“…The granite specimen fulfilled the International Society for Rock Mechanics (ISRM) size requirement. The cylindrical specimen had a surface roughness of less than 0.02 mm as well as end surfaces, which were perpendicular to its axis, of less than 0.001 radians to ensure a flat and smooth specimen surface 50 . Figure 16 Interior characteristic of the granite studied in this work.…”
One element that is essential to consider in underground mining engineering applications is the possibility of pillar failure, which can result in deadly geological disasters, including earthquakes and surface subsidence. Pillars are commonly present under an inclined state and are significantly dependent upon combined compression and shear loading. However, many scholars regard the pure uniaxial compression strength (UCS) of rock as the main evaluation index of pillar strength, which is inconsistent with the field practice. Hence, the present study developed a novel combined compression and shear test (C-CAST) system, which was applied in the investigative acoustic emission (AE) experiments to characterize the failure mechanism and micro-fracture behavior of granite specimens at different inclination angles. The experimental results presented the exponential decrease of UCS of inclined specimens with increase in the shear stress component. Changes in the inclination angle with a range of 0°–10° produced a splitting-shear failure fracture mode from the initial splitting failure. In comparison, an increase in the inclination angle from 10° to 20° produced a single shear failure fracture mode from the initial combined splitting-shear failure. The specimens exhibited nonlinearly reduced microcrack initiation (CI) and damage (CD) thresholds following an increase in the inclination angle, suggesting the dependence of the microcrack initiation and propagation on the shear stress component. The ratio of CI and CD thresholds to inclined UCS varies within a certain range, indicating that the ratio may be an inherent property of granite specimens and is not affected by external load conditions. Additionally, the rock fracture behavior was largely dependent upon the mechanism of shear stress component, as validated by the microcrack initiation and growth. Finally, a modified empirical formula for pillar strength is proposed to investigate the actual strength of inclined pillar. Results of a case study show that the modified formula can be better used to evaluate the stability of inclined pillars.
“…The granite specimen fulfilled the International Society for Rock Mechanics (ISRM) size requirement. The cylindrical specimen had a surface roughness of less than 0.02 mm as well as end surfaces, which were perpendicular to its axis, of less than 0.001 radians to ensure a flat and smooth specimen surface 50 . Figure 16 Interior characteristic of the granite studied in this work.…”
One element that is essential to consider in underground mining engineering applications is the possibility of pillar failure, which can result in deadly geological disasters, including earthquakes and surface subsidence. Pillars are commonly present under an inclined state and are significantly dependent upon combined compression and shear loading. However, many scholars regard the pure uniaxial compression strength (UCS) of rock as the main evaluation index of pillar strength, which is inconsistent with the field practice. Hence, the present study developed a novel combined compression and shear test (C-CAST) system, which was applied in the investigative acoustic emission (AE) experiments to characterize the failure mechanism and micro-fracture behavior of granite specimens at different inclination angles. The experimental results presented the exponential decrease of UCS of inclined specimens with increase in the shear stress component. Changes in the inclination angle with a range of 0°–10° produced a splitting-shear failure fracture mode from the initial splitting failure. In comparison, an increase in the inclination angle from 10° to 20° produced a single shear failure fracture mode from the initial combined splitting-shear failure. The specimens exhibited nonlinearly reduced microcrack initiation (CI) and damage (CD) thresholds following an increase in the inclination angle, suggesting the dependence of the microcrack initiation and propagation on the shear stress component. The ratio of CI and CD thresholds to inclined UCS varies within a certain range, indicating that the ratio may be an inherent property of granite specimens and is not affected by external load conditions. Additionally, the rock fracture behavior was largely dependent upon the mechanism of shear stress component, as validated by the microcrack initiation and growth. Finally, a modified empirical formula for pillar strength is proposed to investigate the actual strength of inclined pillar. Results of a case study show that the modified formula can be better used to evaluate the stability of inclined pillars.
