Journal of Rock Mechanics and Geotechnical Engineering最新文献

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.

Discrete element method (DEM) has been widely utilised to model the mechanical behaviours of granular materials. However, with simplified particle morphology or rheology-based rolling resistance models, DEM failed to describe some responses, such as the particle kinematics at the grain-scale and the principal stress ratio against axial strain at the macro-scale. This paper adopts a computed tomography (CT)-based DEM technique, including particle morphology data acquisition from micro-CT (μCT), spherical harmonic-based principal component analysis (SH-PCA)-based particle morphology reconstruction and DEM simulations, to investigate the capability of DEM with realistic particle morphology for modelling granular soils' micro-macro mechanical responses with a consideration of the initial packing state, the morphological gene mutation degree, and the confining stress condition. It is found that DEM with realistic particle morphology can reasonably reproduce granular materials’ micro-macro mechanical behaviours, including the deviatoric stress–volumetric strain–axial strain response, critical state behaviour, particle kinematics, and shear band evolution. Meanwhile, the role of multiscale particle morphology in granular soils depends on the initial packing state and the confining stress condition. For the same granular soils, rougher particle surfaces with a denser initial packing state and a higher confining stress condition result in a higher degree of shear strain localisation.

Full-length grouted bolts play a crucial role in geotechnical engineering thanks to their excellent stability. However, few studies have been concerned with the degrading performance of grouted rock bolts caused by extensive and continuous heat conduction from surrounding rocks in high-geothermal tunnels buried more than 100 m (temperature from 28 °C to 100 °C). To investigate the damage mechanism, we examined the time-varying behaviors of grouted rock bolts in both constant and variable temperature curing environments and their damage due to the coupling effects of high temperature and humidity through mechanical and micro-feature tests, including uniaxial compression test, pull-out test, computed tomography (CT) scans, X-ray diffraction (XRD) test, thermogravimetric analysis (TGA), etc., and further analyzed the relationship between grout properties and anchorage capability. In order to facilitate a rapid assessment and control of the anchorage performance of anchors in different conditions, results of the interface bond degradation tests were correlated to environment parameters based on the damage model of interfacial bond stress proposed. Accordingly, a thermal hazard classification criterion for anchorage design in high-geothermal tunnels was suggested. Based on the reported results, although high temperature accelerated the early-stage hydration reaction of grouting materials, it affected the distribution and quantity of hydration products by inhibiting hydration degree, thus causing mechanical damage to the anchorage system. There was a significant positive correlation between the strength of the grouting material and the anchoring force. Influenced by the changes in grout properties, three failure patterns of rock bolts typically existed. Applying a hot-wet curing regime results in less reduction in anchorage force compared to the hot-dry curing conditions. The findings of this study would contribute to the design and investigations of grouted rock bolts in high-geothermal tunnels.

This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement, which can consider not only the relative sliding of the pile‒soil interface but also the pile row–soil interaction. The proposed method is verified by comparisons with existing theoretical methods, including the boundary element method and the elastic foundation method. The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling, i.e. the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation. The results also indicate that the stiffness of the pile‒soil interface, including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface, describes the strength of the pile‒soil interaction. The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.