Search Results (1,163)

This study investigates the uniaxial compression failure of magnesium-based wood-like material (MWM) prisms (100 × 100 × 300 mm³) using digital image correlation (DIC). The results revealed an average compressive strength of 8.76 MPa and a dominant failure mode with Y-shaped or inclined penetrating cracks. A novel piecewise constitutive model was established, combining a quartic polynomial and a rational fraction, demonstrating high fitting accuracy. Critically, the proportional limit was identified to be very low (20–35% of peak stress), attributed to early-stage damage from fiber–matrix interfacial defects. DIC analysis quantitatively distinguished dual crack initiation modes, pure mode I (occurring at ≈100% peak load) and mixed mode I/II (initiating earlier at 90.02% peak load), demonstrating that tensile shear coupling accelerates failure. These findings provide critical mechanistic insights and a reliable model for optimizing MWM in sustainable construction. Future work will explore the material’s behavior under multiaxial loading. Full article

The long-term stability of grout-reinforced fractured rock masses in acidic groundwater environments after tunnel fires is critical for the safe operation of underground engineering. In this study, grouting reinforcement tests were performed on fractured diorite specimens using a high-strength fast-anchoring agent (HSFAA), and their mechanical degradation and microstructural evolution mechanisms were investigated under coupled high-temperature (25–1000 °C) and acidic corrosion (pH = 2) conditions. Multi-scale characterization techniques, including uniaxial compression strength (UCS) tests, X-ray computed tomography (CT), scanning electron microscopy (SEM), three-dimensional (3D) topographic scanning, and X-ray diffraction (XRD), were employed systematically. The results indicated that the synergistic thermo-acid interaction accelerated mineral dissolution and induced structural reorganization, resulting in surface whitening of specimens and decomposition of HSFAA hydration products. Increasing the prefabricated fracture angles (0–60°) amplified stress concentration at the grout–rock interface, resulting in a reduction of up to 69.46% in the peak strength of the specimens subjected to acid corrosion at 1000 °C. Acidic corrosion suppressed brittle disintegration observed in the uncorroded specimens at lower temperature (25–600 °C) by promoting energy dissipation through non-uniform notch formation, thereby shifting the failure modes from shear-dominated to tensile-shear hybrid modes. Quantitative CT analysis revealed a 34.64% reduction in crack volume (V_ca) for 1000 °C acid-corroded specimens compared to the control specimens at 25 °C. This reduction was attributed to high-temperature-induced ductility, which transformed macroscale crack propagation into microscale coalescence. These findings provide critical insights for assessing the durability of grouting reinforcement in post-fire tunnel rehabilitation and predicting the long-term stability of underground structures in chemically aggressive environments. Full article

To overcome wellbore instability problems in deep coalbed gas reservoirs in the Ordos Basin, drilling fluid additives were evaluated and a drilling fluid system was designed. According to the SEM and CT analysis results, there were not only face and butt cleats in the coal rock but also bedding and layered fractures. Potassium chloride (KCl) and Potassium formate (HCOOK) drilling fluid systems were formulated. The recovery rate of shale and coal rock cuttings reached 99%, and the linear swelling rates for coal rock in both types of drilling fluid were less than 0.18%. Measured with a servo-controlled compression frame at a loading rate of 1 mm/min, the uniaxial compression strength of coal rock was 11.74 MPa, and it was 9.13 MPa and 10.35 MPa after immersion in KCl and HCOOK drilling fluid, respectively. This indicates that both systems have good inhibition properties. The invasion depth in packed sand was 15.5 mm for KCl drilling fluid and 8 mm for HCOOK drilling fluid, demonstrating good sealing performance by the systems. Compared to KCl drilling fluid, the HCOOK system exhibited better inhibition and sealing performance. After the removal of the 10 mm deep invasion section of drilling fluid, the permeability of the coal rock recovered by more than 90%, and the drilling fluid caused minimum damage to the reservoir. The optimized drilling fluid exhibits excellent sealing and inhibition capabilities, making it highly effective in addressing wellbore stability challenges in carbonaceous mudstone formations at 4000 m in depth in the deep coalbed methane reservoirs of the Ordos Basin. Full article

