International Journal of Rock Mechanics and Mining Sciences最新文献

In this study, rock-like model blast tests with varying toe burdens are conducted and the evolution of blast-induced fractures is analyzed using the digital image correlation (DIC) method. In addition, post-blast fragmentations are image-processed to quantitatively investigate the blasting performance. A three-dimensional numerical model is developed and validated against the experimental results. The effects of blasthole inclination (70°, 80°, and 90°) and short delays on fragment size distribution (FSD) are numerically investigated. Field trials are conducted to verify the numerical results. The experimental results reveal that the overall fragment size increases significantly in proportion to the toe burden. The explosion energy utilization rates range from 3.56 % to 13.16 %, with a tendency to initially increase and subsequently decrease. The numerical results demonstrate that fragments are more evenly distributed with a blasthole inclination of 70°, resulting in a remarkable improvement in rock fragmentation compared to a vertical blasthole. Compared to the toe burden, the influence of short delays on concrete fragmentation is insignificant. The field test results indicate that a narrower FSD range and stable pit walls are achieved by utilizing inclined blastholes in bench blasting. This study provides theoretical guidance for optimizing bench blasting parameters, which has practical significance for improving explosive energy utilization and production efficiency in open-pit mines.

Room-and-pillar mining is one of the oldest and most widely employed underground mining methods worldwide, while in recent years it has also been used for civil engineering projects and applications. The pillar design process is quite straightforward, requiring the assessment of two key elements, namely the pillar's strength and the anticipated loading imposed on it. Lots of research work has been elaborated for the estimation of pillars' strength and the main parameters associated with it, while, on the other hand, in terms of the loading the Tributary Area Theory (TAT) has been traditionally and successfully used as the dominant methodology to assess the post-mining pillar induced stresses. This paper focuses primarily on decoding the pillar loading regime by analyzing the identifying the stresses imposed to them through the use of modern computational tools offered by 2D and 3D numerical analyses, over a series of pillars' type (square, ribs), configurations and initial virgin stress fields. This allows for the development of a benchmarking framework that showcase the differences in the stress conditions and reveal the over-conservative behavior of TAT. More importantly though, it allowed for the expression of two (2) general analytical formulae for the direct estimation of the average vertical elastic stresses on pillars, both for the case of rib & square pillars layout; the most typical patterns applied in this method. They aim at providing an easy to use and more accurate estimation of the pillar stress - as compared to TAT - in alignment with the results obtained from numerical analyses. Thus, with the proposed formulas, the time-consuming numerical process needed for preliminary pillars' dimensioning is tackled in a swift and effective manner.

Blasting is a common activity in mining that can cause significant damage in the remaining rock mass. The most commonly used method for predicting vibrations is the Swedish or Holmberg-Persson approach. It is a simple and fast method that uses empirical formulation to estimate the vibration levels based on the explosive charge weight, distance to the source, and other parameters. However, it has limited accuracy and does not consider the effect of free surfaces or other boundary conditions. On the other hand, recently developed methods as the full-field solution (FFS) can provide more accurate predictions of vibrations due to excitations provoked by cylindrical columns of explosive, but the inclusion of free surfaces in analytical methods is a challenging problem. This paper presents a new approach that includes free surfaces in the FFS to predict vibrations analytically in the near-field. The main obstacle to including free surfaces in the FFS is the belief that the solution is non-decoupleable in P- and SV-waves separately. The Heelan's approach was previously used to decouple them, but it only provides valid radiation patterns in the far-field and does not account for intrinsic attenuation. In this paper, we address this problem, allowing for the inclusion of free surfaces in the FFS.

