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Quick estimates of fluid-induced subsurface deformation are helpful to assess the land uplift/subsidence and to reveal precursors of induced seismicity. Here, we adopt the inclusion theory and Green's function to develop a closed-form solution in a half space for the poroelastic response of a reservoir compartmentalized by an intersecting fault that can be offset and either permeable or impermeable. Simulated results reveal that (1) fault permeability mainly impacts the spatial distribution of displacement while its effect on displacement magnitude is small; (2) ground displacement slightly increases with fault dip while slightly decreases with increasing fault offset; in contrast, reservoir geometry shows a stronger effect than fault geometry: the ground displacement is proportional to the vertical and lateral depth ratios, defined as the ratios of reservoir thickness (h) and width (w) to reservoir depth (D), respectively; (3) the maximum vertical displacement is the double of the horizontal one regardless of fault permeability, fault and reservoir geometries, and mechanical parameters. Comparing the solution in a half space with that in a full space shows that neglecting the free surface underestimates the poroelastic displacement in the overburden. The validity of full-space solutions can be assessed with the product of the lateral and vertical depth ratios, i.e., wh / D 2. The full-space solutions become valid when wh / D 2 decreases to an intrinsic threshold. This threshold may range from 0.01 to 0.02 for displacement, and its specific value depends on the field background and demands of projects, but can be estimated based on our solution. It is larger for stress than for displacement, and wh / D 2 ≤ 0.1 is recommended as a general condition for neglecting the free-surface effects on induced stress. The analytical solution represents a useful tool for estimating ground deformation and for gaining insights of reservoir and fault geometries by analyzing surface deformation patterns. • We propose an analytical solution for displacement induced by pore pressure changes in a reservoir displaced by a fault with an arbitrary dip and offset. • Fault permeability mainly affects the spatial distribution of displacement while its effect on displacement magnitude is small. • Ground displacement slightly increases with fault dip and decreases with increasing fault offset, while reservoir geometry shows a stronger effect than fault geometry. • Traction-free surfaces can enhance the induced displacement in the overburden, a condition for neglecting the free-surface effects is proposed. [ABSTRACT FROM AUTHOR]

We numerically model the thermal-hydrological-mechanical (THM) processes within the rock mass surrounding a cavern used for thermal energy storage (TES). We consider a cylindrical rock cavern with a height of 50 m and a radius of 10 m storing thermal energy of 350 °C as a conceptual TES model, and simulate its operation for thirty years. At first, the insulator performance are not considered for the purpose of investigating the possible coupled THM behavior of the surrounding rock mass; then, the effects of an insulator are examined for different insulator thicknesses. The key concerns are hydro-thermal multiphase flow and heat transport in the rock mass around the thermal storage cavern, the effect of evaporation of rock mass, thermal impact on near the ground surface and the mechanical behavior of the surrounding rock mass. It is shown that the rock temperature around the cavern rapidly increases in the early stage and, consequently, evaporation of groundwater occurs, raising the fluid pressure. However, evaporation and multiphase flow does not have a significant effect on the heat transfer and mechanical behavior in spite of the high-temperature (350 °C) heat source. The simulations showed that large-scale heat flow around a cavern is expected to be conduction-dominated for a reasonable value of rock mass permeability. Thermal expansion as a result of the heating of the rock mass from the storage cavern leads to a ground surface uplift on the order of a few centimeters, and to the development of tensile stress above the storage cavern, increasing the potentials for shear and tensile failures after a few years of the operation. Finally, the analysis shows that high tangential stress in proximity of the storage cavern can some shear failure and local damage, although large rock wall failure could likely be controlled with appropriate insulators and reinforcement. [ABSTRACT FROM AUTHOR]

