Search Results (2,094)

Cement stabilized macadam (CSM) bases are prone to cracking and void damage under long-term traffic loading and environmental actions, which accelerates structural deterioration. Although grouting is an effective method for treating such concealed defects, laboratory-based evaluation of repair effectiveness remains limited. In this study, field-cored CSM specimens were recombined in a cylindrical mold to simulate four void conditions (1/4, 2/4, 3/4, and 4/4), and repaired using an inorganic cementitious composite grouting material based on ultra-fine cement and high-belite sulphoaluminate cement (HBSAC), and modified with ethylene-vinyl acetate (EVA) latex, wollastonite (WO) whiskers, and polyvinyl alcohol (PVA) fibers. The repair effectiveness was evaluated through ultrasonic testing, capacitance measurement, uniaxial compression with acoustic emission (AE) monitoring, and computed tomography (CT). The results show that the longitudinal wave velocity of all repaired groups increases continuously with curing time, with a maximum increase of 21.98% at 28 days. The normalized capacitance response exhibits clear time- and layer-dependent variation, with the 4/4 group showing the most pronounced spatial heterogeneity. In the uniaxial compression tests, the peak load increases from 181 kN in the control group to 201–286 kN in the repaired groups, while the tensile-related AE event proportion increases from 77.35% in the 1/4 group to 89.38% in the 4/4 group. CT analysis shows that the proportion of micropores smaller than 1 mm³ increases from 66.3% to 82.7%, whereas the proportion of pores larger than 100 mm³ decreases from 46.5% to 21.6% after repair. These results demonstrate that the composite grouting material provides effective filling, structural reconstruction, and mechanical enhancement for void-damaged CSM, and that the proposed multi-source characterization framework is suitable for evaluating grouting repair performance. Full article

To achieve the resource utilization of waste tires and improve the mechanical performance of cemented tailings backfill, rubber–cemented tailings backfill (R-CTB) specimens were prepared with four rubber particle sizes (20-, 40-, 60-, and 80-mesh) and four contents (2%, 4%, 6%, and 8%). A 0% rubber control group was introduced to address the lack of quantitative comparison. Uniaxial compression, digital image correlation (DIC), and scanning electron microscopy (SEM) were used to study mechanical behavior, energy evolution, and microstructural characteristics at 7 and 28 days. Results indicate that strength and elastic modulus first increase then decrease with particle size and decrease with content rise. Compared with the control group, R-CTB shows lower strength but significantly higher ductility and energy dissipation. Finer particles cause strain localization; higher content and finer size increase pores and weaken interfaces. Rubber incorporation transforms failure from brittle to ductile, providing a basis for engineering application. Full article

Deep shale of the Lower Cambrian Qiongzhusi Formation in the Sichuan Basin represents a critical frontier for shale gas exploration in China. However, systematic understanding of the multi-scale links among lamination type, mechanical anisotropy, and fracture complexity remains limited. Based on lamination characteristics and total organic carbon (TOC) content, core samples were classified into four types. Using a multi-scale approach (uniaxial compression, Brazilian splitting, in situ CT scanning, QEMSCAN, and SEM), this study elucidates how lamination structure controls mechanical anisotropy, failure modes, and fracture mechanisms. The novelties of this work are threefold: (1) quantitatively linking specific lamination types (ORM, OPM, PAFC, PAF) to anisotropic mechanical responses; (2) introducing 3D fractal dimensions to evaluate fracture network complexity; and (3) integrating micro- (SEM) and macro-scale tests to reveal the coupled control of weak planes and brittle minerals on fracture propagation. Results indicate that laminated shales exhibit pronounced mechanical anisotropy. Loading parallel to laminations induces tensile splitting along weak planes, significantly reducing strength. Conversely, perpendicular loading generates complex fracture networks of horizontal secondary fractures along laminae and vertical main fractures through the matrix. Furthermore, 3D fractal dimension analysis quantifies fracture network complexity as follows: organic-poor clay-feldspar laminated shale > organic-poor clay-feldspar-calcareous laminated shale > organic-rich massive shale. Microscopic observations confirm that fracture propagation is jointly governed by weak plane systems and brittle mineral content, which collectively determine macroscopic failure patterns. These findings clarify how lamination type controls the laboratory mechanical response and fracture morphology of deep shale and provide a laboratory-scale framework for comparing lamination-related differences in mechanical anisotropy and fracture complexity in the Qiongzhusi Formation. Full article

