Search Results (102)

Existing risk assessment approaches for soft rock tunnels in fault-fractured zones typically employ single weighting schemes, inadequately integrate subjective and objective weights, and fail to define clear risk. This study proposes a risk-grading methodology that integrates an enhanced game theoretic weight-balancing algorithm with an optimized cloud entropy extension cloud model. Initially, a comprehensive indicator system encompassing geological (surrounding rock grade, groundwater conditions, fault thickness, dip, and strike), design (excavation cross-section shape, excavation span, and tunnel cross-sectional area), and support (support stiffness, support installation timing, and construction step length) parameters is established. Subjective weights obtained via the analytic hierarchy process (AHP) are combined with objective weights calculated using the entropy, coefficient of variation, and CRITIC methods and subsequently balanced through a game theoretic approach to mitigate bias and reconcile expert judgment with data objectivity. Subsequently, the optimized cloud entropy extension cloud algorithm quantifies the fuzzy relationships between indicators and risk levels, yielding a cloud association evaluation matrix for precise classification. A case study of a representative soft rock tunnel in a fault-fractured zone validates this method’s enhanced accuracy, stability, and rationality, offering a robust tool for risk management and design decision making in complex geological settings. Full article

Red-layer soft rock has characteristics such as softening when encountering water, loose structure, and significant rheological properties. In tunnel engineering, it is necessary to sort out and analyze the stress characteristics of its support structure. This paper focuses on the mechanical behavior and support effect during the construction of Neogene red-layer soft rock tunnels. Through field monitoring, it explores the mechanical characteristics of Huizhou Tunnel under complex geological conditions in depth. This study adopted a remote wireless monitoring system to conduct real-time monitoring of key indicators including tunnel surrounding rock pressure, support structure stress, and deformation, obtaining a large amount of detailed data. An analysis revealed that the stress experienced by rock bolts is complex and varies widely, with stress values between 105 and 330.5 MPa. The peak axial force at a depth of 2.5 m reflects that the thickness of the loosened zone in the surrounding rock is approximately 2.5 m. The compressive stress in the steel arches of the primary support does not exceed 305.3 MPa. Shotcrete effectively controls the surrounding rock deformation, but the timing of support installation needs careful selection. The stress in the secondary lining is closely related to the primary support. The research findings provide an important theoretical basis and practical guidance for optimizing the support design of red-bed soft rock tunnels and enhancing construction safety and reliability. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

Due to the complexity of planning and constructing underground lines, construction challenges—such as close proximity and multi-line interactions—are increasingly being recognized, along with their associated safety hazards. The visual observation of tunnel deformation and changes in the surrounding strata is difficult. In this study, laboratory model experiments were conducted using a mixture of liquid paraffin, n-tridecane, and silica gel powder, combined in specific proportions to create a transparent material that simulates natural soft rock. The new tunnel was designed to simultaneously cross over and under two existing tunnels. The impact of the new tunnel on the existing tunnels was examined, with excavation length and soil layer thickness considered as the primary influencing factors. The results indicate that excavating the new tunnel causes settlement deformation in the tunnels above and heave deformation in the tunnels below. The magnitude of deformation increases as excavation progresses but decreases with the greater thickness of the soil interlayer. For an existing tunnel, variations in the thickness of the soil interlayer not only affect its own deformation but also disturb the tunnel on the opposite side. Therefore, to ensure safer and orderly urban tunnel construction and to address the “black box” effect, it is essential to study the deformation characteristics of existing tunnels and their surrounding rock during the construction of new tunnels. Full article

This study focuses on Neogene red-bed soft rock tunnels in the Huicheng Basin, China. Through engineering geological investigation, remote wireless monitoring systems, and total station multi-parameter monitoring, the deformation characteristics of red-bed soft rock surrounding rock under high in situ stress environments and their influencing factors were systematically analyzed. The findings reveal that the surrounding rock deformation follows a three-stage evolutionary pattern of “rapid, slow, and stable”. Construction disturbances can disrupt the stable state, leading to “deep V-shaped” anomalies or double-step responses in deformation curves. Spatially, the deformation exhibits significant anisotropy, with the haunch area showing the maximum deformation (95 mm) and the vault the minimum (65–73 mm). Deformation stabilization requires 30–42 days, and a reserved deformation of 10 cm is recommended based on specifications. Mechanical behavior analysis indicates that the stress–strain curves of red-bed argillaceous sandstone are stepped, with increased confining pressure enhancing both peak and residual strengths, validating the necessity of timely support. The study elucidates a multi-factor coupling mechanism: rock mass classification, temporal–spatial effects (excavation face constraints and rheological properties), construction methods, in situ stress levels, and support timing (timely support during the rapid phase inhibits strength degradation) significantly influence deformation evolution. The spatiotemporal distribution of surrounding rock pressure shows that invert pressure increases most rapidly, while vault pressure reaches the highest magnitude, with construction disturbances triggering stress redistribution. This research provides theoretical and practical guidance for the design, construction optimization, and disaster prevention of red-bed soft rock tunnels. Full article

