Collapse Mechanism And Stability Analysis Of Surrounding Rock In Tunnel Construction

During the construction of the mountain tunnel,when the tunnel surrounding rock is broken,joint fissures are developed,and the footage is too large during the construction excavation process or the construction plan is unreasonable,a collapse accident may occur.Collapse accidents occur frequently,which will result in delays in construction,increased costs and casualties.Therefore,it is important to study the occurrence mechanismand treatment measures of tunnel collapse,and it has important guidance and reference significance for the treatment of similar collapse accidents.This paper takes the collapse of the right line of the Baiyangshan Tunnel in the first section of the Yongkang-Wuyi reconstruction project in Zhejiang Province as the research object,and studies the occurrence mechanism of the tunnel collapse disaster from the aspects of engineering geological conditions,construction factors and design factors,and objectively evaluates the collapse control measures.The main research contents of the paper are as follows:(1)The occurrence type,failure form and morphology of the tunnel collapse are classified,and the causes of the collapse are described and expounded,combined with the site collapse situation of Baiyangshan tunnel,the occurrence mechanism and type of the collapse are judged.(2)The finite difference software FLAC3D is used to simulate the constrprocess of the collapse section of the mountain tunnel,focusing on the analysis of the variation of the surrounding rock displacement,the plastic zone range and the stress concentration in the reserved core soil-up and down step method,and combining with the results of on-site monitoring measurement,the stability of cavity grouting in the collapse section of tunnel is analyzed.(3)Three different combinations of construction schemes are proposed for the complex geological conditions of the front face of the collapse section.The whole process of excavation and support is analyzed by numerical simulation,and the influence of three different construction schemes on the stability of surrounding rock is analyzed from the aspects of displacement variation,plastic zone range and stress distribution,respectively,and the optimal construction scheme is obtained.(4)The emergency treatment measures for the collapse of the tunnel and the curative measures of the collapsed section are analyzed and elaborated,and the specific collapsed body reinforcement treatment plan and the collapsed tunnel excavation plan are obtained.(5)The geological conditions in front of the tunnelface are detected by means of advanced geological prediction,the possible geological disasters are analyzed,and the effect of treatment measures in collapse section is evaluated.