The delayed breakage of particles significantly affects the long-term mechanical properties of rockfill materials. This study examines the effects of particle strength dispersion on the distribution of time-dependent strength using fracture mechanics and probabilistic methods. Subsequently, the distribution of normalized maximum contact force (NMCF), defined as the ratio of the maximum contact force to instantaneous strength, for specimens with uniform particle size is derived using extreme value theory and Discrete Element Method (DEM). Based on this analysis, the probabilities of delayed breakage in rockfill specimens over various time intervals are calculated using a joint probability delayed breakage criterion. The feasibility of the proposed method is validated by comparing theoretical calculation with DEM triaxial creep simulation results that accounted for particle breakage. The findings offer innovative tools and theoretical insights for understanding and predicting the particle delayed breakage behavior of rockfill materials and for developing macro-micro creep crushing constitutive models.
The flexible joints and segmental lining serve as effective seismic measures for tunnel in high-intensity seismic area. However, the tunnel axial deformation at flexible joints has not been fully incorporated into analytical models. This study presents a novel mechanical model for flexible joints that considers tension (compression)shear-rotation deformations, replacing the traditional shear-rotation springs model. An improved semi-analytical solution has been developed for the longitudinal response of a tunnel featuring a three-way flexible joint mechanical model subjected to fault movement. The nonlinear elastic-plastic foundation spring, the soil-lining tangential interaction, and the axial force of tunnel lining have been considered to improve the applicability and precision of proposed method. The proposed solution is compared with existing models, such as short beams connected by shear and rotation springs, by examining the predictions against numerical simulations. The results indicate that the predictions of the proposed model align much more closely with the outcomes of the numerical simulations than those of the existing models. For the working conditions selected in 4, neglecting the tension-compression deformation at flexible joints an 81.8% error in the peak axial force of the tunnel and a 20.2% error in the peak bending moment. The reason is that ignoring the axial deformation of these joints results in a larger calculated axial force on the lining, which subsequently leads to increased bending moment and shear force. Finally, a parameter sensitivity analysis is conducted to investigate the effect of various factors, including flexible joint stiffness, segmental lining length, and the length of the tunnel fortification zone.
The displacements between segment rings are highly likely to occur in concealed creep fault areas. The dislocation of ring joint easily leads to the crushing of concrete around the bolt hole, which will become a potential safety hazard during tunnel service. For this problem, a composite Tenon was designed to improve the interaction at ring joint. It is necessary to carry out theoretical research to reveal the mechanical property of the ring joint. In this paper, a constitutive model of the Tenon was proposed based on specimen tests and numerical models. And the mechanical characteristics of the ring joint were investigated through prototype experiment and numerical simulation. The research results show that the composite Tenon is a flexible structure that can avoid the hard extrusion between the Tenon and the segments. The Tenon also has obvious protection effect on bolt and concrete around the handhole, which reserves more bearing space for the ring joint. These advantages are more conducive to dealing with potential risks such as earthquake, cyclic train loads, tunnel convergence deformation and uneven soil settlement during operation. The paper provides a theoretical basis for the application and promotion of the composite Tenon structure in the tunnel engineering.
