Search Results (47)

During the construction of deep underground soft rock strata, the adverse effects of high geostress, unfavorable geological conditions, and excavation disturbances are significant, easily triggering Material-Stress-Induced (MSI) large deformation disasters, leading to the failure of support structures or even collapse, thus posing great challenges to the safe construction of this type of underground engineering. Based on this, this study first classifies the large deformations, analyzes the instability mechanism of material-stress-induced large deformation in soft rock, and identifies the influencing factors of this type of large deformation from three aspects. Subsequently, a numerical investigation (FLAC3D 6.00) is utilized to examine the surrounding rock deformation characteristics under different material factors (uniaxial compressive strength and elastic modulus), stress factors (burial depth and lateral pressure coefficient), and construction factors (excavation method, support pattern, and timing of initial support installation). On this basis, a multi-factor sensitivity comparison analysis is conducted, which clarifies the differences and prioritization of parameter influences on large deformation, and reveals the dominant role of controlling factors such as elastic modulus. The analysis demonstrates a strong negative correlation between the examined material factors (uniaxial compressive strength and elastic modulus) and the magnitude of surrounding rock displacement, with both values eventually converging. A significant positive correlation between the examined stress factors and the magnitude of surrounding rock displacement was observed. A pronounced positive correlation was observed between stress factors and surrounding rock deformation. These factors distinctly have different effects on the peak displacement of different surrounding rock parts. Vault settlement demonstrates the most pronounced displacement, while arch bottom deformation is the least apparent. The three excavation methods exhibit relatively low sensitivity to surrounding rock displacement. Similarly, the support patterns demonstrate limited influence on surrounding rock deformation. The material factor of soft surrounding rock is the main controlling factor of the large deformation of soft surrounding rock in deep underground engineering. The elastic modulus has the strongest influence on the displacement of the surrounding rock. When the elastic modulus is less than 2 GPa, the sensitivity coefficient is much higher than the stress factors. The research results can provide some reference and guidance for similar underground projects. Full article

When excavating roadways in underground mines, stress redistribution within the surrounding rock mass leads to stress concentration and release. Should the concentrated stresses exceed the rock mass’s tensile or shear strength, rock deformation and failure occur. Thus, a knowledge of stress distribution around the roadway is of great significance for revealing the roadway instability mechanism and design support methods. In this work, the powerful complex variable function theory was used to solve the surrounding rock stress around the triple-arched roadway and the analytical results were verified with the on-site stress state. The results show that the tensile stress occurs on the roadway roof and floor under low lateral stress coefficients, while concentrated compressive stress emerges on the two sidewalls. However, the surrounding stress distribution exhibits an opposite characteristic under high stress levels. Beyond five times the roadway radius, the stress in the surrounding rock is unaffected by the roadway and approaches the in-situ stress. For the +1890 m level trackless transport roadway in Kunyang No. 2 phosphate mine, it is further calculated that the minimum stress concentration factor in the rib area of the roadway within the stress relief zone is 0.34, while the maximum stress concentration factor in the concentrated stress zone of the roof, floor, and sidewalls of the roadway is 5.87. The measured stress values of two monitoring points in the surrounding rock of this roadway are fairly consistent with the analytical values, suggesting the complex variable method for solving excavation-induced stresses are effective and reliable. Full article

Corrugated steel–concrete (CSC) composite arches, an innovative structural system with simplified construction and enhanced stiffness, are widely used in bridge and tunnel modular engineering. However, insufficient research on their shear performance limits prefabricated applications. Similarly to beams, their shear behavior is significantly affected by loading location. Specifically, as a parameter significantly affected by the loading location, the shear–compression ratio exerts a notable influence on the shear bearing capacity of CSC arches by altering the development pattern of cracks and the inclination angle of shear cracks. To investigate the influence mechanism of the loading location, this study is the first to systematically link shear–compression ratio variation to load location in CSC arches. In this context, shear performance tests were conducted on two CSC specimens with different loading locations (mid-span and quarter-point) to investigate the influence of loading locations on the shear behavior of CSC arches. To further investigate the impact of key parameters on the shear bearing capacity of CSC arches, a validated finite element model was employed to support the parametric analysis. The parameters involved include the span-to-rise ratio, shear connector spacing, strength and thickness of corrugated steel, as well as strength and thickness of concrete. Theoretical calculations for internal forces under varying rise-to-span ratios and loading methods are conducted, proposing an analytical solution method. Validation using 2 experiments and 96 finite element results show that a modified method is applicable, with a mean value of 1.066, corresponding to a standard deviation of 0.071, and all relative errors within 15%. By introducing the shear–compression ratio, this study extends existing methods to make them applicable under single-point loading, thereby enabling their use for guiding engineering. Similarly, the internal force analysis method proposed herein can serve as a theoretical foundation, providing a valuable reference for future research on shear capacity calculation methods for CSC arches with varying cross-sectional configurations and those where bending moments play a more significant role. Full article

