Search Results (542)

Acidic wetting–drying cycles can progressively deteriorate sandstone used in rock engineering, but the link between macroscopic mechanical degradation and three-dimensional pore-crack evolution remains unclear. The objective of this work was to clarify the deterioration mechanism of sandstone under repeated acidic wetting–drying action. Sandstone specimens were subjected to 0, 5, 10, 20, or 30 wetting–drying cycles in a H₂SO₄ solution with an initial pH of 2.00. Triaxial shear testing, micro-CT reconstruction, scanning electron microscopy, and a correlation analysis were combined to characterize changes in the mechanical behavior and microstructure. With an increasing cycle number, the cohesion and internal friction angle decreased by 40.85% and 11.27%, respectively, while the pore network became progressively enlarged, connected, and structurally complex. The pore fractal dimension increased from 2.18 to 2.49. Scanning electron microscopy images showed enlarged pores and cracks, looser particle contacts, and local damage along particle boundaries. Increasing the confining pressure improved the peak resistance and restricted crack development. A correlation analysis indicated that mechanical degradation was closely associated with the evolution of the pore and crack structure. These results establish a multiscale relationship between the loss of mechanical performance and microstructural deterioration, providing a basis for evaluating sandstone stability in acidic environments. Full article

The mechanical properties of moraine soil in cold regions are significantly influenced by freeze–thaw cycles (FTCs). However, current understanding of the quantitative characteristics of its shear behavior under the coupled effect of FTCs and confining pressure is still insufficient. To address this, a series of triaxial unconsolidated-undrained shear tests were conducted on saturated moraine soil, with different numbers of FTCs (N = 0, 1, 4, 8, 10, 12, 15, 20) and various confining pressures (σ₃ = 100, 200, 300, 400 kPa). The experimental results reveal that: (1) With an increase in the number of FTCs, the stress–strain curves gradually change from strain-softening to strain-hardening types. Correspondingly, the pore water pressure development shifts gradually from a peak-decay pattern to a growth-stabilization pattern. The peak pore water pressure rises linearly with increasing confining pressure, whereas it decays linearly with an increasing number of FTCs. (2) Both the secant modulus E₅₀ and the shear strength increase with higher confining pressure and decrease with more FTCs. Confining pressure exerts a significant inhibitory and compensatory effect on freeze–thaw-induced damage, markedly reducing the deterioration rate under high confining pressure. (3) Quantitative prediction models for E₅₀ and q_max were established, effectively capturing the coupled effect of confining pressure and FTCs. It can be inferred that confining pressure mitigates structural damage by compressing frost-induced cracks and enhancing interparticle contacts, while FTCs exacerbate the degradation of soil mechanical properties because of ice crystal expansion or contraction and weakening of cementation. This study quantifies the coupled effect of confining pressure and FTCs, and the proposed prediction model provides a useful reference or preliminary estimation for relevant geotechnical engineering designs. Full article

Looking at the demand for precise matching between the mechanical properties of similar materials and natural soft clay in soft ground visual model tests, this paper proposes a preparation method for graded transparent soil based on optical testing principles and geotechnical similarity theory. Using n-dodecane and 15# white oil as pore fluids, combined with nano-fumed silica and optimally graded fused quartz sand, a graded transparent soil material system with accurately matched refractive indices was constructed. The synergistic effect of nano-fumed silica and graded quartz sand enables dual optimization of material transparency and mechanical performance. The feasibility of simulating soft ground was verified through load-plate tests, jacked pile penetration model tests, and consolidated-drained (CD) triaxial tests. The consolidation compression and direct shear test results show that the material has a compression coefficient of 1.43 MPa⁻¹, a compression modulus of 1.72 MPa, a total internal friction angle φ ranging from 16.53° to 23.21°, and a total cohesion c ranging from 5.42 to 11.34 kPa. Further CD triaxial test results verified that the developed transparent soil exhibits effective shear strength parameters (c′ = 9.65 kPa, φ′ = 16.01°), which are highly consistent with the effective strength indices of natural Shaoxing silty clay (c′ = 12.94 kPa, φ′ = 13.52°), with a relative error of ultimate deviator stress less than 5% under various confining pressures. Moreover, different strength levels can be obtained by adjusting the pre-consolidation pressure. During shear loading, the material presents stable volumetric contraction without dilatancy, conforming to the typical contractive mechanical characteristics of normally consolidated soft clay. PIV velocity-field analysis of the indoor plate load test under constant-settlement-rate conditions revealed that the transparent soil displays a typical Prandtl failure mode, consistent with the failure characteristics of natural soft clay. The model test of jacked-pile penetration further confirmed that this material can effectively simulate the stress-deformation behavior of soft ground under the test conditions adopted in this study. The developed material offers a viable alternative simulant and relevant test reference for laboratory visual model investigations into soft ground deformation, pile–soil interaction and failure evolution in geotechnical model tests. Full article

