Search Results (239)

Targeting the rock burst hazard induced by the hard roof key stratum during deep mining at the Mengcun Coal Mine in the Binchang mining area, this study takes the No. 403109 working face as the engineering background and systematically investigates the rockburst prevention mechanism and effectiveness of ground hydraulic fracturing through theoretical analysis, UDEC numerical simulation, and surface microseismic monitoring. The results indicate that fracturing pre-weakens the overlying key stratum, transforming its load-bearing mode from a long-beam rigid support to a segmented flexible support. This significantly reduces the cantilever length, lowers the accumulation of elastic strain energy, and enables flexible load transfer and stress redistribution in the overburden. Numerical simulations reveal that after fracturing, the breakage timing of the key stratum advances, the fragmentation size decreases, and the over-burden movement shifts from stepwise fracturing to sequential caving, with the stress concentration zone substantially narrowed. In the field, a total of 44 fracturing stages were implemented in wells MC-05L and MC-06L, creating a fracture network with an average fracture length of 317 m and an average fracture height of 55 m, achieving an effective stimulated volume ratio of 86.7%. During the mining period, microseismic events exhibited a median energy of only 868.14 J, characterized by high frequency and low energy. The average weighting interval was 13.69 m, the peak coal stress was controlled within 5.0–6.7 MPa, and the loads on roadway bolts and cables remained within safe limits. This study validates the source-control effect of ground hydraulic fracturing on working faces with strong rock burst risks in deep mining, providing a theoretical basis and engineering reference for mines with analogous conditions. Full article

Rock bolts are the primary ground support mechanism in underground mining. Yet verification of their installation is rarely captured in a spatially precise, retrievable form, leaving operators without an auditable as-built record for regulatory review or post-incident reconstruction. This paper presents an automated rock bolt detection process that closes this documentation gap using dense point clouds from an underground hard rock mine acquired by terrestrial laser scan. The method computes per-point ambient occlusion (AO) on closure plane-sealed chambers using a PCV implementation of the ShadeVIS principle, forms candidates from a multi-scale protrusion field, and segments them by prominence watershed before classifying each candidate with PCA-based geometric descriptors, without machine learning or training data. Installation perpendicularity is applied as a per-detection confidence cue, and detections are reported in confidence tiers that concentrate human review on the ambiguous minority. Validated against a database of 1447 bolts across 20 walls in two areas of an underground mine, the system achieved an overall recall of 83.7%, with human review completing the inventory to 100%. The physics-based design transfers across bolt types and mine geometries through parameter re-tuning rather than retraining, addressing the core limitation of deep learning methods, which require site-specific labelled datasets. Full article

In the construction process of a super-long-span short-distance continuous variable cross-section tunnel, multiple geometric mutations along the alignment induce significant discontinuity and asymmetry in the mechanical response of the surrounding rock-support system, which differs significantly from that of conventional single-variable-section tunnels. This aggravates local asymmetric stress concentration and sudden deformation surges, posing severe construction risks. To reveal the influence of different excavation methods on the mechanical response of the surrounding rock-support system during the construction of this type of tunnel, the Tangshan Road Interchange and Connection Line Project was added based on the Qingdao Qingyin Expressway. The large-span continuous variable cross-section sections of A, B, and C in the north line of the Tangshan Road Tunnel were selected as the research objects, and a three-dimensional finite element numerical model was established and rigorously validated against field monitoring data from three representative cross-sections. Three typical construction methods—the Distributed Bench Excavation Method (DBM), Double Sidewall Drift Method (DSM), and Distributed Double Sidewall Drift Method (DDSM)—were systematically compared and studied. The results indicate that the section transition zones (A → B and B → C) are the most sensitive key control areas. Compared with DBM, DDSM significantly reduced the vault initial support stress in Section A by 38.1% (from 6.51 to 4.03 MPa), the left and right spandrel stresses by 17.9% and 26.9%, respectively, and peak bolt axial forces by over 20%. Although DSM achieves maximum lateral convergence reduction (reducing haunch convergence by 32.8% in Section C), DDSM delivers the optimal comprehensive control by effectively restricting vault settlement and balancing support stress distribution. The field monitoring trend was highly consistent with the numerical simulation results, which confirms the accuracy of the established model. The research results can provide a reference for the selection of construction methods and deformation control of large-span continuous variable cross-section tunnels. Full article

