Search Results (437)

In tunnel blasting, an analytical solution for dynamic stress in the surrounding rock of adjacent tunnels is critical for dynamic response analysis, mechanical evaluations, and crack propagation control. Previous studies on stress field analytical solutions primarily modeled rock as a linear elastic material, focusing mainly on the P-wave effects from instantaneous detonation. Based on Heelan’s short cylindrical cavity model, this paper derives an analytical solution for blast-induced dynamic stresses in adjacent tunnel rock, incorporating both induced SV-waves and a rock mass damage factor through rigorous theoretical analysis. Numerical case studies and field measurements were used to analyze stress propagation during tunnel blasting, and theoretical results were compared with measured data. The key findings were as follows: Radial stress > axial stress > hoop stress. All three stresses decay with increasing distance and damage factor, following an inversely proportional relationship with distance. Radial stress decays faster than axial and hoop stresses. Stress also decays exponentially over time, with the peak occurring after the transverse wave arrival. The theoretical results show approximately 10% deviation from the existing empirical formulas, while field measurements closely match the theoretical model, showing consistent stress trends and an average error of 7.02% (radial), 7.56% (axial) and 7.05% (hoop), confirming the reliability of the proposed analytical solution. Full article

Crack initiation, propagation, and slippage serve as the key mesoscopic mechanisms contributing to the deterioration of deep tunnel surrounding rocks. In this study, a secondary anisotropy of deep tunnels surrounding rocks was proposed: The axial-displacement constraint of deep tunnels forces cracks in the surrounding rock to initiate, propagate, and slip in planes parallel to the tunnel axial direction. These cracks have no significant effect on the axial strength of the surrounding rock but significantly reduce the tangential strength, resulting in the secondary anisotropy. First, the secondary anisotropy was verified by a hybrid stress–strain controlled true triaxial test of sandstone specimens, a CT 3D (computed tomography three-dimensional) reconstruction of a fractured sandstone specimen, a numerical simulation of heterogeneous rock specimens, and field borehole TV (television) images. Subsequently, a novel SSA (strain-softening and secondary anisotropy) constitutive model was developed to characterise the secondary anisotropy of the surrounding rock and developed using C++ into a numerical form that can be called by FLAC^3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). Finally, effects of secondary anisotropy on a deep tunnel surrounding rock were analysed by comparing the results calculated by the SSA model and a uniform strain-softening model. The results show that considering the secondary anisotropy, the extent of strain-softening of the surrounding rock was mitigated, particularly the axial strain-softening. Moreover, it reduced the surface displacement, plastic zone, and dissipated plastic strain energy of the surrounding rock. The proposed SSA model can precisely characterise the objectively existent secondary anisotropy, enhancing the accuracy of numerical simulations for tunnels, particularly for deep tunnels. Full article

During centralizer hydroforming, internal pressure and axial feed critically influence the forming outcome. Insufficient feed causes excessive thinning and cracking, while excessive feed causes thickening and wrinkling. Achieving uniform wall thickness necessitates careful design of the pressure and feed curves. Using max/min wall thickness as objectives and key control points on these curves as variables, the study integrated Non-dominated Sorting Genetic Algorithm (NSGA-II), Multi-Objective Particle Swarm Optimization (MOPSO), Neighborhood Cultivation Genetic Algorithm (NCGA), and Archive-based Micro Genetic Algorithm (AMGA) with LS-DYNA to automatically optimize loading paths. The results demonstrate the following: ① NSGA-II, NCGA, and AMGA successfully generated optimized paths; ② NSGA-II and AMGA produced larger sets of higher-quality Pareto solutions; ③ AMGA required more iterations for satisfactory Pareto sets; ④ MOPSO exhibited a tendency towards premature convergence, yielding inferior results; ⑤ Multi-objective optimization efficiently generated diverse Pareto solutions, expanding the design space for process design. Full article

This study investigates how different longitudinal steel rebars influence the flexural performance and cracking mechanisms of reinforced ultra-high-performance concrete (UHPC) beams, combining axial tensile tests using acoustic emission monitoring with standard four-point bending tests. A series of experimental assessments on the flexural behavior of UHPC beams reinforced with various types of longitudinal reinforcement was conducted. The types of longitudinal reinforcement mainly encompassed HRB 400, HRB 600, and NPR steel rebars. The test results revealed that the UHPC beams reinforced with the three types of longitudinal steel rebar exhibited distinctly different failure modes. Compared to the single dominant crack failure typical of UHPC beams reinforced with HRB 400 steel rebars, the beams using HRB 600 rebars exhibited a tendency under balanced failure conditions to develop fewer main cracks (typically two or three). Conversely, the UHPC beams incorporating NPR steel rebars exhibited significantly more cracking within the pure bending zone, characterized by six to eight uniformly distributed main cracks. Meanwhile, the HRB 600 and NPR steel rebars effectively upgraded the flexural load-bearing capacity and deformation ability compared to the HRB 400 steel rebars. By integrating the findings from the direct tensile tests on reinforced UHPC, aided by acoustic emission source location, this research specifically highlights the damage mechanisms associated with each rebar type. Full article

