International Journal of Rock Mechanics and Mining Sciences最新文献

The disturbance wave caused by excavation or blasting of underground surrounding rock causes fatigue degradation effect of rock and eventually leads to disasters. However, the fatigue damage characteristics and fatigue models of rock under true triaxial disturbance are scare. Therefore, a series of true triaxial disturbance tests were conducted to investigate the rock fatigue deformation, strength and damage behaviors under different conditions. The evolutions of static damage and fatigue damage are separated and investigated respectively. Fatigue deformation and damage of rock under true triaxial stress undergoes three stages: attenuation, constant velocity and acceleration stage. The crack initiation stress can be as the initial condition of the fatigue deformation; the fatigue critical stress σ_dc of rock entering the acceleration failure stage was proposed and explored, with increasing frequency, σ_dc increase slightly and with increasing σ₂, σ_dc increase obviously. Then, a novel fractional fatigue mechanical model considering the fatigue damage and intermediate principal stress effects of rock under true triaxial disturbance was proposed. The theoretical results of the model agree well with the results of the tests. Finally, the sensitivity analysis of stresses and model parameters and the model predictions under other untesting conditions were carried out to improve the understanding and prediction level of fatigue failure in underground engineering.

During deep shale gas production, flowing water-based working fluid inevitably cools shale reservoirs around boreholes and some fractures, and possible extraction methods induce dynamic stresses. To understand the dynamic tensile behavior of deep anisotropic shale reservoir after water-based working fluid cooling, a split Hopkinson pressure bar was used for performing the dynamic Brazilian tests on shale samples with bedding angles of 0°, 30°, 45°, 60° and 90° after reservoir temperature realization (25–200 °C) and water cooling. The results illustrate that dynamic tensile strength of shale samples decreases gradually as reservoir temperature increases under the loading rates 100–1000 GPa/s. From room temperature to 200 °C the most strength deterioration appears on samples with the bedding angle of 90°. A dynamic tensile strength deterioration model for deep shale reservoirs after water-based working fluid cooling is proposed considering the influence of loading rate and bedding angle. Geometrical trajectories of the main failure cracks are separated into three types, i.e., fully central tensile failure, tensile-shear failure and fully shear failure (sliding of bedding planes). For samples with bedding angles of 30°, 45° and 60°, increasing reservoir temperature encourages tensile failure to change into shear failure. The roles that bedding planes play in interacting with failure crack growth are summarized as IP mode (intersecting propagation), TP mode (turning propagation) and PP mode (promoting propagation). Anisotropic dynamic tensile strength responses are systematically discussed by using thermal stress simulation in ABAQUS, microstructure analyses, crack interaction conditions and the one-dimensional stress wave propagation theory. Based on experimental observations, field implications in borehole stability and fracturing of deep shale reservoirs are proposed under medium and high loading rates. This work is instrumental in providing valuable information and technology assistance for real deep shale gas production projects.

A methodology is presented for the back-analysis of convergence measurements in deep tunnels to determine the constitutive parameters of the surrounding rock mass. Since increasing deformations and stresses with time are due to both the face advance and the time-dependent behavior of the ground, the two effects must be considered during the excavations. To that end, an analytical solution assuming an unlined circular tunnel excavated in a homogeneous isotropic ground under an initial isotropic stress field and assuming a fractional viscoelastic plastic behavior is developed. A second closed-form solution is also derived assuming an instantaneous excavation. Additionally, combining the developed analytical solution that takes into account the progressive face advance and an empirical approach, convergences are back-analyzed based on a least-squares optimization method to calibrate the constitutive parameters of the ground. The presented methodology aims to characterize the long-term behavior of tunnels and offers the advantage of being directly applicable during the excavation phase as soon as convergence measurements are available. Finally, the method is illustrated by two case studies related to the Fréjus road tunnel and the Saint-Martin-la-Porte access gallery (SMP2).

