| Xi’an is a typical loess area with a large number of ground cracks distributed,which brings greater difficulties to the construction of underground engineering.Usually,the construction of underground engineering through ground fissures mainly adopts the mining method,which has complicated procedures and low efficiency,which seriously restricts the implementation of underground engineering in Xi’an.Therefore,in this paper,the construction method of shield first and then excavation is proposed with the engineering background of the section of Jingjiu-zhangba North Road of the comprehensive pipeline corridor of Science and Technology 8th Road in Xi’an,and the research is carried out according to the combination of theoretical analysis and numerical simulation and engineering monitoring,and the main contents and results are as follows:(1)Shield expansion scheme and the influence law on the ground deformation:numerical models of different construction methods were established by using finite element software,and the influence law on the ground deformation by using different construction methods in the expansion was revealed by analyzing the deformation trends of surface displacement and vault settlement.The results show that:the construction of shallow buried concealed excavation method using CRD method has the least influence on the ground settlement.(2)Shield excavation construction sequence optimization and ground reinforcement research:analysis of different construction sequences and different pre-reinforcement measures on the influence of ground settlement,research results show that:different construction sequences cause different values of ground settlement,and the construction sequence of excavation process 4 has a better effect on the control of ground settlement,that is the upper left part is excavated first,then the lower left part is excavated,then the upper right part is excavated,then the lower right part is excavated,and finally the bottom is excavated.The most ideal effect of using reinforcement method 4 is the reinforcement of soil by overrunning pipe shed and small conduit grouting.(3)Optimization of demolition of the partition wall and segment during shield expansion construction:The study of the influence law of different partition wall removal length and different segment removal sequence on stratum settlement.The results show:when the length of the partition wall is 3m in one-time removal,the impact on the stratum is the smallest,and the dismantling process 2 is adopted(first remove the odd-numbered ring and then remove the even-numbered ring).It is more reasonable to remove the segments.(4)On-site monitoring data results and analysis:monitor the project site,record the monitoring data,perform regression analysis on the monitoring data,and compare the monitored data with the results of the numerical calculation of the finite element software,which can verify the research method and whether the conclusions are reasonable and correct. |