Microbial Induced Carbonate Precipitation (MICP) is regarded as a promising eco-friendly alternative to traditional Portland cement for soil stabilization. However, the feasibility of applying bio-cemented soil as a road base material remains inadequately studied, particularly in terms of the relationships between MICP treatment parameters—such as solution content, curing age, and the ratio of bacterial solution (BS) to cementation solution (CS) —and key mechanical and durability properties under realistic road conditions. In this study, an optimal curing condition for bio-cemented sand was first determined through unconfined compression strength (UCS) tests and calcium carbonate content (CCC) determination. Subsequently, dynamic triaxial tests were conducted to evaluate its resistance to cyclic loading. Further road performance tests, including splitting tensile strength, freeze-thaw resistance, temperature shrinkage, and arch expansion assessments, were carried out to comprehensively evaluate the material’s applicability. Scanning electron microscopy (SEM) was employed to elucidate the microstructural mechanisms underlying strength development. The results show that the strength (4.28 MPa) of bio-cemented sand cured under optimal conditions (12% bio-cured solution content, a BS-to-CS ratio of 1:4 and 7-d curing age) satisfies the criteria for road base applications. MICP treatment significantly improved the dynamic properties of aeolian sand (AS), reducing the cumulative plastic axial strain (ε_p) by nearly 11–46% and increasing the dynamic elastic modulus (E_d) by approximately 7–31% compared to untreated sand. The material also demonstrates satisfactory performance across all four road performance metrics. Microstructural analysis reveals enhanced interparticle bonding due to calcium carbonate precipitation, with samples prepared near the optimum moisture content exhibiting superior integrity and strength. Overall, bio-cemented sand demonstrates excellent potential as a sustainable road base material. These findings provide a theoretical foundation for practical applications of similar bio-cemented soils in road engineering. Full article

The layered composite roof of a coal mine roadway exhibits heterogeneity, with pronounced variations in layer thickness and strength. Fully grouted rock bolts installed in such layered roofs usually penetrate two or more strata and bond with them to form an integrated anchorage system. Roof failure typically initiates in the shallow strata and progressively propagates to deeper layers; thus, the mechanical properties of the rock at the free surface critically influence the overall stability of the layered roof and the load-transfer behavior of the bolts. In this study, a layered rock mass model was developed using three-dimensional particle flow code (PFC3D), and a triaxial loading scheme with a single free surface was applied to investigate the effects of free-surface rock properties, support parameters, and confining pressure on the load-bearing performance of the layered rock mass. The main findings are as follows: (1) Without support, the ultimate bearing capacity of a hard-rock-free-surface specimen is about 1.2 times that of a soft-rock-free-surface specimen. Applying support strengths of 0.2 MPa and 0.4 MPa enhanced the bearing capacity by 29–38% and 46–75%, respectively. (2) The evolution of axial stress in the bolts reflects the migration of the load-bearing core of the anchored body. Enhancing support strength improves the stress state of bolts and effectively mitigates the effects of high-stress conditions. (3) Under loading, soft rock layers exhibit greater deformation than hard layers. A hard-rock free surface effectively resists extrusion deformation from deeper soft rocks and provides higher bearing capacity. Shallow free-surface failure is significantly suppressed in anchored bodies, and “compression arch” zones are formed within multiple layers due to bolt support. Full article