Safety assessment of geological nuclear waste repositories is essential for the permanent disposal of spent nuclear fuels and high-level radioactive waste. The long-term integrity of the host rock as well as the engineered barrier system (e.g., bentonite buffer) surrounding nuclear waste canisters is of particular importance as decay heat from nuclear waste canisters, which will last over thousands of years, significantly disturbs the thermo-hydromechanical (THM) state of the repository. In this study, THM coupled simulations were carried out to investigate the effect of time-dependent deformation (i.e., creep) of shale on the long-term integrity of a generic subsurface nuclear waste repository. The Norton-Bailey creep model, which is also known as the Lemaitre-Menzel-Schreiner model, was employed to simulate the power-law type creep that is observed in shales. The TOUGH-FLAC simulator was employed for the THM coupled modeling of the repository. The objective of this study is to assess the effect of creep in different shales (i.e., high creep shale vs. low creep shale) on long-term stress and permeability changes in the repository. Results show potential advantages of constructing repositories in the high creep shale, as deviatoric stress levels in the formation decreased to zero in 100 years since the emplacement of nuclear waste canisters and the permeability also decreased to the undamaged, intrinsic levels in 10,000 years. Also, mean effective stress levels in the bentonite buffer increased by 100% in the high creep shale case relative to the low creep shale case at 10,000 years due to creep-induced contraction of the nuclear waste disposal tunnel. However, in earlier periods (e.g., 1000 years), the stress levels in the bentonite buffer were twice smaller in the high creep shale case than in the low creep shale case, which shows a tradeoff between the intermediate- (∼1000 years) and long-term (>10,000 years) compaction levels in the bentonite buffer depending on the creep characteristics of the host shale. • High shale creep improved formation integrity in the near field. • High shale creep also increased buffer compaction in the long term (>1000 years). • In the shorter term, however, buffer compaction was greater with lower shale creep. [ABSTRACT FROM AUTHOR]

We performed a series of 3D thermo-hydro-mechanical (THM) simulations to study the influences of hydromechanical and thermal processes on the development of an enhanced geothermal system, strongly influenced by a network of short fault zones. The model we developed was calibrated by comparing the simulated THM responses to field observations, including ground-surface deformations, well pressure, and microseismic activity. Of particular importance was the comparison between the observed temporal and spatial distribution of microseismic activity, and the calculated shear reactivation of preexisting fractures inferred from simulated elasto-plastic mechanical responses in the short fault zones. Using this approach, we could identify when fault zones were reactivated (as manifested in the field by a surge of local microseismic activity within the fault zone), and we could back-calculate the in situ stress field as being close to the stress conditions required for shear reactivation. Our results show that the main mechanisms of inducing seismicity are related to injection-induced pressure increase and cooling. During injection, the reservoir expansion caused by the pressure increase led to mechanical stress transfer through the reservoir, which prevented or delayed the reactivation of preexisting fractures. After injection stopped, there was an inversion of the mechanical stress transfers that favored shear reactivation, which may explain why microseismic activity occurred after the cessation of the injection. [ABSTRACT FROM AUTHOR]

Abstract: Coupled nonisothermal, multiphase fluid flow and geomechanical numerical modeling is conducted with TOUGH-FLAC, a simulator based on the multiphase flow and heat transport simulator TOUGH2 and the geomechanical simulator FLAC3D, to study the complex thermodynamic and geomechanical performance of underground compressed air energy storage (CAES) in concrete-lined rock caverns. The analysis focuses on CAES in lined caverns at relatively shallow depth (e.g., 100m depth) in which a typical operational pressure of 5 to 8MPa is significantly higher than both ambient fluid pressure and in situ stress. Two different lining options are analyzed, both with a 50cm thick low permeability concrete lining, but in one case with an internal synthetic seal such as steel or rubber. Thermodynamic analysis showed that 96.7% of the energy injected during compression could be recovered during subsequent decompression, while 3.3% of the energy was lost by heat conduction to the surrounding media. Geomechanical analysis showed that tensile effective stresses as high as 8MPa could develop in the lining as a result of the air pressure exerted on the inner surface of the lining, whereas thermal stresses were relatively smaller and compressive. With the option of an internal synthetic seal, the maximum effective tensile stress was reduced from 8 to 5MPa, but was still in substantial tension. One simulation in which the tensile tangential stresses resulted in radial cracks and air leakage though the lining was performed. This air leakage, however, was minor (about 0.16% of the air mass loss from one daily compression) in terms of operational efficiency, and did not significantly impact the overall energy balance of the system. [Copyright &y& Elsevier]

