To reveal the occurrence mechanism of ultra-low friction-typed rockburst,deep coal-rock is used as the study material.Firstly,a self-developed ultra-low friction experimental device was used to reproduce the ultra-low friction-typed rockburst under laboratory conditions.A high-speed camera and an acoustic-emission system were used to capture the dynamic fracture evolution of the coal seam and the associated roadway squeezing induced by unstable ultra-low-friction slip.Based on laboratory tests and engineering examples,we established a model of ultra-low friction-typed rockburst and derived an energy index using an energy-based criterion.,and the energy index of the ultra-low friction-typed rockburst is given based on energy criterion.Using the coal-rock interfacial friction force,vertical displacement difference,and fractured-seam length as key indices,we evaluated how stiffness,damping,perturbation amplitude,perturbation frequency,and elastic-modulus ratio affect the ultra-low friction response.The results show that increasing the stiffness or damping coefficient of the structural plane reduces the possibility of ultra-low friction sliding or mitigates its intensity.High disturbance amplitude is more prone to induce ultra-low friction sliding of the coal seam.Compared to other disturbance frequencies,the disturbance frequency between 14 Hz and 16 Hz most likely trigger ultra-low friction sliding.When the coal-rock interfacial friction forces are comparable,a higher coal elastic-modulus ratio more readily induces ultra-low friction sliding in the fractured coal seam.These findings provide a basis for predicting and preventing rockburst hazards.

Microseismic source localization is a core component of microseismic monitoring technology, crucial for reducing the impact of geological disasters and enhancing early warning and prevention of tunnel water inrush disasters; the accuracy of microseismic source localization significantly influences the efficacy of microseismic analysis. In the actual microseismic signal propagation process, influenced by the non-homogeneous and discontinuous features of rock structure and the variability of water content, the microseismic signal velocity model becomes complicated and challenging to determine accurately, leading to low accuracy in microseismic source localization. To address these issues, this paper explores the application of fusing the artificial bee colony and cuckoo search optimization algorithms (ABC-CS) in microseismic source localization, with the ultimate goal of applying it to the prevention and control of tunnel water and mud inrush. This method adopts the concept of joint positioning, which does not require prior determination of the propagation velocity of microseismic signals in the monitoring area. Its objective is to minimize the temporal discrepancy between the arrival times of microseismic signals detected by sensors and the calculated (theoretical) time differences. By employing intelligent optimization algorithms, the velocity model and the coordinates of the seismic source to be determined are both treated as unknowns for simultaneous solution, overcoming the problem of poor localization effectiveness in classical positioning methods caused by the use of inaccurate velocity models. In this paper, microseismic source localization analysis is conducted in both homogeneous and inclined stratigraphic models using this method. The superiority of the proposed method is verified through on-site blasting tests, showing significant improvements in global optimization capability, localization accuracy—with a positioning error of approximately 5 m—and the stability of output solutions, which lays a solid foundation for its eventual application in the prevention and control of tunnel water and mud inrush disasters.

Large-diameter shield tunneling is more prone to encountering composite ground conditions, where disc cutters are subjected to impact effects at the interface between soft and hard strata, leading to accelerated wear. Therefore, accurately predicting cutter wear is crucial for improving the efficiency of shield tunneling. This study proposes three optimization algorithms-Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Sparrow Search Algorithm (SSA)-to optimize the Backpropagation Neural Network (BPNN) method for predicting the average ring wear of` disc cutters in SPB shield machines. A total of 2128 field data samples collected from rings 540 to 614 of the Shantou Bay Subsea Tunnel in China were used in this study. The dataset includes 10 parameters, including shield operational parameters, mechanical parameters, and geological conditions, as input variables for the prediction model. Correlation analysis of cutter wear was conducted using statistical methods. The models were evaluated based on performance metrics, including ERMS, EMMAP and R2. The results show that the SSA-BP model achieved the highest accuracy in predicting disc cutter wear, with R2 = 0.9604, RMSE = 0.0434 mm and MAPE = 3.11 %. The results demonstrate that SSA significantly enhances the predictive capability of BPNN for disc cutter wear compared to GA and PSO.