High-stress soft rock roadways in deep underground engineering often exhibit significant time-dependent deformation due to strong rheological behavior of surrounding rock. To investigate the deformation characteristics and support effect, a composite viscoelastic constitutive model considering anchored and unanchored rock zones is established based on the Maxwell rheological framework. The equivalent stiffness contribution of rock bolts is incorporated to characterize the interaction between support and surrounding rock. Analytical solutions of radial displacement and creep rate are derived using viscoelastic theory and Laplace transform methods. The effects of bolt spacing, bolt length, and burial depth on the rheological response are analyzed. Numerical simulations based on FLAC3D creep analysis and field monitoring data are used to verify the proposed model. Results show that decreasing bolt spacing effectively reduces long-term deformation, while bolt length has a diminishing effect beyond a critical anchorage length. Increasing burial depth significantly increases creep rate and total deformation. The numerical results agree well with theoretical predictions (R² ≈ 0.985), and field measurements show a relative error within 10%. The proposed model effectively describes the long-term deformation trend of high-stress soft rock roadways and provides a theoretical reference for support design under similar conditions. Full article

The underground powerhouse of a hydropower station in Northwest China features a large height-to-span ratio and complex geological conditions, posing critical challenges for surrounding rock stability. This study employs a systematic framework of “parameter inversion–stability analysis–support optimization”. The main contributions are: (1) A forward-backward analysis method integrating monitoring data, numerical calculation, and parameter optimization was used to invert the physical and mechanical parameters of the surrounding rock, establishing a practice-consistent numerical model. (2) Considering complex geological conditions from a prior collapse, systematic analyses of deformation characteristics, stress distribution, and overall stability during subsequent bench excavation were conducted, revealing evolutionary patterns of deformation, reproducing the collapse mechanism, and evaluating rock mass safety. (3) An optimized reinforcement scheme was proposed, involving additional anchor cables at arch shoulders and two anchor bolts on each sidewall (Sidewalls 2), with comparative analysis confirming its feasibility. Key findings: (i) Based on the inversion of monitoring data, the obtained physical and mechanical parameters of the surrounding rock can effectively reflect the actual characteristics of the rock mass and align with monitoring trends. (ii) Stability analysis of subsequent layered excavation, accounting for prior collapse impacts, shows that while deformation at key points continued to increase, it remained below critical thresholds, maintaining overall stability—prestressed anchor cables significantly controlled deformation. (iii) The optimized support scheme yields comparatively favorable outcomes with respect to the containment of surrounding rock displacement and the internal forces within the supporting. These outcomes provide valuable references for the design and construction of similar underground powerhouses. Full article

To address the engineering challenges of asymmetric large surrounding rock deformation and roadway support failure of deep gob-side entry retaining (GER) in the top-coal roadway, the progressive surrounding rock instability mechanism and fracture spatiotemporal evolution characteristics are revealed via theoretical analysis and universal distinct element code (UDEC) Trigon discrete element simulation. Results show that the top coal first undergoes bed separation and tensile failure, followed by backfill corner crushing and bearing capacity loss, which ultimately induces roadway support failure. Using UDEC simulation and mechanical tests, the influences of top-coal thickness, key block B length, backfill performance, and roadway support mode on roadway support stability are systematically clarified. Results indicate that keeping full top coal within the reinforcement zone, reducing key block B length, adopting a backfill width-to-height ratio of 0.45–0.8, a water–cement ratio of 1.5:1, and combining synergistic anchoring with delayed reinforced support can reduce the risk of roadway support failure. An optimized support scheme for the entry is proposed and field-implemented. Monitoring shows that the backfill has a smooth surface; reinforcement ladder beams and steel mesh have no fracture; coal pillar peak stress reaches 5.95 MPa; coal rib bolt load (178 kN) is significantly higher than that in the backfill section (115 kN); and the backfill adapts well to roof rotation and subsidence. The results support the feasibility of the proposed control scheme under the studied geological and engineering conditions and may provide a useful reference for similar GER projects. Full article