Abstract: Modeling the mechanical deformations of porous and fractured rocks requires a stress–strain relationship. Experience with inherently heterogeneous earth materials suggests that different varieties of Hooke''s law should be applied within regions of the rock having significantly different stress–strain behavior. We apply this idea by dividing a rock body conceptually into two distinct parts. The natural strain (volume change divided by rock volume at the current stress state), rather than the engineering strain (volume change divided by the unstressed rock volume), should be used in Hooke''s law for accurate modeling of the elastic deformation of that part of the pore volume subject to a relatively large degree of relative deformation (i.e., cracks or fractures). This approach permits the derivation of constitutive relations between stress and a variety of mechanical and/or hydraulic rock properties. We show that the theoretical predictions of this method are generally consistent with empirical expressions (from field data) and also laboratory rock experimental data. [Copyright &y& Elsevier]

Abstract: A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes. [Copyright &y& Elsevier]

A coupled multiphase fluid flow and discrete fracturing model is applied to simulate bench-scale gas migration experiments on compacted bentonite. The numerical modeling is based on the linking of the multiphase fluid flow simulator TOUGH2 with a Rigid-Body-Spring Network model, which enables a discrete (lattice) representation of elasticity and individual fractures. The evolution of a complex network of dilatant flow paths is modeled through opening and breakage of lattice interface bonds between porous-elastic matrix elements. To achieve a good match with the experimental results, including an abrupt gas breakthrough along with pressure and stress responses, it was necessary to calibrate model parameters for (1) air-entry pressure, (2) shear and tensile failure of lattice interface bonds, (3) moisture swelling/shrinkage effects on stress, and (4) aperture-dependent permeability of dilatant flow paths. Our best-fit conceptual model considers a pervasive network of discrete flow paths propagating from the gas injection point, whereas some of the experimental data indicate the potential for heterogeneous and unstable flow paths. [ABSTRACT FROM AUTHOR]

We present coupled Thermo–Hydro–Mechanical (THM) modeling of geologic nuclear waste disposal in argillaceous claystone, focusing on thermally-induced pressure changes and the potential for such pressure changes to induce hydro-fracturing. To investigate this possibility, we first conduct a three-dimensional repository scale model, with host rock properties, repository design, and nuclear waste decay heat functions derived from the French concept of geologic disposal in argillaceous claystone. The model simulations show that the highest potential for hydro-fracturing occurs between emplacement micro-tunnels (cells) at the center rather than at the edge of the repository. We further investigate the use of a two-dimensional single cell model as a simpler surrogate for a full three-dimensional model. Our results reveal that such geometric simplification is reasonably accurate for modeling coupled THM processes at the center of the repository, though it overestimates the likelihood for hydro-fracturing and substantially overpredicts ground surface uplift. A parameter study shows the importance of adjacent higher permeability geological layers that play a significant role in dissipating overpressure in the host rock layer. Finally, the study shows the importance of the spacing between emplacement tunnels, which if too short results in a higher fluid pressure and a strongly increased potential for hydro-fracturing. Overall, the study suggests, the limiting factor in the thermal management and design of a repository is not necessarily the maximum temperature in the engineered barrier system near the waste packages, but rather the more modest host rock temperature between emplacement tunnels, due to the potential for thermal damage. [ABSTRACT FROM AUTHOR]