“…is is because the freeze-thaw process leads to significant changes in the microstructure of rock resulting in irreversible structural damage of rock [29]. Moreover, the cyclic freeze-thaw action also has a clear effect on rock brittleness [16]. Here, it is worth emphasizing that the temperature treatment (freeze-thaw) is only used to control the brittleness of the test samples.…”
Section: Determination Of Brittleness Index (Bi)mentioning
confidence: 99%
“…Xia et al and Li et al considered that the variations in rock mechanical parameters, such as strength, elastic modulus, and Poisson's ratio, would inevitably lead to variations in rock brittleness [14,15]. Moreover, based on the cyclic freeze-thaw experimental results in the lab, Zhang et al explored the influence of freeze-thaw action on the sandstone brittleness, and the results revealed that the freezethaw effect had a clear impact on rock brittleness [16].…”
As one of the most crucial mechanical parameters of the rock materials, the effect of brittleness on the deformation and failure is of great practical significance for geotechnical construction and disaster prevention and mitigation. In this paper, the deformation and failure behaviors of the different brittle samples under dynamic loading were investigated using a split Hopkinson pressure bar (SHPB) experimental system. Besides, scanning electron microscopy (SEM) was also employed to study the relationship between the microscopic failures and rock brittleness and strain rate effects. The results revealed that the brittleness indexes BI3 and BI5 of the samples under uniaxial compression follow a linearly decreasing trend affected by the temperature changes, while the brittleness of the sample shows an increasing trend with the increase of strain rate under the dynamic loading. Also, the decline in the brittleness leads to an increase in the prepeak yield deformation phase of the sample under dynamic loading; after the peak point, the sample failure mode transitions from type I to type II with self-sustaining failure. Moreover, it was found that the dynamic strength increase factor presents a negative correlation with the sample brittleness. Finally, the macroscopic failure mode of the sample changes from split failure with multiple cracks to shear failure with few cracks due to the effect of decreasing brittleness. The failure surface of the sample gradually becomes smooth with the increase of brittleness, which manifests as a decrease in microcracks, and the gradual increase of the strain rate makes the failure surface rough, accompanied by an increase in microcracks.
“…First, the spline curves were generated using ANSYS command flows, then, the curved surface will be generated. Finally, the 3D model of the target layer was generated based on the trend surface analysis theory [56]- [58]. The 3D FEM model of the He8 member was divided into 4 layers (Fig.…”
Section: A Model Building and Unit Divisionmentioning
The study of the construction of a micro-scale rupture parameter from the perspective of rock stress and strain is a frontier in geoscience. The strain energy density (U) can quantitatively characterize the probability of internal micro-scale ruptures in different types of rock. Based on this, in this paper, a systematic forecasting method for tight sandstone sweet spots in a low-amplitude tectonic zone based on U-value calculations was proposed. The specific steps are as follows. First, a geological model of the target layer was created, and a new rock mechanics parameter assignment method based on sedimentary facies control principle was proposed. Then, the palaeo-tectonic stress field of the target layer in the Yanshanian period was recovered through the boundary loading. Finally, the strain energy density distribution of the target layer was obtained based on energy conservation principle. The simulation results of the paleo-tectonic stress field show that, the distribution of horizontal stress is mainly affected by lithology and local structure, and the vertical stress is mainly affected by the burial depth. Stress diffusion occurs in some areas, which are mainly affected by lithologic mutations or complex structures. The U values of the target layers have a band-like distribution and are mainly distributed between 0.12 and 0.30 J•m −3. The relationship between strain energy density and productivity of tight sandstone reservoirs was analyzed, and the criteria for distinguishing sweet spot areas based on U values were proposed. This method is applicable to strongly heterogeneous tight sandstone reservoirs in the low-amplitude tectonic zone of the Ordos Basin and have reference values for similar types of reservoirs around the world. INDEX TERMS Tight gas sandstone, strain energy model, finite element method, tectonic stress field.
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