This paper studies the influence of the pick structure on the cutting characteristics of the cutting head when cutting rocks with a tunneling–bolting combined machine. A simulated model of the breaking of soft rock with a cutting pick was established. Dynamic simulation of the cutting head during the cutting process enabled the force characteristics to be obtained. The validity of the simulation was verified by carrying out cutting experiments. A numerical simulation of the pick parameters made it possible to analyze the influence of the pick’s included angle, taper angle, and established angle on the cutting performance. The results showed that the average values for the cutting resistance and traction resistance when the cutting head cut rocks were 14.21 kN and 7.19 kN, respectively. An included angle of between 70° and 75° was found to be most suitable. Within a specific range, the cutting force was found to increase with an increase in the taper angle. An established angle between 40° and 45° proved to have the highest cutting efficiency. At present, the results have been applied to the Shendong Coalmine. Thus, the proposed model provides a sound theoretical basis for the optimal design of the cutting head. Full article

Permanent displacements caused by active faults can lead to the severe deformation of tunnel liners. To investigate the effect of fault fracture deformation patterns on the deformation of tunnel liners under fault dislocation, this paper categorized three fault-zone fracture deformation patterns and conducted numerical simulations for tunnel’s surrounding rock-liner systems under different fracture deformation patterns. Furthermore, the longitudinal displacement, relative deformation, axial stress, and shear stress of the tunnel liner were measured to characterize the mechanical response of the tunnel, and the effects of fault geometric parameters on the mechanical response of the tunnel liner were explored. The results showed that fracture deformation patterns were broadly categorized into uniform fracture deformation, linear fracture deformation, and nonlinear fracture deformation patterns. The distribution patterns of tunnel liner stress and deformation under these fracture deformation patterns were similar, but the magnitude of the peaks and the intensity of their effects differed. Under reverse fault dislocation, the peak values of tunnel liner deformation and shear stress occurred at the rupture plane. In contrast, the maximum axial stress was observed at the interface between soft and hard rock masses. When the core width of the fault zone decreased and the fault dip direction increased, the intensity of the mechanical response of the tunnel liner increased. With the fault dip decreased, the axial stress in the tunnel liner transitions from tensile-compressive stress to compressive stress, the shear stress decreases, and the intensity of the relative deformation of the tunnel liner increases. These research results can provide significant guidelines for tunnel design crossing the reverse fault. Full article

The strength of soft rock masses progressively deteriorates under dissolution effects, leading to extensive pore development and structural loosening within the rock matrix. This process induces water and sand inrush phenomena at excavation faces, posing substantial challenges to construction safety. This study systematically investigates the strength degradation mechanisms and engineering disaster evolution of soft rock subjected to water–rock interactions. Utilizing representative water-rich soft rock specimens from a tunnel in central Yunnan, a multi-scale analytical framework incorporating X-ray diffraction mineral analysis systems, triaxial mechanical testing systems for rocks, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) was implemented. This integrated methodology comprehensively elucidates the macro–meso damage evolution mechanisms of soft rock under water–rock coupling interactions. The results indicate that as the dolomite content decreases and the impurity content increases, the softening grade of the rock rises, leading to more extensive pore development. Uniaxial compression tests revealed that the Poisson’s ratio of soft rock is significantly higher than that of typical rock. Triaxial compression tests demonstrated that confining pressure has a substantial impact on soft rock, particularly affecting Poisson’s ratio. Increased water content was found to significantly reduce the strength of the soft rock. Compared to loose soft rock, the radial strain of denser soft rock was markedly greater than the axial strain, and the soaking damage effect was more pronounced. This study provides a valuable insight into the mechanical and permeability behavior of soft rock under different conditions, and provides valuable insights into the solutions for soft rock in geological engineering such as tunnel excavations. Full article

