Accurate prediction of the temperature field in high geothermal tunnels holds significant engineering value for ensuring the safety of tunnel construction and stability of long-term operation. The paper proposed a transient temperature field prediction model based on physics-informed neural network (PINN) for high geothermal tunnels, which can accurately predict the spatiotemporal distribution characteristics of the tunnel temperature field with only a small amount of monitoring data. Firstly, the physical mechanism of heat transfer in high geothermal tunnels was innovatively integrated into a deep learning framework, incorporating the residual block and hard boundary constraint operator to form a PINN model. Secondly, the PINN model was validated through the numerical simulation and physical model test. Ultimately, influencing elements of the tunnel temperature field were comprehensively analysed using the PINN model. The principal conclusions are as follows: (1) The proposed PINN model demonstrates high prediction accuracy. The absolute error between PINN and the finite element numerical solution is less than 0.6 degrees C, and the MAPE metric between PINN and the physical model test result is controlled within 2 %. (2) The MSE, RMSE, and MAPE of the PINN model are all smaller than those of the data-driven DNN model, indicating that the PINN model has better prediction accuracy and reliability. (3) Both the surrounding rock temperature and secondary lining temperature show an upward trend with rising initial rock temperature and ambient temperature, while demonstrating a downward trend with increasing return air speed. Through sensitivity analysis, it is found that the sensitivity of factors influencing the rock temperature at the radial distance r = 9m is as follows: initial rock temperature > ambient temperature > return air speed, and the sensitivity of factors affecting the secondary lining temperature is as follows: ambient temperature > initial rock temperature > return air speed.

This study investigated the hydro-mechanical interaction among a tunnel, stabilizing piles, and a slope under dry and heavy-rainfall conditions. Field measurements were compared with finite element simulations to validate predictions of ground and pile deformation. The validated model was used to evaluate rainfall-induced changes in pore-water pressure, soil displacement, pile response, and slope stability. A parametric analysis examined the effects of pile position, diameter, and length and identified an optimal configuration. Grout injection was assessed under dry and rainfall conditions to determine its influence on soil–structure interaction and deformation control. Comparison between dry and rainfall conditions showed that the maximum settlement under dry conditions was approximately 10 mm, whereas rainfall produced heave deformation of up to 30 mm. Horizontal pile displacement was governed mainly by the lateral movement of the sliding mass, whereas vertical displacement was controlled primarily by tunnel-induced stress redistribution and ground settlement. The optimized pile arrangement and grouting improved deformation control and enhanced the stability of the tunnel–pile–slope system.

Residual rock bridges in unstable rock masses along reservoir banks are subjected to long-term deterioration caused by wet-dry cycles and cumulative seismic disturbances. Their progressive damage and eventual failure directly affect the stability of unstable rock masses. In this study, cyclic direct shear tests were conducted on limestone rock bridges under different numbers of wet-dry cycles and cyclic shear stress ranges. Digital image correlation (DIC) and acoustic emission (AE) techniques were used to monitor crack propagation, damage development, and fracture coalescence under shear cyclic loading. The associated AE response was also analyzed. The results show that wet-dry cycles and higher cyclic shear stresses jointly accelerate deformation accumulation and damage development. All samples subjected to a cyclic shear stress range of 1–5.5MPa remained stable during loading. Under a cyclic shear stress range of 1–7MPa, the samples subjected to 20 and 30 wet-dry cycles failed after 428 and 331cycles, respectively. Damage first spread along the rock bridge and then intensified within the damaged region. Accordingly, the damage connectivity degree (Pc) increased earlier than the overall damage degree (Dc). The damage evolution process comprised four stages: damage initiation, initial damage propagation, sustained damage intensification, and accelerated damage evolution. With increasing numbers of wet-dry cycles and cyclic shear stresses, AE events with high counts and large amplitudes became concentrated in the middle and late loading stages. The b value generally decreased during Stages III and IV. The increasing contribution of large-scale fracture events and the gradual transition toward localized crack propagation and fracture coalescence. These results provide a basis for the long-term prevention and mitigation of unstable rock masses in reservoir areas.