The significance of improving the drilling productivity and reducing the cost and non-productive time of drilling process, substantially relies on the efficiency of drilling performance. This paper provides a comprehensive understanding of drilling process, aiming to predict drilling performance and investigate drilling parameters using a validated finite element (FE) model. Experimental validation of the FE model was achieved through testing on a laboratory drilling rig, ensuring the accuracy and reliability of the numerical simulations. To accurately capture the nonlinear characteristics of bit-rock interaction, the Riedel–Hiermaier–Thoma model was adopted as a material model, and its parameters were identified through a series of carefully conducted experimental tests. The numerical results obtained from the FE rock failure model during the compressive and tensile tests demonstrated a robust correlation with the experimental data. The verified material model was then employed into another FE drilling model to simulate rock breaking in an actual drilling scenario. This analysis sheds light on the impact of drill-bit interaction with the rock formation, providing valuable insights into its behaviour during drilling operations. The FE drilling model was further utilised in a parametric study to predict the effects of critical drilling parameters, like loading rate and rotary speed, on the weight on the bit, torque on the bit, and rate of penetration. Both the FE drilling and experimental results provided a significant consistency when the drilling parameters were compared, and nonlinear dynamic phenomena, such as stick–slip and bit-bouncing, were observed. By investigating these effects, this study contributes to optimising drilling operations, enabling better control of premature vibrations and enhancing drilling efficiency.

Analysis of compressive wellbore failure, or breakouts, is one of the primary methods of constraining the maximum horizontal stress in deep boreholes. To estimate stress using the observation of breakouts, one needs to measure the breakout width from image logs and use a failure theory to predict the stress that led to the development of the measured breakout. Most commonly, Mohr–Coulomb failure criterion has been used which disregards the influence of intermediate stress on strength. Hence, various polyaxial criteria have been proposed to include this effect. Here, we first review some selected polyaxial criteria: Drucker–Prager, Mogi, Modified Wiebols–Cook, and Modified Lade, and we conclude that their application in breakout analysis may be cumbersome and often unreliable. One reason for these problems is that the criteria are defined using stress invariants, while the stress estimation is most easily performed and analyzed in the principal stress space. Therefore, an alternative is to define the polyaxial criterion as a simple relation between maximum and intermediate stresses. We propose to define such an empirical criterion as a second order polynomial which fits trends observed in polyaxial laboratory strength data. Such approach allows to limit strength overestimation, often associated with the use of previous polyaxial criteria, and to easily relate uncertainties in strength estimation to uncertainty in maximum horizontal stress prediction.

Engineered fractures play a critical role in enhancing energy extraction efficiency. In this study, energised fracturing with CO₂, as an alternative approach to conventional water-based hydraulic fracturing, is investigated via numerical simulations. We validated the CO₂ finite element-based fracturing model against analytical as well as CO₂-fracturing laboratory experiments, then utilised the model to investigate the effects of pressure-temperature dependent properties of CO₂ on energised fracturing process. To account for the temperatures expected in a real field, four cases with injection temperatures of CO₂ varying between 250 K and 350K, under both isothermal and adiabatic conditions have been considered. In the adiabatic conditions, the temperature variation during compression of CO₂ is captured using the Joule-Thompson coefficient, assuming no thermal exchange between the CO₂ and the surrounding medium. The results highlight the significant influence of CO₂ phase on the fracturing process, during the pressurisation stage, as well as post-breakdown, the speed of fracture growth after the breakdown and subsequent depressurisation and associated cooling of CO₂. In the designed cases, the phase-change from gas to liquid or supercritical occurs during the pressurisation and prior to breakdown, while the phase remains unchanged post breakdown and during fracture propagation. Liquid CO₂ presents a fast-pressurising process while gaseous CO₂ undergoes a lengthy compression stage. Supercritical CO₂ is the best performing as the pressurisation is not too lengthy, while the instantaneous post breakdown fracturing is significant. Results show that higher temperature of supercritical CO₂ is causing larger instantaneous fracture propagation as it has lower viscosity for the given in situ stresses (>10 MPa).

The Callovo-Oxfordian (COx) claystone is selected as the host rock in the French project for geological disposal of radioactive waste. In its initial state, the host rock is fully saturated. Due to the low permeability, the pore fluid pressure can locally evolve in a quasi undrained condition due to subsequent mechanical and thermal loading, and then significantly affects deformation and cracking process of geological barrier. Most previous studies were carried out in quasi drained conditions or with constant pore pressure. Poromechanical behavior of COx claystone in undrained condition has been so far rarely investigated. In the present work, we carry out a new series of laboratory tests. Two representative loading paths are considered: triaxial compression with constant confining pressure and triaxial extension with constant mean stress. The variations of strain and pore pressure are measured during the tests. It is found that the poromechanical behavior of the claystone is clearly affected by loading path. The failure strength is higher in triaxial compression than in extension. The evolution of pore fluid pressure is correlated with volumetric strain. Compared with the results obtained in drained tests, it seems that the Terzaghi effective stress can be used for the description of pore fluid pressure effect on failure strength.

