International Journal of Rock Mechanics and Mining Sciences最新文献

Rockburst hazards exhibit different spatiotemporal characteristics in deep tunnel excavation. Failure characteristics and energy evolution process of delayed and instantaneous rockburst of basalt rock were investigated based on single-sided unloading experiments under true triaxial conditions. High-speed photography and acoustic emission (AE) monitoring were used, and computed tomography (CT) scanning, fractal theory, and crack classification were employed for failure analysis. A three-dimensional damage model considering variable stiffness of testing machine was established to calculate the energy evolution of rock-machine system during the entire process of rockbursts. Results show that delayed rockburst includes three stages of small particles ejection, rock slab buckling, and violent mixed ejection, while instantaneous rockburst is characterized by rock slab spalling accompanied with slight particles ejection. Delayed rockburst exhibits a progressive failure mode of large-scale expansion of tensile cracks (before failure) to small-scale penetration of shear cracks (upon failure), while instantaneous rockburst shows a large-scale shear failure and abrupt penetration of shear planes upon failure. Delayed rockburst consumes less energy, and most of dissipated energy is converted into kinetic energy of ejected rock fragments, causing a higher intensity level of rockburst; instantaneous rockburst consumes more energy, but almost all dissipated energy comes from internal friction energy of shear failure, causing a higher scale of rock damage. Before rockburst failure, elastic strain energy stored in rock remains basically unchanged, while the energy stored in testing machine continuously decreases, indicating that rockburst is triggered by energy release of loading system. Energy dissipation rate (EDR) can be used as a precursory index for rock failure induced by quasi-static loading such as delayed rockburst. High EDR means damage intensification, stress drop, active AE events, and acceleration of shear crack expansion inside the rock. The findings of this study can provide new perspectives for the mechanisms and early warning of rockbursts.

In many engineering applications, understanding gas adsorption and its induced swelling in nanoporous materials is crucial. In this study, we propose a novel coarse-grained molecular dynamics (CGMD) model with gas-gas, solid-solid, and gas-solid interactions explicitly controlled to achieve the coupling between gas transport and solid deformation at the microscale. The CGMD model has the capability to recover solid and gas properties, including density, Young's modulus of the solid, and viscosity of the gas to generate a broad range of swelling ratios relevant to nanostructures by using the innovative bead-spring chain networks. A comparison is made between gas transport through deformable and non-deformable nanochannels of varying sizes (35.4–123.9 nm), which is also compared with the macroscopic Hagen-Poiseuille equation. The proposed model has been further tested in a simplified nanoporous medium composed of four randomly distributed spherical solids. The Kozeny-Carman equation can generally describe the relationship between permeability and porosity, but small deviations are observed in the case of swelling porous media. Our results justify the effect of swelling on reducing gas permeability and provide a new approach to modeling gas transport in swelling porous media at the microscale within the framework of CGMD, with potential applications spanning nanofluidics, energy storage technologies, and environmental nanotechnology.

Direct measurement of the real contact area of rock joints under normal loading is crucial for comprehending the subsurface geological processes. However, measuring this phenomenon quantitatively at site-scale or laboratory-scale is challenging. Here, we investigate the evolution mechanism of the real contact area in rock joints by conducting closure tests on artificial and saw-cut sandstone joints under normal stresses up to 50 MPa. Geometrical shapes of contact patches are quantified by the pressure-sensitive film using the adaptive threshold method. An extensive range of contact stress within contact patches is innovatively measured by integrating the results from multi-type pressure-sensitive films. Experimental results demonstrate that the real contact area increases with the increasing normal stress hyperbolically. Such a nonlinear contact evolution behavior can be attributed to the coalescence of adjacent contact patches. The fractal dimension of composite surface governs the geometrical shapes of contact patches and the distribution of contact stress. The relationship between patch areas and bearing loads follows the Hertzian theory when the patches are small, while it gradually becomes linear with the increasing patch size. A power model with exponential cut-off is proposed to predict the size distribution of contact patches. This work can provide new insights for estimating the patch-dependent seismic nucleation length and slip stability of subsurface joints.