In weak surrounding rock, the closely spaced tunnel group in this study adopts a downward in-situ enlargement restricted to the overlapping segment between the existing and the new tunnels, where the interaction of evolving excavation paths and construction sequences markedly amplifies deformation and stability challenges. To examine the applicability of a non-typical stepwise "remove-backfill-downward enlargement" scheme (hereafter abbreviated as fill-then-excavate) for such settings, an ongoing closely spaced tunnel group in weak surrounding rock project along the new Chengdu-Chongqing Central Line was investigated. Laboratory tests were performed to characterize the mechanical behavior of mudstone interbedded with sandstone, and numerical simulations were integrated with in-situ monitoring to compare ground and structural deformations. Alternative backfilling strategies prior to enlargement and reinforcement options for the inter-tunnel rock pillar were assessed for construction optimization. Results indicate that stress-strain curves remain similar in shape across confining pressures, while triaxial strength and deformation characteristics vary markedly; bedding and sand-lens heterogeneity leads to pronounced mechanical anisotropy. Rightward advancement after backfilling induces early unloading in the upper-right transition zone, shifting the settlement center toward the upper-right and forming an asymmetric, unimodal pattern aligned with the enlargement contour. Excavation of the upper-bench core triggers a jump in circumferential displacement around the enlarged tunnel, with a peak of 7.79 mm. Distinct backfilling schemes perturb the surrounding rock at different stages and thereby affect both surface and lining deformations; the full backfill followed by unified enlargement scheme reduces crown settlement by 3 mm. Moreover, small-pipe grouting lowers crown settlement by approximately 20%, raises the cumulative vertical stress at the core of the middle rock pillar to 3.77-4.43 MPa, and-with simple procedures and low disturbance-emerges as a preferred option for reinforcing the pillar in closely spaced tunnels within weak rock.

ABSTRACT In the equivalent area method, composite foundations are simplified as homogeneous materials, by which the efficiency of shear strength calculation is significantly improved. This method has been widely applied in the quick evaluation of subgrade stability. However, the interaction between piles and soil, as well as the actual failure modes of composite foundations are neglected. As a result, deviations between the predicted and actual shear strength are often observed. In this study, direct shear tests and discrete element numerical simulations were conducted. The shear mechanical properties of CFG pile composite foundations were systematically investigated from both macroscopic and microscopic perspectives. Based on the findings, a modified equivalent area method was proposed and validated. The results indicate that significant differences in the shear strength and failure mode exist between soft soil and CFG piles. As the replacement area radio increases, the shear strength of the composite foundation significantly increases, and the failure mode of the pile changes accordingly. During shearing, the piles and the surrounding soil gradually form a coherent overall structure that undergoes coordinated deformation and jointly bears the shear load. The piles near the shear direction exhibit denser particle displacement, crack distribution, and bond failure, showing a progressive failure pattern. The shear strength calculated by the modified method is more conservative than that obtained by the equivalent area method. The modified method can more accurately reflect the actual situation of the composite foundation.

The cooling effectiveness of single-head ventilation systems in high-temperature tunnels with multiple working faces is often insufficient, posing risks to both personnel and machinery. This study investigates the synergistic cooling mechanism between single-head ventilation and mechanical refrigeration through field monitoring, numerical simulations, and parametric analysis in a high geothermal tunnel. A three-dimensional coupled heat transfer model was developed to assess the effects of various parameters, including the refrigeration equipment output parameters (air temperature T-m: 5 similar to 25 degrees C, air volume V-m: 10 similar to 30 m(3)/s) and the relative positioning of the refrigeration equipment air duct and the main ventilation duct (their outlets distance L) on the tunnel cooling efficiency and temperature distribution. The model was validated using field data, with an absolute error <= 0.94 degrees C and a relative error <3%. Additionally, a polynomial regression model was used to predict the environmental temperature at the excavation face (T-a) based on Tm and V-m. Results show that: (1) Mechanical refrigeration reduced the average tunnel temperature by up to 7.0 degrees C (18.4%), with a maximum drop of 9.1 degrees C at the excavation face. (2) When the refrigeration equipment and main air duct outlets are aligned, the cooling effect at the excavation face is maximized. To optimize both the cooling efficiency and the temperature uniformity at the excavation face, it is recommended to connect the r refrigeration equipment air duct directly to the main ventilation duct. (3) The relationship between T-m, V-m, and T-a follows distinct trends: T-a increased linearly with T-m and decreased with V-m in a concave-down power-law fashion. (4) Considering both cooling effectiveness and economic efficiency, the output parameters of the refrigeration equipment are set to T-m = 18.8 degrees C and V-m = 30 m(3)/s, with the main ventilation air volume remaining unchanged.

