| In recent years,with the rapid development of urban rail transit,there are a large number of new subway lines crossing existing subway projects.In order to ensure the safety of existing subway line operation and construction of new lines,it is particularly necessary to study the influence of short-distance underpass construction of mine tunnel on the existing tunnel structure and new large section tunnel structure deformation.Based on guangzhou Metro Line 18 mine tunnel undercrossing the existing Line7 project,numerical simulation and field test methods are used to study the mechanical behavior and control technology of large section mine tunnel undercrossing the existing subway tunnel in close distance.The main contents and research results are as follows:(1)Three-dimensional numerical simulation is used to study the displacement and stress changes of surrounding rock,stratum settlement,internal force state of new tunnel support structure and stress,deformation characteristics of existing tunnel structure caused by large section mine tunnel using CRD method and both side drift method.By comparison,it is found that the safety control effect of both side drift method is better than that of CRD method,and has better engineering applicability.(2)Through the field mechanical test,the deformation characteristics and mechanical evolution law of its own supporting structure in the underpassing construction of large section mine tunnel are explored,and the safety performance of lining structure is evaluated.The test results show that the initial support structure of the large section tunnel was particularly vulnerable at the arch waist.The initial support structures of the middle and lower arches were less stressed and safer.After the initial support formed into a ring,structural stress tended to be stable.The optimization scheme of "constructing secondary lining first and removing temporary support braces later" was adopted for twin large-section tunnels,which greatly reduces the disturbance to the stratum and the existing tunnel after removing braces,and the safety performance of the lining structure after removing braces meets the the criteria of the designed code.(3)Based on site settlement monitoring,the real influence characteristics of underground tunnel construction with large section mining method on the existing subway tunnel and surface settlement are studied.The monitoring results show that the settlement of the existing tunnel and the ground surface exceeds the limit caused by the undercrossing construction of large section tunnel,and the main influencing factors are,continuous water loss of the stratum,adjustment of construction procedure,improper control of grouting lifting measures and construction working environment.(4)By using fluid-structure coupling numerical simulation,the influence mechanism of groundwater seepage and the effect of water sealing effect of reinforcement ring on settlement and deformation of existing subway tunnel in tunneling construction of large section mining method are deeply analyzed,and settlement control measures of large section tunnel crossing existing subway are discussed.The sealing effect of the stratum reinforcement ring determines the formation of groundwater seepage channel,which is the key factor affecting the settlement of the stratum and the existing tunnel.The construction should be based on the premise of improving the formation water stop condition.This thesis includes 95 figures,19 tables,and 84 references. |
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