Slopes excavated in coal-measure strata are prone to rainfall-induced landslides because water-induced disturbances progressively degrade rock-mass shear strength. This study investigated six coal-measure lithologies from the unloading zone of the Fushun West Open-Pit Mine using triaxial compression tests after separate wetting–drying and continuous-immersion treatments. Condition-dependent cohesion, c, and internal friction angle, φ, were fitted with exponential functions and incorporated into the Mohr–Coulomb criterion. For scenario analysis, the retention ratios measured in the two separate treatment series were applied sequentially in a separable empirical parameterization. This no-interaction approximation was used to update coal-measure strength inputs in representative slope models. Cohesion and φ decreased exponentially within the tested ranges, with in-sample R² values greater than 0.85, and cohesion was generally more sensitive. Continuous immersion produced rapid early softening, whereas wetting–drying cycles produced cumulative deterioration. Limit-equilibrium and finite-element calculations showed lower safety factors and more concentrated deformation under more severe parameter-reduction scenarios. Model-specific cumulative-displacement reference values of 52.36–213.82 mm were paired with Fs levels of approximately 1.15, 1.05, and 1.00 and compared qualitatively with historical monitoring curves. The findings provide a reference for rainy-season slope-stability prediction and staged warning in open-pit coal mines. Full article

Understanding the failure behavior of cylindrical-hole hard rocks is essential for rockburst prevention in deep underground engineering. In this study, fractal–statistical analysis was combined with true triaxial testing and discrete element modeling to quantify the rate-dependent failure and crack-network evolution of holed granodiorite. The results showed that, with an increasing loading rate, the peak axial stress increased from 143 to 190 MPa, the peak axial strain decreased from 1.24% to 0.86%, and the post-peak brittleness index increased from 0.83 to 1.19. The final failure pattern evolved from multi-crack tension–shear coupled failure to localized dominant fracture and intense hole-wall exfoliation. The mass fractal dimension of rockburst fragments increased with loading rate, reflecting a transition toward finer and more dispersed fragmentation. To extend the experimentally observed hole-wall failure mechanism to adjacent openings, a calibrated PFC3D double-hole model was further established. The numerical results revealed that crack interaction was governed by stress-concentration superposition and progressive rock-bridge damage, and the hole-spacing ratio controlled the connectivity and complexity of the crack network. As S/2R increased from 1.25 to 2.00, the dominant fracture-band inclination increased from 27° to 54°, reflecting a transition from steep inter-hole coalescence to more inclined and spatially dispersed fracture development. Full article

The shear behavior of loess is closely linked to its microstructural evolution, and understanding this relationship is essential for deciphering the mechanisms of loess hazards. In this study, consolidated-drained (CD) triaxial tests were conducted on intact Q₃ Malan loess from the Dongzhi tableland, China, under varying water contents and confining pressures. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analyses were performed on specimens before and after shearing to quantitatively and qualitatively characterize the changes in pore and particle properties and their connection to shear deformation. The results reveal three failure modes, including shear, homogeneous, and plastic failure. They are governed by the combined effects of microstructural variation and microcrack development, depending on confining pressure and water content. Quantitatively, as water content increases from 9% to 20%, cohesion decreases by 86.8% and peak shear strength reduces by 68.4%, while the internal friction angle decreases only slightly. Water-induced strength deterioration is governed primarily by cohesion loss rather than friction angle reduction. Thus, 20% water content was identified as the critical threshold marking the transition from cohesion-dominated to friction-dominated strength degradation. A critical threshold at approximately 27% water content is identified, beyond which about 70% of mesopore and macropore volumes undergo collapse, after which the strength is almost entirely sustained by interparticle friction. Based on these findings, the water-induced strength decay mechanism is categorized into three stages: rapid cement degradation, friction-dominated transition, and slow attenuation. These macroscopic phenomena are closely linked to the continuous adjustment of the microstructure, manifested by the softening, dispersion, and disintegration of cementations, particle movement and rearrangement, and the reduction and mutual transformation of inter-aggregate pores under loading and wetting. The three-stage mechanism and threshold characteristics of loess strength degradation upon wetting revealed in this study can provide theoretical support for early slope-instability warning in loess irrigation and heavy rainfall regions, as well as engineering reinforcement prioritizing the recovery of cohesion. Full article