To address the durability issues of fiber-reinforced concrete (FRC) in sulfate environments, this study investigates the macroscopic performance and microstructural evolution of polypropylene fiber systems (fine polypropylene fibers [FPF] 0.8 kg/m(3), coarse polypropylene fibers [CPF] 6 kg/m(3)) under a 150-day wet-dry cyclic sulfate attack test in a 5% sodium sulfate (Na2SO4) solution. The synergistic reinforcement mechanisms of FPF and CPF were analyzed. The results indicate that the hybrid fiber group (B5: 0.8% FPF + 8% CPF) exhibited the best performance, with a mass loss rate of only 1.49%, a compressive strength of 38.8 MPa, and a relative dynamic modulus retention of 83.3% after 150 days of sulfate exposure. Fine fibers played a crucial role in inhibiting microcrack initiation, while coarse fibers were more effective in controlling the propagation of macrocracks. Their synergistic effect reduced pore connectivity and delayed sulfate ion penetration, enhancing sulfate resistance. The log-normal distribution model was employed to quantify the nonlinear characteristics of strength deterioration (coefficient of determination > 0.93), while microscopic analysis confirmed that the fiber network effectively mitigated stress accumulation and interfacial damage. This study provides a multiscale synergistic reinforcement strategy for the design of FRC in sulfate environments, significantly improving the durability and service life of concrete structures.

As tunnels are increasingly constructed at greater depths and lengths, high rock temperatures and hot water gushing are becoming significant challenges for the safety of tunnel construction and operation. The problem of crystallization blockage in the drainage system is one of the main forms of tunnel diseases during operation. When the drainage system of a high-temperature water gushing tunnel encounters crystallization blockage, the hot water cannot be discharged from the tunnel in time and accumulates outside the supporting structure. The coupled effect of high water pressure and additional thermal stress will significantly increase the risk of lining cracks, which is a long-term safety hazard for high-temperature water gushing tunnels. To prevent the crystallization blockage problem of the drainage system in such tunnels, on-site sampling and testing were conducted in a representative hot water gushing tunnel to determine the main components of the crystalline deposits. Through laboratory tests, the influence of high water temperature on the ion leaching rate from shotcrete was investigated. The crystallization rate and crystal morphology evolution of calcium carbonate under high water temperature conditions were also analyzed to further reveal the clogging mechanism. The results indicate that the leakage water on the outer surface of shotcrete contains high concentrations of Ca2+, CO32-, and HCO3-, with the main component of the crystalline deposits being calcium carbonate. The calcium leaching process from shotcrete is accompanied by the leaching of other ions. The conductivity of the leaching solution gradually increases with the increase of water temperature. At elevated water temperatures, both the initial crystallization rate and the final mass of calcium carbonate deposits are significantly increased. Both the nucleation and growth rates of calcium carbonate are accelerated under higher water temperatures (T >= 50 degrees C). When the crystallization time reaches 240 min, the mass of calcium carbonate formed at 50 degrees C, 70 degrees C, and 90 degrees C is 216.8%, 344.0%, and 392.1% of that formed at 30 degrees C, respectively. Additionally, elevated water temperatures promote the mutual transformation between calcite and aragonite crystals. The findings of this study can provide essential insights for the prevention of crystallization blockage in the drainage system of high-temperature water gushing tunnels.

