| Based on the Yushichang Tunnel of the Dianzhong Water Diversion Project in Yunnan Province,this paper aims to solve the problem of tuff interlayer encountered during tunnel excavation.Through numerical simulation,the original initial support structure is optimized,and on the basis of the optimized initial support structure,a set of advanced pipe shed grouting scheme is designed to form a joint support system with the initial support mechanism.Finally,combined with on-site arch monitoring measurements and regression analysis calculations,the deformation laws of surrounding rock and the rationality of the combined support system for the Yushichang tunnel are studied and analyzed,providing certain support and reference for the safe construction of the tunnel crossing the tuff interlayer section.(1)Based on existing theories,the characteristics of basalt intercalated with tuff and the classification and judgment criteria for large deformation of soft rock are summarized.The construction technology of Yushichang tunnel is summarized and the surrounding rock conditions in front of it are comprehensively predicted.The construction technology mainly includes advanced geological prediction technology,advanced reinforcement technology,tunnel excavation technology,and initial support technology of the tunnel.Finally,it is determined that anchor bolts The steel concrete structure is combined with a combined support system of advanced pipe shed grouting reinforcement,while taking into account the nature of broken tuff that is prone to falling or collapsing,the circumferential spacing of the pipe shed is densified to 0.3m,and the high-density pipe shed grouting reinforcement technology is used to strengthen the surrounding rock at the upper part of the tunnel.(2)The mechanism of the action of anchor rods,steel arch frames,and sprayed concrete in the initial support during tunnel construction is summarized.The finite element software MIDAS GTS is used to analyze the displacement field,stress field,and stress variation of the support structure when the Yushichang tunnel passes through the tuff interlayer.On this basis,the initial support structure is optimized and designed,and the initial support parameters are determined as follows: anchor rod spacing of 1m,steel arch frame spacing of 1m,the thickness of sprayed concrete is 22 cm.(3)The mechanism of the pipe shed structure in tunnel construction is summarized,and its mechanical theory analysis is conducted.The calculation formulas for calculating the bending moment,shear force,and displacement of the pipe shed are obtained.On the basis of the optimized initial support,and in response to the problem that the upper structure of the tunnel is prone to fall off or collapse when passing through the broken tuff interlayer,the finite element software MIDAS GTS is used to optimize the design of the high-density large pipe shed advance grouting support for the Yushichang tunnel,and to study the displacement field,stress field,and stress changes of the support structure during the construction process after the high-density large pipe shed advance grouting of the tunnel,Based on this,by comparing different grouting support parameter schemes,the final determination of pipe shed grouting parameters is pipe shed diameter 108 mm,pipe shed spacing 0.3m,scope of arch grouting 140 °,and grouting thickness 1.5m.(4)Based on the actual project of the Yushichang tunnel,the arch crown settlement monitoring is carried out,the monitoring measurement data are collated and analyzed,compared with the simulation calculation results,and the data are subjected to regression analysis and calculation.Based on the calculation results,the deformation law function of the tunnel arch crown is summarized,verifying the rationality of the tunnel support system,and providing an important basis for judging the safe excavation of the tunnel,It also provides certain guidance and reference for the support technology of similar diversion tunnels when crossing the tuff interlayer. |
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