International Journal of Rock Mechanics and Mining Sciences最新文献

Cracks are always a serious concern in the stability analysis of gravity dams. One of the main reasons for the initiation of cracks is overflows. In evaluating dam safety under flood conditions, it is crucial to consider the balance between the strength of the dam body and the propagation of cracks. In this context, simplified equations serve as valuable tools in dam design as they offer a quick and efficient way to estimate the behavior of the dam structure. In this study, firstly using a polygonal material-based model (P-MBM), which is improved in considering the softening behavior of joints, the micro-crack propagation in masonry material is investigated. Then, based on performing 81 numerical simulations in a parametric study on the geometrical and geotechnical properties of the dam subjected to overflow, a great database of the behavior of different dams is investigated. Then, using the genetic algorithm, a set of equations is proposed, and their accuracy is validated through UDEC simulations and some theoretical methods from existing literature. For all models, the crack tends to be horizontal at the initial phase. Then, due to increasing the compressive stresses on the downstream side, the fractures tend to the dam toe. The results also indicate that the proposed equations can reasonably determine the behavior of gravity dams and the development of cracks in the dam body. The outcomes highlighted the considerable effects of geometry and geotechnical properties on dictating the trajectory of crack growth.

Rocks are subjected to different loading rates at different construction stages and engineering applications. The strength of rock usually increases with loading rate. This rate dependency is one of the time-dependent behaviors of rock, whereby the micro-mechanisms are believed to be the subcritical crack growth due to stress corrosions. However, no evidence is provided yet. This study investigated rate effects of rocks through a novel implementation of Parallel-Bonded Stress Corrosion (PSC) model in Discrete Element Method (DEM). Long-term microparameters in PSC are first calibrated through creep test. Then, a series of uniaxial compressive strength, direct tensile strength, and triaxial compressive strength tests are performed, with strain rates ranging from $1\times {10}^{-7}$/s to $1\times {10}^{-3}$/s. Results show that the uniaxial compressive strength is highly dependent on strain rates which quantitatively matches with the experimental data. At lower strain rate, more subcritical cracks propagate due to longer stress-corrosion reaction time, resulting in a lower strength. Besides, strain rate also influences the failure patterns in post-peak, with single failure plane at lower strain rates and multiple failure planes at higher strain rates. Rate effects are also observed in direct tensile strength tests, with similar rate of increase in strength and a transition in cracking pattern, which align with the experimental data, indicating tension-induced subcritical cracking is the unified underlying micro-mechanism of rate effects for both cases. However, in triaxial compressive strength tests, rate effects become less obvious with increasing confining pressure, consistent with experimental findings, as subcritical crack growth is suppressed in shearing processes.

Grouting is the most commonly used methods in dealing with water inrush issue in mine and tunnel engineering. In order to better predict the grouting effect, research on slurry diffusion mechanism became a hotspot for scholars. At present, the mainstream theoretical model used to study the slurry diffusion mechanism are the circle diffusion model and the modified ones in plane plate fracture. However, these models cannot explain the “contradiction” between the rapid setting characteristics of quick-setting slurry and the continuous long-term injection of slurry in grouting engineering, which cannot accurately predict the grouting pressure or grouting diffusion range. Therefore, a “circle-outburst diffusion model” which can explain the above “contradiction” was proposed in this paper. Based on the new model, stepwise algorithms were developed to predict the grouting pressure and slurry diffusion range. By means of conducting fracture grouting simulation test and collecting grouting pressure data in an actual grouting project, the new model was verified and the slurry diffusion mechanism was studied. Comparison results indicate that the new model can reveal the intrinsic reason for the irregular diffusion phenomenon of the slurry and forecast the outburst moment accurately. The circle diffusion stage and outburst diffusion stage elaborated in the new “circle-outburst diffusion model” were consistent with the staged characteristics of the grouting process presented in the grouting simulating test. Differences between theoretical and experimental pressure value were within 10 %, indicating a high degree of consistency. The number and distribution of outburst diffusion points determine slurry diffusion form and significantly influence the diffusion range. The grouting pressure and the length of slurry flow path increase nonlinearly with time in each diffusion stage. It is hoped that the new model can provide a theoretical basis for the study of diffusion mechanism of quick-setting slurry.

