A Coupled Thermal–Hydrological–Mechanical Damage Model and Its Numerical Simulations of Damage Evolution in APSE
This paper proposes a coupled thermal–hydrological–mechanical damage (THMD) model for the failure process of rock, in which coupling effects such as thermally induced rock deformation, water flow-induced thermal convection, and rock deformation-induced water flow are considered. The damage is considered to be the key factor that controls the THM coupling process and the heterogeneity of rock is characterized by the Weibull distribution. Next, numerical simulations on excavation-induced damage zones in Äspö pillar stability experiments (APSE) are carried out and the impact of in situ stress conditions on damage zone distribution is analysed. Then, further numerical simulations of damage evolution at the heating stage in APSE are carried out. The impacts of in situ stress state, swelling pressure and water pressure on damage evolution at the heating stage are simulated and analysed, respectively. The simulation results indicate that (1) the v-shaped notch at the sidewall of the pillar is predominantly controlled by the in situ stress trends and magnitude; (2) at the heating stage, the existence of confining pressure can suppress the occurrence of damage, including shear damage and tensile damage; and (3) the presence of water flow and water pressure can promote the occurrence of damage, especially shear damage.
Numerical Studies on the Failure Process of Heterogeneous Rock Material with Preexisting Fracture under Uniaxial Compression
It is of vital importance to understand the failure processes of the heterogeneous rock material with different kinds of preexisting fractures in underground engineering. A damage model was introduced to describe the initiation and propagation behaviors of the fractures in rock. Reduced parameters were applied in this work because the microcracks in the rock were neglected. Then, the numerical model was validated through comparing the simulation results with the laboratory observations. Finally, a number of numerical uniaxial compressive tests were performed on heterogeneous rock specimens with preexisting fracture, and the influence of the heterogeneity of the rock and the angle and length of the preexisting fractures was fully discussed. The results showed that the brittleness of the rock increased with the increase of the homogeneity index, and tensile failure was the main failure form for relatively heterogeneous rock, whilst shear failure was the main failure form for relatively homogeneous rock. The uniaxial compressive strengths of the specimens with the angles of 0, 30, 45, and 60 of the preexisting fracture dropped 62.7%, 54.7%, 46.6%, and 38.2% compared with that of the intact specimen; the tensile cracks were more difficult to form, and the required load was increasing with the increase of the angle of the preexisting fracture; besides, antiwing cracks were difficult to form than wing cracks because the tensile stress in wing cracks’ area was greater than that in antiwing cracks’ area. The uniaxial compressive strengths of the specimens with the lengths of 20 mm, 25 mm, 30 mm, and 35 mm of preexisting fracture dropped 38.6%, 46.6%, 53.4%, and 56.6% compared with that of the intact specimen, and the damage conditions of the samples with different lengths of preexisting fracture were similar.
Double structure THM analyses of a heating test in a fractured tuff incorporating intrinsic permeability variations
This paper presents thermo-hydro-mechanical (THM) analyses simulating the Drift Scale Test (DST) performed at Yucca Mountain. A double structure approach based on two superimposed domains is adopted. Intrinsic permeability changes with deformations imply full THM coupling. Temperatures and gas permeabilities were measured during 4 years and are used to validate the model. Measured gas permeability variations show patterns that are successfully explained by the model calculations. These gas permeability variations may be attributed to thermo-hydraulic effects, and also to mechanical effects. Different cases of intrinsic permeability variations have been considered in the model and their influence on the calculated temperatures, degree of saturations and gas permeabilities are presented. Volumetric deformation, in contraction or dilatancy, implies changes in the aperture of rock fractures that in turn lead to changes in intrinsic permeability. Dilatancy, caused by shear stresses, increases intrinsic permeability. Consideration of this factor contributes significantly to improve the agreement of calculated gas permeability with the measured values obtained during the DST experiment.