In tunnel engineering, the uniaxial compressive strength (UCS) of surrounding rock is of great significance for design of support, construction parameters, and related engineering decisions. Traditional testing methods mainly involve rock sampling and laboratory measurements, which are time-consuming and costly. Measurement-While-Drilling (MWD) combined with machine learning has emerged as a rapid way to obtain the UCS of surrounding rock. However, most existing MWD-based approaches rely solely on data, while neglecting the physical law of rock fragmentation. This reduces their generalization ability and may lead to lower accuracy. To address these issues, this paper proposes a prediction method for the UCS of tunnel surrounding rock based on a physics-informed neural network (PINN). Experiments on rock drilling with a geological drilling rig were carried out, and 100 sets of drilling data were collected. The formula describing the relationships between the UCS and drilling data during the fragmentation process was derived, and the genetic algorithm was used to determine the contribution factors of different drilling parameters. By embedding the physical model into the loss function, a dual-drive model combining data and physical laws was constructed. The results show that the proposed PINN achieves high prediction accuracy and good generalization capability. Compared with support vector regression (SVR), multi-layer perceptron (MLP), and extreme gradient boosting (XGBoost), the PINN exhibits superior performance while maintaining real-time prediction capability.

The permeability of oil shale governs the migration of oil and gas products as well as heat transfer, making it a key parameter for efficient in situ oil shale exploitation. This study used a self-designed real-time high-temperature triaxial stress permeability testing system for oil shale, considering depths of 200–700 m, temperatures of 300–600 °C, and pore pressures of 1–3 MPa. Mercury intrusion porosimetry was used to characterize the pore structure, revealing the permeability evolution mechanism of the oil shale parallel and perpendicular to bedding under temperature–stress coupling. The results indicate that at different depths, the permeability of the oil shale parallel to bedding (ka) and perpendicular to bedding (ke) with increasing temperature can be divided into three stages. As the temperature increases from 300 to 600 °C, the ka and ke increase on average by 50.4 times and 42.7 times, respectively, with average rate changes of 0.36 × 10–16 m2·°C−1 and 0.13 × 10–18 m2·°C−1. 450 °C and 550 °C are the threshold temperatures at which the ka and ke undergo changes. When the depth increases from 200 to 700 m, the maximum ka and ke decrease by 53.4

In the construction of shield tunnels in hard-soft composite strata, abnormal damage to disc cutters caused by interfacial impact loads severely impacts construction safety and efficiency. As the excavation diameter of shield tunnels increases, the cutter impact issues become more pronounced. In this study, the dynamic response of disc cutters and the variation of impact load on disc cutters in composite rock masses with different soft-hard strength contrasts and interface bonding conditions were investigated through linear cutting tests. A new impact load prediction model for the composite strata interface was proposed, which incorporates rock damage effects and explains the origin of impact loading in composite strata. The test results show that the interface impact load governed by the strength difference between soft and hard rocks and the interface bonding conditions. With increasing penetration depth, the failure mode of the composite rock mass transitions from plastic crushing brittle crushing. The rock mass damage at the soft-hard composite interface exhibits discontinuous variation due to lithological contrast. This study reveals the interfacial impact mechanism of the disc cutter and provides practical prediction method for stress analysis of disc cutters in composite strata.

With the wide application of large-diameter tunnel engineering in complex stratum, the rock-breaking efficiency of shield cutter has become a key factor restricting the tunneling efficiency. Most of the existing studies focus on the force and spacing optimization of single-edged disc cutters, and the systematic analysis of the coupling mechanism between blade spacing and lithology of double-edged disc cutters is still lacking. In this paper, based on the discrete element method, the rock breaking process of double-edged hobs with different blade spacing in soft rock to extremely hard rock is simulated, and the stress response, crack propagation and specific energy change are analyzed. The results show that the large spacing in soft rock is helpful to realize fracture penetration and reduce specific energy. There is an optimal spacing interval of 70-80 mm in medium-hard rock. The small spacing in hard rock can enhance the stress concentration effect, while the spacing effect in extremely hard rock is significantly weakened, and the damage is dominated by crushing under the blade. This study reveals the coupling law between blade spacing and rock strength. Quantitative results show that the optimal spacing of 70-80 mm in medium-hard rock reduces the specific energy by 19.6 % compared to 65 mm spacing (from 1.53 & times; 107 J/m3 to 1.23 & times; 107 J/m3). In soft rock, large spacing (100 mm) achieves the lowest specific energy of 1.45 & times; 106 J/m3 with a rock-breaking volume of up to 1.91 & times; 10-3 m3. In extremely hard rock, increasing spacing from 65 mm to 100 mm causes a 51.1 % increase in specific energy. These findings provide a theoretical basis and engineering reference for the design of shield cutterhead and the dynamic optimization of tunneling parameters in complex stratum.