This study presents a predictive manufacturing framework for customizing the biomechanical response of a 3D printed ergonomic armrest based on relaxed Voronoi metamaterials. A double curved armrest geometry was combined with parametric lattice generation, stereolithography printing in BioMed Elastic 50A resin, uniaxial compression testing of cylindrical lattice specimens, and homogenized finite element simulations using a CT derived forearm model under 15, 30, and 45 N loading. The results showed that both cell size and ligament thickness strongly affected compressive behavior, with smaller cells and thicker ligaments producing higher stiffness and earlier densification. Among the uniform configurations selected for simulation, the E-9-1.5 lattice provided the most balanced response, maintaining contact pressure below about 70 kPa up to 45 N, whereas the stiffer E-7-1.5 configuration exceeded 160 kPa and the E-7-1 configuration surpassed 100 kPa at higher load. Based on these findings, a functionally graded Voronoi concept was developed to combine a more compliant central zone with a stiffer peripheral support region while preserving conformity to the complex armrest boundary. Overall, the results show that relaxed Voronoi lattices offer a computationally efficient route toward anatomically conforming and mechanically tunable cushioning interfaces. Full article

The nominal maximum aggregate size (NMAS) plays a critical role in determining the mechanical performance of cement-stabilized macadam (CSM), yet its meso-mechanical influence mechanism remains insufficiently understood. In this study, three skeleton-dense CSM mixtures with different NMAS values were designed, and a combined experimental–numerical approach was adopted to investigate the macro- and meso-scale mechanical behavior. Uniaxial compression tests and aggregate crushing value tests were conducted to evaluate strength development and load-transfer characteristics, while a three-dimensional discrete element method (DEM) model incorporating realistic aggregate morphology was established to analyze the evolution of contact forces and crack propagation. The results show that increasing NMAS significantly improves the mechanical performance of CSM. Compared with CSM-30, the 7-day compressive strength of CSM-40 and CSM-50 increased by approximately 10.3% and 37.3%, respectively. The stress–strain response indicates that mixtures with larger NMAS exhibit higher stiffness and a higher strain. At the meso-scale, a larger NMAS promotes the formation of a more efficient force-chain network dominated by coarse aggregates. Strong contacts were predominantly carried by aggregates larger than 9.5 mm, and in CSM-50, the proportion of strong contacts in the 37.5–53 mm fraction exceeded 90%, indicating that the largest particles likely form the primary load-bearing skeleton. In addition, increasing NMAS delayed crack initiation, reduced crack propagation rate, and decreased the total number of cracks at failure. These findings demonstrate that macroscopic strength improvement is closely associated with meso-scale optimization of the aggregate skeleton and enhanced load-transfer efficiency. This study provides a mechanistic basis for NMAS selection and gradation optimization in semi-rigid base materials. Full article

Broken gangue in goafs exhibits complex mechanical deformation and seepage evolution under coupled loading and hydraulic action, which directly affects the hydraulic stability and water-hazard prevention of mining engineering. In this study, a systematic investigation was carried out to elucidate the evolution of seepage characteristics in a granular broken-rock assemblage under coupled hydraulic–mechanical loading. Four mono-sized specimen groups with particle-size ranges of 5–10 mm, 10–15 mm, 15–20 mm, and 20–25 mm were prepared. Using a modified rock triaxial–hydraulic testing system, nominal uniaxial compression tests, triaxial compression tests under different moisture conditions, and staged axial loading–seepage coupling tests were conducted. The results indicated pronounced particle-size effects: with increasing particle size, the nominal uniaxial compressive strength decreased (maximum reduction of 41.26%), while the crushing ratio increased (from 0.99% to 28.89%). The compression–densification process exhibited a staged evolution characterized by “slow increase–rapid increase–stable increase.” Water-induced deterioration intensified with increasing water content, and the compressive strength reduction reached 29.8% under saturated conditions. The evolution of seepage behavior was jointly governed by loading rate and particle size. Both pore pressure and pore-pressure gradient increased with loading rate. The permeability–porosity relationship was nonmonotonic, with an inflection occurring at a porosity of approximately 0.30–0.32, accompanied by an order-of-magnitude variation in the Darcy-flow deviation factor, indicating a progressive nonlinear deviation from Darcy behavior. These observations reflected a competitive mechanism involving “compaction-induced flow resistance increase–fragmentation and rearrangement–local channel regeneration.” Numerical simulations performed in COMSOL6.2 further confirmed, at the microscopic level, that the development of preferential local seepage channels and the expansion of stagnant-water zones were the fundamental causes of locally enhanced seepage capacity under an overall compaction background. The findings provide a theoretical basis for understanding water–rock interaction mechanisms in goafs and offer reference for mine water-hazard mitigation and groundwater resource protection. Full article