Microseismic source mechanisms in underground mines can provide information about the rock mass response to mining. Conventional approaches to such studies rely upon moment tensor solutions that are susceptible to modeling assumptions and need reliable information about source locations and high-resolution velocity models. We propose the application of unsupervised clustering to group microseismic events into different classes directly from the waveform data such that the events in a specific class have similar source mechanisms. Our method has three main steps, first using spectral decomposition to separate the source terms from the path-receiver contributions in the observed amplitude spectra of events occurring in spatially dense clusters. Second, reducing the number of features from the source spectra using independent component analysis (ICA). Third, applying a Gaussian mixture model (GMM) to the reduced feature matrix to obtain event clusters. To test our method, we generate synthetic waveform data using the receiver network and the recorded microseismic event locations in an underground potash mine in Saskatchewan. Results show the ability of our method to separate events into different classes corresponding to differences in source mechanisms. Application to field data recorded in the mine during February 2021 successfully discriminates between blasts and microseismic events. The data recorded between 1 March and 30 June 2021 that contain microseismic events only are divided into two dominant classes. Using known moment tensors (MT) of some of these events for labeling, we interpret one of the two classes as having dominant double-couple mechanisms as compared to the other which most likely corresponds to the linear dipole-tensile mechanisms. Our method, combined with some expert knowledge such as MT of some larger magnitude events, can offer an assessment of source types of large microseismic populations as often encountered in induced seismicity.

Axial studies on cable bolts can be conducted using various scale testing apparatuses. Large scale testing, while providing a powerful platform for testing, is expensive and time consuming. This study presents details of a small scale pull out testing campaign on cable bolts and investigates the results achieved. Six popular types of cable bolts were studied using an anti rotation apparatus while encapsulated in cementitious grout and resin. The resin samples were tested under both monotonic and cyclic loading patterns. The results showed that grouted bulbed cables require higher displacement to reach their maximum load capacity which is lost at failure, while plain cables tend to hold lower loads for a longer time. Resin samples provided strain softening behaviour with low capacities, particularly in absence of cable indentation or bulbs. Cyclic loading tended to adversely affect the post peak behaviour of the resin samples, especially in the bulbed cables. Failed samples inspected after the testing suggested a non-uniform damage profile along the cable with extensive damage at the exit point transitioning into almost no damage at the entry point.

In geotechnical engineering, activities such as landslides, rockfalls, blasting, and excavation often subject jointed rock masses to dynamic shear loads, impacting project stability. With continuous innovation of anchoring support technology, the appearance of energy-absorbing bolts has provided more options for rock support. This study selected fully-grouted bolts and energy-absorbing bolts, considering the roughness of natural rock joints. Indoor shear tests were conducted on bolted specimens at varying shear velocities. A comprehensive analysis was conducted on the failure morphology of joint surfaces and the fracture characteristics of bolts. Subsequently, the shear performance of both bolt types was quantitatively assessed through absorbed shear energy. At the interface between fully-grouted bolts and joint surfaces, stress concentration phenomena were observed. In contrast, energy-absorbing bolts exhibited significant necking phenomena. Under external forces, the bolt body detached from the grout, enabling it to accommodate large deformations of the rock mass and absorb energy. The results indicate that energy-absorbing bolts demonstrate better adaptability and energy absorption capacity under high-velocity shearing, while fully-grouted bolts exhibit higher peak shear stresses. Based on the experimental findings, for projects requiring consideration of dynamic shear loads and energy absorption capabilities, energy-absorbing bolts may be more suitable, providing additional safety assurance. Conversely, fully-grouted bolts may be more appropriate for applications with higher requirements for shear resistance, such as structural support under general static loads.

The Cerchar test is the most commonly used method for evaluating rock abrasivity and estimating tool wear. The conventional test results are reported based on the measured changes of the wear parts, and little attention is paid to what happens on the rock surface and scratching force. Since the cutting process is the interactive behavior between cutting tools and rock materials, the changes in both parts are important to represent rock-tool interaction and evaluate cutting efficiency. In the present study, the Cerchar tests have been carried out on eleven types of monomineralic rocks by using an improved West apparatus. The related abrasive parameters have been comprehensively and systematically analyzed, including stylus tip wear, rock material loss, applied horizontal force, and scratching energy. The variation characteristics of those abrasive parameters have been studied. The specific abrasivity ratio (SAR) and scratching specific energy (SSE), which represent the tool wear and energy consumption per unit of rock removal respectively, have been developed to evaluate the cutting efficiency of different rocks. The results show that the SAR and SSE values of the tested rocks have comparable data ranges and variation trends due to the same mathematical treatment of the indices. Under the given rock removal volume, the SAR and SSE could be used to compare and classify the relative cutting efficiency of different rocks. The lower the SAR and SSE values, the less stylus wear and lower energy consumption in the cutting process, indicating higher cutting efficiency. According to their values, the cutting efficiency of the tested rocks is divided into four categories: high cutting efficiency, medium cutting efficiency, low cutting efficiency, and very low cutting efficiency. The SAR-based and SSE-based classifications are consistent for most of the tested rocks, and the SAR-based classification is lower to higher abrasive rocks (pyroxene, hematite, and quartz) due to it considering the influence of stylus tip wear. Hence the SAR-based classification is more suitable for hard and highly abrasive rocks.