This paper discusses whether the principal response features of composites subjected to fatigue loadings, including residual strength and lifetime statistics under variable amplitude (VA) loadings, can be resolved based on constant amplitude (CA) fatigue life data. The approach is based on the strength-residual strength-life equal-rank assumption (SRSLERA), providing a statistical correspondence between the static strength, residual strength, and fatigue life distribution functions under CA loadings. Under VA loadings, the strength degradation progression and then the fatigue lifetime are calculated by dividing the loading spectrum into a sequence of CA block loadings of given extents (including one cycle), and assuming that the strength at the end of a generic block loading equals the strength at the start of the consecutive one, namely the equivalent residual strength assumption (ERSA). The consequences of SRSLERA and ERSA are first discussed by re-elaborating a series of uniaxial, statistically sound CA residual strength and fatigue life data obtained under different loading ratios, R, ranging from pure tension to mixed tension–compression to pure compression. It is shown that the static strength Weibull’s shape and scale parameters, as well as the fatigue formulation parameters recovered under pure compression or tension loadings, represent the fingerprint of composite materials subjected to fatigue and characterize their uniqueness. The residual strength statistics, fatigue probability density functions (PDFs), and constant life diagram (CLD) construction are theoretically reported. Then, based on ERSA, the statistical lifetimes under VA loadings and the cycle-by-cycle damage progressions of block repeated loadings are analyzed, and a residual strength-based damage rule is compared to Miner’s rule. Full article

This study elucidated the evolution and catastrophic failure mechanisms of concrete’s mechanical properties under high-temperature and moisture-coupled environments. Specimens underwent hygrothermal shock simulation via constant-temperature drying (100 °C/200 °C, 4 h) followed by water quenching (20 °C, 30 min). Uniaxial compression tests were performed using a uniaxial compression test machine with synchronized multi-scale damage monitoring that integrated digital image correlation (DIC), acoustic emission (AE), and infrared thermography. The results demonstrated that hygrothermal coupling reduced concrete ductility significantly, in which the peak strain decreased from 0.36% (ambient) to 0.25% for both the 100 °C and 200 °C groups, while compressive strength declined to 42.8 MPa (−2.9%) and 40.3 MPa (−8.6%), respectively, with elevated elastic modulus. DIC analysis revealed the temperature-dependent failure mode reconstruction: progressive end cracking (max strain 0.48%) at ambient temperature transitioned to coordinated dual-end cracking with jump-type damage (abrupt principal strain to 0.1%) at 100 °C and degenerated to brittle fracture oriented along a singular path (principal strain band 0.015%) at 200 °C. AE monitoring indicated drastically reduced micro-damage energy barriers at 200 °C, where cumulative energy (4000 mV·ms) plummeted to merely 2% of the ambient group (200,000 mV·ms). Infrared thermography showed that energy aggregation shifted from “centralized” (ambient) to “edge-to-center migration” (200 °C), with intensified thermal shock effects in fracture zones (ΔT ≈ −7.2 °C). The study established that hygrothermal coupling weakens the aggregate-paste interfacial transition zone (ITZ) by concentrating the strain energy along singular weak paths and inducing brittle failure mode degeneration, which thereby provides theoretical foundations for fire-resistant design and catastrophic failure warning systems in concrete structures exposed to coupled environmental stressors. Full article

Conducted against the background of a highway project in Zhuji, Zhejiang Province, this study investigates the deterioration behavior of tuffaceous sandstone under the combined action of acid rain and wet–dry cycles. Laboratory experiments were carried out to explore its mechanical properties and damage evolution mechanisms. Standard specimens prepared from field rock samples were subjected to wet–dry cycles using an acidic solution with pH ≈ 5.0. By integrating uniaxial compression, Brazilian splitting, ultrasonic wave monitoring, and acoustic emission techniques, a systematic analysis was carried out to evaluate the degradation of mechanical parameters, the evolution of wave velocity, and the underlying damage and failure mechanisms. The results indicate the following: (1) With the increase in the number of acidic dry–wet cycles, the compressive and tensile strengths of tuffaceous sandstone decrease significantly; the deterioration rate first decreases and then increases, with 150 cycles identified as the critical threshold for strength deterioration, beyond which the material enters a stage of rapid degradation. (2) The evolution of ultrasonic wave velocity shows a significant negative correlation with strength deterioration, and the attenuation rate of wave velocity exhibits a consistent trend with the number of cycles as that of strength deterioration. (3) Acoustic emission RA-AF analysis reveals that tensile cracks in tuffaceous sandstone gradually decrease while shear cracks slowly increase, with cracks primarily developing along the weakly cemented tuffaceous areas. (4) This study established fitting formulas for the deterioration of compressive and tensile strengths with the number of cycles, as well as a damage calculation formula based on changes in wave velocity. (5) This study provides practical support for mitigating natural disasters, such as slope instability, induced by this type of combined weathering. Full article

