Journal of Rock Mechanics and Geotechnical Engineering最新文献

Through high-precision engraving, self-affine sandstone joint surfaces with various joint roughness coefficients (JRC = 3.21–12.16) were replicated and the shear sliding tests under unloading normal stress were conducted regarding various initial normal stresses (1–7 MPa) and numbers of shearing cycles (1–5). The peak shear stress of fractures decreased with shear cycles due to progressively smooth surface morphologies, while increased with both JRC and initial normal stress and could be verified using the nonlinear Barton-Bandis failure criterion. The joint friction angle of fractures exponentially increased by 62.22%–64.87% with JRC while decreased by 22.1%–24.85% with shearing cycles. After unloading normal stress, the sliding initiation time of fractures increased with both JRC and initial normal stress due to more tortuous fracture morphologies and enhanced shearing resistance capacity. The surface resistance index (SRI) of fractures decreased by 4.35%–32.02% with increasing shearing cycles due to a more significant reduction of sliding initiation shear stress than that for sliding initiation normal stress, but increased by a factor of 0.41–1.64 with JRC. After sliding initiation, the shear displacement of fractures showed an increase in power function. By defining a sliding rate threshold of 5 × 10⁻⁵ m/s, transition from “quasi-static” to “dynamic” sliding of fractures was identified, and the increase of sliding acceleration steepened with JRC while slowed down with shearing cycles. The normal displacement experienced a slight increase before shear sliding due to deformation recovery as the unloading stress was unloaded, and then enhanced shear dilation after sliding initiation due to climbing effects of surface asperities. Dilation was positively related to the shear sliding velocity of fractures. Wear characteristics of the fracture surfaces after shearing failure were evaluated using binary calculation, indicating an increasing shear area ratio by 45.24%–91.02% with normal stress.

Despite the extensive studies conducted on the effectiveness of microwave treatment as a novel rock pre-conditioning method, there is yet to find reliable data on the rock failure mechanisms due to microwave heating. In addition, there is no significant discussion on the energy efficiency of the method as one of the important factors among the mining and geotechnical engineers in the industry. This study presents a novel experimental method to evaluate two main rock failure mechanisms due to microwave treatment without applying any mechanical forces, i.e. distributed and concentrated heating. The result shows that the existence of a small and concentrated fraction of a strong microwave absorbing mineral will change the failure mechanism from the distributed heating to the concentrated heating, which can increase the weakening over microwave efficiency (WOME) by more than 10 folds. This observation is further investigated using the developed coupled numerical model. It is shown that at the same input energy, the existence of microwave absorbing minerals can cause major heat concentration inside the rock and increase the maximum temperature by up to three times.

In nature, there are widely distributed bi-modulus materials with different deformation characteristics under compressive and tensile stress states, such as concrete, rock and ceramics. Due to the lack of constitutive model that could reasonably consider the bi-modulus property of materials, and the lack of simple and reliable measurement methods for the tensile elastic parameters of materials, scientists and engineers always neglect the effect of the bi-modulus property of materials in engineering design and numerical simulation. To solve this problem, this study utilizes the uncoupled strain-driven constitutive model proposed by Latorre and Montáns (2020) to systematically study the distributions and magnitudes of stresses and strains of bi-modulus materials in the three-point bending test through the numerical method. Furthermore, a new method to synchronously measure the tensile and compressive elastic moduli of materials through the four-point bending test is proposed. The numerical results show that the bi-modulus property of materials has a significant effect on the stress, strain and displacement in the specimen utilized in the three-point and four-point bending tests. Meanwhile, the results from the numerical tests, in which the elastic constitutive model proposed by Latorre and Montáns (2020) is utilized, also indicate that the newly proposed measurement method has a good reliability. Although the new measurement method proposed in this study can synchronously and effectively measure the tensile and compressive elastic moduli, it cannot measure the tensile and compressive Poisson's ratios.

We investigate the accuracy and robustness of moment tensor (MT) and stress inversion solutions derived from acoustic emissions (AEs) during the laboratory fracturing of prismatic Barre granite specimens. Pre-cut flaws in the specimens introduce a complex stress field, resulting in a spatial and temporal variation of focal mechanisms. Specifically, we consider two experimental setups: (1) where the rock is loaded in compression to generate primarily shear-type fractures and (2) where the material is loaded in indirect tension to generate predominantly tensile-type fractures. In each test, we first decompose AE moment tensors into double-couple (DC) and non-DC terms and then derive unambiguous normal and slip vectors using k-means clustering and an unstructured damped stress inversion algorithm. We explore temporal and spatial distributions of DC and non-DC events at different loading levels. The majority of the DC and the tensile non-DC events cluster around the pre-cut flaws, where macro-cracks later develop. Results of stress inversion are verified against the stress field from finite element (FE) modeling. A good agreement is found between the experimentally derived and numerically simulated stress orientations. To the best of the authors’ knowledge, this work presents the first case where stress inversion methodologies are validated by numerical simulations at laboratory scale and under highly heterogeneous stress distributions.

Swelling geomaterials in northwestern and northeastern China are exposed to both seasonal wetting-drying (DW) and freezing-thawing (FT) processes. The influence of full-process wetting-drying-freezing-thawing (WDFT) cycles on their hydro-mechanical behaviour has not been well investigated. In this study, a series of swelling and compression tests was conducted on Yanji weathered mudstone subjected to different WD, FT and WDFT processes and the effects of seasonal processes and cyclic number on the swelling strain, compression index, rebound index and hydraulic conductivity were experimentally determined. With the increasing WD, FT and WDFT cycles, the starting time of primary swelling decreased first due to the increasing water infiltration with the appearance of large pores, and then increased because of the decreasing swelling potential of compact aggregates after two cycles. Moreover, as the cyclic number increased, the final swelling strain declined. Upon loading, the specimens after cyclic processes exhibited a smaller compression index at low stresses due to their smaller inter-particle distance after swelling, but a larger one owing to the collapse of large pores and cracks at high vertical stresses. After unloading, the rebound index decreased with the increase of cyclic number due to the irreversible collapse of large pores and cracks. The hydraulic conductivity increased with the increasing cyclic number at low vertical stresses (large void ratios). With the further increase of vertical stress, the increase of hydraulic conductivity induced by cyclic processes became indiscernible. Moreover, a comparison among three processes suggested that the WDFT process exerted a more pronounced influence on the hydro-mechanical behaviour of Yanji mudstone than the separate WD or FT process.