This paper details the preconditioning blasting strategy that was developed and used while sinking the third deepest shaft/winze in Canada in a brittle rock mass. The high-stress conditions presented at the construction site resulted in seismic activity, uncontrolled spalling, and rockbursting. For comparison, muck is thrown away from the face in a lateral development round, leaving the round partially unconfined, which allows for immediate stress redistribution when operators are not present. A vertical blast will fill the created void with broken muck, which confines the bench and inhibits stress redistribution from occurring. As confinement is reduced from mucking out the round, there is an increase in strainburst risk when operators are required to mark bootlegs and prepare for drilling/loading the next advance. Due to the nature of shaft sinking, which relies heavily on physical labor and handheld mining equipment, there is increased operator exposure to rockburst risk compared with mechanized mining. Therefore, preconditioning blasting becomes a critical control for managing high-stress conditions. There are limited guidelines in published literature for preconditioning blasting in shaft sinking operations and less evidence that preconditioning blasting is providing a benefit. Therefore, the preconditioning blasting strategy that was used for the shaft sink was entirely original and was optimized based on visual inspections and seismic monitoring. This method should be beneficial for managing rockburst risks in deep shaft sinking in future operations.

The complex geological conditions of coal mine, especially the geological characteristics of coal-bearing strata, determine that mining is one of the most hazardous occupations worldwide. Strong mining-induced earthquakes (E ≥ 10⁵ J) frequently occur in coal mines, where the high-strength thick and hard roofs are developed above coal seams. It seriously threatens the safety of underground miners and ground residents, as well as the productivity and effectiveness of mining activities. The fracture characteristics of the overlying strata and the distribution of mining-induced earthquake characteristics before and after field experiment of hydraulic fracturing is analyzed and revealed using the methods of field monitoring and numerical analysis, and reveals the effect of hydraulic fracturing technology in preventing and controlling strong mining-induced earthquakes, for the frequent occurrence of mining-induced earthquakes in Dongtan coal mine. Combined with the results of microseismic monitoring after hydraulic fracturing, as mining advances, the frequency of small-energy microseismic events is dominant, and the percentage of strong mining-induced earthquakes was reduced by 51.3 %. Numerical calculations show that the existence of hydraulic fractures provided the necessary paths for the expansion of the fracture network in the overlying strata. This results in rock masses near the hydraulic fracture slipping along the fracture under the action of mining stresses. The implementation of hydraulic fracturing can effectively weaken and fracture the integrity of thick and hard rock strata to reduce or eliminate the occurrence of hazardous mining-induced earthquakes with large energy.

This study investigates the rock mechanics and anisotropic properties of the Montney Formation, Alberta, through two sets of experiments: unconfined compressive strength tests and triaxial compression tests, supplemented by ultrasonic wave velocity measurements. These tests enabled the calculation of dynamic and static stiffness properties and Thomsen anisotropy parameters (ε, δ, γ). Our findings reveal that the Montney Formation exhibits weak anisotropy, with ε values generally below 0.10, contrasting with other strongly anisotropic shale formations. Specimens exhibiting higher clay content and total organic carbon levels show more pronounced anisotropy. Static measurements exhibit a higher degree of anisotropy compared to dynamic measurements. The investigation also explored loading and unloading stiffness parameters, noting a higher E loading-to-unloading ratio for rock specimens with lower elastic properties. This provides important information on the rock's response to stress path effects during stimulation and exploitation. The study also discusses other rock mechanics parameters including Poisson's ratio, tensile strength, and brittleness. The research contributes to a more comprehensive understanding of the geomechanical and petrophysical behavior of the Montney Formation, aiding reservoir characterization and hydrocarbon exploration and production.

Gas seepage and progressive failure of coal are common energy-driven mining phenomena. A comprehensive understanding of the energy-driving mechanism behind the catastrophic behavior of mining-induced coal is fundamental to innovating the technology of coal and gas co-mining. Thus, this study simulated three typical mining stress evolution process in protective coal-seam mining (PCM), top-coal caving mining (TCM), and non-pillar mining (NM) to investigate the energy evolution and distribution patterns of coal. The results indicate a strong correlation between energy dissipation and gas seepage. By transitioning from PCM and TCM to NM, the peak elastic strain energy of gas-bearing coal increased by 155.92 %, and the ratio of peak dissipative energy decreased from 51 % to 41 %. Under the PCM stress path, gas seepage decreased the energy storage by 13.52 %, whereas the pre-mining pressure relief and enhanced permeability simulation increased in peak dissipation energy by 49.66 %. Using the cumulative dissipative energy as a damage variable reveals that the degree of coal damage evolution under PCM is higher than other mining methods. Based on the energy-driven damage mechanism, a new coal permeability model was established, and its comparison with classical permeability model demonstrated its excellent fitting effectiveness.