To elucidate the active–passive reinforcement mechanisms of rock bolts and the evolution of shear strength in anchored rock joints, this study integrates theoretical analysis, laboratory direct shear tests, and numerical simulations to investigate the deformation and failure characteristics of fully grouted, end-anchored, and prestressed bolted specimens. The results show that bolt reinforcement can be classified into prestress-dominated active action and dislocation-induced passive action. The shear strength curve of anchored rock joints exhibits four distinct stages with increasing shear displacement: initial slip, elasticity, yielding, and softening. Fully grouted bolts fail primarily by tensile–shear fracture, enabling a rapid increase in shear strength at small displacements. In contrast, end-anchored bolts undergo S-shaped bending and form symmetrical plastic hinges on both sides of the joint, sustaining resistance under large displacements albeit with lower peak strength. While the laboratory tests experimentally clarified the distinct failure modes and passive shear resistance mechanisms of fully grouted and end-anchored bolts, the quantitative partitioning between active and passive contributions was derived from a numerically simulated prestressed bolt model. The simulations indicate that for prestressed bolts, the active contribution accounts for approximately 69.6% of the total shear strength enhancement, while the passive contribution is about 30.4%. These findings yield actionable design criteria: end-anchored or yielding bolts are recommended for high-geostress environments or scenarios involving large potential deformations to exploit the large-deformation bearing capacity of passive action; conversely, prestressed bolts should be prioritized where strict control of early-stage deformation is required to maximize active support efficiency. Full article

Roof stability plays a crucial role in maintaining the overall stability of surrounding rocks to ensure safety of tunnel construction and operation. In this work, tension cut-off (TC) technique is introduced to modify the Hoek–Brown (HB) criterion to describe the tensile failure of rock strata. Thereafter, stability analysis of anchor bolt-reinforced tunnel roofs in rock strata subjected to a hybrid tensile-shear fracture is performed. The work balance equation is established by equating the external work rates of the falling block and the anchor bolts to the internal energy dissipation rate. Two stability indicators, that is the stability number (N) and the factor of safety (FoS) are proposed to quantitatively analyze the stability of tunnel roofs. Optimization algorithms combining genetic algorithm and particle swarm optimization are programmed to capture the optimal upper bound solutions. The influences of TC, strength criterion parameters, and anchor bolt-reinforcement strength on roof stability are explored in this work. It was found that increasing the anchor tension T improves the FoS of reinforced tunnel roofs, with an increase of up to 68% observed for rectangular tunnel roofs under the selected representative case, while the improvement is relatively less pronounced for circular tunnel roofs. Regarding anchor support, as ξ increases, the N for rectangular tunnels nearly doubles. This work provides a theoretical basis for preliminary designing of tunnels in reinforced rock strata. Full article

With deep coal mining in China, high in situ stress frequently causes severe floor deformation, bolt-cable support failure, and excessive floor heave, which critically threaten mine safety. In this study, we use physical experiments, numerical simulation, and theoretical analysis to explore how hydraulic fractures with different azimuth angles affect stress transfer in roadways under floor dynamic pressure. Prefabricated fractures simulate weak planes induced by hydraulic fracturing. Uniaxial compression tests and PFC2D fluid–solid coupling simulations analyze mechanical properties, failure modes, acoustic emission behavior, and stress distribution. Results show that fracture azimuth significantly controls rock damage and failure modes. As the angle increases from 0° to 90°, failure changes from gradual degradation to sudden instability. Peak strength first decreases then increases, reaching the minimum at 22.5°, while roadway damage is minimal at 45°. Small-angle fractures lead to shear failure with clear precursors, and large-angle fractures cause sudden tensile failure. Hydraulic fractures form directional stress-relief zones and enable effective stress transfer and pressure relief. The results support parameter optimization of hydraulic fracturing and stability control for deep roadways under floor dynamic pressure. Full article