Lattice structures have been widely studied in various fields due to their lightweight and high-energy absorption capabilities. In this study, we propose the use of lattice structures in the design of sports protective equipment for contact sports athletes. A total of six specimens were additively manufactured either with a bending-dominated rhombic dodecahedron (RD) structure or stretch-dominated re-entrant (RE) structure. Elastic resin was used to investigate the specimens’ compressive strength and energy absorption, impact reduction, and flexural properties in comparison with those of conventional foam and rigid polyethylene (PU). Despite having a lower relative density, the RE structure exhibits greater stiffness, showing up to 40% greater hardness and averaging 30.5% higher bending rigidity compared with the RD structure. However, it unexpectedly shows less stability and strength under uniaxial loading, which is 3 to 6 times weaker when compared with the non-auxetic RD structure. Although conventional PU has higher loading than 3D-printed lattices, the lattice shows excellent bendability, which is only 1.5 to 3 times stiffer than that of foam. The 3D-printed lattice in this study shows an optimal improvement of 43% in terms of impact absorption compared with foam and a 2.3% improvement compared with PU. Amongst the six different unit cell dimensions and structures studied, the RD lattice with a cell size of 5 mm is the most promising candidate; it has superior elasticity, compressive strength, and impact resistance performance whether it is under low- or high-impact conditions. The findings of this study provide a basis for the development of 3D-printed lattice sports protective chest equipment, which is more comfortable and offers improved protection for contact sports players. Full article

This study experimentally investigates the mechanical and dynamic hygrothermal behavior of compressed earth block (CEB) walls subjected to simulated climatic cycles representative of a tropical humid environment. Four formulations were tested: raw soil (D0), soil with kenaf fibers (DF), soil with fibers and cement (DFC), and soil with fibers, cement, and slag (DFCL). Performance was assessed in an instrumented bi-climatic cell, enabling the determination of thermal and hygroscopic attenuation factors and time lags, complemented by standardized uniaxial compression and three-point bending tests. DFCL achieved a compressive strength of about 10 MPa, nearly twice that of DF (~6 MPa), exceeding the threshold required for buildings up to R + 1. Regarding hygrothermal behavior, DFCL exhibited the highest thermal attenuation factor (2.24) and a hygroscopic attenuation factor of 2.05, with corresponding time lags of ~0.9 h (thermal) and ~1.1 h (hygroscopic). These results highlight superior thermal inertia and moisture regulation, well suited to the constraints of tropical humid climates. Overall, the findings confirm the potential of kenaf fiber-reinforced cement–slag stabilized CEBs as a sustainable construction solution, particularly for load-bearing walls in hot and humid regions. In addition to technical performance, DFCL also offers environmental and economic advantages, as the use of local fibers and slag reduces Portland cement consumption and costs, reinforcing its sustainability potential in tropical contexts. Full article

Argillaceous slate (AS) is a typical metamorphic rock with well-developed bedding, widely distributed globally. Its bedding structure significantly impacts slope stability assessment, and the challenges associated with slope anchoring and support arising from bedding characteristics have become a focal point in the engineering field. In this study, with bedding dip angle as the key variable, mechanical tests such as uniaxial compression, triaxial compression, direct shear, and Brazilian splitting tests were conducted on AS. Additionally, field anchoring grouting diffusion tests on AS slopes were carried out. The aim is to investigate the basic mechanical properties of AS and the grout diffusion law under different bedding dip angles. The research results indicate that the bedding dip angle has a remarkable influence on the failure mode, stress–strain curve, and mechanical indices such as compressive strength and elastic modulus of AS specimens. The stress–strain curves in uniaxial and triaxial tests, as well as the stress-displacement curve in the Brazilian splitting test, all undergo four stages: crack closure, elastic deformation, crack propagation, and post-peak failure. As the bedding dip angle increases, the uniaxial and triaxial compressive strengths and elastic modulus first decrease and then increase, while the splitting tensile strength continuously decreases. The consistency of the bedding in AS causes the grout to diffuse in a near-circular pattern on the bedding plane centered around the borehole. Among the factors affecting the diffusion range of the grout, the bedding dip angle and grouting angle have a relatively minor impact, while the grouting pressure has a significant impact. A correct understanding and grasp of the anisotropic characteristics of AS and the anchoring grouting diffusion law are of great significance for slope stability assessment and anchoring design in AS areas. Full article

