Study On The Instability Mechanism Of Shallow Soft Rock Tunnel And Treatment Measures Of The Collapse Disaster

This paper is based on statistical analysis of the past collapse disaster research ofshallow soft rock tunnel. Collapse accident in Ziyin tunnel construction is takened as aspecific example. By using different numerical simulation software in analyzing tunnelcollapse and comprehensive study of the reason and mechanism of collapse, someeffective treatment methods are found. Main research and achievements are as follows：①Through statistical analysis of collapse case in a large number of highway tunnel,collapse is classified into several types and the main influencing factors resulting in thecollapse and the preventive measures are found.②Collapse accident in Ziyin tunnel construction is taken as a specific example. Byusing different numerical simulation software for tunnel collapse and comprehensivestudy of the reason and mechanism of collapse, some effective treatment methods arefound. In arch shoulder of45°direction, stress mutation area appears and the partialarea of plastic zone is obvious. Shear failure has already formed within a certain range.Collapse has occurred at the point for transfixion of plastic zone.③Considering joint rock, the surrounding rock slides obviously along joint plane,the instability may appear and evenly collapse will appear. Due to the broken rock andfracture development, besides large blasting vibration, finally the collapse in Ziyintunnel happens. The main pattern of collapse appears in vault and collapse arch occursobviously. The crack appears in hance and the surface subsidence may appear.④Compared to these numerical simulation methods for the analysis of tunnelcollapse, the fast lagrangian analysis of continua calculation can present initiative stateof rock collapse. And the universal distinct element code can simulate collapse moreactually through the gradual damage analysis and large deformation circular iterativecalculation.⑤The tunnel collapse results of numerical simulation by the UDEC are analyzedcomprehensively. The different buried depth, different level of surrounding rock anddifferent joint of surrounding rock are studied, and then the reason and mechanism ofcollapse from a different perspective are discussed.