Rock properties are estimated using objective lab/in-situ testing and subjective judgements invoking different types of uncertainties, i.e., aleatory, and epistemic, along them, often indicated by varying information levels. This study presents a unified reliability method to integrate the spatial variability of inputs modelled via alternate uncertainty models (intervals and probability-boxes (p-boxes)) with those modelled as stochastic variables via probability distributions. The methodology employs advanced Karhunen–Loève decomposition to generate interval and random fields of inputs modelled via alternate and stochastic models, respectively. Input properties are allocated to the zones of the numerical model in Fast Lagrangian Analysis of Continua-2D (FLAC-2D) based on their spatial dependency and correlation functions through a developed MATLAB-FLAC coupled code. The methodology is demonstrated for a deep tunnel in Canada to be constructed along a massive rock prone to brittle failures. Intact rock properties are modelled as stochastic variables due to objective estimation, while Geological Strength Index (GSI) and deformation modulus are modelled using alternate models (interval and p-box, respectively) due to subjective and hybrid estimation (double uncertainty propagation algorithm). The results of the methodology are compared with those of traditional deterministic and random field methods. The methodology reduces the subjectivity invoked by including unavailable additional information (e.g., assuming probability distributions of inputs based on literature) and propagates the originally available information of inputs accurately. The final outputs are the p-boxes of response parameters (i.e., displacements and damage zone) instead of their fixed values (deterministic analysis) and probability distributions (traditional reliability analysis), indicating the propagation of both impreciseness and variability of inputs by the method. For this case study, the p-boxes of outputs were bounding their values/distributions estimated via traditional analyses, verifying the accuracy of the methodology. Further, the impreciseness in the outputs, highest in the damage zone extent, was due to imprecision in the estimated GSI.

Stope structural parameters, which are human-controllable, directly impact the safety and economics performance of underground mineral extraction. Current stope design still relies heavily on empirical methods such as stability graphs, due to the complex nature of rock masses and varied stope failure mechanisms. This study aims to enhance stability graphs with machine learning techniques. Firstly, a dataset of 980 records from unsupported stopes was compiled, representing perhaps the largest dataset of its kind so far in the literature. This was achieved through extensive literature review and the collation of an additional 289 records from Chinese mines which were previously not included. An analysis of data reveals that over 90 % of the records fall within a stability coefficient of 0–100 and a hydraulic radius of 0–20 m. Secondly, a stability graphs optimization process was established using Python, eliminating the subjectivity of partitioning. Nine supervised machine learning algorithms were employed and trained to test their performance in partitioning form and predicting accuracy. It was found that the neural network algorithm demonstrated the best overall performance. At last, a neural network with the Keras framework was used to establish a new multilayer perceptron model to generate safety factor probability curves, which were then used to construct the stability graph. To facilitate practical use, mathematical functions fitting safety factor curves within the unstable zone were further formulated. Compared with other empirical stability graphs, our new approach allows designers to more efficiently and reliably select safety factors to determine the stability state according to site specific conditions and technical support systems, thereby providing enhanced guidance for stope design.

This study investigated the crack propagation processes and established the lifetime prediction methods of the concrete-rock interfaces under constant loading. Firstly, the constant loading tests were performed under three-point bending loading on the composite concrete-rock beams with three kinds of interfaces, i.e. natural, 4 × 4, and 7 × 7 interfaces, and under three constant load levels, i.e. initial cracking load, 80 % and 97 % of the peak loads. Then, the clip gauge method and digital image correlation method were employed to detect the crack lengths under constant loading. Finally, the effects of constant load levels on fracture properties of the concrete-rock interfaces were analyzed and the crack propagation processes under constant loading were discussed. The results indicated that the clip gauge method was an available and accurate method to detect the crack lengths of the concrete-rock interfaces under constant loading. Crack propagation processes and crack mouth opening processes under constant loading exhibited the three-stage feature, i.e. deceleration stage, uniform stage and acceleration stage. In addition, the logarithms of the constant loading lifetimes showed an approximate linear relationship with the logarithms of the crack mouth uniform opening rates, and a quantitative relationship was established by using the linear regression analysis to establish the lifetime prediction methods. This study proposed a practical method to predict the service life of concrete structure-bedrock interface. When the crack mouth uniform opening stage was recognized, the lifetime of concrete structure-bedrock interface in service can be predicted by substituting the crack mouth uniform opening rate into the pre-established prediction model. This study can provide the theoretical support for the safety assessment of the concrete structure-bedrock interface in service.