An understanding of the tectonic stress field distribution in the carbonate reservoirs of the Tahe Oilfield is essential for oil and gas migration and reservoir reconstruction. This study adopts a geological genesis perspective and integrates the unique attributes of the carbonate reservoirs in the Tahe Oilfield to simulate three-dimensional stress fields using the finite element method and Petrel software. The simulation, which takes pore pressure and boundary constraints into consideration, aligns with the findings of acoustic emission tests conducted by previous researchers and validates the model by corroborating the maximum horizontal principal stress direction with imaging logging interpretations. With subsequent utilization of the generalized Coulomb-Mohr shear failure criterion and the Griffith generalized maximum tensile stress criterion, the simulated stress enables the prediction of the total fracture intensity. To complement this analysis, we integrate seismic data and fault formation mechanisms to characterize variations in fracture intensity within distinct regions of the study area. Three key findings emerge from this investigation. First, due to the Hercynian thermal event, X-shaped conjugate faults display a disproportionately high degree of development compared to other primary fractures. Analyzing the mechanisms of formation and development of these X-shaped strike-slip faults reveals discernible differences in deformation characteristics between NW-trending and NE-trending faults, with the former exhibiting a greater propensity for fracture rupture and efficient oil-gas migration. Second, fault intersections are critical and efficient conduits for fluid accumulation and thereby contribute to reservoir formation. Lastly, exclusive of X-shaped conjugate faults, NE-trending faults exhibit the greatest propensity for oil and gas accumulation and migration. Collectively, these findings facilitate the identification of areas favorable for oil and gas migration and provide a crucial mechanical analysis that can inform the exploration and development of the Tahe Oilfield.

This work aims to investigate some typical fatigue behaviors of a sandstone under cyclic loading. At the microscopic scale, the heterogeneous sandstone is viewed as a composite comprising a solid matrix and randomly distributed microcracks. Within the framework of thermodynamics, three main dissipation mechanisms, plastic deformation of matrix, microcrack propagation and frictional sliding, are considered in monotonic compression. However, during the cyclic compression period, the material’s progressive degradation is mainly attributed to microcrack growth and frictional sliding, which are separately described by a fatigue damage law and a non-associated flow rule. The fatigue lifetime (the number of cycles to failure) is regarded as an equivalent time with regard to the loading frequency and physical time. After calibrating the parameters, the proposed model is validated on describing mechanical behaviors of a sandstone in both conventional and cyclic triaxial compression tests. Compared with test data, the model can well predict fatigue lifetime and three-stage deformation under various loading conditions, including confining pressure, upper limit stress, and loading frequency.

Flow of typical non-Newtonian fluids such as cement grouts can experience different regimes as the Reynolds number (Re) changes, understanding of which is important for design and operation of rock grouting in various rock engineering applications. Here, flow regimes of representative non-Newtonian fluids, i.e., Bingham and Herschel–Bulkley (H–B) fluids, are numerically investigated with experimental validations. Three tensile rock fracture surfaces originated from a fine-grained sandstone, a medium-grained sandstone and a medium-grained granite samples are used to create rough-walled fracture models with variable aperture structures. Flow of groundwater, Bingham and H–B fluids through these fractures is numerically simulated respectively, by solving the full mass and momentum conservation equations with the Re ranging from 0.01 to 1000. The regimes for these fluids flowing through the fractures are characterized. Laboratory flow tests are conducted in a cylindrical granite fracture sample to verify the characterized flow regimes. The results reveal important differences of flow regimes between Newtonian and non-Newtonian fluids. Specifically, the transmissivity for water flow is constant when Re is relatively small until the Re reaches certain critical values; the transmissivity for Bingham and H–B fluids flow increases with increasing Re until asymptotically reaches certain peak values, followed by a descending stage when Re is relatively large. The critical (water) and peak (Bingham and H–B fluids) values are affected by surface roughness, that is, a rougher surface results in smaller critical and peak values as well as greater discrepancies compared to the analytical solutions based on the smoothed parallel plates model. These results show that a peak or optimum transmissivity is achievable in a specific range of Re (Re = 10–100 for the fractures studied). This new finding can potentially help optimize the injection pressure or flow rate in rock grouting practices.

Understanding the energy transformation mechanism in rockbursts is essential for predicting and mitigating potentially catastrophic rock failures. In this study, Double Springs Release Tests (DSRTs) were proposed in a laboratory setting to investigate the energy transformation of rockbursts from inception to development. High-speed cameras and image processing algorithms were utilized to calculate different types of energy throughout the duration of the burst. Theoretical analyses, grounded in structural dynamics and stress wave equations, was conducted and cross-referenced with the experimental results. The study found that wave impedance $\sqrt{\rho E}$ is a key indicator of burst intensity. The research demonstrated that the impact energy in DSRTs originates from both the impact medium and the surrounding medium, and explored how these two components contribute to the total impact energy of the impact medium.