Rock masses are often exposed to dynamic loads such as earthquakes and mechanical disturbances in practical engineering scenarios. The existence of underground caverns and weak geological structures like columnar jointed rock masses (CJRMs) and interlayer shear weakness zones (ISWZs) with inferior mechanical properties, significantly undermines the overall structural stability. To tackle the dynamic loading issues in the process of constructing subterranean caverns, a programmable modeling approach was utilized to reconstruct a large-scale underground cavern model incorporating ISWZs and columnar joints (CJs). By conducting dynamic simulations with varying load orientations, the analyses focused on the failure patterns, deformation characteristics, and acoustic emission activity within the caverns. Results revealed that the failure modes of the underground caverns under dynamic loading were predominantly tensile failures. Under X-direction loading, the failed elements were mainly distributed parallel to the CJs, while under Y-direction loading, they were distributed parallel to the transverse weak structural planes. Furthermore, the dynamic stability of the overall structure varied with the number of caverns. The dual-cavern model demonstrated the highest stability under X-direction loading, while the single-cavern model was the least stable. Under Y-direction loading, the cavern stability increased with the number of caverns. Importantly, different weak structures affected the dynamic response of caverns in different ways; the CJRMs were the primary contributors to structural failure, while ISWZs could mitigate the rock mass failure induced by CJs. The findings could offer valuable insights for the dynamic stability analysis of caverns containing CJRMs and ISWZs. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
The prestressed glass fiber-reinforced polymer (GFRP) rock bolt, characterized by its lightweight, high-strength, fatigue-resistant, and corrosion-resistant, effectively addresses the durability challenges associated with rock bolts in soil applications. This study was based on the shear test of GFRP anchor rods under varying levels of prestressing. The present study designed and conducted shear tests on GFRP anchor bolt joint surfaces under varying prestress levels, utilizing the double shear test method. Based on the experimental results, this research analyzed the influence of prestress on failure modes, shear bearing capacity, and shear deformation of GFRP anchor bolt joint surfaces. Furthermore, by employing an equivalent strain assumption in conjunction with damage mechanics theory, a predictive model for shear displacement-shear stiffness and shear displacementshear stress was established for GFRP anchor bolts. The results indicated that the failure mode of the prestressed GFRP anchor rod joint surface shear specimen was the shear failure following the splitting of the GFRP anchor rod. The shear carrying capacity of the joint surface with 20 % and 40 % pre-stressed GFRP anchor rods increased by 8.2 % and 20.3 % compared to the non-prestressed anchor rod, respectively. However, the ultimate displacements decreased by 22.7 % and 49.7 %, respectively. The initial stiffness of the 20 % and 40 % prestressed GFRP anchor rods was higher than that of non-prestressed GFRP anchor rods. However, under shear loading, the fracture strain of prestressed GFRP anchor rods decreased by 33 % and 44 %, respectively, compared to non-prestressed counterparts. The shear displacement-shear stiffness and shear displacement-shear stress relationships of prestressed GFRP anchor rods under the action of shear load were found to conform to the exponential distribution and Weibull distribution, respectively. The mechanical models proposed in this paper for shear displacement-shear stiffness and shear displacement-shear stress could effectively predict the mechanical behavior of shear damage on the joint surface of prestressed GFRP anchor rods.
When tunnels in loess traverse sections of alternating soil and rock layers, variations in soil properties can induce an arching effect, potentially leading to the shear failure of the tunnel's structural components. Therefore, seismic design in these areas is particularly crucial. To address these challenges, this paper analyzes the mechanical behavior of damping joints under dynamic earthquake loads using a pseudo-static approach. Based on Bernoulli-Euler beam theory and Pasternak's dual-parameter elastic foundation beam theory, a closed-form solution is derived for the longitudinal response of tunnels in loess with damping joints under seismic loading. The solution is further validated through numerical modeling. Additionally, the study investigates the effects of filling materials (used in damping joints) and design schemes on the effectiveness of damping joints, supported by practical engineering cases. The findings indicate that installing damping joints can reduce the restraining forces on the tunnel lining, allowing the structure to better accommodate the deformation of the surrounding rock. Among the tested materials, rubber was identified as the optimal material for damping joints due to its excellent elasticity and energy absorption capacity. However, the exclusive use of damping joints may result in excessive localized deformation, potentially compromising the tunnel's normal operation. Therefore, careful design of these joints is essential. This research provides theoretical support for the seismic design of tunnels in loess in alternating soil-rock strata.
This study systematically examines the influence of joints on the mechanical properties of loess, highlighting the impact of joint dip angles on soil deformation and failure mechanisms. By employing an innovative layered compaction method to prepare jointed specimens, and conducting comparative experiments with different simulation materials (wax paper, rice paper, and plastic film), a series of controlled indoor triaxial compression tests were performed. The key findings are as follows: (1) The joint dip angle plays a decisive role in the evolution of failure mode, with five typical failure mechanisms identified based on fracture characteristics: shear failure, sliding failure, conjugate shear failure, sliding-shear failure, and sliding-conjugate shear failure. (2) The weakening effect of joints exhibits confining pressure dependency: Under low confining pressure (50 kPa), jointed specimens demonstrate increased axial displacement and a reduced shear strength attenuation ratio. (3) Mechanical parameters are significantly influenced by the dip angle: When the joint dip angle falls within the critical dip range of 60 degrees-75 degrees, both cohesion and internal friction angle reach their minimum values, forming zones of weakened mechanical properties. (4) A comparative analysis of simulation materials indicates that single-layer rice paper, due to its optimal thickness and tensile strength, effectively replicates the contact behavior of natural joint surfaces. This study establishes the quantitative relationship between joint geometric parameters and mechanical responses, providing an experimental basis for the engineering geological assessment of loess.