Freeze-thaw cycles are recognized as one of the key triggers for some major landslides in cold regions around the world. Though the effects of freeze-thaw cycles on the rock strength degradation have been studied extensively, little effort has been made to qualitatively evaluate how it contributes to the evolution from a stable rock slope to a large-scale mass movement. In this study, we use a discrete element-based numerical model to simulate the entire process of the initiation of landslide under the action of freeze-thaw cycles in a slope with randomly distributed initial cracks. The main goal of this work is to quantitatively describe the landslide evolution process regarding the slope displacement, crack propagation, stress chain and load-bearing structure. Our results show the essence of the displacement evolution of a landslide subjected to freeze-thaw cycles; namely frost heave pressure induces the generation of new cracks, leading to the failure and reconstruction of the load-bearing structure of the slope. Deep-seated landslides can occur when the slope is crossed by a fault; otherwise, the slope is prone to surface erosion or shallow landslides.

This paper presents a three-dimensional numerical analysis of multiple fracture growth leading to the development of excavation disturbed zones and spalling around deposition boreholes in a geological disposal facility. The development of fracture patterns is simulated with the Imperial College Geomechanics Toolkit, a finite-element based simulator that can model the simultaneous nucleation, growth, and coalescence of multiple fractures in quasi-brittle rock. In these simulations, fractures develop due to the stress concentrations around the borehole wall, caused by the local in situ stresses, and due to the thermal stresses caused by the radioactive decay of the waste. Fracture patterns, and the extent of the spalled zone, are computed after the borehole drilling, heating, and cooling stages, at the Forsmark repository site in Sweden. The effect of temperature on the nucleation and growth of spalling fractures, as well as on the reactivation of pre-existing fractures, is assessed qualitatively, by comparing fracture patterns, and quantitatively, in terms of the maximum spalling depth, width, and increase in the total fractured surface area. Overall, the simulations presented herein indicate that thermal spalling will increase the depths (away from the borehole) and angular widths of the spalled zone, but is not likely to lead to major increases in fracture aperture, and concomitant increases in hydraulic transmissivity and permeability of the spalled zone, above that which has already been caused by mechanical spalling.

The study of rock creep phenomena is of paramount importance due to its potential to trigger geological disasters, such as landslides. To predict and prevent such disasters, creep constitutive models are widely employed to comprehend the time-dependent deformation of rocks. These models encompass various mechanical parameters that describe the intricate stress-strain behaviors. Nevertheless, significant challenges persist in achieving accurate and consistent parameter estimation and state prediction. In this study, we introduce three advanced data assimilation (DA) methods, including one Markov chain Monte Carlo method, DREAM_(KZS), and two ensemble smoother methods, ESMDA and ILUES. This marks the first application of such methods for calibrating rock creep models in the scenario of geological disaster prevention. We conducted numerical simulations under both low- and high-dimensional conditions to assess the performance of these DA methods. For the single partition model, all three DA methods demonstrated promising results. In the high-dimensional case, DREAM_(KZS) displayed inefficiency, while both ESMDA and ILUES proved to be still effective. ESMDA offered improved data matching but tended to underestimate parameter uncertainties, whereas ILUES excelled in addressing the issue of equifinality. In a real-world case focusing on characterizing creep deformation at the Mogu tilting deformation body near the Lianghekou Dam, China, we employed all three DA methods, and they collectively demonstrated satisfactory performance. Particularly noteworthy is the enhanced performance of the DREAM_(KZS) method during the accelerated creep phase, even in the presence of limited data. The findings of this research bear significant importance in reducing uncertainties associated with model parameters in the realm of rock mechanics, thereby advancing our capabilities in predicting and preventing disasters.