As a part of the mining-induced stress redistribution process during coal mining, the repeated loading and unloading process with increasing peak stresses will cause more severe deformation and damage to mining roadways, which is different from the findings in other underground engineering practices. Consequently, cyclic triaxial compression tests with increasing amplitudes were carried out to investigate the mechanical behavior, acoustic emission (AE) characteristics, and damage evolution of coal materials. It is found that peak deviatoric stress and axial residual strain at the failure of coal specimens increase with increasing confining pressures, while the changes in circumferential strain are not obvious. Moreover, the failure patterns of coal specimens exhibit shear failure due to the constraint of confining pressures while some local tensile cracks occur near the shear bands at both ends of the specimens. After that, the damage evolution of coal specimens was analyzed against the regularity of AE counts and energies to develop a damage evolution model. It is concluded that the damage evolution model can not only quantify the deformation and failure process of the coal specimens under cyclic loads with increasing amplitudes but also takes into account both the initial damage due to natural defects and the induced damage by the cyclic loads in previous cycles. Full article

This article considers the effect of constant and variable Poisson’s ratio on cracking in concrete and rock specimens under uniaxial compression using mechanical systems modeling methods. The article presents an analysis of the data confirming the increase in Poisson’s ratio under specimen loading. A system of equations for modeling the effect of Poisson’s ratio on cracking under uniaxial compression is proposed. The comparison showed that the model with a constant Poisson’s ratio predicts a thickness of the surface layer with cracks that is underestimated by approximately 10%. In practice, this means that the model with a constant Poisson’s ratio underestimates the risk of failure. A technique for analyzing random deviations of Poisson’s ratio from the variable mathematical expectation is proposed. The comparison showed that the model with a variable Poisson’s ratio leads to results that are more cautious, i.e., it does not potentially overestimate the safety factor. The model predicts an increase in uniaxial compression strength when using external reinforcement. An equation is proposed for determining the required wall thickness of a conditional reinforcement shell depending on the axial compressive stress. The study contributes to understanding the potential vulnerability of load-bearing structures and makes a certain contribution to increasing their reliability. Full article

Pores of different sizes and quantities are formed during the molding process of recycled aggregate concrete (RAC). However, few studies have examined the individual and combined effects of porosity and mesoscale pore size (pore size) on the axial compressive mechanical properties of RAC. In this study, the influence of porosity and pore size on the axial compressive mechanical behavior of RAC was examined by incorporating expanded polystyrene (EPS) particles to create prefabrication of pores. Additionally, crack development influenced by pores was analyzed using high-energy X-ray computed tomography (CT). Gray correlation analysis was employed to quantify the influence of pore size and porosity on compressive mechanical parameters. Furthermore, the combined effects of pore characteristics were assessed by introducing damage variables. It was shown that the compressive strength, strength reduction, elastic modulus, and modulus reduction exhibited linear correlations with porosity and exponential correlations with pore size. Cracks within the specimen predominantly propagate through the pores or along their edges. The influence of porosity on both strength and elastic modulus is more substantial than that of pore size. Moreover, the deterioration in mechanical properties is more pronounced when small pore size is coupled with high porosity, compared to the combination of large pore size and low porosity. Full article

Different from general underground engineering, the micro-damage prior to failure of the surrounding rock has a significant influence on the geological disposal of high-level radioactive waste. However, the quantitative research on pre-failure dilatancy damage characteristics and stress path influence of hard brittle rocks under high stress levels is insufficient currently, and especially, the stress path under simultaneous unloading of axial and confining pressures is rarely discussed. Therefore, three representative mechanical experimental studies were conducted on the Beishan granite in the pre-selected area for high-level radioactive waste (HLW) geological disposal in China, including increasing axial pressure with constant confining pressure (path I), increasing axial pressure with unloading confining pressure (path II), and simultaneous unloading of axial and confining pressures (path III). Using the deviatoric stress ratio as a reference, the evolution laws and characteristics of stress–strain relationships, deformation modulus, generalized Poisson’s ratio, dilatancy index, and dilation angle during the path bifurcation stage were quantitatively analyzed and compared. The results indicate that macro-deformation and the plastic dilatancy process exhibit strong path dependency. The critical value and growth gradient of the dilatancy parameter for path I are both the smallest, and the suppressive effect of the initial confining pressure is the most significant. The dilation gradient of path II is the largest, but the degree of dilatancy before the critical point is the smallest due to its susceptibility to fracture. The critical values of the dilatancy parameters for path III are the highest and are minimally affected by the initial confining pressure, indicating the most significant dilatancy properties. Establish the relationship between the deformation parameters and the crack-induced volumetric strain and define the damage variable accordingly. The critical damage state and the damage accumulation process under various stress paths were examined in detail. The results show that the damage evolution is obviously differentiated with the bifurcation of the stress paths, and three different types of damage curve clusters are formed, indicating that the damage accumulation path is highly dependent on the stress path. The research findings quantitatively reveal the differences in deformation response and damage characteristics of Beishan granite under varying stress paths, providing a foundation for studying the nonlinear mechanical behavior and damage failure mechanisms of hard brittle rock under complex loading conditions. Full article

