Research On The Tunneling Parameters And Soil Improvement Technique Of The Epb Shield Tunneling In Water-rich Sandy Cobble Layer Of Chengdu City

The subway tunnel project in Chengdu has the"three high"characteristic:high groundwater level,high cobble content and high formation strength.Engineering and hydrology features are both rare comparing to other urban subway tunnel projects.Based on the statistics and analysis of the stratigraphic distribution and soil characteristics data in the water-rich sandy cobble area,the field test,the indoor experiment and the numerical calculation are used as the research methods.Combining with the methods of research,theoretical deduction and summary analysis,technical route of this research is extended from the research of soil property of water-rich sandy cobble Layer and soil improvement to the research of soil pressure,volume of excavated earth,and synchronous grouting.Thus,an efficient scheme on soil improvement,soil pressure,synchronous grouting,and control of the volume of excavated earth was established,which has vast importance to the development of the research on the mechanical properties of water-rich sandy cobble layer and enriching the construction instruction of the shield tunneling in metro tunnel construction.Based on the subway project of Chengdu Metro Line 1,2,3 and 7,this study has carried on the following research:Based on the statistics and analysis of data of stratigraphic distribution and soil characteristics in the water-rich sandy cobble area,the influence rule and interaction of moisture content and fine grain content on the strength of sandy cobble soil was obtained by combining with the laboratory test.Meanwhile,the effects of water pressure and fine grain content on permeability of sandy cobble Soil can also been gain.There is non-adaptability in EPB shield tunneling crossing long-distance,water-rich sandy cobble stratum,so,a comprehensive study on the soil conditioning and parameter optimization is carried out.The modifier selection,mix ratio,and optimized incorporation ratio range in middle dense sandy cobble stratum,dense sandy cobble stratum,composite stratum and other different soil conditions can been obtained.This paper systematically analyzes the soil conditioning law of shield tunnel in sandy cobble stratum with different modifier,different water content and different soil conditions.The analysis method the guidance are both strong,which can provide reference for shield construction under similar geological conditions.Pressure holding mode is efficient in the shield tunneling in water-rich sandy cobble layer.Range of the limit value of the parameter of the volume of excavated earth was summarized.Range of the volume coefficient and density coefficient of the excavated soil was obtained.Also,it is concluded that normal distribution and T estimation method is suitable in the parameter processing of the volume of excavated earth in water-rich sandy cobble layer.Therefore,volume of excavated earth can be estimated,and excavated soil layer can be identified based on volume of excavated earth.Thus,shield tunneling mode and tunneling parameters can be adjusted timely.A soil pressure parameter model was built based on FEM software ABAQUS and construction data.Ground settlement was set as reference.Influence law of the soil pressure on the ground settlement was analyzed.The limit support pressure of the tunnel face of the shield tunneling in water-rich sandy cobble layer was obtained as 0.1.According to the peculiar nature of water-rich sandy cobble,the permeation and compacted grouting model is put forward,and the equilibrium condition of the simultaneous grouting from the infiltration grouting diffusion and the compaction diffusion,and the limit equilibrium equation of the segment are obtained.Meanwhile,the minimum pressure of the simultaneous grouting of the shield machine is also obtained,which can solve the hysteretic settlement problem.The formula of grouting for each digging ring is gained,and the results show that the grouting volume of shield tunnel in the middle sandy cobble stratum is 6.5 m~3,which can be used as a parameter for the simultaneous grouting of shield tunnel in water-rich sandy cobble stratum.Using finite element software to simulate the tunneling process of earth pressure balance shield machine in water-rich sandy cobble strata.Comparing with the results of numerical simulation and actual monitoring results,the feasibility of the numerical calculation model is verified.And the influence of the critical parameters such as soil conditioning,soil pressure,excavation and grouting is analyzed by means of numerical simulation.The effect of soil conditioning and the auxiliary technology before and after the building are verified and the rules are summarized,which will provide reference for the construction under similar conditions.