Study On Deformation Characteristics And Parameter Optimization Of Adjacent Dense Pipelines In Combined Open And Hidden Excavation Construction Of Subway Passage

The underground structures such as existing pipelines often exist around subway stations,so it is necessary to ensure the safety of pipelines during construction.Take the Nanchang Metro Dengbu Station No.1 entrance passage project as an example,there are underground pipelines such as sewage pipes,water supply pipes,and national defense pipes above the passage,and experts propose that the paragraphs crossing the pipelines be changed from open excavation to hidden excavation method construction.In view of the continuous disturbance of the adjacent dense pipeline during the construction of the combined open and hidden excavation of the subway passage,the study of the deformation characteristics of the dense pipeline is necessary.This paper focuses on analyzing the deformation characteristics of the dense pipeline adjacent to the construction of the combined open and hidden excavation of the subway passage,analyzing the sensitivity of the pipeline deformation parameters,and optimizing the construction parameters of the passage from the perspective of economy based on the pipeline deformation control.The main work and results of this paper are as follows:(1)Through the use of finite element simulation combined with relevant theories and field measurements,the spatial and temporal effects of ground and pipeline deformation,pipeline-pipeline and pipeline-soil interaction effects are analyzed during construction.The study found that the maximum surface settlement was reduced by about 18% in the area crossed by the pipeline group,and the settlement trough width increased by about 36%;The horizontal displacement of the underground pipeline gradually shows "S-shaped" deformation characteristics with the construction excavation,and this characteristic becomes more and more significant as the distance between the pipeline and the open excavation section decreases;Excavation construction will make the pipeline-soil settlement difference,resulting in the phenomenon of "disengage" between the two,while the pipeline-soil settlement difference increases with the increase of the bending stiffness of the pipeline.(2)Based on the orthogonal model test,the relevant factors were reasonably selected from soil parameters,support parameters and pipeline parameters,and the sensitivity and significance level of each factor on pipeline deformation were initially explored by using range and variance analysis;and the concept of sensitivity ratio was introduced to quantitatively evaluate the sensitivity of each factor.Taking sewage pipe settlement as an example,among the above three parameters,the factors with the highest sensitivity are the effective internal friction angle,the equivalent thickness of the enclosure pile and the pipeline-open excavation section distance,with sensitivities of 0.732,0.375 and 0.432,respectively.(3)From the perspective of engineering economy,the equivalent thickness of retaining pile,the thickness of initial support and the range of stratum grouting reinforcement are selected as the optimization parameters.Based on pipeline deformation control,eight groups of proposed optimization schemes were proposed and compared,and the optimal scheme was equivalent thickness of retaining pile 350 mm,initial supporting thickness 50 mm and grouting reinforcement range 2.10 m.The settlement of sewage pipe,storm pipe,water supply pipe and defense pipe in the optimal scheme is 75.55%,58.50%,58.60% and 73% of the control value,respectively.At the same time,compared with the original project scheme,the optimization scheme can greatly save construction materials and significantly improve the engineering economy.This study can provide reference for similar projects in the future.