In order to explore the surface displacement law caused by the entire process of rectangular shield tunneling, the effects of the additional cutterhead thrust (p 1) of the cutterhead, the shield shell friction (p 2), the additional grouting pressure (p 3) at the tail of the shield, and ground loss caused by the quasi-rectangular shield tunneling were considered. The traditional integration method for the above four factors was simplified, and a simplified calculation method for surface displacement values was proposed. Based on the Zhengzhou Metro Line 8 project, the surface displacement values caused by each factor were calculated. The simplified method calculation values were compared and verified with the integration method calculation values and measured data. The influence of parameter changes on the accuracy of displacement calculation values and simplified methods was further analyzed. The results show that the surface displacement values calculated by the simplified method are in good agreement with the values calculated by the integral method and the measured data. The Poisson's ratio of soil (mu), the internal friction angle (phi), and the depth-to-diameter ratio (H d) are the main parameters that affect the accuracy of the simplified method. The conditions that need to be met to control the calculation error of surface displacement within 5%, 10%, and 20% are given, and the applicable working conditions of the simplified method are summarized.

When a shield tunnel passes beneath an existing tunnel, the existing tunnel exhibits a shielding effect, which influences ground and shallow soil settlement. To investigate this mechanism, a model describing the impact of tunnel shielding on overlying strata was developed based on the principle of tunnel-soil synergistic deformation. The soil uplifted effect was introduced to simulate the influence of the shielding effect on settlement in the upper soil layers, and a calculation method for soil settlement considering the shielding effect of existing tunnels was proposed. This method was applied to a case study of an expressway tunnel passing beneath Line 2 of the Hangzhou Metro. The calculated settlements at different depths were analyzed and validated for reliability. Furthermore, the influences of existing tunnel burial depth (Hs), diameter (D), tunnel stiffness, and undercrossing angle (alpha) on the magnitude of the shielding effect and soil settlement were examined. The findings indicate that the shielding effect of the existing tunnel is significant during shield undercrossing. The calculated surface settlement curve, which accounts for the tunnel shielding effect, aligns more closely with measured data, demonstrating improved accuracy. The shielding effect notably reduces surface settlement and settlement at various depths near the crossing center. At the centers of three cross-sections, surface settlement decreased by 29.1 %, 15.1 %, and 14.0 %, respectively. The degree of reduction is related to the horizontal distance from the existing tunnel, with the shielding effect diminishing as distance increases. A decrease in Hs, an increase in D, and greater tunnel stiffness all lead to reduced ground settlement in the central area, though the spatial extent over which the settlement curve is lowered is predominantly controlled by Hs. The shielding effect of the existing tunnel on ground settlement varies with the alpha. For alpha values of 90 degrees and 60 degrees, both the magnitude of reduction in central surface settlement and the spatial extent of the influence are similar. In contrast, when alpha is 30 degrees, the effectiveness of the shielding in reducing central settlement decreases, but the area affected by the shielding becomes larger.

In viscoelastic-plastic surrounding rock, rheological processes gradually increase support reaction forces, affecting the stress state. Analyzing such rock requires consideration of stress path influences. In high-temperature environments, rock properties change with temperature, further impacting stress paths. Therefore, studying deep buried high geothermal tunnels necessitates analyzing viscoelastic-plastic surrounding rock while accounting for both high-temperature effects and stress paths. The coupling of high-temperature effects and stress paths influences the stress state of tunnel rock. By combining the Mohr-Coulomb strength criterion with the generalized Kelvin rheological model, we optimize stress, strain, and displacement calculations for supported viscoelastic-plastic surrounding rock. We derive analytical solutions for stresses, wall displacements, and plastic zone radii in viscoelastic-plastic surrounding rock, considering strength parameter deterioration due to high-temperature effects and stress paths. Using existing research on granite’s physical and mechanical parameter variations with temperature, we develop temperature-dependent fitting equations for granite's physical parameter deterioration. We theoretically calculate and analyze relationships among surrounding rock stress, tunnel wall displacement, and plastic zone radius. Results indicate that as temperature increases, its impact on rock’s physical properties significantly affects stress and strain. Moreover, as temperature gradually rises, the rock’s physical properties undergo additional changes, amplifying the impact of high-temperature effects.

With the rapid expansion of metro networks in China, the cumulative length of shield tunnels constructed in soft soil has exceeded 6000 km. While extensive engineering experience has been accumulated, these tunnels are still increasingly affected by service-related issues, such as long-term settlement, deformation, structural damage, and water leakage. These defects impose challenges to both operational safety and maintenance costs. This study provides a systematic overview of the major defect types and their spatial distribution patterns, highlighting their implications for the resilience and safety of shield tunnels. The coupled development and interaction of these defects are analyzed, and the limitations of existing research methodologies are critically examined. Based on these findings, this paper introduced a novel load mode to consider service tunnel’s environmental load variations, thereby proposing insights for enhancing the resilience of shield tunnel design from the tunnel–soil interaction perspective. Meantime, an elastic–plastic resistance model is also developed to address the degradation of lateral resistance at the tunnel waist caused by the fluidity of soft soils. A mathematical formulation of system stiffness is further developed by treating the tunnel and soil as an integrated system. Building upon this formulation, a resilience‑based design method is proposed to ensure the resilient performance of shield tunnels throughout the entire life cycle. The method is validated through its application to the Foshan and Shaoxing metro systems, with results demonstrating that optimizing system stiffness can significantly improve the resilience of shield tunnel structures in soft soils.