The construction mechanical response of small-spacing tunnel groups is strongly influenced by surrounding rock grade, tunnel spacing, and burial depth. Based on the close-stacked tunnel group project in Hongyan Village, Chongqing, this study establishes a PLAXIS 3D numerical model to investigate the deformation and stress response of the tunnel group under different conditions. The results show that surrounding rock grade mainly controls the deformation magnitude. As the surrounding rock grade decreases from Grade I to Grade IV, the maximum arch crown settlement of the main tunnel increases from 1.51 mm to 10.45 mm. Tunnel spacing mainly affects the interaction intensity between adjacent tunnels. When the spacing decreases to 1.0 m, the arch crown settlement reaches 8.94 mm, indicating a strengthened group-tunnel effect. Burial depth primarily amplifies the overall deformation level. When the burial depth increases from 3.0 m to 23.8 m, the arch crown settlement increases by 7.81 mm. These results indicate that the stability of small-spacing tunnel groups is jointly controlled by surrounding rock quality, spatial spacing, and burial-depth-induced stress conditions. The findings provide a reference for stability evaluation and support design of close-stacked tunnel groups under complex geological conditions.

In view of the geological disasters caused by the deterioration of rock mass in the fluctuation zone of the Three Gorges Reservoir area, the marl of the Wuxia section was selected as the object, and laboratory acid corrosion and wet-dry cyclic tests were conducted to reveal the damage and deterioration mechanism of marl in the fluctuation zone with acidic environment. The results show that: (1) When the pH was 3, 5 and 7, the mass loss rate was 0.019%~0.066%, 0.010%~0.029% and 0.006%~0.017% with 5 ~ 15 circles, respectively. (2) When the pH values were 3, 5 and 7, after 15-time acidic erosion and dry-wet cycles, the average porosity increment of the samples was 0.104%, 0.093% and 0.092%, respectively, and the initial porositywas found to influence the rate of porosity increase during the early stage of the experiment. (3) At the microscopic level, the pore volume and crack length were increased, and the number of pores and cracks increased under the scanning election microscope analysis, which revealed the damage and deterioration mechanism of samples. (4) The uniaxial compressive test of the sample was inversely proportional to the number of acidic erosion and dry-wet cycles. At pH values of 3, 5, and 7, the reduction rate of rock uniaxial compressive strength ranged from 5.65% to 28.25% after 5, 10, and 15 cycles of acid corrosion-drying-wetting, respectively. (5) The variation range of the mass loss rate, pore growth rate and the uniaxial compressive strength reduction rate of rock samples were all initially slow, later fast and then slow, and finally tended to be stable. (6) The error between the result of calculation with uniaxial compressive strength fitting formula and the test is less than 10%, which could prove the fit is reasonable, universally. The research could provide theoretical support for unstable rocks mass of geological disasters in the Three Gorges Reservoir area.

Microseismic monitoring of highway slopes is one of the key technologies for the early warning of geological hazards such as unstable rockfalls of highway slopes. To address the problems of severe noise interference and highly imbalanced microseismic event samples in actual monitoring scenarios, a Denoising Attention Loss Network was proposed for identification of microseismic events of highway slopes. First, a deep time–frequency denoising module with dual time–frequency constraints was designed, in which an encoding-sampling module was constructed and combined with time–frequency loss optimization to enhance noise suppression capability. Second, a hybrid attention mechanism incorporating channel attention and temporal attention was introduced to improve the feature extraction ability of microseismic signals. Finally, a momentum-adaptive weighted class-balanced loss was proposed to dynamically adjust loss salience and address the data imbalance problem. Extensive experiments conducted on highway slope microseismic datasets demonstrated the robustness of the proposed method under strong noise interference and class imbalance, highlighting its practical value for highway slope rockfall monitoring.