The TBM disc cutter cuts soft–hard composite strata during shield construction, and the cutter–rock cutting process generates high temperatures and severe wear. In this research, different strength types of rocks are taken as objects to analyse the interacting rock-breaking force and cutter motion model. The effects of rock properties on wear are investigated, and the cutter ring wear mechanism and damage types are discussed. Combined with the thermal stress theory of elastomer and the abrasive wear theory, a prediction model for cutter wear depth and wear mass is proposed. The results of the study show that the type of wear is dominated by abrasive wear, with the highest probability of uniform wear occurring in cutting hard rock. Hard rock is the most abrasive to the steel material of the cutter ring, and the percentage of abrasive wear decreases for cutting soft–hard composite strata. The amount of abrasive wear is negatively correlated with the hardness of the cutter ring. The rock damage patterns are different when cutting soft and hard rocks, and the wear areas are located at the bottom and sides of the cutter ring, respectively. Considering the thermal effect, the depth of wear for cutting hard rock has a power function relationship with the installation radius, which is closer to the actual value. The theoretical models are generally lower than the actual measured values. The wear prediction model is useful for determining the replacement interval of the cutter and improving the rock-breaking efficiency. Full article

In geotechnical engineering, traditional anchor bolts often have problems such as an insufficient bearing capacity, their ease of loosening, and an unsatisfactory support effect under complex geological conditions (such as soft soil or broken surrounding rock), resulting in it being difficult to guarantee engineering stability. In order to solve these problems, this paper studies the supporting performance of a hollow grouting anchor with an umbrella-shaped expansion head with an expansion pipe. Through theoretical analysis, mechanical performance analysis, and experimental analysis, the supporting mechanisms and mechanical characteristics of a hollow grouting anchor with an umbrella-shaped expansion head are systematically discussed. The calculation formula for the maximum pull-out force of the umbrella-shaped expansion head is clarified, and the fixed range of the expansion body section in relation to the loose ring is quantified. Based on the analysis results, the structural parameters and material properties of the bolt were optimized, and the optimization effect was verified by numerical simulation. The results show that the optimized bolt has significantly improved the pull-out bearing capacity, shear resistance, and reinforcement effect on the soil. The maximum pull-out force of the umbrella-shaped expansion head can be increased by up to 35%, and the fixed range of the expansion body section can be expanded by 45%. The research provides an efficient and reliable support solution for geotechnical engineering fields, such as roadway engineering and tunnel engineering, which significantly improves the stability and safety of engineering under complex geological conditions. At the same time, it provides an important theoretical basis and practical reference for the design and construction of similar projects. Full article

To address the problem of large deformation in deep-buried high geostress soft rock tunnels, the Yuelongmen Tunnel was selected as the research subject and adopting the methods of on-site measurements, laboratory experiments and theories, the characteristics of large deformation and its mechanism in high geostress soft rock tunnels are studied in depth, and based on the mechanism of large deformation in tunnels and the concept of active and passive synergistic control, an optimized support scheme that dynamically adapts to the deformation of the surrounding rock is put forward. The results show that (1) the deformation volume and rate of tunnel surrounding rock is large, the duration is long, and the deformation damage is serious; (2) the main factors of tunnel surrounding rock deformation damage are high geostress and stratum lithology, followed by geological structure, groundwater and support scheme; (3) the tunnel deformation hierarchical control scheme effectively controls the deformation of surrounding rock, and reduces the deformation of steel arch and the risk of sprayed concrete cracking, which verifies the applicability of this scheme to the project. It verifies its engineering applicability. The research results provide important technical reference and theoretical support for the design and construction of similar projects. Full article

Tunnel excavation in water-rich and saturated loess layers often encounters a series of engineering disasters, including surface settlement, large deformations of surrounding rock, collapses, water inrushes, mud inrushes, and lining cracks. This paper presents an analogy of 16 cases of instability and collapse of surrounding rock during the excavation of water-rich loess tunnels in China’s loess regions. The weight of influence of various factors affecting the stability of surrounding rocks has been analyzed based on the Fuzzy Analytic Hierarchy Process (FAHP), addressing the engineering challenges encountered during the construction of the Tuanjie Tunnel. Measures such as deep well-point dewatering of the surface, reinforcement of locking foot anchors, and construction treatment with large arch feet are proposed. The effectiveness of these treatments is then monitored and analyzed. The results show that after 30 days of dewatering, the average water content of the surrounding rock decreased from 28.8% to 22.3%, transforming the surrounding rock from a soft plastic state to a hard plastic state. Phenomena such as mud inrushes at the tunnel face and water seepage through the lining are significantly reduced, and the self-stabilizing capacity of the surrounding rock is markedly improved. By optimizing the excavation method and enhancing support parameters, the construction progress rate for Grade VI surrounding rock has increased from 10–15 m per month to 40 m per month, validating the effectiveness of the proposed measures. Full article