The LaRC02 criterion is a classical criterion for determining fiber kinking failure of UD laminates under longitudinal compression (LC), but its basis for determining matrix cracking in a fiber kinking coordinate system is based on stress-invariant theory rather than on a physical mechanism. Herein, three Puck-like physical-mechanism-based inter-fiber failure criteria are extended to LC failure of UD composites, and thus three failure criteria (denoted as LC-Guo, LC-Li, and LC-Puck failure criteria) are constructed for fiber kinking failure determination. The stresses in the global coordinate system are transformed to the fiber kinking coordinate system by a three-level coordinate system transformation, and then the failure determination is performed using the three Puck-like criteria. The results show that the overall accuracy of the three proposed criteria is higher than that of the LaRC02 criterion, especially the LC-Guo criterion. Additionally, an analysis of the influence of material properties shows that the failure envelope curves tend to be conservative, and the predicted off-axial compression strength decreases as the transverse compression strength and in-plane shear strength increase and the transverse tensile strength decreases. This work proposes a more reasonable assessment methodology for the determination of LC failure of UD composites, which has important theoretical significance and engineering value. Full article

This study addresses a critical gap in blast-resistant design by investigating the influence of axial compression ratio—a previously underexplored parameter—on the dynamic response of reinforced concrete (RC) shear walls under close-in explosions. While existing research has focused on conventional loading scenarios, the interplay between axial compression and blast effects remains poorly understood, despite its practical significance for structural safety in high-risk environments. Through a combined experimental and numerical approach, three half-scale RC shear walls were tested under blast loading, complemented by simulations analyzing key parameters (aspect ratio, axial compression ratio, boundary conditions, and charge weight). The results demonstrate that a moderate axial compression ratio (around 0.3) enhances structural stiffness and reduces displacement, effectively helping to control wall damage. Boundary conditions were also found to affect failure modes: walls with stiffer end restraints exhibited reduced deformation but more brittle cracking. Lower aspect ratios (i.e., wider walls) improved blast resistance, and peak displacement progressively increased with the charge weight. These findings provide actionable insights for optimizing RC shear wall design in blast-prone infrastructures, balancing ductility and load capacity. By linking theoretical analysis to practical design criteria, this study advances blast-resistant engineering solutions. Full article

This study takes limestone crushed stone concrete as the research object and systematically investigates its mechanical property changes and microstructural damage characteristics under different confining pressures using triaxial compression tests, scanning electron microscope (SEM) tests, and digital image processing techniques. The results show that, in terms of macro-mechanical properties, as the confining pressure increases, the peak strength increases by 192.66%, the axial peak strain increases by 143.66%, the elastic modulus increases by 133.98%, and the ductility coefficient increases by 54.61%. In terms of microstructure, the porosity decreases by 64.35%, the maximum pore diameter decreases by 75.69%, the fractal dimension decreases by 19.56%, and the interfacial transition zone cracks gradually extend into the aggregate interior. The optimization of the microstructure makes the concrete more compact, reduces stress concentration, and thereby enhances the macro-mechanical properties. Additionally, the failure characteristics of the specimens shift from diagonal shear failure to compressive flow failure. According to the Mohr–Coulomb strength criterion, the calculated cohesion is 6.96 MPa, the internal friction angle is 38.89°, and the breakage angle is 25.53°. A regression analysis established a quantitative relationship between microstructural characteristics and macro-mechanical properties, revealing the significant impact of microstructural characteristics on macro-mechanical properties. Under low confining pressure, early volumetric expansion and rapid volumetric strain occur, with microcracks mainly concentrated at the aggregate interface that are relatively wide. Under high confining pressure, volumetric expansion is delayed, volumetric strain increases slowly, and microcracks extend into the interior of the aggregate, becoming finer and more dispersed. Full article