To investigate the mechanism by which the rheological properties of drilling fluids affect the stability of the wellbore in brittle mud shale, this study systematically examines the influence of drilling fluids with different rheological properties on the hydration dispersion and rock strength of brittle mud shale through a series of laboratory experiments, including thermal rolling tests and uniaxial compressive strength tests on core samples. The results reveal that for weakly dispersible brittle mud shale, the rheological properties of drilling fluids have a minor effect on hydration dispersion, with rolling recovery rates consistently above 90%. However, the rheological properties of drilling fluids significantly influence the strength of brittle mud shale, and this effect is coupled with multiple factors, including rock fracture intensity index, soaking time, and confining pressure. Specifically, as the viscosity of the drilling fluid increases, the reduction in rock strength decreases; for instance, at 5 MPa confining pressure with an FII of 0.46, the strength reduction after 144 h was 69.8% in distilled water (from an initial 133.2 MPa to 40.2 MPa) compared to 36.3% with 3# drilling fluid (from 133.2 MPa to 88.7 MPa, with 100 mPa·s apparent viscosity). Both increased soaking time and confining pressure exacerbate the reduction in rock strength; a 5 MPa confining pressure, for example, caused an additional 60.9% strength reduction compared to 0 MPa for highly fractured samples (FII = 0.46) in distilled water after 144 h. Rocks with higher fracture intensity indices are more significantly affected by the rheological properties of drilling fluids. Based on the experimental results, this study proposes a strength attenuation model for brittle mud shale that considers the coupled effects of fracture intensity index, soaking time, and drilling fluid rheological properties. Additionally, the mechanism by which drilling fluid rheological properties influence the strength of brittle mud shale is analyzed, providing a theoretical basis for optimizing drilling fluid rheological parameters and enhancing the stability of wellbores in brittle mud shale formations. Full article

The response of the microscopic structure and macroscopic mechanical parameters of SRM under F–T cycles is a key factor affecting the safety and stability of engineering projects in cold regions. In this study, F–T tests, EIS, and uniaxial compression tests were conducted on SRM. The construct equivalent model of different conductive paths based on EIS was constructed. A peak strength prediction model was developed using characteristic parameters derived from the equivalent models, thereby revealing the mechanism by which F–T cycles influenced both microscopic structure and macroscopic strength. The results showed that with increasing cycles, both $R_{CP}$ and $R_{CPP}$ exhibited an exponential decreasing trend, whereas C_DSRP and D_f increased exponentially. Peak strength and peak secant modulus decreased exponentially, but peak strain increased exponentially. The expansion and interconnection of pores with different radii within $CPP$ and $CP$ caused smaller pores to evolve into larger ones while generating new pores, which led to a decline in $R_{CPP}$ and $R_{CP}$. Moreover, this expansion enlarged the soil–rock contact area by connecting adjacent gas-phase pores and promoted the transformation of $CSRPP$ into $DSRPP$, enhancing the parallel-plate capacitance effect and resulting in an increase in $C_{DSRP}$. Moreover, the interconnection increased the roughness of soil–soil and soil–rock contact surfaces, leading to a rising trend in $D_f$. The combined influence of $C_{DSRP}$ and $D_f$ yielded a strength prediction model with higher correlation than a single factor, providing more accurate predictions of UCS. However, the increases in $C_{DSRP}$ and $D_f$ induced by F–T cycles also contributed to microscopic structure damage and strength deterioration, reducing the load-bearing capacity and ultimately causing a decline in UCS. Full article

The surrounding rocks of roadways are typically subjected to cyclic loading–unloading stress states in underground engineering. In addition, cyclic loads are discontinuous under real working conditions, usually while loading rock mass in a cycle–intermission–cycle manner. Based on the XTDIC 3D (XTOP Three-dimensional Digital Image Correlation) full-field strain measurement system and AE (Acoustic Emission) system, the work performed uniaxial cyclic loading–unloading tests with constant-pressure durations of 0, 0.5, 2, and 6 h. The purpose was to investigate the damage degradation mechanism of sandstone under multi-stage equal-amplitude intermittent cyclic loading and unloading. The results are as follows. (1) As the constant-pressure duration increased, the uniaxial compressive strength of sandstone samples decreased, along with a decline in elastic modulus and a deterioration in stiffness and deformation recovery capacity. (2) The evolution of deformation localization zones became more intense in sandstone samples during cyclic loading and unloading with the increased constant-pressure duration. The maximum principal strain field became more active at failure. Sandstone samples exhibited shear failure accompanied by spalling failure and an increased failure degree. (3) As the constant-pressure duration increased, the damage variable of sandstone samples increased, indicating that the constant-pressure stage promoted the damage degradation of sandstone samples. The above results reveal the damage degradation mechanism of sandstone under multi-stage equal-amplitude intermittent cyclic loading and unloading, which is of significant importance for maintaining the safety of underground engineering. Full article