Tunnel Boring Machines (TBMs) play a vital role in modern tunnel construction due to their efficiency and adaptability across various geological conditions. However, when tunneling through geologically altered zones, such as fault zones and soft ground, significant challenges arise, including increased wear, reduced advance rates, and heightened safety risks. This study explores advanced support measures for TBM excavation in altered zones, focusing on deformation characteristics and the bearing capacity of different support strategies in both normal and altered rock masses. Through numerical simulations on the FLAC3D platform, we compare the stress distribution and disturbance evolution in the surrounding rock with and without pre-reinforcement, as well as with single-layer and double-layer pipe-shed supports. The findings reveal that a lack of advance support leads to severe surrounding rock instability and an increased risk of TBM jamming. While single-layer pipe roofing offers partial mitigation, its limited stiffness constrains its effectiveness. In contrast, double-layer large pipe roofing provides superior bending stiffness, effectively minimizing settlement and deformation while significantly reducing the likelihood of TBM jamming. These findings offer practical guidance for the design and implementation of robust TBM support systems, enhancing tunneling safety and efficiency in complex geological conditions. Full article

The excavation of the rock mass at the tunnel entrance in regions characterized by high altitudes and elevated stress levels results in the direct exposure of the surrounding rock to atmospheric conditions. This surrounding rock is subjected to the compounded effects of excavation-induced unloading damage and freeze–thaw erosion, which contribute to the degradation of its mechanical properties. Such deterioration has a negative impact on production and construction operations. Following tunnel excavation, the lateral stress exerted by the surrounding rock at the tunnel face is reduced, leading to a predominance of uniaxial compressive stress. As a result, the failure mode and mechanical behavior of the rock exhibit characteristics similar to those observed in uniaxial loading tests conducted in controlled laboratory environments. This study conducts laboratory-based uniaxial loading and unloading tests, as well as freeze–thaw tests, to examine the strength, deformation characteristics, and fracture attributes of unloading sandstone subjected to freeze–thaw erosion. A damage deterioration model for unloading sandstone under uniaxial conditions is developed, and the patterns of damage response are further analyzed through the identification of compaction points and the definition of damage response points. The results indicate that (1) as the degree of freeze–thaw erosion increases, the failure threshold of the sandstone significantly decreases, with the residual rock fragments on the fracture surface transitioning from hard and sharp to soft and sandy; (2) freeze–thaw erosion has a pronounced negative impact on the cohesion of the sandstone, while the reduction in the internal friction angle is relatively moderate; and (3) the strain induced by damage following three, six, and nine freeze–thaw cycles exhibits a gradual decline and appears to reach a state of stabilization when compared to conditions without freeze–thaw exposure. Investigating the mechanical properties and deterioration mechanisms of the rock in this specific context is crucial for establishing a theoretical foundation to assess the stability of the tunnel’s surrounding rock and determine the necessary support measures. Full article

With the further development of China’s coal resources, mining operations are constantly transferred to the deep soft rock. As such, the mine roadway is under the action of high geostress, the surrounding rock body engineering properties are poor, the overall strength is low, the traditional support method struggles to meet the needs of safe production, and the surrounding rock control has become a major technical challenge. This paper relies on the actual project, analyzes the destabilization mechanism of the roadway, analyzes the deformation of the peripheral rock of the deep roadway, determines the physical and mechanical parameters of the peripheral rock through indoor tests, establishes numerical analysis model, proposes to adopt the joint support scheme of anchor rods + anchor cables + a 36U-type steel metal bracket + a laying net + a laying mat + filling behind the wall, and monitors the displacement of peripheral rock of the roadway on a regular basis by using the numerical display convergence meter, and then obtains the displacement of the peripheral rock of the roadway after excavation as well as under the influence of the quarrying movement. Under the influence of the roadway perimeter rock displacement, we evaluate the reasonableness of the support program, as well as the safe and effective control of the roadway perimeter rock, to achieve the ideal roadway perimeter rock support and control effect. Full article