Correct understanding of rock dilatation plays a non-negligible role in the safety of rock engineering and the efficiency of geological resources extraction. Although the significance of dilatation under quasi-static loading or unloading conditions is well-studied, its behavior under dynamic loads remains poorly understood. This is largely because conventional dynamic testing system fails to capture the volumetric strain evolution of rock under confinement. This study develops a transparent confining chamber in SHPB system with which high-speed 3D-DIC is capable of measuring both axial and circumferential strain history of dynamically compressed rock. The progressive failure stages and volumetric change of red sandstone under confining pressure of 3.5 MPa and strain rates of 129∼292 s⁻¹ were studied and compared with those in quasi-static case. Results show that, the normalized stress thresholds of crack initiation and dilatancy in dynamic cases are much smaller than those in the quasi-static one. The volumetric variation of soft rock is characterized by four distinct stages: elastic contraction, pre-peak dilatancy, strain-softening dilatancy and strain-recovery dilatancy. The pre-peak elastic contraction is negligible compared to the post-peak dilation, and the ultimate dilation observed in dynamic compression is significantly greater than that in quasi-static compression. Increasing strain rate delays the onset of dilatancy, decreases the dilatant rate but remarkably extends the strain-softening dilatant process which is dominant in total dilation. A rate-dependent piecewise model incorporating key strain thresholds and a dilatancy rate factor was established to characterize the dynamic dilatancy behavior. The research results provide a new insight and possible method in dilation prediction for underground engineering subjected to dynamic loading.

Rock salt, due to its water solubility, low permeability, high plasticity, and damage self-healing ability, is one of the best candidate rock types for underground energy storage. Utilizing salt caves to construct compressed air energy storage (CAES) facilities can effectively enhance the utilization of renewable energy. Due to the need for peak shaving, the surrounding rock of the salt cavern will undergo discontinuous cyclic loading with varying gas injection rates and pressures, namely, alternating creep–fatigue loading. Considering the actual peak-shaving cycle of a CAES plant, long-term creep–fatigue tests of rock salt with different loading cycles and stress levels were conducted. The results indicate that in long-term creep–fatigue tests for rock salt, the lower the loading stress rate is, the greater the deformation of the rock salt. The variation in the stress limit has a greater effect on creep than on fatigue loading and unloading. The deformation rate of rock salt is influenced by alterations in the stress state. Based on the test results, according to the Norton creep model, a new creep–fatigue constitutive model for rock salt was established by defining a state variable that characterizes the level of rock hardening and introducing unloading as well as crack factors. This model can accurately describe the impact of historical loading and unloading processes on the viscoplastic mechanical characteristics of rock salt. The rock salt creep–fatigue test results were used to verify the constitutive model. A comparison of the fitting curve of the different stress loading paths with the test curve reveals good consistency, indicating that the model comprehensively considers the effects of time, load, and state on rock salt creep–fatigue, effectively describing the viscoplastic deformation characteristics of rock salt under different stress paths. These research findings provide important guidance for ensuring the stability of salt caverns used for CAES.

Mining engineering with layered structures often obtains extensive geological data to ensure reliability of mining operations. Effectively utilizing these data to characterize the spatial distribution of mechanical parameters in layered rock mass is crucial for slope stability analysis. This study focuses on the Heishan open-pit mine as a case study, leveraging the distinctive characteristics of mining engineering geological data. A three-dimensional fracture network was then generated based on the distribution of fractures in the rocks, and the representative elementary volume of the rock mass was determined by calculating the volumetric joint count (Jv). Statistical characteristics of various geological data are analyzed, and a geological statistical method combining the Kriging method and inverse distance power method is applied to establish a spatial distribution block model for geological strength index (GSI) and rock mechanical properties. Subsequently, a spatial variability model of the mechanical parameters of the layered rock mass was generated based on the Hoek–Brown criterion. Furthermore, the heterogeneous mechanical model is implemented in numerical software for stability analysis and slope angle optimization. The findings indicate that each engineering zone of layered slopes exhibits unique mechanical parameters while demonstrating significant layered distribution patterns at a macro level. Considering spatial variability, the mechanical model significantly impacts slope stability and slope angle optimization outcomes. Our research methodology facilitates accurate quantification of the heterogeneity of mechanical parameters in layered slopes without incurring excessive additional survey costs, enabling more rational explanations of slope landslides and the provision of suitable slope angle optimization designs.