Research On Techniques Of Earth Pressure Balanced Shield Tunneling In Upper-soft-low-hard Composite Ground

The traditional methods of excavation engineering make the problems of urban traffic congestion and shortage of available land more serious.As a modern trenchless pipeline engineering technology,the earth pressure balance shield method construction has been widely used due to its engineering characteristics with little impact on the environment,traffic and the advantages of safety,economy and high efficiency.However,with the full-scale development of shield construction,complex geological conditions have also brought a series of problems for shield construction,and brought great cost increase and potential safety hazards for earth pressure balance shield construction.This paper takes the shield section of the Hangzhou Damaowu~Renhe Avenue water supply pipeline project as a background,combined with theoretical analysis,numerical simulation,and on-site experimental methods to study the key problems of the earth pressure balance shield construction in the upper soft lower hard composite soil layer,and The corresponding control strategy is proposed to ensure the smooth excavation of the shield in this stratum.In the first place,according to the geological characteristics of the upper and lower soft soil layers of the interval,the advantages and disadvantages of different types of shields for tunneling were analyzed.Finally,the earth pressure balance shield was selected for the tunneling.In the past ten years,statistical research was conducted on typical projects of soil pressure balance shield tunneling in upper and lower hard soil layers.Combined with geological conditions in the interval,the geological adaptability problems and risks of earth pressure balance shield tunneling in upper and lower hardsoil layers were analyzed.The geological adaptability problem and main risk of the upper soft and lower hard strata obtained by the earth pressure balance shield tunneling are the disturbance control of the surrounding soil during the excavation process,and the mud cake in the silty clay layer,the pebble layer and the weathered rock layer during the excavation,The risk of spiral machine gushing,and the risk of shield deflection,difficult attitude control,and excessive tool wear when driving in different strata.In order to study the disturbance of shield tunneling on the surrounding soil,MIDAS GTS NX software was used to establish a shield tunnel model under the corresponding working conditions of the three sections ZK2 + 960,ZK3 + 290,and ZK3 + 360.By studying the different distribution of excavation surface strata Under the conditions of construction disturbance,it is proved that the vertical settlement of the ground and the surface and the lateral deformation of the ground caused by the construction of the earth pressure balance shield in the upper soft and lower hard composite soil layers;at the same time,the Gaussian function is used to fit the lateral surface settlement value.And put forward a method to evaluate the fit of the curve.Through the comparison and analysis of the measured value,the fitted value and the simulated value,the commonality and deviation of the measured data and the simulated data are obtained and the conclusion is corrected;Taking the settlement control as the starting point,aiming at the attitude control and soil improvement problems during shield tunneling,the grey correlation analysis is combined with the actual engineering to find out the influence of the main construction parameters on the surface settlement and the mechanism of action,and then proposes different strata distribution to shield The control range of tunneling parameters and shield posture control measures,and at the same time,based on field experiments,proposed a method for improving the slag in different strata,which effectively avoids the occurrence of mud cakes and gushing of the cutterhead,ensuring that the shield machine is in Smooth excavation of this stratum;Aiming at the risk of excessive rapid wear of interval tools,based on parameter control,slag improvement and shield attitude control strategies,a method for evaluating the distribution of upper and lower soft soil layers,geological adaptability of shieldconstruction and earth pressure balance are proposed The tool control strategy of the tool wear when the shield is driving in the upper soft and lower hard formations,combined with engineering practice,is verified.