| The dissertation is focus on the urgent key mechanical problems in tunnelconstruction through fault zone: the in-situ stress field of the complex fractured zone,dilatancy and anisotropic non-linear property of jointed rock in fault zone, thedeformation localization in the fault zone during the tunnel excavation, the supportmethod and time of the tunnel. Numerical simulation, theory analysis and in-situmeasurement were carried out, by using displacement discontinuity method(DDM)and finite element method(FEM) as calculation methods, and combing rockmechanics, fracture mechanics, mathematical optimization algorithm, these problemswere studied: the distribution feature of in-situ stress field near fault zone, theregression analysis method of in-situ stress field in fault zone, deformation anddilatancy mechanism of jointed rock in fault zone, the evaluation method of rockmechanical parameters in fault zone, the support theory and method consdering thesupport strength and deformation. The gist and primary new findings of thisdissertation includes:1) An iterative algorithm was proposed to solve non-linear structural plane inDDM, and then the linear and non-linear joint model can be considered in DDM tosimulate actual fractured rock mass, no longer be limited to the simplification offriction-slide, which broadened the application of DDM in the non-linear limitedstructural plane deformation proplem.2) The disturbance effect of non-linear fault on the surrounding in-situ stress fieldwas quantitativly investigated. The effect of fault size, occurrence and mechanicalproperty were analyzed:①the disturbance decreases as the normal and shear stiffnessof fault increase;②the disturbance increases as the ratio of fault thickness and lengthincreases;③the disturbance decreases as the cohesion c and internal friction angle φincrease;④As the angle between the fault and the load increases, the disturbanceinfluence scope of fault on the in-situ stress field firstyly increases and the decreases,which reach the peak at45°;⑤Calculation with the linear Mohr-Coulmb joint modeland the non-linear BB model are carried out respectively by DDM, it shows that therock stress, displacement and the disturbance scope of stress field is larger with thenon-linear BB model, but the fault sress and deformation is larger with linearMohr-Coulmb model, the difference is needed to be considered in engineeringpractice;3) The multivariable regression method and DDM were combied to obtain thein-situ stress field based on the limited measured value. The in-situ stress field wasassumed to be the sum of gravity stress field and tectonic stress field, and regressionanalysis was conducted for these stress fields. The DDM regression program was incorporated in the Nelder-Mead optimization algorithm, the optimal rock parameterswas obtained during the in-situ stress field regression, and this method was applied inan underground chamber engineering, compared with the results by FEM regressionresults, the DDM regression result is closer to the measured value.4) For the engineering without measured in-situ stress, a DDM regression methodbased on the occurrence of fault was proposed. This method assumes that theoccurrence of fault is caused by the gravity and geological tectonism, and was appliedin two tunnel engineering sites, whcich provided advice for design and construction.5) One dimensional columnar elasto-visco-plastic model of jointed rock wasestablished, and by combining the three-dimensional spherical coordinates, it wasapplied in the quantitative simulation of anisotropic non-linear deformation of jointedrock in fault zone. By the three-dimensional distribution of mechanical parameters,the evaluation method of the anisotropy state of the jointed rock was proposed basedon the mean value of the mechanical properties and its variance of probabilitydistribution. The critical value and the method for the determination of mechanicalparameters was proposed.6) The crack dilatancy of jointed rock was quantitativly investigated, it revealedthe mechanism of the crack dilatancy of jointed rock. The volume change of jointedrock is separeted into two parts: the intact rock and the joint. The crack dilatancy isdivided into two steps:‘the joint propagates under load: the old joint close and thenewly propagated joint open; unloading: the newly propagated joint close and the oldjoint open back’, the total joint volume change is the sum of the old and new jointvolume change. When the ratio of joint normal stiffness and the rock elastic modulusis larger than a value, the jointed rock volume increases, which means dilantancy, andthe critical ratio is named ‘ciritcal stiffness ratio’. The critical stiffness ratio is lowestwhen the load-joint angle is30°, which means the dilantancy is most likey to occure atthis time;7) The tunnel deformation localization characters in fault zone were revealed: therelation between the surrounding rock deformation and the rock elastic modulus ratioof the fault zone and the other zone(Ej/Er) is negative exponent, the deformationlocalization is more obvious when Ej/Eris lower; the axial horizontal pressure barelyaffects the tunnel displacement, and the horizontal pressure perpendicular to the tunnelsignificantly affects the tunnel displacement.8) The relation between the support structure stress and tunnel nomaldisplacement was obtained, the tunnel supporting theory and method based onoptimization of supporting structure strength and deformation was proposed, andmethod determining the time for the second support was proposed. |
