Research On The Ground Settlement Law Of Shield Construction In Guiyang Rail Transit Section Tunne

Shield tunneling in soft soil will face problems such as increased propulsion resistance and difficulty in controlling shield attitude and direction due to uneven force or mud cake on the cutter disc.In addition,the lower strength of the soft soil at the soilrock interface also makes it easy for the shield to produce greater disturbance to the ground,which may lead to excessive surface settlement,posing a great threat to project safety and surface construction.Relying on the scientific research project of Guiyang Rail Transit Line 3 Phase I Project,for the tunnel project between Tongmuling Station and Taohuazhai Station,we study the surface settlement law caused by shield crossing the upper soft and lower hard strata through theoretical analysis,field monitoring and numerical simulation.The main research contents are as follows:(1)To study the settlement formula of the two-lane tunnel applicable to the composite stratum in Guiyang area.Based on the lateral surface settlement monitoring data of the upper soft and lower hard strata in the interval of Tongmuling Station-Taohuazhai Station,the surface settlement formula is initially obtained by regression fitting with Peck’s formula,and then the formula is modified by introducing the maximum surface settlement correction coefficient α and the correction coefficient βfor the width of the settlement trough to derive the surface settlement formula for the shield crossing the upper soft and lower hard strata,and the correction coefficient is proposed and the range of correction coefficients.(2)To study the key factors influencing the surface settlement caused by shield tunnel crossing composite strata.Combining the characteristics of the composite stratum,the mechanism of surface settlement and the general situation of the tunnel in the area,the factors such as the soil-rock ratio of the excavation surface,the spacing between the two-lane tunnel,the mechanical properties of the red clay,and the construction boring parameters will affect the surface settlement,and then use the finite element software to carry out the univariate control analysis to study the law of surface settlement caused by the shield crossing the upper soft and lower hard strata.The final conclusion is that the thickness ratio of the excavation surface,the elastic modulus and Poisson’s ratio of the red clay and the grouting pressure have the most critical influence on the surface settlement.(3)To study the settlement control measures for shield tunnel crossing composite stratum.According to the key influencing factors and numerical simulation results,corresponding control measures for surface settlement in upper soft and lower hard strata can be given: pay attention to grouting pressure and slurry quality,timely adjustment of jacking force before excavation,and control of the size of upper and lower jacking force at the soil-rock intersection.For the case of more serious surface settlement,the reinforcement measures for different parts of the soil layer and the improvement measures for different lengths of the surrounding rock are used.