Accurate classification of rock fracture modes is essential for understanding rock mass instability mechanisms. To address the limitation of traditional acoustic emission (AE) classification methods that treat a single AE signal as a single fracture event, overlooking its composite nature from multiple fracture events and leading to misclassification, this study proposes a novel rock fracture mode classification method based on AE spectral analysis. This study details the development framework, theoretical model, classification criteria, application process, and experimental validation of the new rock fracture mode classification method. Uniaxial compression tests on granite, marble, and limestone, along with rockburst simulation tests on granite, were conducted to validate the classification of fracture modes. In rockburst simulations, shear fracture signals accounted for 48% on average, composite signals 40%, and tensile signals 12%. The method effectively distinguishes multiple fracture events within a single AE signal, accurately classifies fracture modes, and elucidates the dynamic evolution of fracture modes during the rockburst precursor stage, offering significant advantages for rock fracture mode classification and mechanistic insight. Full article

In goafs formed by underground mineral resource extraction, the remaining pillars are often subjected to uniaxial loading at different loading rates, and their mechanical responses and failure mechanisms directly affect the long-term stability of the goafs. This study uses rock-like materials to conduct uniaxial compression tests at loading rates ranging from 0.001 mm/min to 0.05 mm/min, combined with acoustic emission (AE) monitoring, to systematically investigate the effects of loading rate on the mechanical properties, energy distribution, constitutive model, and AE characteristics of the material. The results show that an increase in loading rate significantly enhances the stiffness and strength of the material, promotes a transition in failure mode from a shear–tension composite to tension-dominated, intensifies brittle characteristics, and simultaneously inhibits full crack development and fragments generation. In terms of energy evolution, an increased loading rate enhances the pre-peak total strain energy and elastic strain energy storage but reduces the efficiency of energy dissipation, leading to an intensified mismatch between energy storage and dissipation capacities at peak stress. A damage variable induced by loading rate was proposed, and a damage constitutive model considering the loading rate was established, with the theoretical curves showing good agreement with the experimental data. AE characteristic analysis further reveals that an increase in loading rate causes the crack type to transition from shear-dominated to tension-dominated, and the fluctuating increase in the b-value reflects a reduction in pre-peak fracture scale and a decrease in the degree of material fragmentation. The research findings are expected to deepen the understanding of the damage and failure mechanisms of rock materials under different loading rates, thereby laying a research foundation for the stability assessment of goaf pillars and disaster warning. Full article

As a heterogeneous rock cemented by gravel and matrix, understanding the mechanical behaviour and failure mechanism of conglomerate is of great significance for engineering projects. A three-dimensional grain-based model (3D-GBM) incorporating both microstructural and material heterogeneity of conglomerate is developed based on particle flow code (PFC3D). With the model’s rationality and microscopic parameters validated, the failure process and fracture mechanism of conglomerate under uniaxial and triaxial compression are numerically investigated. The numerical results reveal that the established 3D-GBM can simulate the mechanical behaviour and fracture characteristics of conglomerate. As the confining pressure increases, the failure mode of the specimen transitions from matrix tensile cracking to matrix shear cracking. During the loading process, the microcrack evolution and contact force distribution in the gravel, matrix, and cementation area exhibit pronounced heterogeneity. Confining pressure promotes the fragmentation of gravel and the initiation of shear microcracks. In addition, the effect of gravel size and content on the mechanical behaviour and microcracking characteristics of conglomerate is quantitatively investigated. Variations in gravel size and content influence the distribution of inter-particle contact forces, thereby altering the failure characteristics and mechanical properties of the specimen. Full article

