Journal of Rock Mechanics and Geotechnical Engineering最新文献

Cleats are the dominant micro-fracture network controlling the macro-mechanical behavior of coal. Improved understanding of the spatial characteristics of cleat networks is therefore important to the coal mining industry. Discrete fracture networks (DFNs) are increasingly used in engineering analyses to spatially model fractures at various scales. The reliability of coal DFNs largely depends on the confidence in the input cleat statistics. Estimates of these parameters can be made from image-based three-dimensional (3D) characterization of coal cleats using X-ray micro-computed tomography (μCT). One key step in this process, after cleat extraction, is the separation of individual cleats, without which the cleats are a connected network and statistics for different cleat sets cannot be measured. In this paper, a feature extraction-based image processing method is introduced to identify and separate distinct cleat groups from 3D X-ray μCT images. Kernels (filters) representing explicit cleat features of coal are built and cleat separation is successfully achieved by convolutional operations on 3D coal images. The new method is applied to a coal specimen with 80 mm in diameter and 100 mm in length acquired from an Anglo American Steelmaking Coal mine in the Bowen Basin, Queensland, Australia. It is demonstrated that the new method produces reliable cleat separation capable of defining individual cleats and preserving 3D topology after separation. Bedding-parallel fractures are also identified and separated, which has historically been challenging to delineate and rarely reported. A variety of cleat/fracture statistics is measured which not only can quantitatively characterize the cleat/fracture system but also can be used for DFN modeling. Finally, variability and heterogeneity with respect to the core axis are investigated. Significant heterogeneity is observed and suggests that the representative elementary volume (REV) of the cleat groups for engineering purposes may be a complex problem requiring careful consideration.

The network of Himalayan roadways and highways connects some remote regions of valleys or hill slopes, which is vital for India's socio-economic growth. Due to natural and artificial factors, frequency of slope instabilities along the networks has been increasing over last few decades. Assessment of stability of natural and artificial slopes due to construction of these connecting road networks is significant in safely executing these roads throughout the year. Several rock mass classification methods are generally used to assess the strength and deformability of rock mass. This study assesses slope stability along the NH-1A of Ramban district of North Western Himalayas. Various structurally and non-structurally controlled rock mass classification systems have been applied to assess the stability conditions of 14 slopes. For evaluating the stability of these slopes, kinematic analysis was performed along with geological strength index (GSI), rock mass rating (RMR), continuous slope mass rating (CoSMR), slope mass rating (SMR), and Q-slope in the present study. The SMR gives three slopes as completely unstable while CoSMR suggests four slopes as completely unstable. The stability of all slopes was also analyzed using a design chart under dynamic and static conditions by slope stability rating (SSR) for the factor of safety (FoS) of 1.2 and 1 respectively. Q-slope with probability of failure (PoF) 1% gives two slopes as stable slopes. Stable slope angle has been determined based on the Q-slope safe angle equation and SSR design chart based on the FoS. The value ranges given by different empirical classifications were RMR (37–74), GSI (27.3–58.5), SMR (11–59), and CoSMR (3.39–74.56). Good relationship was found among RMR & SSR and RMR & GSI with correlation coefficient (R²) value of 0.815 and 0.6866, respectively. Lastly, a comparative stability of all these slopes based on the above classification has been performed to identify the most critical slope along this road.

The composite pile consisting of core-pile and surrounding cement-enhanced soil is a promising pile foundation in recent years. However, how and to what extent the cement-enhanced soil influences the ultimate lateral resistance has not been fully investigated. In this paper, the ultimate lateral resistance of the composite pile was studied by finite element limit analysis (FELA) and theoretical upper-bound analysis. The results of FELA and theoretical analysis revealed three failure modes of laterally loaded composite piles. The effects of the enhanced soil thickness, strength, and pile-enhanced soil interface characteristics on the ultimate lateral resistance were studied. The results show that increasing the enhanced soil thickness leads to a significant improvement on ultimate lateral resistance factor (N_P), and there is a critical thickness beyond which the thickness no longer affects the N_P. Increasing the enhanced soil strength induced 6.2%–232.6% increase of N_P. However, no noticeable impact was detected when the enhanced soil strength was eight times higher than that of the natural soil. The maximum increment of N_P is only 30.5% caused by the increase of interface adhesion factor (α). An empirical model was developed to calculate the N_P of the composite pile, and the results show excellent agreement with the analytical results.

Injecting carbon dioxide (CO₂) into coal seams may unlock substantial carbon sequestration potential. Since the coal acts like a carbon filter, it can preferentially absorb significant amounts of CO₂. To explore this further, desorption of the adsorbed gas due to pressure drop is investigated in this paper, to achieve an improved understanding of the long-term fate of injected CO₂ during post-injection period. This paper presents a dual porosity model coupling gas flow, adsorption and geomechanics for studying coupled processes and effectiveness of CO₂ sequestration in coals. A new adsorption−desorption model derived based on thermodynamics is incorporated, particularly, the desorption hysteresis is considered. The reliability of the proposed adsorption-desorption isotherm is examined via validation tests. It is indicated that occurrence of desorption hysteresis is attributed to the adsorption-induced pore deformation. After injection ceases, the injected gas continues to propagate further from the injection well, while the pressure in the vicinity of the injection well experiences a significant drop. Although the adsorbed gas near the well also decreases, this decrease is less compared to that in pressure because of desorption hysteresis. The unceasing spread of CO₂ and drops of pressure and adsorbed gas depend on the degree of desorption hysteresis and heterogeneity of coals, which should be considered when designing CO₂ sequestration into coal seams.