We present results from an international model comparison study involving a series of controlled fault activation experiments in Opalinus Clay at the Mont Terri Laboratory, Switzerland. The fault activation experiments were conducted in situ by water injection at variable pressure from boreholes targeting different parts of the Main Fault crossing several tunnels and galleries of the Mont Terri Laboratory. The model simulations focused on (1) an experiment activating a discontinuity (fracture or minor fault) within the damage zone of the main fault, and (2) an experiment activating discontinuities close to the core of the Main Fault. The experimental data consist of coupled hydraulic and mechanical responses monitored at an injection borehole and a monitoring borehole located a few meters away. After overcoming several modeling issues along with necessary model developments, a reasonably good agreement was achieved between the modeling results and the field observations. The fault activation experiments displayed an abrupt flow rate increase associated with a sudden fracture opening and rupture propagation after the injection pressure reached above the estimated normal stress on the fracture. This was followed by an abrupt flow rate decrease, indicating hydraulic closing, once the injection pressure decreases to an estimated 1–2 MPa below the stress normal to the opened fracture. The models were able to capture this abrupt hydromechanical behavior, including an observed dominant opening behavior along with the rupture propagation, while the spatial extent of the shear rupture and the quantity of peak injection flow were the most challenging to predict. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the hydro-mechanical behaviour of a fractured rock domain at 1000 m depth below the land surface as a function of different levels of fluid pore pressure. A 2D fractured rock domain is adopted based on data obtained from outcrop mapping, displaying multiple fracture sets, fracture intersections, dead-end and curved fractures. A continuum based numerical model is used to evaluate the effects of compressive boundary stresses, cracking by tension failure in the intact rock and fractures and shear displacement along fractures on its equivalent permeability. Two in situ stress boundary conditions are considered: an isotropic case SR1 with the two horizontal boundary compressive stresses having the same magnitude, and an anisotropic case SR2 with the ratio between these compressive stress components set to be 2. In the SR2 case, changes in the local stress and stress ratio distributions due to different fluid pore pressure levels are anisotropic and more significant than in the SR1 case, because of tension failures in the intact rock forming bridges between fractures. These failure regions opened new flow connections between fractures and thereby caused important anisotropic changes in the flow paths, and significant decrease in local gradients of fluid pore pressure. The equivalent permeability increases sharply when the fluid pore pressure is approximately 90% of the magnitude of the minimum stress at the boundaries of the fractured rock domain. Results show that the equivalent permeability of the fractured rock domain is most sensitive to the fractures normal stiffness, the permeability of the tension failure regions and the power-law exponent for permeability change. [ABSTRACT FROM AUTHOR]

This paper presents a coupled thermal-hydraulic-mechanical (THM) model for simulating failure processes in geological media. The coupling between stress/strain and heat transfer describing how thermal expansion affects stress is based on the theory of thermo-elasticity. Additionally, the coupling between stress/strain and fluid flow describing how pore-pressure affects stress is governed by Biot's consolidation theory. Stress/strain-dependent porosity/permeability/capillary-pressure defines the influence of stress on fluid flow and thermal fields. The THM model is implemented in the solver module that links the multiphase, multicomponent fluid flow simulator TOUGH2 with the geomechanical simulator RFPA (Rock Failure Process Analysis), which is based on the concept that heterogeneity leads to non-linearity and progressive failure behavior. Capability of TOUGH-RFPA simulator was verified by two benchmark problems related to hydraulic-mechanical and thermal-mechanical response in a hollow cylinder. Then the applicability of TOUGH-RFPA was demonstrated for modeling cooling-induced damage around a very deep geothermal well with mesoscopic heterogeneous properties, which showed complex damage evolution and fracturing during well cooling and fluid pressurization. [ABSTRACT FROM AUTHOR]

It is critical to rigorously determine the mechanical properties of granitic rocks to effectively analyze and manage subsurface engineering activities, such as geothermal energy exploitation and nuclear waste disposal. However, the required deep drilling and sampling for macroscale rock mechanics experiments (macro-RME) are challenging and expensive. In this study, we developed a novel accurate grain-based modeling (AGBM) using the results of microscale rock mechanics experiments (micro-RME) to determine the elastic properties of arbitrarily shaped granite. The microstructure of each sample and Young's modulus of rock-forming minerals were measured with a TESCAN Integrated Mineral Analyzer (TIMA) and nanoindentation test. The geometry and Young's modulus of interphases between different minerals were determined using an advanced algorithm with atomic force microscopy (AFM) test. With the microstructure and microscale mechanical properties obtained from the micro-RME, the AGBM was applied to derive the macroscale mechanical properties of the granite samples. This new methodology was demonstrated on small test specimens extracted from granite fragments. Because we can use test specimens from arbitrarily shaped and small rock fragments, this new methodology has been proven to be a breakthrough from the conventional technology of macro-RME. • Minerals and interphase in granites were measured by microscale mechanics experiments. • Accurate Grain-Based Modeling was developed to determine the macroscale property. • Specimens can be arbitrarily-shaped, avoiding the difficulty of drilling intact rock. [ABSTRACT FROM AUTHOR]

