on-site ground subsidence measurement,shield real-time monitoring system,theoretical analysis and numerical simulation to carry out systematic research,and the specific research contents and achievements are as follows:?1?The shield tunnels in the northern section of Qingdao Metro Line 1 are divide d into 12 sections;taking a water-rich shield section in the north section as an engine ering example,considering comprehensively the stratum-crossing and the construction e nvironment risk along the line,the shield tunnels in the water-rich stratum are divided into five kinds of safety risk groups.The safety risk group is the basis for the subseq uent research;the selection of shields in the water-rich stratum is carried out,and the composite earth pressure balance shield is selected to obtain three working modes in t he excavation process under different water-rich stratum.?2?Through Peck's prediction formula,the measured data of different sections of t he monitoring section in the interval are regressed and analyzed,and the curve fitted i s in good agreement with the measured data.It shows that the linear regression metho d can better predict the ground subsidence law caused by shield tunnel construction in the interval;The Peck's prediction formula is modified by introducing the maximum se ttlement correction coefficient andthe width correction coefficient of settlement trough u nder the water-rich stratum.When the range of a is 0.4?0.7,the range of b is 1.1?1.4,the modified Peck's prediction formula can accurately predict the interval shield gr ound settlement caused by tunnel construction;The measured data of other shields are selected for verification.The results show that the range of correction coefficients can be used in the water-rich stratum similar to the study interval.The longitudinal groundsubsidence data of different sections change with the distance of cutter head and the influence of tunneling can be divided into three stages: slow deformation stage,main d eformation development stage and stable stage and the vertical settlement law of the g round in different stages of different groups is compared and analyzed.?3?Considering the fluid-solid coupling effect,firstly based on the seepage continuity equation and the seepage differential equation,the theoretical formula of seepage pressure in the surrounding rock of interval is deduced.The C_? group is used as the numerical simulation object,and The FLAC^3D5.0 software is used to simulate the real shield tunneling process in the water-rich stratum,and the ground is numerically simulated.The settlement results are basically consistent with the measured data and the Peck's fitting curve,which indicates that the calculation model establishment and parameter selection are reasonable and accurate;The pore water pressure field is analyzed: the closer the pore force of the tunneling excavation area is to the tunnel,the denser the potential surface is.After the shield excavation is completed,the pore pressure on the segment surface is 0,and the seepage vector at the arch waist is larger,which is seepage.which is a strong seepage area;the analysis of the stress field shows that the stress field is formed around the excavation part,and the influence range of the surrounding soil stress field is about 2 times the shield diameter,and the stress occurs between the arch waist and the arch foot position.Concentration phenomenon;analysis of the plastic zone: shearing and tensile failure occurred at the vault.The plastic zone of the surrounding rock of the tunnel is mainly caused by shear deformation.?4?The key technologies of ground settlement control in the water-rich stratum are studied.The variation trend and control range of the main tunneling parameters of the shield passing through different water-rich sections are obtained.The shield encounters high permeability of sand in the process of water-rich stratum excavation.For soil,the calculation method of water and soil pressure should be used.The actual amount of soil in the interval should be controlled at 55.75m³?65.04m³;the composite shield is equipped with 4 simultaneous grouting pipes.The upper left and upper right synchronous grouting pressures in the water-rich stratum are controlled.3?3.5bar,the lower left and lower right synchronous grouting pressure is controlled at 1?1.5bar;under the water-rich condition,the synchronous grouting of B_? group should be controlled at about 5.63m³,and the synchronous grouting of CI group should be controlled at about 6.89m³,DII group segment synchronous grouting should be controlled at around 6.02m³.