Study On The Law Of Ground Settlement Caused By Shield Tunnel Construction In Nanning

During the construction of shield tunnel,regardless of the depth and section size of the tunnel,it will cause some disturbance to the nearby soil,which caused a series of problems of surface subsidence,damage of surrounding buildings and underground pipeline etc...With the wide application of shield method in metro construction,more and more attention is paid to the influence of shield tunnel construction on the ground surface settlement.Therefore,it is very important to accurately predict the surface subsidence,and take effective control measures in the design and construction,so as to prevent the occurrence of accidents.Because of the application of shield method is the first time in Nanning area,so at present,the research on the application of shield construction in Nanning is still less,and the study of the surface subsidence caused by shield tunnel construction under special geological condition in Nanning is almost blank.In this paper,the research object is based on the shield section of Nanning Metro Line 1 and line 2.The strata combination model is established through investigation and data analysis of the geological condition,and the subway line is divided into six Engineering Geology Division.The surface subsidence caused by shield tunnel construction in Nanning area are analyzed and summarized through the field investigation and data analysis.The related prediction formula and parameter recommended value are given in this paper.Research results show that:(1)The ground surface settlement caused by shield tunnel construction in Nanning area is basically in accordance with the Gauss distribution law.By using the Peck method to analyze and forecast,the prediction formula of ground surface settlement in 6 engineering geology division is introduced,and the corresponding calculation parameters are given.The comparison between the calculated results and measured values show that the prediction error rate does not exceed 11%.(2)The longitudinal surface settlement induced by shield tunnel construction in Nanning Metro can be divided into three stages,which are the shield machine has not yet arrived,and the the shield machine is passing through,and the shield machine has passed.The statistical results show that the settlement and settlement rate of the second stage are highest,the settlement reached 73%of the total settlement,the settlement of the first stage is about 9%of the total settlement,the settlement of third stage is about 18%of the total settlement.(3)The paper based on the measured settlement data,and using the improved Peck formula to analyze the ground surface longitudinal settlement in the influence range of shield tunneling,the prediction formula and the corresponding calculation parameters are given.The comparison between the calculated results and the measured values shows that the prediction error rate is no more than 13%.Based on the results of data analysis of surface subsidence,the sensitivity of the shield construction parameters to the ground surface settlement is analyzed by the gray correlation analysis method.The results show that the construction parameters of the Earth Pressure Balanced Shield tunneling construction method on the sensitivity of surface subsidence from large to small is as follows:the pressure of the soil chambert,grouting amount,cutterhead torque,grouting pressure,tunnelling velocity.The on-site monitoring data of surface subsidence were compared with the existing control standard,found that the surface subsidence value is smaller when shield tunnel through No.1 Geology Division,No.3 Geology Division and No.4 Geology Division by the Earth Pressure Balanced Shield tunneling construction method.The surface subsidence value is larger when shield tunnel through No.2 Geology Division,No.5 Geology Division and No.6 Geology Division.In addition,the surface subsidence curve is steep and the rate is large,and the control of the ground surface subsidence is unfavorable to the shield tunnel passing through No.3 Geology Division.The proposed value of the construction parameters for the reasonable control of ground settlement is put forward for No.2 Geology Division,No.5 Geology Division and No.6 Geology Division that the surface subsidence is larger and No.3 Geology Division that the settlement rate is bigger.