This paper presents a complete three-dimensional stress determination using hydraulic fracturing data from three inclined boreholes, drilled from the floor of an underground cavern at a depth of about 100 m. Both conventional hydraulic fracturing (HF) and hydraulic testing of pre-existing fractures (HTPF) were carried out at all test points to acquire reliable data and conduct the integrated stress analysis. We determined 3-D stress states using a numerical inversion code that integrates the entire data set from HF and HTPF methods, and employs a nonlinear least-squares optimization routine based on a modified Levenberg–Marquardt method and a finite-difference Jacobian algorithm. We present the trend of complete three-dimensional stress states, with depth expressed by correlation equations. We compare the 3-D stress inversion result for the integration of all data from the three boreholes with the results determined independently for each individual borehole. The results showed that the maximum principal stress was subhorizontal and oriented approximately NNE–SSW, and the ratio of maximum to minimum principal stress was 2.0 on average. The inverted scatter of misfit remained within 10% for both the integrated analysis of the entire data set and the measurement data for each individual borehole. From these findings, we conclude that the 3-D stress determination made by integration of HF and HTPF data from multiple inclined boreholes resulted in a reliable inversion of the 3-D stress field. [ABSTRACT FROM AUTHOR]

In cold mountainous regions, the freeze-thaw cycling often leads to rock weathering, which might trigger spalling, significant landslides and rockfalls. In this work, we used combined experimental, theoretical and numerical approaches to investigate the mechanisms of frost cracking as a result of coupled effects of freeze-thaw cycling, confining stress and the interaction of multiple cracks. The experimental facility with a temperature cycling chamber and a high-pressure cell has been developed. We used rock-like materials (rock analogue samples made from cured cement and quartz-sand mixtures) to conduct the experiments. The rock-like samples contain pre-existing single or double initial cracks, which are then water filled and exposed to freeze-thaw cycling. The coupled thermal-hydro-mechanical modeling for analyzing fractures induced by freeze-thaw cycling was achieved by using a code that was previously developed named TOUGH-AiFrac. Good agreements between the TOUGH-AiFrac modeling and the laboratory experiments have been achieved including the exact paths of crack propagation. The experimental and numerical results show that the frost cracks tend to propagate in the direction of maximum principal stress. The results further show that the interaction effect between two frost cracks is significantly influenced by the position, orientation and offset of initial cracks, as well as the orientation of intact rock bridges between the cracks. At last, the stress shadow that was calculated by the TOUGH-AiFrac model between two cracks was discussed. [ABSTRACT FROM AUTHOR]

This study reveals the important role of hydromechanical responses of large hydraulic fractures in the cause and mechanisms of induced seismicity associated with the M w 5.5 earthquake at the Pohang geothermal site, South Korea. Fractures intersecting two stimulation wells, PX-1 and PX-2, were identified through a comprehensive analysis of various data produced from drilling and hydraulic stimulations, including injection flow-pressure and seismicity data. Coupled hydromechanical numerical modeling of five stimulations performed in the PX-1 and PX-2 wells, showed that injection-induced hydraulic jacking and fracture shearing induce immediate stress transfer that plays a significant role in understanding seismic response at the M w 5.5 fault. The friction coefficient times fluid pressure change by the PX-2 stimulations accounts for only 20% of the total CFS change at the location of the M w 5.5 earthquake. The absence of seismic events at the M w 5.5 fault by the PX-1 stimulations is attributed to the transfer of reduced shear stress at the PX-1 fracture due to shear slip. Kaiser effects in the seismic response observed during the PX-1 stimulation is explained by the irreversible nature of shear slip of the PX-1 fracture for the first time. In addition, post-injection seismicity, observed during the PX-2 stimulations, is attributed to a low permeability of the PX-2 fracture. The current modeling study suggests that coupled hydromechanical analysis with appropriate consideration of fractures is a powerful approach in understanding the mechanism of injection-induced seismicity in fractured geological media. [ABSTRACT FROM AUTHOR]