The bedded salt rock strata in China are suitable for constructing horizontal salt cavern gas storage. To ensure the long-term safety of a proposed salt cavern gas storage, the long-term operational process of which under different minimum internal pressures and initial permeability of salt rock was simulated through numerical simulation means. Based on the simulation results, the evolution of stability indicators (e.g., cavern wall displacement, volume shrinkage) and tightness indicators (e.g., seepage range, pore pressure) was analyzed, the influences of minimum internal pressure and initial permeability of salt rock on these indicators were discussed, and the reasonable range of minimum internal pressure and the threshold of initial permeability for gas storage construction were identified. The results show that as minimum internal pressure increases, both the cavern wall displacement and volume shrinkage rate gradually decrease, while gas seepage ranges in both horizontal and vertical directions progressively expand; as initial permeability of salt rock increases, the cavern wall displacement, volume shrinkage rate, and vertical gas seepage range gradually increase, while the horizontal gas seepage range first decreases and then increases. On this basis, an integrated evaluation system for the long-term safety of horizontal salt cavern gas storage was developed by incorporating both stability and tightness factors using the analytic hierarchy process, and a quantitative assessment of long-term safety on the proposed salt cavern gas storage was conducted through fuzzy comprehensive evaluation method. The results indicate that the safety level of the proposed salt cavern gas storage corresponds to Grade III (Generally Safe), which meets the long-term safety requirements.

Soil-rock mixture (S-RM), an important geotechnical material, is widely used in subgrade and slope engineering. Triaxial shear test can effectively simulate the complex mechanical properties and test the mechanical parameters. However, there is a specimen size effect during testing, and the choice of different specimen sizes can influence the test results. In order to investigate the specimen size effect in the test, this paper first proposes a three-dimensional discrete element refined modeling method for S-RM, then develops a flexible boundary loading method for triaxial shear test using coupled PFC3D with FLAC3D, and subsequently conducts triaxial shear tests on S-RM of different sizes. The test results show that as the ratio of specimen diameter to maximum particle size of the rock block (lambda) or the aspect ratio (alpha) increases, both the quantity of force chains and cracks increase, while shear band evolves into conjugate "X" shape. With the increase of lambda and alpha, the stress-strain curves transition from strain hardening to strain softening. Both cohesion (c) and internal friction angle (phi) exhibit continuous reduction, characterized by an initial rapid decline followed by a gradual deceleration in rate, eventually stabilizing when lambda and alpha reach sufficiently large values. Therefore, the specimen size effect becomes less significant when the specimen size is relatively large. When the lambda exceeds 5.0 and the alpha surpasses 2.0, the specimen size effect in triaxial shear tests for S-RM diminishes to an acceptable range. Consequently, it is rec-ommended to employ specimens with lambda greater than 5.0 and alpha greater than 2.0 in triaxial shear tests for S-RM.

To address the unclear bearing mechanism of single-layer lining structures constructed with high-performance fiberreinforced shotcrete under layered construction, this paper investigates the influence of layered construction on the failure mechanism of single-layer lining structures. Uniaxial compression tests were conducted on specimens with six thickness ratios lambda h (the ratio of the second layer to the first layer of fiber-reinforced shotcrete). The failure process of specimens under uniaxial compression was monitored using three-dimensional digital image correlation (DIC) technology and acoustic emission (AE) technology. The results indicate that the uniaxial compressive strength of the specimens initially increases and then decreases with increasing thickness ratio, reaching its maximum when the thickness ratio is 1. All fiber-reinforced shotcrete specimens exhibit combined tensile-shear failure, but layering increases the proportion of shear failure cracks. Layered construction delays the development of microcracks in the specimens, with large-area cracks appearing later. Moderate layering can effectively enhance the energy storage and deformation capacity of the concrete structure, while an excessively thin lower layer may induce instability. The findings of this study provide a reference for similar engineering designs.

