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To investigate crack initiation and propagation of rock mass under coupled thermo-mechanical (TM) condition, a two-dimensional coupled TM model based on the numerical manifold method (NMM) is proposed, considering the effect of thermal damage on the rock physical properties and stress on the heat conductivity. Then, the NMM, using empirical strength criteria as the crack propagation critical criterion and physical cover as the minimum failure element, was extended for cracking process simulation. Furthermore, a high-order cover function was used to improve the calculation accuracy of stress. Therefore, the proposed method consists of three parts and has a high accuracy for simulating the cracking process in the rock mass under the coupled TM condition. The ability of the proposed model for high accuracy stress, crack propagation, and thermally-induced cracking simulation was verified by three examples. Finally, the proposed method was applied to simulate the stability of a hypothetical nuclear waste repository. Based on the outcome of this study, the application of NMM can be extended to study rock failure induced by multi-field coupling effect in geo-materials. [ABSTRACT FROM AUTHOR]

One significant factor influencing geothermal energy exploitation is the variation of the mechanical properties of rock in high temperature environments. Since rock is typically a heterogeneous granular material, thermal fracturing frequently occurs in the rock when the ambient temperature changes, which can greatly influence the geothermal energy exploitation. A numerical method based on the numerical manifold method (NMM) is developed in this study to simulate the thermo-elastic fracturing of rocklike granular materials. The Voronoi tessellation is incorporated into the pre-processor of NMM to represent the grain structure. A contact-based heat transfer model is developed to reflect heat interaction among grains. Based on the model, the transient thermal conduction algorithm for granular materials is established. To simulate the cohesion effects among grains and the fracturing process between grains, a damage-based contact fracture model is developed to improve the contact algorithm of NMM. In the developed numerical method, the heat interaction among grains as well as the heat transfer inside each solid grain are both simulated. Additionally, as damage evolution and fracturing at grain interfaces are also considered, the developed numerical method is applicable to simulate the geothermal-related thermal fracturing process. [ABSTRACT FROM AUTHOR]

A micro-mechanical based numerical manifold method (NMM) is proposed in this study to investigate the micro-mechanisms underlying rock macroscopic response and fracture processes. The Voronoi tessellation technique is adopted to create randomly-sized polygonal rock micro-grains. A rock micro-grain based broken criterion is proposed and a corresponding grain breaking technique is developed. To better represent the contact behavior of rock grain bonds, a cohesive fracture model that considers tensile, shear and compressive behaviors together, is adopted to interpret the failure of rock grain bonds. The developed program is first validated by reproducing biaxial tests of Transjurane sandstone. Finally, the influences of micro-parameters on the rock macroscopic response and failure modes are investigated. The results show that the developed micro-based model can mimic the deformation and failure characteristics of the test closely. A parameter study shows that the grain contact cohesion has significant effects on the model uniaxial compressive strength. The fracture process and failure mode of rock are dependent on the ratio of grain contact shear stiffness to normal stiffness. With the increase of the contact stiffness ratio, the failure mode of rock under uniaxial compression changes from a diffuse pattern to a concentrated shear band. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of tunnel supports for large squeezing deformation hazards, the explicit cohesive element-based numerical manifold method (ECo-NMM) is extended. First, for modeling the compound effect of the artificial supports and tunnel face, a layer-based tunnel support algorithm is proposed to simulate the interaction between the supports, tunnel face and surrounding rock mass and represent the geometric and mechanical properties of the tunnel supports. Then, to investigate the influence of tunnel support timing, a mapping algorithm is proposed to correlate simulated processes with real excavation processes, based on which the installation timing of tunnel supports is characterized. In addition, a reconstruction algorithm is proposed to illustrate 2D simulation results in 3D. To validate the accuracy and applicability of this improved method, numerical cases are conducted using the developed method, and the predicted results are compared with analytical solutions, test observations and original numerical results. Finally, this improved method is applied to investigate the influence of the tunnel support timing, and the predicted results indicate that the squeezing stress acting on the tunnel supports first decreases and then increases with the continuous increase in the delay in the tunnel support, based on which the tunnel support timing is optimized. [ABSTRACT FROM AUTHOR]

Recent attempts to solve rock mechanics problems using the numerical manifold method (NMM) have been regarded as fruitful. In this paper, a coupled hydro-mechanical (HM) model is incorporated into the enriched NMM to simulate fluid driven fracturing in rocks. In this HM model, a “cubic law” is employed to model fluid flow through fractures. Several benchmark problems are investigated to verify the coupled HM model. The simulation results agree well with the analytical and experimental results, indicating that the coupled HM model is able to simulate the hydraulic fracturing process reliably and correctly. [ABSTRACT FROM AUTHOR]

• A novel algorithm for modeling the reinforcement effect after the slurry coagulation was proposed. • A higher computation efficiency for simulating fluid-solid coupling processes under the framework of NMM was achieved. • The effect of the grouting reinforcement in a deeply buried rock tunnel was studied. In this study, a numerical manifold method (NMM) based simulator, which is able to simulate the whole process of grouting reinforcement, including the migration and coagulation process of injected slurries in rock fractures networks, is developed for evaluating the effectiveness of grouting reinforcement in deep rock tunnels. To implement the migration process, the grouting hole generation algorithm, the Bingham fluid model, the migration network searching algorithm as well as the framework for fluid–solid (FS) coupling process are introduced into the zero-thickness cohesive element (ZE) based NMM (Co-NMM). To reflect the reinforcement effect of the slurry coagulation after the migration process, a bonding reinforcement algorithm based on the ZE model is proposed. To improve the computational efficiency, an explicit integration scheme is introduced. To validate and illustrate the capability of the developed method, an uncoupled and a coupled numerical examples are conducted and the simulation results are in good accordance with the analytical solutions or laboratory observations. In addition, a series numerical direct tensile test and uniaxial compressive test are conducted to verify the capability of the proposed bonding reinforcement algorithm. Finally, to demonstrate the capability of the developed simulator in simulating problems with large scale, grouting reinforcement in a deep rock tunnel model is conducted and the predicted results show that the convergence deformation and fragmentation-bulking phenomenon induced by excavation in the deep rock tunnel are effectively controlled through the grouting reinforcement. [ABSTRACT FROM AUTHOR]