There are abundant oil and gas resources in China's continental shale formations, and these formations often contain sandy lamina, tuffaceous lamina and carbonate lamina parallel to the bedding planes, resulting in complex geomechanical properties. During the drilling process, the mechanical weak surface structure inside the shale and the hydration effect of drilling fluid may easily cause wellbore instability, which reduces the safety and benefit of drilling. To explore the geomechanical properties of laminated shale and bedding shale after water absorption, a series of tests were conducted on the Chang 7 laminated shale and bedding shale in the Ordos Basin. The result indicates that the compressive strength and elastic modulus of laminated shale and bedding shale show a trend of decreasing first and then starting to drop as β (the angle between bedding/lamina and the direction of stress) keeps increasing, and laminated shale has stronger anisotropy, lower compressive strength and elastic modulus. The moisture content of laminated shale and bedding shale increases as the soaking time increases, which leads to a decrease in the compressive strength. Compared to bedding shale, laminated shale reaches water saturation faster and has a higher moisture content. Based on the macroscopic and microscopic images before and after shale hydration, it can be concluded that natural microfractures are easily formed at the interface between the lamina and shale matrix, and brittle minerals at the edges of natural microfractures are prone to detachment, thereby increase the hydration area and intensify the hydration process. Compared to bedding shale formations, laminated shale formations have a higher hole-size elongation ratio and are more prone to collapse according to on-site data. This study reveals the geomechanical properties of laminated shale under the dual influence of anisotropy and hydration, provides support for drilling design in such formations.

3D printing technology offers a unique advantage in fabricating rock specimens with precise internal defects. However, the low strength and stiffness of sand-type 3D printed samples limit their application in rock mechanics. This study primarily focuses on the microstructural characteristics of the specimens, including changes in pore structure, cementing materials, and brittleness properties. Three distinct post-processing methods were employed to explore effective approaches for enhancing the strength of specimens while preserving their desired brittleness. The findings indicate that infiltration treatment significantly reduces the porosity of the specimens and increases the roughness of particle surfaces. In contrast, freezing treatment slightly decreases the porosity and augments the roughness of particle surfaces. Moreover, while the specimens treated only with infiltration exhibited noticeable plasticity, those subjected to both permeation and freezing showed marked brittleness. Furthermore, specimens treated solely with infiltration experienced a modest increase in strength and displayed noticeable plasticity, whereas combined treatment of infiltration and freezing resulted in a substantial increase in strength and conspicuous brittleness. Additionally, the mechanical properties, failure modes, and fracture surface microstructure of the combined-treated specimens resemble those of natural granite. These findings offer solutions for addressing the low strength and stiffness of sand-type 3D printed rock-like specimens.

This study investigates the in-situ borehole breakout formation using true-triaxial laboratory experiments on cubic Gosford sandstone. Four series of tests have been conducted under varying stress conditions following two approaches: PD method (loading onto specimens with pre-drilled boreholes) and PS method (loading onto intact specimens and then conducting drilling). Borehole camera observations show that a large amount of rock debris remains within the breakout zone under the PD conditions, while clear V-shaped notches are observed in the PS tests. The breakout geometries are extracted based on point cloud data obtained from 3D scanning. Both breakout width and normalised depth under both testing approaches exhibit positive correlations with the maximum horizontal stress while decreasing with minimum horizontal stress. The PS tests tend to yield wider and deeper breakouts compared to the PD tests. The difference in breakout width is generally consistent across various stress conditions at approximately 10° – 15°, whereas the variation in the normalised breakout depth increases with the severity of the borehole failure. The discrepancies are believed to be attributed to the excavation unloading induced strength-weakening and removal of rock debris by circulating fluid and drilling vibration. The outcomes of this study demonstrate that the stress path has critical impacts on the rock failure behaviours around openings, and the PS tests are suggested for investigating the borehole breakout phenomenon.