During shield tunnelling in karst strata, cavities cause uneven excavation faces, leading to abnormal cutter wear or breakage and reduced efficiency. This study investigates the mechanical characteristics of shield disc cutter triggered by karst cavity, using full-scale linear cutting experiment on rock specimen containing cavities and collaborative cutters numerical simulation considering cavities size and position. Firstly, the linear cutting experiment investigates the process of cutting cavity boundaries with penetration depth and rock strength. As penetration depth increases, fragments at the cavity-boundary exit are larger than those at the entry side. With increasing rock strength, the peak normal force at the cavity boundary gradually exceeds the average force during continuous rock breaking. Numerical simulations show that cavity size and position strongly affect cutter force and cutterhead loads. When a cavity exists in the tunnelling face, cutters near the cavity show increased normal force, while distant cutters show decreased force. As the number of overhanging cutters increases, the force variation becomes more significant. The maximum variation rates of single-edge and double-edge cutters increase from 21.9% to 36.8% and from 23.8% to 33.7%, respectively. Compared with the no-cavity condition, cutterhead thrust and torque decrease, while the overturning moment increases. For twin cavities, the cutter force variation decreases with increasing cavity angle and increases with cavity eccentricity. This study provides a basis for optimizing tunnelling parameters in karst strata.

With the continuous advancement of rail transit construction in China, the shield tunneling method has become the mainstream technique for tunnel engineering. When a shield machine traverses karst strata, karst features such as karst caves and dissolution zones result in an uneven excavation face. The contact state between the disc cutters and the rock mass during cutting undergoes dynamic changes, leading to abnormal wear or even failure of the cutters. This results in poor rock fragmentation efficiency and reduced shield driving performance. Based on explicit dynamic analysis and the Drucker-Prager plasticity criterion, this study employs Abaqus to investigate the mechanical responses of disc cutters and the cutterhead during cutting karst cave boundaries. In contrast to previous investigations that primarily address surrounding rock stability, lining mechanical behavior in karst formations, or cutter performance in homogeneous ground, this study focuses on the mechanical behavior of disc cutters and the cutterhead under uneven excavation surfaces caused by karst caves. It investigates the variation patterns of the peak and mean vertical forces during the process of cutting at the karst cave boundary under different cutting parameters. The deformation of the cutterhead corresponding to different numbers of suspended disc cutters under the condition of containing caves was studied. Numerical simulations were performed for scenarios with and without karst caves. Asymmetric loading and overturning moments are significantly more pronounced under karst cave conditions than in intact rock. The influence of cutterhead rotational speed and advance rate on the specific energy and overturning moment is explored.

The construction of shield tunnelling under river channels at short range faces risks of excavation face instability and stratum settlement. This paper systematically investigates the influence of river channel geometric parameters on stratum deformation and face stability, combining theoretical derivation with laboratory model tests. A parameterized formula considering slope ratio and depth is established to transform non-uniform overlying-soil loads. Based on a three-dimensional wedge instability model, a five-stage calculation method is proposed to determine the ultimate support force dynamically as the tunnel face advances beneath the channel. The method is validated through three-dimensional finite element simulations, with a deviation of 6.9% between the theoretical prediction (92.76 kPa) and numerical result (86.35 kPa). Model tests were conducted to monitor surface, subsurface and river channel settlement of different sections, as well as earth pressure. Results show that settlement above the tunnel axis is greatest, followed by the river slope, where the maximum surface settlement reaches 9.60 mm, slightly exceeding the subsurface value of 9.32 mm. The disturbance range increases with tunnelling distance to about 600 mm. Earth pressure exhibits phased variation, increasing upon approach and decreasing after passage. Numerical simulations provide quantitative validation, while model tests offer qualitative insight into deformation mechanisms.