The deformation and failure mechanism of deep mudstone under high temperature and high pressure (HTHP) is a critical issue constraining deep-drilling efficiency. Taking an HTHP mudstone formation in the western South China Sea as the research object, this study integrates X-ray diffraction, scanning electron microscopy, nanoindentation, HTHP triaxial compression tests, and FDEM numerical modeling incorporating mineral heterogeneity and Weibull strength distribution. The mudstone is predominantly composed of clay minerals (44.67%) and quartz (32.37%), with low hardness (1.42–2.96 GPa) and moderate elastic modulus (43.9–58.2 GPa). Under ambient conditions, uniaxial compressive strength is approximately 19.5 MPa with axial splitting failure; at 40 MPa confining pressure, strength increases to 121.8 MPa with shear failure; at 150 °C and 40 MPa, peak strength slightly decreases, yield point is delayed, and post-peak decline accelerates. The FDEM model, calibrated against experimental data, reasonably reproduces crack evolution and failure modes. However, due to limited tests (one per condition) and variations in specimen depth, statistical robustness is constrained; thus, this study does not yet establish a generalizable quantitative cross-scale correlation, and the findings are primarily applicable to the specific formation investigated. Full article

Reservoir landslides pose a persistent threat to the safe operation of hydropower projects, particularly where altered rock masses within water-level fluctuation zones undergo repeated wetting–drying and seepage-induced deterioration. This study investigates the mechanical behavior and long-term strength evolution of altered granite from the Guobu Slope near the Laxiwa Arch Dam in Qinghai, China. Rock masses with four alteration degrees, ranging from complete to slight alteration, were examined through an integrated experimental program involving torsional shear tests, hydro-mechanical coupled triaxial tests, large-scale direct shear and ring shear tests, Brazilian splitting tests, and long-term P-wave velocity monitoring. The results demonstrate that increasing water content progressively weakens the shear strength of altered granite, while elevated seepage pressure further reduces its strength and deformation resistance under hydro-mechanical coupling. Residual shear behavior also shows a clear dependence on water content, indicating that post-peak strength deterioration should be considered in slope stability assessment. Long-term P-wave monitoring further reveals that mechanical degradation is more pronounced during the early stage and gradually approaches a relatively stable state, suggesting a site-specific decelerating deterioration process rather than unlimited strength loss. Based on the experimental results, empirical relationships between shear-strength parameters and water content are established, and long-term lower-bound strength parameters are proposed for altered granite with different degrees of alteration. These findings provide experimental support for understanding the hydro-mechanical deterioration and long-term deformation behavior of reservoir-bank altered rock masses and offer a basis for parameter selection and stability assessment when combined with rock-mass reduction, field calibration, and sensitivity analysis. Full article

Understanding the failure mechanism of soft rock roadways in high-humidity environments, as well as designing appropriate control measures, are critical for ensuring their stability. In this study, swelling and triaxial compression tests on argillaceous sandstone were first performed. Results show that the triaxial compressive strength (TCS), elastic modulus, cohesion, and internal friction angle of argillaceous sandstone are all decreased due to the water weakening effect. Then, a self-developed finite-element-based numerical code was employed to elucidate the role of humidity diffusion in the deformation and failure of soft rock roadways. Simulation results indicate that under the influence of humidity, high stress concentration zones develop, initiating microcracks within these regions. As humidity continues to diffuse, the high stress concentration zones expand and migrate deeper into the surrounding rock, causing microcracks to propagate and accelerating humidity diffusion. This cyclical process repeats, ultimately resulting in macroscopic fracturing. The failure of roadway exhibits a tensile–shear mixed mode during humidity diffusion. A comparative analysis of four control measures reveals that conventional non-waterproof shotcrete primary support is of limited effectiveness in ensuring the stability of high-humidity soft rock roadways. It is essential to promptly establish a closed waterproof support structure. Furthermore, localized support defects significantly impact control effectiveness. Full article