Tunnel lining structures, which are subjected to the combined effects of water and soil pressure as well as a water-rich erosion environment, undergo a corrosion-induced damage and degradation process in the reinforced concrete, gradually leading to structural failure and a significant decline in service performance. By introducing the Cohesive Zone Model (CZM) and the concrete damage plastic model (CDP), a three-dimensional numerical model of the tunnel lining structure in mining method tunnels was established. This model takes into account the multiple effects caused by steel reinforcement corrosion, including the degradation of the reinforcement’s performance, the loss of an effective concrete cross section, and the deterioration of the bond between the steel reinforcement and the concrete. Through this model, the deformation, internal forces, damage evolution, and degradation characteristics of the structure under the effects of the surrounding rock water–soil pressure and steel reinforcement corrosion are identified. The simulation results reveal the following: (1) Corrosion leads to a reduction in the stiffness of the lining structure, exacerbating its deformation. For example, under high water pressure conditions, the displacement at the vault of the lining before and after corrosion is 4.31 mm and 7.14 mm, respectively, with an additional displacement increase of 65.7% due to corrosion. (2) The reinforced concrete lining structure, which is affected by the surrounding rock loads and expansion due to steel reinforcement corrosion, experiences progressive degradation, resulting in a redistribution of internal forces within the structure. The overall axial force in the lining slightly increases, while the bending moment at the vault, spandrel, and invert decreases and the bending moment at the hance and arch foot increases. (3) The damage range of the tunnel lining structure continuously increases as corrosion progresses, with significant differences between the surrounding rock side and the free face side. Among the various parts of the lining, the vault exhibits the greatest damage depth and the widest cracks. (4) Water pressure significantly impacts the internal forces and crack width of the lining structure. As the water level drops, both the bending moment and the axial force diminish, while the damage range and crack width increase, with crack width increasing by 15.1% under low water pressure conditions. Full article

Fatigue endurance anisotropic behavior was evaluated for an API 5L X42 pipeline steel through axial force-controlled fatigue tests amongst Longitudinal, Diagonal, and Circumferential directions. This study shows that fatigue life anisotropy is mainly controlled by pearlite banding degree (A_i) and ferritic grain orientation (Ω₁₂). Also, it is foreseen that the observed behavior can be related to the dislocation arrays generated by the cyclic loading in relation to microstructure orientation, and the interactions of the fatigue crack tip with the microstructure during the crack propagation stage. Full article

Existing studies have not considered the impact of interface bond strength on the ease of crack propagation at the cement sheath interface. Through Brazilian splitting and direct shear tests, the normal and shear bond strengths at interfaces I and II of a cement sheath were quantified. Based on this, a crack propagation model for the cement sheath interface was established using cohesive zone elements. The propagation characteristics of cracks along the axial and circumferential directions at interfaces I and II of a cement sheath during hydraulic fracturing were analyzed, along with their influencing factors. The results show that, due to the difference in interface bond strength, the crack propagation rate and length at interface I in the axial direction are greater than those at interface II, while the interface II crack is more likely to propagate in the circumferential direction. The elastic modulus of the cement sheath is a key factor affecting the integrity of the cement seal. Both excessively low and high elastic moduli can lead to different forms of failure in the cement sheath. It is recommended to control the elastic modulus of the cement sheath between 7 and 8 GPa. As the internal casing pressure increases, the axial propagation length of cement sheath interface cracks also increases. During fracturing, reducing pump pressure can reduce the axial crack propagation length in the cement sheath, alleviating or preventing the risk of fluid migration between stages and clusters. The findings of this study provide theoretical references and engineering support for the control of cement sheath seal integrity. Full article

This study investigates the thermal and residual stress development in multi-layer lined pipe welding through numerical simulation and experimental validation. The focus is on the weld overlay/liner transition region, a critical area prone to stress concentrations and fatigue crack initiation. Using finite element analysis (FEA) with the Goldak double-ellipsoidal heat source model, the research examines the temperature evolution, residual stress distribution, and deformation characteristics during the welding process. Key findings reveal that the peak temperature in the weld overlay region reaches 3045.2 °C, ensuring complete metallurgical bonding. Residual stresses are predominantly tensile near the three-phase boundary, with maximum von Mises stress observed in the base pipe at 359.30 MPa. This study also employs Response Surface Methodology (RSM) to optimize welding parameters, achieving a 20.5% reduction in residual axial stress and a 58.1% reduction in residual circumferential stress. These results provide valuable insights for optimizing welding processes, improving quality control, and enhancing the long-term reliability of bimetallic composite pipelines. Full article