Optimization Research For Construction Programs Of Soft Rock Tunnel With Large Deformation And Small Static Distance

The deformation of surrounding rock of small spacing tunnel of large deformation of softrock are few studied at home and abroad, and some the built small spacing tunnel of largedeformation of soft rock emerged lining cracks, surface cracks,hole wall cracks, for such atunnel mechanical behavior’s theory research and it is necessary to explore.In this dissertation, background with the building Xin Chengzi tunnel In the territory ofDangchang County of Longnan city in Gansu Province, using the large-scale general finiteelement analysis software (MIDAS/GTS), to analyze the tunnel construction process by FEMnumerical simulation, study respectively in different step excavation length and distancebetween the two working faces conditions, using the same method of construction excavation,to control the tunnel’s deformation and support unit’s stress, comprehensive monitormeasuring data, obtained the following results:（1）The main reason for large deformation of Xin Chengzi tunnel is that the tunnel is inthe condition of Extremely high geostress.The rock has been segmented and extruded to smallblocks.these conditions lead to the low rock’self.stability. The rock around the tunnel has longtime period of deformation increasing and great total deformation.（2）According to the monitoring data, The deformation law of using the three stepexcavation method excavate the small spacing tunnel of large deformation of soft rock: Vaultsettlement change is288mm, The horizontal convergence of the upper steps is354mm; Thetime of the rapid change of deformation of displacement at the upper step is25days; The timeof the rapid change of deformation of displacement at the middle step is20days; The time ofthe rapid change of deformation of displacement at is15days. The pressure of thesurrounding rock growth for a period of70days; Contact pressure increase for a period of50days, from the arch to the lateral wall, the ultimate stress value decreases gradually from topto bottom of space; and through the contrast analysis, long anchor has good effect to controlthe surrounding rock convergence.（3）By simulating three kinds of conditions of tunnel excavation，Comparison of crownsettlement, horizontal convergence and supporting stress, painted the curve of theirdisplacement and stress with the change of construction step, analysis: using ConditionⅠoftunnel excavation by numerical simulation of the construction process, Vault settlement,horizontal convergence, the stress of the primary support unit, the axial stress of steel arch,the stress of sprayed concrete, The two stress of lining concrete, the axial force of bolt smallerthan using Condition Ⅱ or Condition Ⅲ. Considering controlling the deformation and thestability of tunnel, etc, Think in under the condition of Xin Chengzi tunnel, The3M step length is reasonable, Conducive to the self stability of the rock, the vault crown settlementand horizontal convergence value is small, the initial support and two lining unit forceuniform, More weakened the stress concentration range of the primary support unit and thetwo lining unit, To ensure the stability of tunnel.（4）Simulation results around working face from different lines have shown that vaultsettlement and horizontal convergence value were decremented when the distance of tunnelworking face were gradually increased, and the rate of change also were reducessimultaneously. However,during the construction process of the working conditions one, twoand three,the displacement of tunnel have greater changes,and there are significantdifferences among three construction conditions,and deformation of working condition fivewere slightly greater than working condition four. The influences on vault settlement andconvergence which were based on the distance changes of tunnel working face,comprehensively have been analyzed. Both vault settlement and horizontal convergence valuewere small when the distance of tunnel working face was30m or40m. Thus the vaultsettlement and horizontal convergence deformation could be effectively controlled,and moreconducive to maintain the stability of caverns.