Thin spray-on liner (TSL) technology provides rapid and highly automated surface support for underground coal mine roadways. However, in deep roadways affected by high in situ stress, mining-induced disturbances, and fractured surrounding rock, conventional TSL materials require improved tensile–shear resistance, deformation compatibility, and support adaptability. Although fiber reinforcement is an effective method for enhancing polymer composites, systematic studies on the effects of fiber type and dosage in reactive polymer-based TSL materials remain limited. In this study, a commercially available two-component polyurea-silicate-based TSL matrix was reinforced with polyvinyl alcohol (PVA) fibers, polypropylene mesh fibers, and toughened polypropylene fibers at volume fractions of 0.25–1.50%. A stepwise experimental program, including uniaxial compression, variable-angle shear, tensile, circular-indenter buffered shear, and true triaxial tests, was conducted to evaluate the mechanical behavior and support-related performance of the fiber-reinforced TSL materials. The basic mechanical tests showed that the 0.75% toughened polypropylene fiber group maintained favorable compressive and shear resistance, achieving a cohesion of 8.65 MPa and an internal friction angle of 24.12°. PVA fibers exhibited higher tensile reinforcement efficiency at relatively low contents, with the 0.25% PVA fiber group reaching a peak tensile stress of 13.61 ± 1.00 MPa. The 1.0% PVA fiber group showed good deformation coordination, with a compressive strength of approximately 49.87 MPa. In the circular-indenter buffered shear test, the 1.0% PVA fiber group reached a peak load of 0.636 ± 0.055 kN and an absorbed energy of 3.118 ± 0.832 J at 10 mm displacement. Under true triaxial loading, the 1.0% PVA fiber group absorbed 311.4 J of energy at a displacement of 10 mm, approximately 5.5% higher than that of the 0.75% toughened polypropylene fiber group. Therefore, 1.0% PVA fiber reinforcement is recommended as the optimal reinforcement scheme for polymer-based TSL materials used in deep, fractured, and large-deformation coal mine roadways. Full article

The exploration of oil and gas resources is shifting toward ultra-deep and extra-deep reservoirs, including in the Tarim Basin, where various types of carbonate rocks are buried. Owing to the extreme burial depths, the mechanical behavior of these rocks under extra-deep conditions differs significantly from that of shallow formations, making it essential to understand their mechanical responses. This study investigated the mechanical properties and failure modes of carbonate rocks, specifically dolomite, argillaceous limestone, and pure limestone. Samples from extra-deep formations were initially analyzed for mineral composition and microstructure, after which uniaxial and triaxial compression tests were conducted to evaluate strength, static elastic modulus, and axial strain at peak stress. The results indicate that dolomite exhibits the highest mechanical strength and stiffness among the three lithologies. Under conditions of a high confining pressure of 100 MPa and a temperature of 160 °C, its elastic modulus and triaxial compressive strength are 65.4 GPa and 611.2 MPa, respectively, compared with 52.8 GPa and 444.2 MPa for limestone. Strength increases with confining pressure for all lithologies, with dolomite showing the most pronounced strengthening response. Although elevated temperature reduces rock strength, its effect is weaker than that of confining pressure. The failure mode is strongly controlled by confining pressure. At low confining pressures, failure is dominated by localized shear bands and brittle fracturing, whereas increasing confining pressure promotes a transition toward quasi-brittle deformation or ductile plastic flow. Dolomite predominantly maintains a quasi-brittle failure mode, argillaceous limestone exhibits a clear brittle-to-ductile transition, and pure limestone shows the greatest tendency to develop ductile plastic flow under high confining pressure conditions. The results further demonstrate that mineral composition and microstructural characteristics play critical roles in controlling the deformation and failure mechanisms of carbonate rocks. High-calcite pure limestone can exhibit ductile-like deformation behavior due to cataclastic processes, allowing significant strain without localization failure. These insights enhance understanding of carbonate rock behavior under extra-deep formations, informing practical applications in geology science. Full article

Determining the shear strength parameters of granular materials in high waste rock dump slopes is essential for reliable slope stability analysis. In this study, dump materials were sampled from six benches (elevations 2800–2950 m) of an open-pit mine dump slope, and in situ density tests, gradation analyses, and large-scale consolidated drained (CD) triaxial tests were performed. Two PFC2D slope models—one with uniform (spatially averaged) parameters and one with elevation-dependent (layered) parameters—were then established to quantify how spatial heterogeneity affects stability predictions. The results show pronounced vertical heterogeneity: density, porosity, gradation, and shear strength parameters vary systematically among benches, reflecting the combined effects of compaction history and particle segregation during dumping. All specimens exhibited strain hardening and continuous shear contraction, and specimens with a denser, better-graded structure showed higher strength and lower compressibility. The layered model yields a higher factor of safety and shallower, bench-scale slip surfaces, whereas the uniform model underestimates stability and misplaces the critical slip zones. These findings demonstrate that elevation-dependent parameter assignment better represents the heterogeneous failure mechanism of high dump slopes and should be preferred over uniform parameterization in stability analyses of similar waste rock dumps. Full article