With the deepening implementation of the coordinated development strategy for energy exploitation and ecological conservation, green coal mining technology has become a critical pathway to achieve balanced resource development and environmental protection. This study investigates the stress field evolution and dynamic fracture propagation mechanisms in overlying strata during shallow coal seam mining in the Shenfu mining area. By employing a multidisciplinary approach combining triaxial compression tests (0–15 MPa confining pressure), scanning electron microscopy (SEM) microstructural characterization, elastoplastic theoretical modeling, and FLAC3D numerical simulations, the synergistic failure mechanisms of overlying strata were systematically revealed. Gradient-controlled triaxial tests demonstrated significant variations in stress-strain responses across lithological types. Notably, Class IV sandstone exhibited exceptional uniaxial compressive strength of 106.7 MPa under zero confining pressure, surpassing the average strength of Class I–III sandstones (86.2 MPa) by 23.6%, attributable to its highly compacted grain structure. A nonlinear regression-derived linear strengthening model quantified that each 1 MPa increase in confining pressure enhanced axial peak stress by 4.2%. SEM microstructural analysis established critical linkages between microcrack networks/grain-boundary slippage at the mesoscale and macroscopic brittle failure patterns. Numerical simulations demonstrated that strata failure manifests as tensile-shear composite fractures, with lateral crack propagation inducing bed separation spaces. The stress field exhibited spatiotemporal heterogeneity, with maximum principal stress concentrating near the initial mining cut during early excavation. Fractures propagated obliquely at angles of 55–65° to the horizontal plane in an ‘inverted V’ pattern from the goaf boundaries, extending vertically 12–18 m before transitioning to the bent zone, ultimately forming a characteristic three-zone structure. Experimental and simulated vertical stress distributions showed minimal deviation (≤2.8%), confirming constitutive model reliability. This research quantitatively characterizes the spatiotemporal synergy of strata failure mechanisms in ecologically vulnerable northwestern China, proposing a confining pressure-effect quantification model for support parameter optimization. The revealed fracture dynamics provide critical insights for determining ecological restoration timelines, while establishing a novel theoretical framework for optimizing green mining systems and mitigating ecological damage in the Shenfu mining area. Full article

Frozen ground regions have recently experienced increasing construction activity due to the vast undeveloped resources they contain. However, frozen soils exhibit thermal and mechanical properties that differ substantially from those of temperate soils, leading to a range of engineering challenges. This study investigates the influence of organic matter content on the freezing behavior of soils through a series of laboratory experiments and machine learning (ML) modeling. Soil samples were collected from Alberta, Canada, and Gangwon Province, South Korea, and their organic matter contents were adjusted using the loss-on-ignition method combined with peat moss addition. Standard Proctor compaction tests and uniaxial compression tests under subzero conditions were performed to evaluate compaction characteristics and strength development. The unfrozen water content was measured at different subzero temperatures to assess thermal and hydraulic responses. The resulting experimental dataset was then used to develop ensemble ML models—random forest (RF) and extreme gradient boosting (XGB)—for predicting unfrozen water content. The results indicate that higher organic matter contents reduce compaction efficiency, increase residual unfrozen water content, and influence strength development under freezing conditions. Both RF and XGB achieved high predictive accuracy, demonstrating their potential as reliable tools for evaluating the freezing behavior of organic soils. Full article

To meet the demand for simulative materials exhibiting suitable hydraulic characteristics in geomechanical model tests, this research developed a type of simulative material using iron powder, quartz sand, and barite powder as aggregates, white cement as binder, and silicone oil as additive. An orthogonal experimental design L₁₆(4⁴) was employed to prepare 16 distinct mix proportions. Advanced statistical methods, including range analysis, residual analysis, Pearson correlation analysis, and multiple regression performed with SPSS 27.0.1, were applied to analyze the influence of four factors—aggregate-to-cement ratio (A), water–cement ratio (B), silicone oil content (C), and moisture content (D)—on physical and mechanical parameters such as density, uniaxial compressive strength, elastic modulus, angle of internal friction, and permeability coefficient. Range analysis results indicate that the aggregate-to-cement ratio serves as the primary controlling factor for density and elastic modulus; moisture content exerts the most significant effect on compressive strength and permeability; while the water–cement ratio is the dominant factor influencing the internal friction angle. Empirical formulas were established through multiple regression to quantitatively correlate mix proportions with material properties. The resulting similitude materials cover a wide range of mechanical and hydraulic parameters, satisfying the requirements of large-scale physical modeling with high similitude ratios. The proposed equations allow efficient inverse design of mixture ratios based on target properties, thereby supporting the rapid preparation of simulative materials for advanced model testing. Full article