Vertical drains are used to accelerate consolidation of clays in ground improvement projects. Smear zones exist around these drains, where permeability is reduced due to soil disturbance caused by the installation process. Hansbo solution is widely used in practice to consider the effects of drain discharge capacity and smear on the consolidation process. In this study, a computationally efficient diameter reduction method (DRM) obtained from the Hansbo solution is proposed to consider the smear effect without the need to model the smear zone physically. Validated by analytical and numerical results, a diameter reduction factor is analytically derived to reduce the diameter of the drain, while achieving similar solutions of pore pressure dissipation profile as the classical full model of the smear zone and drain. With the DRM, the excess pore pressure u obtained from the reduced drain in the original undisturbed soil zone is accurate enough for practical applications in numerical models. Such performance of DRM is independent of soil material property. Results also show equally accurate performance of DRM under conditions of multi-layered soils and coupled radial-vertical groundwater flow.

Enzyme-induced carbonate precipitation (EICP) is an emanating, eco-friendly and potentially sound technique that has presented promise in various geotechnical applications. However, the durability and microscopic characteristics of EICP-treated specimens against the impact of drying-wetting (D-W) cycles is under-explored yet. This study investigates the evolution of mechanical behavior and pore characteristics of EICP-treated sea sand subjected to D-W cycles. The uniaxial compressive strength (UCS) tests, synchrotron radiation micro-computed tomography (micro-CT), and three-dimensional (3D) reconstruction of CT images were performed to study the multiscale evolution characteristics of EICP-reinforced sea sand under the effect of D-W cycles. The potential correlations between microstructure characteristics and macro-mechanical property deterioration were investigated using gray relational analysis (GRA). Results showed that the UCS of EICP-treated specimens decreases by 63.7% after 15 D-W cycles. The proportion of mesopores gradually decreases whereas the proportion of macropores increases due to the exfoliated calcium carbonate with increasing number of D-W cycles. The microstructure in EICP-reinforced sea sand was gradually disintegrated, resulting in increasing pore size and development of pore shape from ellipsoidal to columnar and branched. The gray relational degree suggested that the weight loss rate and UCS deterioration were attributed to the development of branched pores with a size of 100–1000 μm under the action of D-W cycles. Overall, the results in this study provide a useful guidancee for the long-term stability and evolution characteristics of EICP-reinforced sea sand under D-W weathering conditions.

Monitoring shear deformation of sliding zones is of great significance for understanding the landslide evolution mechanism, in which fiber optic strain sensing has shown great potential. However, the correlation between strain measurements of quasi-distributed fiber Bragg grating (FBG) sensing arrays and shear displacements of surrounding soil remains elusive. In this study, a direct shear model test was conducted to simulate the shear deformation of sliding zones, in which the soil internal deformation was captured using FBG strain sensors and the soil surface deformation was measured by particle image velocimetry (PIV). The test results show that there were two main slip surfaces and two secondary ones, developing a spindle-shaped shear band in the soil. The formation of the shear band was successfully captured by FBG sensors. A sinusoidal model was proposed to describe the fiber optic cable deformation behavior. On this basis, the shear displacements and shear band widths were calculated by using strain measurements. This work provides important insight into the deduction of soil shear deformation using soil-embedded FBG strain sensors.

The traditional standard wet sieving method uses steel sieves with aperture ≥0.063 mm and can only determine the particle size distribution (PSD) of gravel and sand in general soil. This paper extends the traditional method and presents an extended wet sieving method. The extended method uses both the steel sieves and the nylon filter cloth sieves. The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm, 0.038 mm, 0.014 mm, 0.012 mm, 0.0063 mm, 0.004 mm, 0.003 mm, 0.002 mm, and 0.001 mm, respectively. The extended method uses five steps to separate the general soil into many material sub-groups of gravel, sand, silt and clay with known particle size ranges. The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups. The extended method is demonstrated with a general soil of completely decomposed granite (CDG) in Hong Kong, China. The silt and clay materials with different particle size ranges are further examined, checked and verified using stereomicroscopic observation, physical and chemical property tests. The results further confirm the correctness of the extended wet sieving method.

To investigate the mechanism of rockburst prevention by spraying water onto the surrounding rocks, 15 experiments are performed considering different water absorption levels on a single face. High-speed photography and acoustic emission (AE) system are used to monitor the rockburst process. The effect of water on sandstone rockburst and the prevention mechanism of water on sandstone rockburst are analyzed from the perspective of energy and failure mode. The results show that the higher the absorption degree, the lower the intensity of the rockburst after absorbing water on single side of sandstone. This is reflected in the fact that with the increase in the water absorption level, the ejection velocity of rockburst fragments is smaller, the depth of the rockburst pit is shallower, and the AE energy is smaller. Under the water absorption level of 100%, the magnitude of rockburst intensity changes from medium to slight. The prevention mechanism of water on sandstone rockburst is that water reduces the capacity of sandstone to store strain energy and accelerates the expansion of shear cracks, which is not conducive to the occurrence of plate cracking before rockburst, and destroys the conditions for rockburst incubation.