Cement-sodium silicate (C-S) double slurry grouts are widely employed for surrounding rock reinforcement and water plugging in subsea tunnel construction. However, their performance is highly sensitive to mix proportions and environmental exposure. The long-term durability of these materials and the tunnels they protect is particularly challenged by persistent seawater immersion. This study systematically investigates the effect of real seawater chemistry from four major sea regions in Southeast China on the durability of C-S grouts prepared with a practical engineering mix ratio. The evolution of mechanical properties, hydration products, and microstructure was analyzed to establish correlations between seawater ionic composition and material degradation. Results indicate that a mix proportion of 0.6 water-to-cement ratio (w/c) with 34 Baumé degree (°Bé) sodium silicate delivered optimal performance across all tested marine environments. Early-age strength and compactness were improved by seawater ion infiltration of 1-10 μm, whereas mid- to long-term degradation varied due to sulfate-induced ettringite formation, linked to differing SO42- concentrations. Optimizing the mix proportion generated a dense matrix that converted expansive ion-reaction products into pore-filling materials, thereby enhancing durability in seawater environments. These findings provide practical guidance for optimizing grout mix design to enhance the long-term durability of subsea tunnels in diverse marine environments.

The ultra-low friction effect is easy to induce the sliding instability of deep coal rock, resulting in serious rockburst accidents. Using the self-developed ultra-low friction test device, the mechanical properties and precursor characteristics of deep coal seam sliding instability were analyzed from the perspective of ultra-low friction effect, and the effects of interface roughness (JRC), particle size (D), and filling thickness (H) on ultra-low friction-induced rockburst were revealed. The results show that: The main stage characteristics of the coal block slip instability process are “pre-slip-dynamic fracture-dynamic slip”. In the pre-slip stage, normal force and friction force decrease slightly, and the pre-slip accounts for about 31

During tunnel construction in the southwestern region of China, it is common to traverse soft-rock geological areas. To minimize deformation after tunnel excavation, anchoring materials need to exhibit properties such as high strength, rapid setting, and slight expansion. Meanwhile, to address the high carbon emissions and cost issues associated with cement-based anchoring materials in tunnel construction, and in response to the national requirements for ecological construction and the 2030 carbon peak plan, we developed an environmentally friendly anchoring material based on blast-furnace slag (BFS)-ordinary portland cement (OPC)-rapid-hardening sulfoaluminate cement (RSAC) ternary system, using the theory of synergy. This study systematically investigated the effects of BFS, lithium carbonate, and united expansive agent (UEA) on the setting time, mechanical strength, and linear expansion of the OPC-RSAC binary system. Micromechanism analysis was conducted through hydration heat analysis, X-ray diffraction, and scanning electron microscopy. The pullout model tests on the anchoring body verified the bonding performance and engineering application potential of the new material. The experimental results indicate that the optimal mix ratio, determined through range analysis of orthogonal test data, is 100 parts OPC-RSAC binary cement (with a ratio of 2 & ratio;8), 10% slag powder, 0.1% lithium carbonate, and 2% UEA expansion agent. The 24-h compressive strength is 34.85 MPa, which is an increase of 0.26 MPa compared to RSAC special cement. The initial setting time is 1.74 min, which is 47% faster, with a cost reduction of 30% and a threefold increase in hydration heat within 3 h. Microanalysis shows that the BFS-OPC-RSAC ternary cement-based environmentally friendly material exhibits sufficient hydration reactions, with ettringite crystals interwoven with calcium silicate hydrate (CSH) gel, calcium hydroxide (CH), and calcium aluminate hydrate (CAH) gels to form a dense and stable network. The filling effect of slag particles further densifies the material. Compared to RSAC, the higher aluminum and lower calcium content in slag powder enhances early strength hydration within a certain range, promoting the formation of ettringite and hydrated metal oxides, thereby improving the expansion rate and mechanical strength of the anchoring material. Based on synergy theory, BFS-OPC-RSAC material uses RSAC as the primary base material, fully utilizes BFS waste resources, and combines low-cost OPC materials, reducing the production cost of similar anchoring materials by 30% and lowering carbon emissions. This promotes the green and sustainable development of cement materials.