Preventing progressive collapse induced by accidental events poses a critical challenge in the design and construction of resilient structures. While substantial progress has been made in planar structures, the progressive collapse mechanisms of precast concrete spatial structures—particularly regarding the effects of precast slabs—remain inadequately explored. This study develops a refined finite element modeling approach to investigate progressive collapse mechanisms in fully bonded prestressed precast concrete (FB-PPC) spatial frames, both with and without precast slabs. The modeling approach was validated against available test data from related sub-assemblies, and applied to assess the collapse performance. A series of pushdown analyses were conducted on the spatial frames under various column removal scenarios. The load–displacement curves, slab contribution, and failure modes under different conditions were compared and analyzed. A simplified energy-based dynamic assessment was additionally employed to offer a rapid estimation of the dynamic collapse capacity. The results show that when interior or side columns fail, the progressive collapse process can be divided into the beam action stage and the catenary action (CA) stage. During the beam action stage, the compressive membrane action (CMA) of the slabs and the compressive arch action (CAA) of the beams work in coordination. Additionally, the tensile membrane action (TMA) of the slabs strengthens the CA in the beams. When the corner columns fail, the collapse stages comprise the beam action stage followed by the collapse stage. Due to insufficient lateral restraints around the failed column, the development of CA is limited. The membrane action of the slabs cannot be fully mobilized. The contribution of the slabs is significant, as it can substantially enhance the vertical resistance and restrain the lateral displacement of the columns. The energy-based dynamic assessment further reveals that FB-PPC spatial frames exhibit high ductility and residual strength following sudden column removal, with dynamic load–displacement curves showing sustained plateaus or gentle slopes across all scenarios. The inclusion of precast slabs consistently enhances both the peak load capacity and the residual resistance in dynamic collapse curves. Full article

Dynamic impact experiments based on high-speed photography and digital image correlation (DIC) techniques were carried out on sandstone specimens containing arched holes to investigate the effect of the incident angle. In addition, the complex function method based on conformal mapping was used to theoretically calculate the transient dynamic stress distributions around the arched holes. The test results indicated that the strength and modulus of elasticity of the specimens under dynamic impact decreased and then increased with the increase of the inclination angle of the holes from 0 to 90° at intervals of 15°, reaching a minimum value at 60°, due to the large stress concentration at this angle leading to the shear failure of the specimen. During the experiment, rock debris ejections, spalling, and heaving were observed around the holes, and the rock debris ejections served as an indicator to identify the early fracture. The damage mechanism around the holes was revealed theoretically, i.e., the considerable compressive stress concentration in the perpendicular incidence direction around the arched hole and the tensile stress concentration on the incidence side led to the initiation of the damage around the cavity, and the theoretical results were in satisfactory agreement with the experimental results. In addition, the effect of the initial stress on the dynamic response of the arched tunnel was discussed. Full article

This study evaluates four compression testing methods to determine the most reliable and reproducible technique for assessing the compression strength of murine lumbar vertebral bodies. Twenty female C57BL/6 mice (12 weeks old) were randomized into four groups: Group 1, compression of the complete lumbar vertebral body (LVB) with dorsal spinal processes; Group 2, compression at the vertebral body surface; Group 3, compression at the vertebral body surface after vertebral arch resection; Group 4, resection of the vertebral arch with straightening of the intervertebral joint surface. A mono-axial static testing machine applied compression, measuring load to failure, stiffness, yield load, and elasticity modulus. Method 1 resulted in significantly higher load-to-failure and yield-to-failure (25.9 N compared to 18.2 N, and twice 12 N for Methods 2–4), with the least variation in relative values. Method 3 had increased stiffness and a significantly higher Young’s modulus (232 N/mm, in contrast to 101, 130, and 145 N/mm for Methods 1, 2, and 4, respectively) but yielded inconsistent results. Method 4 showed the greatest variability across specimens. Method 2 yields suitable data quality as well, albeit with a slightly higher variation, and is the recommended procedure if the spinal processes have to be excluded from the measurement. Based on these findings, Method 1 produced the most consistent and reproducible data and is recommended for future studies evaluating vertebral biomechanics in mice. Full article