Abrasive waterjet (AWJ) cutting is an emerging technique for efficient and environmentally friendly rock fragmentation, especially in confined or high-risk underground construction scenarios. However, accurately measuring and predicting cutting depth under varying geological and operational conditions remains a challenge. To address this issue, a CT-based 3D reconstruction and Python image recognition system was developed to enable semi-automated and accurate depth measurement, replacing subjective surface observation. A specific-energy-efficiency-guided intelligent prediction model is further established through dimensional analysis, similarity theory, and GA-based calibration. A series of orthogonal and comparative experiments on sandstone and limestone reveal that traverse speed is the dominant influencing parameter, and sandstone exhibits 5-6 times higher specific energy efficiency compared to limestone. The calibrated model achieves high predictive reliability (R 2 = 0.996 for limestone, 0.991 for sandstone) and is further validated using published granite data (R 2 = 0.984), demonstrating its cross-material generalization capability. This study contributes a digital metrology approach for AWJ cutting evaluation and lays the foundation for intelligent, energy-aware measurement and control in extreme excavation applications such as tunneling, mining, and lunar drilling.

The mechanical response characteristics of the adjacent structures involving non-parallel complex subway tunnels significantly affect the stability of tunnel structures and ground settlement. To analyze the mechanical stability of both the main and auxiliary tunnels in the vicinity of the subway station, an integrated methodological framework that combines physical model testing with advanced numerical simulation techniques was adopted to precisely identify the deformation characteristics of adjacent non-parallel main and auxiliary tunnels. In addition, the study systematically investigated the influence mechanisms associated with construction sequence, construction methods, and excavation step spacing on the mechanical behavior of the tunnel structures and the stability of stratum. The results indicate that the disturbance-induced settlement of the main tunnel crown gradually decreases as adjacent non-parallel auxiliary tunnels are excavated upward. Meanwhile, as the vertical elevation difference between the main and auxiliary tunnels increases, the principal stress borne by the main tunnel lining is gradually transferred toward the lining of the auxiliary tunnel. Excavation of Auxiliary Tunnel No. 6 and the wind pavilion trigger sudden mutual deformation and abrupt stress release in the intervening rock mass; therefore, particular attention should be paid to its stability and reinforcement. The deformation of the tunnel group and the ventilation shaft structure mainly occurs during the excavation process. Construction method and step length significantly affect vault deformation and surface settlement of the tunnel group, whereas construction sequence mainly impacts stress disturbance among individual tunnels.

Column-shaped unstable rocks are commonly developed in canyons and karst regions, and their instability is strongly affected by the mechanical characteristics of the underlying base. In this study, the Zengziyan W12# unstable rock and the Wangxia W2 unstable rock in Chongqing, China, were selected as representative cases of a soft-hard interlayered base and a homogeneous weak base, respectively. Finite element models were established to compare the distributions of equivalent stress, shear stress, and displacement under self-weight loading. The results show that, in the soft-hard interlayered base, stress is mainly concentrated in the hard layers, and the high shear-stress zones are segmented by these interlayers. The instability-controlling location tends to shift upward to the degraded zone at the bottom of the unstable rock mass, indicating a fracture-collapse tendency. In contrast, the homogeneous weak base shows more continuous stress transmission and shear-stress development, which is favorable for the formation of a through-going shear zone within the base. These results indicate that the base structure type regulates the stress transfer path, shear-zone continuity, and instability-controlling location of column-shaped unstable rocks, thereby providing a mechanical basis for stability assessment and targeted prevention.

The interface failure between shotcrete and rock is a critical defect in underground construction. However, the macroscopic undulating morphology of the hard surrounding rock surface formed by tunnel blasting significantly affects the interfacial adhesion performance. Previous studies have primarily focused on interfaces with regular morphologies, which fundamentally differ from the surface morphology of hard rock surrounding tunnels formed by blasting. To address this gap, this study proposes a three-dimensional point cloud-based characterization metric (PZD) to quantify the macroscopic undulation features of surrounding rock surfaces after blasting. Based on actual tunnel data, rock-fiber shotcrete composite specimens simulating the random undulating characteristics of surrounding rock surfaces were prepared. The experimental results demonstrated a non-monotonic relationship between interfacial adhesion performance and PZD variations. The adhesion strength of the composites initially increased and subsequently decreased with increasing PZD values, reaching a peak of 1.834 MPa at PZD = 4-5. The study identifies an optimal PZD range of 2-5 for hard surrounding rock and characterizes three corresponding failure modes. This discovery provides an experimental foundation for enhancing the integrity and stability of tunnel support systems.