The construction sector is experiencing increasing demand for deep underground structures in urban environments, where excavations frequently intersect fractured aquifers. Such conditions pose significant risks to structural stability and long-term durability due to groundwater inflow and elevated hydrostatic pressures. This study investigates the influence of deep underground construction on fractured aquifer systems using the Abu Dhabi Plaza development in Kazakhstan as a case study. An integrated methodological approach combining hydrogeological monitoring, hydrochemical analysis, and engineering–geological testing was applied. Groundwater levels were monitored using observation wells, while triaxial and uniaxial compression tests were conducted to evaluate the mechanical properties of rock and soil materials. Hydraulic gradients, flow velocities, and hydrostatic pressures were estimated using Darcy’s law and the Boussinesq equation, supported by GIS-based spatial analysis. Groundwater mineralisation is consistently represented in this study by total dissolved solids (TDS), expressed in g/L. The results indicate that groundwater in the Quaternary aquifer is fresh to slightly mineralised, with TDS ranging from 0.47 to 1.50 g/L, whereas groundwater in the fractured Ordovician aquifer exhibits a more stable hydrochemical regime with TDS values of 0.72–0.73 g/L. Statistical analysis identifies two primary controls on groundwater chemistry: (i) natural geochemical processes associated with water–rock interaction and (ii) technogenic influences related to urban activities. Hydrodynamic calculations indicate a hydraulic gradient of approximately 0.136, a filtration velocity of about 0.35 m/day, well discharge reaching 0.11 L/s, and hydrostatic pressure ranging from 1.45 to 2.81 atm. Groundwater drawdown caused by excavation dewatering reached 29–30 m. The findings demonstrate that groundwater inflow is primarily controlled by fracture-controlled permeability and structural heterogeneity within the aquifer system. These results highlight the importance of integrated hydrogeological and hydrochemical assessment, in which TDS serves as the principal quantitative indicator of groundwater mineralisation, for the effective management of groundwater-related risks during deep underground construction. Full article

In engineered cementitious composites (ECCs), the use of fine quartz sand is associated with high cost and is unfavorable for reducing ECC shrinkage. Moreover, the mining and processing of fine quartz sand impose negative environmental impacts. At the same time, the polyethylene (PE) or polyvinyl alcohol (PVA) fibers added to ensure ECC ductility are expensive, which limits the widespread application of ECCs. With the aim of waste utilization and cost reduction while improving efficiency, this study employs geopolymer aggregate (GPA) as an alternative to fine quartz sand and partially replaces PE fibers with steel fibers to develop an economical and environmentally friendly geopolymer aggregate ECC. Six groups of ECC specimens with different mix proportions were designed and tested under uniaxial compression, flexural loading, and uniaxial tension. Different aggregate types (fine quartz sand and geopolymer aggregate) and volume fraction ratios of PE fibers to steel fibers (0:2.0, 0.5:1.5, 1.0:1.0, 1.5:0.5, and 2.0:0) were adopted to investigate their effects on mechanical properties, microstructural characteristics, and material sustainability. The experimental results reveal the failure process and deformation characteristics of the ECCs at different loading stages. The results indicate that geopolymer aggregate, owing to its lower stiffness and fracture energy, can promote multiple cracking behavior in ECCs. Although the complete replacement of quartz sand with porous GPA initially causes a slight reduction in the compressive and flexural strengths of the matrix, the hybridization strategy—partially replacing PE fibers with steel fibers—effectively compensates for this strength loss while maintaining excellent ductility. By comparing sustainability indicators with those of conventional ECCs, the results demonstrate that hybrid fiber geopolymer aggregate ECCs can effectively reduce material costs and carbon dioxide emissions. These findings verify the sustainability of producing green ECCs using industrial solid waste as an aggregate and provide guidance for the application of environmentally friendly geopolymer aggregate ECCs. Full article

