| With the rapid development of our economy,the ground space in big cities can not satisfy the need of development.Under the current background,the development of urban underground space changes with each passing day,among which subway construction is an inevitable trend.We will face many technical problems in the excavation of subway tunnel with vast territory and complex geological conditions.The paper takes the construction of Shield Tunnel of Zhengzhou Metro Line 7 as the engineering background,which is involved in the“Research project of China Railway No.7 Bureau”,and studies the technical problems when tunneling through water-rich sand layer.Sand generally has the characteristics of large internal friction Angle,poor fluidity and high permeability coefficient,and is prone to problems such as groundwater gusher and large surface settlement,which has a great impact on the construction safety progress and economic benefits.Therefore,it is of practical significance to carry out the muck improvement test research on silty sand and fine sand layer.The main contents of the paper are as follows:(1)The bentonite amendment optimization test was conducted on the high viscosity bentonite with soil-water ratio(mass ratio)of 1:6,1:8,1:9,1:10 and 1:12,and it was found that different soil-water ratios had significant effects on the viscosity of bentonite.According to the mud viscosity of the actual project is controlled within 30-50 s,the mixing ratio of bentonite slurry for residue improvement is determined to be bentonite: water(mass ratio)=1:9,and the optimal swelling time is 10 h.(2)Based on the silty sand and fine sand stratum of Zhengzhou Metro Line 7,the permeability test,direct shear test and slump test were carried out by adding high viscosity bentonite with soil-water ratio(mass ratio)of 1:9.It was found that with the increase of injection rate,the permeability coefficient of silty sand and fine sand decreased,the permeability resistance increased significantly,the internal friction Angle decreased,the cohesion increased,and slump gradually increased.The optimum bentonite injection rate of silty sand and fine sand is obtained to meet the requirement of "ideal soil" in shield construction.(3)The settlement monitoring data of the construction site was analyzed,and it was found that before the slag was improved,shield tunneling was prone to gusher,and the surface settlement was far beyond the warning value;After adding bentonite to improve the slag,no gusher occurs in shield tunneling,and the settlement value is greatly reduced,which indicates that the improved slag has a positive effect on controlling the surface settlement.(4)FLAC3D finite element software was used to simulate the settlement in the process of shield tunnel excavation.The numerical simulation was used to verify that the residual soil was settling before and after the improvement.The simulation results were compared with the real monitoring data,and it was found that the change trend was consistent with the real monitoring data,which verified the feasibility of the numerical simulation and further improved the research means of shield residual soil improvement engineering. |
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