To determine a rational, narrow coal-pillar width and support scheme for gob-side entry driving in thick coal seams, the 4904 return airway of the No. 9 coal seam at Zhongshui Coal Mine was investigated using limit-equilibrium analysis, FLAC3D numerical simulation, and field monitoring. The theoretical pillar width was calculated as 6.73–7.90 m, and sensitivity analysis showed that the selected 7 m pillar remained within the reasonable range under variations in key empirical and mechanical parameters. Numerical results indicated that a 7 m pillar could form a relatively complete central load-bearing core and effectively control surrounding-rock deformation, whereas further increasing the pillar width provided limited additional deformation reduction but caused greater coal loss. Compared with the 7 m pillar, the 9 m and 11 m schemes would cause additional coal losses of approximately 9.09 × 10³ t and 1.82 × 10⁴ t, respectively. A hierarchical synergistic support scheme consisting of high-strength bolts, long and short roof cables, and pillar-rib reinforcement cables was proposed. Compared with the equal-length roof-cable-plus-bolt scheme, the proposed scheme provided better control of roof subsidence and rib convergence. Field monitoring showed that roadway deformation gradually stabilized after support installation and remained within a controllable range under the monitored engineering conditions. Full article

Although rock bolts are widely used in tunnel engineering, their effectiveness remains uncertain under specific geological conditions. This study investigates a single-track railway tunnel excavated in gently dipping stratified mudstone to evaluate the applicability of sidewall rock bolts. Field measurements, including tunnel deformation, initial support reaction, and bolt axial force, were conducted. An equivalent support force of bolts was quantified, and a coupled relationship between bolt axial force and surrounding rock displacement was established based on interfacial mechanics. In addition, a physics-constrained inversion framework was developed to reconstruct the displacement field from measured bolt responses. The results show that tunnel deformation is minimal, with a maximum crown settlement of 4.7 mm and convergence of 3.6 mm. The initial support bears 93.4% of total support capacity, compared with merely 6.6% from rock bolts, revealing that primary support dominates load bearing under small deformation. Further parametric analysis indicates that increasing bolt length beyond 1 m does not further enhance the support performance. These findings suggest that there is potential for optimizing the length of fully grouted sidewall rock bolts in heterogeneous, gently dipping layered mudstone tunnels. Full article

Rock bolt corrosion can weaken support systems and affect the long-term stability of water-flooded roadways. This study investigates the symmetry evolution of roadway deformation induced by bolt deterioration in alkaline water-flooded roadways, using Sanxin Coal Mine, Xinjiang, as a case. Electrochemical accelerated corrosion tests were conducted in 10% Na₂SO₄ solutions at pH = 9, 11, and 13 for 3, 6, and 9 d, followed by uniaxial tensile tests and FLAC3D numerical simulations. Under the controlled accelerated electrochemical conditions, the mass loss rate and corrosion rate generally increased with corrosion duration, with the greatest deterioration observed in the pH = 13 group after 9 d. The tensile curves of corroded bolts still exhibited elastic deformation, yielding, strain hardening, and post-peak softening stages. However, the yield load decreased with increasing mass loss rate, with fitted slopes of −0.1842, −0.07531, and −0.04998 kN/% for pH = 9, 11, and 13, respectively. Numerical results showed that bolt deterioration intensified roadway deformation and stress redistribution. Under severe corrosion, the horizontal displacement of the two sidewalls reached approximately −153.7 mm and 155.4 mm, while the maximum roof subsidence and floor heave reached about −188.7 mm and 191.3 mm, respectively. The shallow stress release zone expanded, and the deep stress concentration became more pronounced. Moreover, bolt deterioration intensified the roadway response while largely preserving its left–right symmetry. The numerical results incorporating the experimentally derived bolt deterioration showed increased roadway deformation and stress redistribution, indicating that bolt-capacity degradation can adversely affect roadway stability. These findings provide a reference for evaluating residual support performance and designing reinforcement measures for water-flooded roadways. Full article