Understanding the mechanism of fracture evolution in underground stacked coal–rock composite structures is crucial for the accurate prediction and prevention of mine disasters. In this study, the fracture evolution characteristics of a coal–rock–coal (CRC) composite structure under uniaxial compression were monitored and studied using three-dimensional digital image correlation and an RA-AF method based on acoustic emission (AE) parameters. The fracture mechanisms of the CRC composites were revealed based on experimental results and theoretical analyses. The results indicate that the compressive strength and elastic modulus of CRC composites increase with the thickness of the rock layer and the strength of the coal and rock. Owing to the differences in the thickness and strength characteristics of coal and rock in CRC composites, three fracture modes were identified. The fracture of the CRC composite structure is determined by the stress redistribution and energy release, which are dominated by the mechanical and size effects of coal and rock. Full article

Moderate thermal exposure can significantly influence the mechanical behavior of volcanic rocks by inducing microcrack development and altering crack network characteristics. However, quantifying such damage processes remains challenging when relying solely on conventional mechanical parameters. In this study, the evolution of crack network complexity in andesite and andesitic–basaltic rocks subjected to moderate thermal exposure (200 °C) is investigated using fractal analysis integrated with mechanical and mineralogical observations. Six core specimens were tested under uniaxial compression, including three natural specimens and three specimens thermally treated at 200 °C prior to loading. After failure, crack surfaces were digitized and fractal dimensions (D) were calculated using the box-counting method. Petrographic observations and X-ray powder diffraction (XRPD) analyses were conducted to characterize the mineralogical composition and microstructural features controlling crack development. The results indicate that thermal exposure primarily reduces rock stiffness rather than peak strength. While the uniaxial compressive strength (UCS) of two specimens remains nearly unchanged after heating, the elastic modulus (E) decreases in all thermally treated specimens. Mineralogical observations reveal a heterogeneous volcanic fabric dominated by plagioclase and pyroxene within a fine-grained groundmass, with secondary calcite phases occurring in veins and pocket fillings. Fractal analysis shows generally lower D values in thermally treated specimens, suggesting crack redistribution and coalescence rather than increased network complexity, consistent with the observed reduction in stiffness and a tendency toward more ductile deformation behavior. Full article

To systematically investigate the combined effects of moisture content, confining pressure, and loading rate on the mechanical properties of weakly cemented soft rock, this study focuses on the Jurassic coal measures from the Hoxtolgay coalfield in Xinjiang. A series of uniaxial and triaxial compression tests were conducted under varying moisture states, loading velocities, and confining pressures. Complementary X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brazilian splitting tests were performed to analyze the microstructural evolution and tensile failure characteristics. The experimental results demonstrate that moisture content acts as the primary governing factor for mechanical degradation; increased hydration promotes clay mineral swelling and attenuates inter-granular cementation, leading to a continuous reduction in both compressive and tensile strengths, as well as the elastic modulus. Conversely, confining pressure consistently enhances these macroscopic mechanical parameters by restricting lateral deformation. While the loading rate alters the mechanical response, its impact is secondary compared to the definitive effects of moisture and stress constraints. Furthermore, by utilizing established stress–strain-based indices, the study quantitatively evaluates the brittleness characteristics, confirming that hydration fundamentally drives the rock mass from a brittle state toward ductility. This research elucidates the coupled degradation mechanisms of highly sensitive soft rock, providing a theoretical foundation for stability design and risk assessment in underground geotechnical engineering. Full article

This study evaluated how the ice dosage and water-to-binder (W/B) ratio affect the uniaxial response of roller-compacted concrete (RCC). Three levels of W/B, 0.40, 0.45, and 0.50, were examined. For every W/B level, five proportions of ice substitution, namely 0%, 25%, 50%, 75%, and 100%, were adopted in the mixing process, producing 15 distinct mixture categories. In each group, three prismatic specimens and three cubic specimens were fabricated for compression testing. Uniaxial compression experiments were conducted to determine the failure characteristics and full stress–strain behavior, whereas scanning electron microscopy (SEM) was used to analyze the internal microstructure. Based on the test data, a constitutive expression describing RCC under uniaxial compression was established. The experimental results showed that, within the investigated range, compressive strength displayed a rise-then-fall trend as the W/B ratio increased from 0.40 to 0.50, and the best overall performance was obtained at W/B = 0.45. Microscopic examination further confirmed that this ratio produced a denser and more integrated internal structure. In addition, the role of ice dosage in governing the mechanical response of RCC varied significantly with the W/B level. The outcomes of this study provide useful support for RCC mix proportion optimization and practical engineering design. Full article