Abstract: We present in situ measurements of fluid pressure, deformation and seismicity in natural fractures together with coupled hydromechanical simulations. We conducted a step-rate water injection (~3.5MPa and 1200 s) to induce the local pressurization of a critically stressed fractured carbonate reservoir layer located at 250m-depth in the Low Noise Underground Laboratory (LSBB), southern France. An observed factor-of-3 increase in the fracture permeability was associated with the injection-induced fluid pressure increase and about 100 triggered seismic events. Both normal opening (a few microns) of the fluid-injected fracture and the associated tilt (<1 micro-radian) of the fracture near field displayed inelastic behavior highlighting an irreversible fracture shear and dilatant failure, amounting to about 1/3–1/2 of the maximum measured deformations. Using a plane-strain finite-difference coupled hydromechanical model, our calculation shows that tensile failure first occurred in the injection zone and then shear failure spread along fractures into the surrounding unsaturated rock through stress transfer from the injection zone. The most striking result of these model simulations is that the mechanical weakening of the fractures in the near field induced a 2–5×105 Pa release of the normal stress across the fluid-injected fracture that provoked fracture slip and increase in permeability. A geological exploration of the fracture zone after the experiment showed that no major failure had occurred, and we therefore relate these strength and permeability variations to the slight reactivation (~microns) of pre-existing fractures. [Copyright &y& Elsevier]

Fault reactivation due to water injection is assessed within the scope of nuclear waste disposal design. A model using the distinct element method is applied to reproduce the fault reactivation during an experiment carried out at the Mont Terri Underground Research Laboratory in Switzerland. A conceptual model is first presented to understand the hydro-mechanical coupling behavior between water pressure and rock joint movement. The model simulations show that the dominant factors on fault slip are shear stress and frictional resistance. Moreover, modeling shows that fault reversible opening in the normal direction occurs first at a lower pressure, whereas shear displacement as a result of shear slip is produced once a sufficiently high pressure is reached. We demonstrate that a coupled numerical analysis of the rock displacement trend and fluid pressure measured at the injection point allow an in-situ estimation of the principal stresses. • Fault reactivation due to injection of water pressure. • Fully hydro-mechanical coupling using the Distinct Element Method. • In-situ stress estimation based on the rock displacement trend during the fluid injection test. • Flow connection between two elements via crack propagation. [ABSTRACT FROM AUTHOR]

The present study is aimed at developing a numerical model to reproduce coupled hydro-mechanical processes associated with fault reactivation by fluid injection in low permeability rock, as part of the DECOVALEX-2019 project Task B. We proposed a modeling approach for simulating the processes using the TOUGH-FLAC simulator, and modeled a fault reactivation experiment conducted at Mont Terri Rock Laboratory in Switzerland. The first step of the study involved benchmark calculations considering a simplified fault plane and geometry. Fluid flow along a fault was modeled using elements of aperture-sized thickness on the basis of Darcy's law and the cubic law in TOUGH2, whereas the mechanical behavior of a single fault was represented by zero-thickness interface elements in FLAC3D upon which a slip and/or separation is allowed. A methodology to connect a TOUGH2 volume element to a FLAC3D interface element was developed for handling the hydro-mechanical interactions on the fault during fluid injection. Two different fault models for describing the evolutions of hydraulic aperture by elastic fracture opening and failure-induced aperture increase were considered in the benchmark calculations. In the coupling process, the changes in geometrical features and hydrological properties induced by mechanical deformation were continuously updated. The transient responses of the fault and host rock to stepwise pressurization were examined during the simulation. The hydro-mechanical behavior, including the injection flow rate, pressure distribution around the borehole, stress conditions, and displacements in normal and shear directions were monitored in the surrounding rock and along the fault. The results of benchmark calculations suggest that the developed model reasonably represents the hydro-mechanical behavior of a fault and the surrounding rock. This modeling approach was applied to the fault reactivation experiment of the Mont Terri Rock Laboratory. In this interpretive modeling, a parametric study was conducted to examine the effects of input parameters regarding in situ stress and fault properties on the hydro-mechanical responses of the fault to water injection. Then, an optimal parameter set to reproduce the field experiment results was chosen by trial-and-error. The injection flow rate and pressure response during fault reactivation closely matched those obtained at the site, which indicates the capability of the model to appropriately capture the progressive pathway evolution during fault reactivation tests at the site. The anchor displacements were overestimated by the model, but a fair agreement was obtained in terms of the order of magnitude and the variation tendency. • We propose a modeling approach for fault activation using TOUGH-FLAC simulator. • Dual simulation of fault elements overcomes inherent problems from each method. • The model reasonably reproduces fault failure process and pathway evolution. [ABSTRACT FROM AUTHOR]