To investigate dynamic fracture characteristics and failure behavior of different sections of tunnel surrounding rock mass, six kinds of model tunnels were fabricated using green sandstone, and impact tests were performed using a split Hopkinson pressure bar system. The dynamic compressive strength and energy change behaviors of samples comprising different-shaped tunnels were assessed, and crack propagation paths were analyzed employing a digital image correlation method. Numerical calculations were carried out using the software LS-DYNA (v. 2021R1), and the dynamic stress concentration factors of different model tunnel samples were determined. The results of the research indicated that the shape of the tunnel affected the dynamic compressive strength. The elliptical tunnel had the smallest percentage of dissipated energy, and the three-centered circular tunnel had the largest percentage of dissipated energy. The maximum tensile stress concentration factor in the model tunnels consistently occurred at the top or bottom; so, the locations of initiation were most commonly at the bottoms and tops of the tunnels. Sample failure resulted from a combination of tensile and shear cracks, with the failure mode being primarily tensile-dominated. Finally, the inverted arch had an obvious alleviating action on the stress concentration phenomenon at the bottom of the three-centered circle. Full article

In the context of advancements in deep resource development and underground space utilisation, deep underground engineering faces the challenge of investigating the mechanical behaviour of rocks under high-stress conditions. The present study is based on a gold mine, and the bulk ore taken from the mine perimeter rock was processed into two sets of specimens containing semicircular arched roadways with half and full penetrations. The tests were carried out using a true triaxial rock test system. The results indicate that the true triaxial stress–strain curve included stages such as compression density, linear elasticity, yielding, and destructive destabilisation following the peak; the yield point was more pronounced than that in uniaxial and conventional triaxial tests; and the peak stress and strain of the semi-excavation were higher than those of the full excavation. Furthermore, full excavation led to greater deformation along the σ₃ direction. The acoustic emission energy showed a sudden increase during the unloading stage, then fluctuated and increased with increasing stress until significant destabilisation occurred. Additionally, increased burial stress in the half-excavation decreased the proportion of tension cracks and shear cracks. Conversely, in semi-excavation, the proportion of tensile cracks decreased, while that of shear cracks increased. However, the opposite was observed in full excavation. In terms of fractal dimension, semi-excavation fragmentation due to stress concentration followed a power distribution, while the mass fragmentation in full excavation followed a random distribution due to uniform stress release. Furthermore, the specimen strength was positively correlated with fragmentation degree, and primary defects also influenced this degree. This study provides a crucial foundation for predicting and preventing rock explosions in deep underground engineering. Full article

For arch dams, the joint surface has a certain bond strength after grouting the contraction joints, which can withstand the arch-wise tensile stress to a certain extent and influence the stress distribution of the dam blocks on both sides. The seismic response analysis of arch dams needs to consider the influence of the initial tensile and shear strengths generated by the contraction joint grouting. Thus, a modified B-differentiable equation method is proposed by introducing the initial tensile strength and the initial shear strength of contraction joints the into traditional B-differentiable equation method. In the proposed method, the shear strength varies with the contraction joint opening. The modified B-differentiable equation method can still be solved by the B-differentiable damped Newton method with theoretical guarantee of convergence. Then, a seismic calculation model for the dam–reservoir–foundation system is developed based on the modified B-differentiable equation method, the Westergaard additional mass method, and multiple transmission boundary conditions. The influence of the initial tensile and shear strength of the contraction joints on the arch dam seismic response is discussed. The results show that the initial tensile and shear strength of the contraction joints have an influence on the opening and distribution range of the contraction joints and the maximum values of the principal tensile and compressive stress in the dam body. The initial tensile and compressive strength of the contraction joints should be considered when carrying out seismic response analysis of arch dams. Full article

High slopes with multi-layer weak interlayers are a type of special slope that tends to fail due to the unfavorable mechanical properties of interlayers. In this study, the influence of the position, length, diameter, and ratio of on-center spacing to the pile diameter on the stability of such slopes is investigated using the three-dimensional strength reduction elastoplastic finite element method. Based on a high slope with multi-layer weak interlayers, two models were created, and three states (an initial state, a state with a safety factor of 1.35, and a limit equilibrium state) were considered. The pile can improve slope stability when the it is located at the lower to lower-middle part of a high slope. The resistance effect no longer has a strengthening property if it exceeds a critical pile length (28 m and 30 m in the two models); 30 m was found to be the optimal pile length for the high slope. As the diameter increased, the safety factor increased from 1.38 (1.37) to 1.41 (1.40) in Model 1 (or in Model 2), while the maximum compressive stress, the maximum shear stress of the pile, and the maximum displacement of the pile head decreased in the two models from 20.84 (81.24) MPa to 16.15 (18.8) MPa, 11.19 (42.02) MPa to 7.77 (10.43) MPa, and 714.1 (4585.00) mm to 396.3 (1272.00) mm, respectively. The pile diameter should be >1.4 m in such cases. When stress and displacement increased, the arching effect and the pile group effect weakened, and the safety factor decreased as the ratio of on-center spacing to diameter increased. The ratio should be <3 to ensure slope ability. Full article

