Mechanical Effect And Surrounding Rockmass Control Of High Stress And Soft-surrounding Rock Tunnel In Process Of Contruction

Due to the high stress area of soft rock mechanics influence was more rapid and intense,study of soft rock engineering from the construction process began to concern the mechanicaleffect, influence and rock damage regular, to guide the engineering design and constructionscheme optimization. After the excavation of tunnel, the redistribution of surrounding rockstress, soft rock was inevitably destroyed under the effect of secondary stress, so in most casessurrounding rock in the state of after peak. Previous studies focus on the surrounding rockpeak strength, selection of proper support scheme to keep the rock and anchorage system inthe pre peak and is not destroyed, and the majority of rock strength criterion for elastic andplastic model, but especially the soft rock post-peak have evident strain softening, modulus ofelasticity is negative. Therefore, combined with the specific project practice to carry out largedeformation mechanism and disaster prediction research, as well as the basis for further studyof large deformation control measures and comprehensive management of technology, tosolve the actual problems of the project, to promote the study of large deformation progress,have very important significance.According to Muzhailing tunnel of Lanyu railway, use methods of Laboratory rockmechanics experiment, theoretical analysis, numerical simulation and field tests, studied softpost-peak mechanical propertiesunder different confining pressure,as well as anchor on thesurrounding rock reinforcement; Analysis of soft surrounding rock deformation failureregularity and surrounding rock stress fracture field evolution mechanism under theconditions of different supporting technology. Using the elastic-plastic mechanics theory, withMohr-Coulumn strength criterion and strain softening model for distinguishing method, inhigh stress soft rock plastic zone analysis, is proposed to distinguish the degree and range ofthe plastic zone destruction of theoretical formula, and the Muzhailing tunnel the supportingdesign. The main conclusions are as follows:(1) Weak rock’s physical mechanics parameters of the Muzhailing tunnel were tested indetail, and has carried on the classification, sandstone rock belongs to surrounding rock of Ⅴgrade and sandy mudstone belongs to surrounding rock of Ⅳgrade. (2) When the strength of the rock mass is given, the E, C andφof before peak and afterpeak both improved to some extent along with the pretightening force of anchoring rock massincrease. Anchoring rock mass to the loading direction deformation mainly before peak, afterpeak performance for the free surface of lateral deformation and main rupture surface, andthen to the face dilatancy deformation mainly.(3) The stress-strain full curve of the sample after anchoring and the anchorage force ofbolt there exists a corresponding relation, yield before anchoring body, bolt stress increasesslowly; the yield point, the stress increased dramatically; post-peak softening stage anchorforce increased gradually, flow stage bolt force in the constant adjustment of fall. The samepretightening force, the higher the strength of rock, stress ring stress increased amplitudesmaller; the same rock conditions, high pretightening force of bolt stress amplitude is smaller;weak strata, preload loss than the hard rock, preload bolt in soft rock role than hard rock isobvious.(4) Discussed the change characteristics of stress-strain curve after the rock materialpeak, according to the test, mechanical response characteristics (stress-strain curve), usingthe software of FLAC strain softening model function, the elastoplastic model and strainsoftening model of rock mechanics characteristic characterization are compared. Strainsoftening model for the calculation of the construction site and supporting in rock in theprocess of the mechanical response is more real.(5) Analysis of anchoring effect and anchor pretightening force to the specimen on themechanical properties of. Anchor bolt strength increase3~4times than no anchor. Usingelastic-plastic model to calculate sample,not only maximum intensity increased, residualstrength was increased correspondingly, in fact the anchoring effect has only increased theoverall strength of samples before failure, when the specimen is destroyed, the anchoringfunction failure, the specimen will resume the original mechanical properties.(6) Anchor add intensity is increased than no pretightening force, but the increase is notobvious. The result of numerical calculations pretightening force is using stress loading, theloading calculation process of pretightening force exists all the time, so in the sample matrixunit is destroyed, the pretightening force is still work, so that after the destruction of the specimen still has a certain bearing capacity and deformation. The results show that, in the useof anchor rod mainly active supporting way to maintain the tunnel, anchor applied to certainpretightening force is necessary, but in high stress soft rock conditions, tunnel deformation isoften unavoidable, but in the roadway deformation after certain level, want to continue toexert a certain pretightening force of bolt, this can effectively to already have the deformationdamage of surrounding rock deformation constraint, to prevent continued to expand, but alsoincrease the strength of rock-bolt system, assume greater stress.(7) On the basis of Mohr-Coulmn strain softening model of soft rock tunnel surroundingrock stress field and plastic zone of theoretical analysis, put forward each partition rangedetermination methods of the soft rock tunnel surrounding rock under high stress, and on thisbasis put forward the control method of deformation of the surrounding rock.