| In recent years, with the rapid development of the national economic constructionand deepening of the western development, a large number of deep buried, long andlarge scale tunnel engineering emerged. However, the geological environment in thewestern region is very complex, fragile, making these tunnels engineering under themulti-field coupling action of high geo-stress, high temperature, and high hydraulicpressure. For example, Motuo Hydropower Station Diversion Tunnel, depth of4000m,weight stress of108MPa, ground temperature up to90℃. Under the multi-fieldcoupling process, with the increasing of stress and the action of thermal expansion,micro-cracks in the field rock mass will gradually emergence, growth, coalesce, thenthe bumps in macro crack surface will be crushed, wearing, and mylonitization,resulting in the damage evolution of the rock mass; furthermore, the damage of therock mass will lead to the weakening of the properties of the rock mass, bringingabout significant anisotropic characteristics. This complex and fragile environmentmakes the possibility of the occurrence of sudden occurrence of tunnel engineeringgeological disasters increased, posing a great threat to the safety of the tunnelengineering. Therefore, analyzing rock mass mechanical model, deformation featuresand failure mechanism are the important basement for reducing geo-harzard in deeprock engineering under the action of thermal-mechanical, being of significant totheory and engineering practice.In this dissertation, the characteristics of hard rock deformation behaviors, failure,and mechanical behaviors under thermal-mechanical action was firstly described fromthe perspective of macro and micro, on those basis, macro mechanics and micromechanics of hard rock under thermal-mechanical action were established; then thethermal damage evolution equation and thermal-mechanical-damage constitutivemodel. Finally, the preliminary application effect of the constitutive model wasdiscussed. The main results as follows:(1) According to the results under the action of the thermal-mechanical abouthard rock uniaxial tests, triaxial tests and triaxial unloading tests, the hard rockfracture process in thermal-mechanical action could be mainly divided into six stages: Compaction stage, approximate linear elastic stage, micro-crack evolution stage,crack accelerated expansion stage, stress dropping stage and residual strength stageetc. For fracture characteristics: when the rock was in low temperature and lowconfining pressure（20℃~40℃、0~5MPa）, it was mainly tension-shear failure modebased on shear background; while in low temperature and high confining pressure（20℃~40℃、15~30MPa）,it was tension failure mode; then in high temperature and lowconfining pressure（60℃~130℃、0~5MPa）, it was tension failure mode; finally inhigh temperature and high confining pressure（60℃~130℃、15~30MPa）, it was shearfailure mode.(2) Through mathematical statistics summarizing and sorting of the rock samples’failure feature and corresponding mechanics analysis, it was concluded the hard rockruptured macro mechanics under thermal-mechanical action: one, when the thermalstress caused by temperature increasing was larger than the stress caused by confiningpressure, it was tension failure mode; two, when the stress difference was little, it wasshear and tension mixed failure mode; three, when the stress caused by temperatureincreasing was smaller than the stress caused by confining pressure, it was shearfailure mode.(3) Combined with rock mineral morphology and microscopic damage features,considering that under the same thermal-mechanical action, black mica was the mostprone to damage due to its low hardness, complete cleavage and flaky and otherfeatures, and its failure mode were flaky (crystal inner fracture), tear-shaped(transgranular fracture), layered (intergranular fracture); Feldspar (anorthose,potassium feldspar) was the next, and its failure mode was12%the next wassecondary cleavage stepped (transgranular or intergranular fracture); quartz was thelast, and its failure mode was irregular shape (agate-like or coral-like).(4) Combined with extreme value theorem, geological engineering analysisprinciple theory and Griffith theory, rock crack conditions, failure process andmechanism were analyzed under the thermal-mechanical action, considering that thehard rock (granite) micromechanics under thermal-mechanical action: When the stressvalue was larger than its inner cohesion, the cracks began to break. The breakingevolution process could be summarized into three stage: first, the new cracks werefirstly emergence near the original crack, and black mica inner or near it where weremainly the weak interface with limited resistance, then the rock began to damage;second, with the stress increasing, when the bond between the mineral particlessmaller than the stress caused by external load, the cracks began to extend, spread, and form fracture network, then transgranular or intergranular fracture appeared inquartzgranule and around it, afterwards locking point was broken; Third, all thelocking points were broken, and the shear plane was cut-through, eventuallymacroscopic fracture appeared.(5) On the assumption that rock infinitesimal body strength k obeyed Weibulldistribution conditions and introducing the Drucker-Prager criterion as rockinfinitesimal body failure criteria, hard rock damage evolution equation wasestablished which considered the thermal effect; According to Lemaitre strainequivalence theory and principle of effective stress, hard rockthermal-mechanical-damage constitutive model was established; According to therock stress strain curve geometry, the model parameter expressions were deduced. Onthis basis, combining with the triaxial test results, using the model experimentalcurves of the triaxial compression tests (confining pressure25MPa), were fitted ateach temperature condition. The results showed that: the hard rockthermal-mechanical-damage constitutive model established by the dissertation hadbetter ability to fit the rock stress-strain curve, and the curve fitting effect were good,which effectively reflected the rock curve process characteristics, softeningcharacteristics and residual strength characteristics.(6) Combined with the UDM file in FLAC3D, thermal-mechanical-damageconstitutive model were compiled, and on the basis of the program, numericalsimulation study on the APSE test were carried out. The results showed that: themaximum principal stress concentration on both sides of the disposal of the hole, andthe maximum principal stress value was larger at a depth of approximately2m, andthe value was43.38MPa; the maximum displacement was in the center of the roadway,and the value was1.18mm; The plastic zone was mainly distributed in roadway sidesand the disposal holes surface, and the failure process would occur around thedisposal holes surface. The simulation results were consistent with the experimentalfeatures, which better reflected the disposal hole mechanical response characteristics,pillar surface failure and extension features. Then combining rock burst criterion, thisnumerical simulation results could be preliminary used to predict and inversion rockburst characteristic, which could illustrates the use of constitutive model from acertain extent. But the minimum principal stress simulation results had somediscrepancy with the actual test, failed to reflect the features that the minimumprincipal stress concentration was on pillar top, which might be related to the actualrock mass with cranny, anisotropic and heterogeneous characteristics and the constitutive model parameters, and further improvement and research were needed. |
PDF Full Text Request