High-strength concrete-filled steel tube (CFST) arches have been widely applied in underground engineering, among which there are special-shaped arches such as D-shaped sections. At present, most studies have concentrated on members with square or circular sections, while relatively few studies have been conducted on D-shaped section members. In this study, firstly, D-shaped sections were initially transformed into sections with a part square and part elliptical shape using an equivalent section method. The formulas for the axial compression and pure bending bearing capacities of the basic D-shaped CFST members were deduced using unified theory, and the bearing capacity of the D-shaped members was calculated in a given case. Secondly, numerical simulations of axial compression and pure bending of the basic CFST members with three section types (square, circular, and D-shaped) were carried out using ABAQUS software. To ensure the reliability of the numerical simulations, the concrete damage constitutive model and the elastic–plastic model were adopted to simulate the core concrete and the steel tube, respectively. In the results, the axial compression and pure bending bearing capacities of the D-shaped section obtained via theoretical calculation were 2339.6 kN and 84.8 kN·m, respectively, while the results obtained via numerical simulation were 2335.8 kN and 85.4 kN·m, respectively, which were relatively close. Among the three section types of members, the D-shaped members had the highest axial compression bearing capacity, which was 1.45% and 4.58% higher than those of the circular and square section members, respectively. However, their bending moment bearing capacity was relatively low. The stress distribution of the D-shaped members presented a characteristic where the circular part dominated, and the stress transfer effect of the members was favorable. In practical engineering, when the surrounding rock pressure is high and evenly distributed, D-shaped section arches can be selected, and increasing the proportion of the square area in D-shaped sections can enhance the overall flexural capacity of arches. Full article

Due to the impact of disordered mining activities in previous years, numerous abandoned roadways exist in the second mining district of the 13# coal seam in Chejiazhuang Coal Mine. The stability of the new roadway roof was analyzed under various distributions of abandoned roadways above. It was determined that the ultimate stable thickness of the coal layer between the new and abandoned roadways is 4.0 m. When the thickness between the two is less than 4.0 m, the roof becomes unstable after excavation, posing a risk of collapse. Advanced grouting reinforcement is required to enhance roof stability before installing U-shaped steel arches. Mechanical experiments were conducted on the polymer grouting consolidation of fractured coal, showing a significant increase in residual strength compared to intact coal. Furthermore, the uniaxial compressive strength of the polymer grouting consolidation partially recovered. On average, the consolidation coefficient and recovery coefficient were 5.28 and 85.51%, respectively. Grouting increased the ductility of the fractured surrounding rock, enhancing its resistance to deformation and plasticity. A polymer grouting consolidation technology for supporting fractured surrounding rock under the unstable roof of abandoned roadways is proposed, along with the design of corresponding support schemes and parameters. Monitoring the results of mine pressure indicated that the surrounding rock remained stable after roadway excavation, validating the effectiveness of the support schemes and parameters. Full article

A deeper understanding of the fracture evolution of hole-containing rocks is helpful for predicting the fracture of engineering rock mass. Based on this, uniaxial compression tests and two-dimensional numerical tests were conducted on red sandstone containing three different shapes of holes before and after reinforcement. The mechanical properties, stress field evolution, and AE energy and AE events during the sample fracture process were studied. The conclusions are that: (1) The reinforced specimens exhibited a significant increase in Young’s modulus and strength compared to the unreinforced specimens (containing a semicircular arch hole). (2) The sample always cracks from the loaded axial direction of the hole, presenting as tensile cracks. Subsequently, stress concentration at the corners of the hole results in shear cracks. Finally, the cracks gradually expand and merge with the holes; there are obvious macroscopic cracks and fracture surfaces on the sample surface, which proves that the sample has been fractured. (3) The reinforcement of the hole-containing sandstone can effectively inhibit the expansion of cracks in the rock. (4) When the stress on the specimen is less than its peak stress, the accumulation of the AE energy and AE events in the reinforced sample are greater than those in the unreinforced sample. The specimen experiences more intense compression-induced fracturing and has a stronger load-bearing capacity. Full article