Study On Construction Mechanical Behavior Of Tunnel Primary Support Under Complex Geological Condition

At present, non-uniform case of soft-weak surrounding rocks and effect ofresidual tectonic stress aren’t reckoned in the method of tunnel support structuredesign basing on empirical analogue methods, so the design of primary supportadopting empirical analogue methods in that layer has a certain blindness, whichcan’t guarantee the construction successfully. Therefore, it has strong guidingsignificance for on-site construction to study construction mechanical behavior andpossible failure modes of primary support under non-uniform case of soft-weaksurrounding rocks and effect of residual tectonic stress with bringing forwardconstruction assistant measures.Basing on comprehensive analyses of home and abroad research results onsupport structure design and combined with datas of tunnel construction andmonitoring of Xiangshan tunnel in the region of soft-weak surrounding rocks whichcontain boulders and structural trace which is complicated, this paper analyzes theinfluence of boulders and residual tectonic stress to pressure distribution ofsurrounding rock, and then studys internal force distribution of primary supportunder the influence of boulders and residual tectonic stress by respectively adoptingstratum structure method and load structure method. Further, mechanical behaviorand possible failure modes of primary support are analyzed and construction assistantmeasures are put forward. We can abtain the follow main conclusions:(1) For the soft-weak surrounding rocks which contain boulders, primary supportendures biggish pressure of surrounding rock, bending moment and shear because ofthe existing of boulders. When the boulder are larger and closer from the primarysupport, the bad effect to the primary support is more obvious. The paper deeplystudys the rules of primary support under the influence of boulder size and boulderdistance from primary support when boulders locate at the top of arch crown andlateral of hance.(2) Construction assistant measures under the soft-weak surrounding rocks whichcontain boulders are studyed in the paper. Researches show that the reinforcement effect of primary support can be better by adopting grouting reinforcement aroundthe boulder and exerting radial anchor after the detecting of orientation and size ofboulders by using geological radar.(3) By comprehensive analyses of geological sketching and pressure monitoring ofsurrounding rock of Xiangshan tunnel and use of basic principles of geomechanicalmodel, distribution characteristics of pressure of surrounding rock, deformationcharacteristics of primary support and on-site recognition of residual tectonic stressunder different structural traces in the deep region of Xiangshan tunnel can beconcluded, which is helpful to the design and construction of deep region of thetunnel.(4) Taking test pressure of surrounding rock of different structural traces inXiangshan tunnel as load and adopting load structure method, constructionmechanical behavior and possible failure modes of primary support under differentpressure ratios, folds, faults and bias pressure are analyzed, and then studyconstruction assistant measures of different structural traces. The researches showthat the reinforcement effect of primary support can be better by groutingreinforcement of lacuna region of surrounding rocks and exerting feet-lock bolts inthe part of biggish pressure of surrounding rock.