Advanced High-Strength Steel (AHSS) exhibits stress-state-dependent competing shear–tensile fracture modes that limit the applicability of conventional ductile fracture criteria based solely on equivalent plastic strain accumulation, such as the Forming Limit Diagram (FLD) approach and the classical Gurson–Tvergaard–Needleman (GTN) model. This paper proposes an extended GTN damage model incorporating Hill’48 anisotropy and the Nahshon–Hutchinson shear mechanism, regulated by a stress-state-dependent weighting function. The experimental program comprised uniaxial tension tests for constitutive calibration, notched plate specimens with shear angles ranging from 0° to 90° (spanning pure shear to tensile–shear stress states), and tension-bending tests. The fracture initiation point was identified from the abrupt load drop on the experimental force–displacement curve and further located in the finite element simulation to extract the corresponding stress-state history. SEM fractography was employed to characterize the microscopic damage mechanisms, revealing a continuous transition from shear-dominated to void-dominated damage at a critical stress triaxiality of approximately 0.35. A weighting function dependent on both stress triaxiality and the normalized Lode angle was formulated to couple void evolution with shear band localization. Following calibration via finite element inverse fitting, the model, implemented as an ABAQUS VUMAT subroutine, successfully reproduced fracture strains and crack paths across stress states ranging from pure shear to high hydrostatic tension. Comparative simulations indicate that this approach yields improved prediction accuracy over the classical GTN model, particularly under mixed-mode conditions, thereby offering a practical numerical tool for analyzing AHSS formability. Full article

Clayey sand is a typical transitional coastal alluvial soil controlled by both coarse-grain friction and fine-grain cementation. Current studies focus mostly on remolded samples, lacking systematic understanding of water-induced structural degradation and quantitative physico-mechanical correlations for natural undisturbed clayey sand. In this work, 74 intact undisturbed specimens (0.5–23.0 m depth) were tested via basic physical tests, one-dimensional consolidation and consolidated-undrained triaxial shear tests. Pearson correlation analysis was performed to establish prediction relationships between routine physical indices and mechanical parameters. Results show the soil is classified as SC clayey sand with 39.70% fines and an average natural water content of 23.17%. Natural water content dominates soil engineering performance, presenting strong linear correlations with dry density and void ratio (|r| = 0.90). Higher water content and void ratio increase compressibility and reduce shear strength. The compression coefficient and compression modulus exhibited a consistent nonlinear relationship, reflecting the inherent linkage between these two compression parameters. Burial depth has little influence on soil properties, and plasticity index only serves for soil classification. Mechanistically, increasing moisture may thicken adsorbed water films, weaken interparticle contact and matric suction, and the fine particle-filled skeleton may further enhance the water sensitivity of the soil. The established prediction models support fast evaluation of soil mechanical behaviors, offering theoretical and practical support for geotechnical design of similar coastal clayey sand strata. Full article

Mechanical properties such as viscoelastic, rheological, and textural properties, particularly adhesiveness and cohesiveness, play a significant role in the optimization of handling, processing and drying of dewatered sludge. However, there is no currently standardized methodology for quantifying these properties, leading researchers to adopt various techniques based on economic feasibility, equipment availability, and research objectives. This review systematically compiles and analyzes the most relevant experimental methodologies for evaluating the mechanical properties of dewatered sewage sludge (DSS). This work presents a general overview of the composition and structure of DSS, followed by a comprehensive bibliometric analysis that revealed literature gaps (particularly in adhesiveness evaluation) and identified regulatory frameworks that incremented interest in researching DSS’ properties in the broader push for sustainability. Consequently, a discussion of the experimental set-ups, data treatment and visualization, advantages and disadvantages, and mathematical models with their physical significance is presented for the different techniques identified. The methods analyzed include oscillatory rheology, penetrometry (cylinder and cone), uniaxial compression tests (TPA), shear testing (e.g., Jenike shear test, Atterberg limit test, direct box shear test, triaxial shear test, unconfined shear test, and vane shear test), tomography and slump tests. By comparing these techniques, this study provides insights into the most appropriate approaches for sludge characterization, emphasizing the need for a unified framework to standardize the evaluation of viscoelastic and textural properties in DSS. Full article