This study addresses asymmetric large surrounding rock deformation induced by narrow coal pillar instability in a gentle-dipping coal seam gob-side coal roadway (GSCR) under water-immersed and high-humidity conditions. The corresponding instability mechanism and control technology are systematically studied via integrated laboratory, theoretical, numerical and field methods. From constant temperature–humidity rock deterioration tests, SEM and XRD analysis, it is revealed that hydration of hydrophilic minerals (kaolinite, chlorite) in immediate roof mudstone intrinsically drives its macro–micro structural disintegration and mechanical degradation, and the catastrophic chain mechanism of water-induced mudstone weakening–force transmission medium failure of coal pillars and overlying strata–sliding instability of key voussoir beam blocks–linked large surrounding rock deformation is clarified. A mechanical model of the overlying voussoir beam structure for the target roadway is established considering both mudstone weakening and excavation-induced load transfer effects. The sliding criterion of key overlying blocks is derived, which quantitatively confirms that higher mudstone weakening and excavation-induced stress concentration elevate the sliding instability risk of the voussoir beam structure. Based on the findings and field conditions, a combined near-field and low-position field support scheme is proposed, including near-field reinforcement (shotcreting sealing, bolt–cable cascade reinforcement, deep grouting modification) and low-position field pressure relief via liquid CO₂ phase transition long–short boreholes roof cutting. Field application verifies that the maximum roadway deformation is controlled within 172 mm, with excellent surrounding rock control performance. Full article

To improve construction efficiency for large-section tunnels in sandstone–mudstone strata, this study investigates the applicability of the two-bench method and the three-bench method for grade IV and grade V surrounding rock, respectively. Based on FLAC3D, numerical simulations of excavation and support for the two benching methods were conducted to analyze deformation responses, including ground settlement, crown settlement, haunch convergence, floor uplift, and face extrusion. The simulation results were then compared and validated against field monitoring data to evaluate the applicability and feasibility of the construction methods. The results show that, for grade IV surrounding rock excavated using the two-bench method, crown settlement, floor uplift, and horizontal convergence converge and stabilize on days 17, 15, and 25, with stable values of 14.0 mm, 10.3 mm, and 13.2 mm, respectively. For grade V surrounding rock excavated using the three-bench method, these indices stabilize on days 24, 22, and 32, with stable values of 26.3 mm, 20.3 mm, and 20.8 mm, respectively. The surrounding rock pressures at the crown and spandrel gradually attenuate after excavation and stabilize at 1–4 MPa after approximately 20–26 days, whereas stress release at the haunch lasts longer and the stabilized stress level remains higher. Meanwhile, the anchor bolt axial force at the haunch is significantly greater than that at the spandrel, indicating that the haunch is a critical zone for support load-bearing and deformation control. The benching method can effectively control surrounding rock deformation under grade IV and V surrounding rock conditions in sandstone–mudstone strata; however, in engineering practice, the haunch should be treated as a key monitoring target, and targeted support and reinforcement measures should be implemented. Full article

The maintenance of gate roadways after longwall retreat is a critical geomechanical and technological problem in underground coal mining, particularly under conditions of increasing mining depth and complex geological settings. This study investigates the influence of support elements on the stress state of surrounding rocks and the stability of gate roadways intended for repeated use in coal mines of Ukraine and Kazakhstan. The research combines numerical modeling and analysis of field experience from Dniprovska Mine of PJSC “DTEK Pavlogradugol”, Kostenco Mine, and PJSC “Mine Administration Pokrovske”. Elastoplastic deformation of the rock mass was simulated using the finite element method within a stationary formulation, with the Mohr–Coulomb criterion applied to describe rock failure. Different support schemes were analyzed, including steel arch frames, protective structures, rock bolts, and cable bolts. The geomechanical response was evaluated using the parameters Q* and P*, which characterize the heterogeneity of the stress field and the degree of stress relief, respectively, as well as the extent of inelastic deformation zones. The results showed that protective structures significantly improve the condition of surrounding rocks at relatively shallow depths by reducing stress heterogeneity and limiting the development of inelastic deformation. Rock bolting promotes the formation of a reinforced rock–bolt arch in the roof, increasing roadway stability after longwall passage. However, under deep mining conditions, protective structures alone are insufficient, and reinforcement with cable bolts becomes necessary to maintain the integrity of the reinforced roof zone and reduce the load on individual bolts. Field observations from operating mines confirmed the practical efficiency of the proposed support approaches. The study demonstrates the role of each support element in forming a stable reinforced structure around the roadway and provides a basis for selecting rational support systems for gate roadways reused for ventilation or repeated use. Full article