The connection between subway stations and tunnels in subway systems is a critical consideration in the design of underground transportation systems. Expansion joints may be introduced between the station and tunnel to reduce the stress and deformation transmitted to the structure and mitigate the potential structural damage. However, adverse conditions such as large deformations in liquefiable sites and extreme earthquakes can severely impact the integrity of this connection. This study employs three-dimensional finite element numerical models of dynamic soil-structure interaction in liquefiable sites to investigate the seismic response of the subway station-tunnel connection structure under different distributions of liquefied soil layers and considering various structural connection methods. The results demonstrated that subway station-tunnel structure placed in liquefied interlayer sites experiences greater seismic damage compared to structures with their upper parts embedded in homogeneous liquefiable sites. In addition, using expansion joints between the station and tunnel can indeed reduce the seismic stresses and deformations transmitted to the structure, which can mitigate the extent and severity of its damage. However, the expansion joint can lead to misalignment between the subway station and the tunnel. The findings provide theoretical references for seismic design and disaster mitigation measures for subway structures in liquefiable sites.
The joint roughness coefficient (JRC) is a key parameter in the assessment of mechanical properties and the stability of rock masses. This paper presents a novel approach to JRC evaluation using a genetic algorithm-optimized backpropagation (GA-BP) neural network. Conventional JRC evaluations have typically depended on two-dimensional (2D) and three-dimensional (3D) parameter calculation methods, which fail to fully capture the nonlinear relationship between the complex surface morphology of joints and their roughness. Our analysis from shear tests on eight different joint types revealed that the strength and failure characteristics of the joints not only exhibit directional dependence but also positively correlate with surface dip angles, heights, and back slope morphological features. Subsequently, five simple statistical parameters, i.e. average dip angle, median dip angle, average height, height coefficient of variation, and back slope feature value (K), were utilized to quantify these characteristics. For the prediction of JRC, we compiled and analyzed 105 datasets, each containing these five statistical parameters and their corresponding JRC values. A GA-BP neural network model was then constructed using this dataset, with the five morphological characteristic statistics serving as inputs and the JRC values as outputs. A comparative analysis was performed between the GA-BP neural network model, the statistical parameter method, and the fractal parameter method. This analysis confirmed that our proposed method offers higher accuracy in evaluating the roughness coefficient and shear strength of joints. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
Understanding the shear mechanical behaviors and instability mechanisms of rock joints under dynamic loading remains a complex challenge. This research conducts a series of direct shear tests on real rock joints subjected to cyclic normal loads to assess the influence of dynamic normal loading amplitude (Fd), dynamic normal loading frequency (fv), initial normal loading (Fs), and the joint roughness coefficient (JRC) on the mechanical properties and instability responses of these joints. The results show that unstable sliding is often accompanied by friction weakening due to dynamic normal loads. A significant negative correlation exists between cyclic normal loads and the normal displacement during the shearing process. Dynamic normal load paths vary the contact states of asperities on the rough joint surfaces, impacting the stick-slip instability mechanism of the joints, which in turn affects both the magnitude and location of the stress drop during the stick-slip events, particularly during the unloading phases. An increasing Fd results in a more stable shearing behavior and a reduction in the amplitude of stick-slip stress drops. The variation in fv influences the amplitude of stress drop for the joints during shear, characterized by an initial decrease (fv = 0.25-2 Hz) before exhibiting an increment (fv = 2-4 Hz). As Fs increases, sudden failures of the interlocked rough surfaces are more prone to occur, thus producing enhanced instability and a more substantial stress drop. Additionally, a larger JRC intensifies the instability of the joints, which would induce a more pronounced decline in the stick-slip stress. The Rate and state friction (RSF) law can provide an effective explanation for the unstable sliding phenomena of joints during the oscillations of normal loads. The findings may provide certain useful references for a deeper comprehension of the sliding behaviors exhibited by rock joints when subjected to cyclic dynamic disturbances. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).