In deeply buried, high-geothermal, and high-geo-stress tunnels, the coupling effects of regional stress and structural features are the primary factors influencing the stability of the surrounding rock. In this study, taking a deeply buried, high-geothermal tunnel crossing multiple active fault zones in western China as the research object, we investigated the coupling of the regional geo-stress and stratigraphic structural characteristics using temperature and in-situ stress data from deep boreholes. The impacts on geoengineering projects, including the stability of the active fault zones along the tunnel, the rockburst characteristics, which are influenced by the high-geothermal gradient, and the large deformation of the surrounding rock, were analyzed. The results showed that (1) the geo-stress and stratigraphic structural characteristics exhibited strong coupling effects in the high-geothermal tunnels. This was prominently manifested by the orientation of the maximum horizontal principal stress in the fault zone, which is either parallel to the fault strike or intersects with it at a very small angle, leading to structural segmentation of the fault. (2) The high-geothermal gradient intensified the stress concentration in the surrounding rock after tunnel excavation, accelerating the occurrence of rockbursts and increasing the intensity as the temperature increased. (3) The heat flow in the deep strata in the region created a high-geothermal environment for the tunnel, which generated additional thermal stress in the surrounding rock, leading to stress accumulation during the stress release process. This causes crack initiation, development, propagation, aggregation, and penetration in the surrounding rock, resulting in large rock deformation and a high-temperature-induced strong rheology. In conclusion, the research findings provide scientific references for ensuring the stability of the surrounding rock and for designing support structures in deeply buried, high-geothermal, and high-geo-stress tunnels.

The dynamic mechanical response of rocks remains poorly understood under true three-dimensional (3D) stress conditions during underground excavation. Furthermore, there is a scarcity of constitutive models that can adequately capture the coupled effects of 3D static and micro-dynamic disturbances. To address this gap, a novel testing methodology for true triaxial coupled static-dynamic loading is developed. This approach is designed to replicate the disturbance and damage processes experienced by surrounding rock. The experimental program began with true triaxial static tests on monzogabbro, employing various confining pressures for σ2 and σ3. This was followed by multistage disturbance tests that investigated the rock's deformation and strength response under combined static-dynamic loads by varying σ2, σ3, amplitude (A), and frequency (f). On the theoretical side, leveraging the principles of irreversible thermodynamics and the Mogi-Coulomb 3D strength criterion, a novel elastoplastic dynamic damage constitutive model was formulated and implemented numerically. The study concluded with a sensitivity analysis to quantify the impact of key model parameters (Bm and Cm) on the simulated disturbance behaviors. Parameter Bm controls the nonlinear characteristics of rock disturbance deformation deceleration and constant speed stages, while parameter Cm controls the nonlinear characteristics of rock disturbance deformation acceleration stage. This model could simulate the experimental results well under different σ2, σ3, amplitude A, and frequency f.

Study region The arid region of northwest China Study focus Intense evaporative losses threaten the construction and safe operation of pumped storage plants (PSP). To address the issue of rapid water level fluctuations in the upper and lower reservoirs, floating ball coverage technology is one of the ideal measures to reduce reservoir surface evaporation. However, the upper and lower reservoirs of PSP are located in different meteorological environments (with high water heads), and their characteristics such as frequent mutual exchange of water bodies and their heat, as well as frictional heating between water flow and units, result in a significant difference in the evaporation calculation model compared with traditional single reservoir. This study integrates the operating conditions, meteorology and ball properties into the model, which is applied to evaluate the water-saving effects, and potential benefits of floating ball coverage on the reservoirs. New hydrological insights The results show that: when the floating ball coverage rate is 74%, the water-saving effect of the reservoirs reaches 61.2%. The simulation results are consistent with the observation data from field tests of small evaporation ponds. Furthermore, the water temperature drop rate of the covered reservoirs is significantly reduced, which can effectively inhibit water freezing in winter. This study can provide a reference for the planning, design, and safe operation of PSP in arid regions.

The characteristics of the coupling between the high geothermal temperatures and high in-situ stresses in deep rock masses, as well as the characteristics of the plastic-zone evolution, are important reference indicators for safety control of the rock surrounding deeply buried tunnels. To thoroughly analyze the expansion and evolution characteristics of the plastic zone in rock with a high geothermal temperature that surrounds a deeply buried tunnel, high-geothermal-temperature and high-in-situ-stress data were measured using the high-temperature borehole hydraulic-fracturing method. Using these data, the effects of the coupled high geothermal temperature and high in-situ stress in a deeply buried tunnel were studied. The variations in the thermal stresses in the high-temperature rock mass were quantitatively analyzed, and the expansion and evolution of the plastic zone in the surrounding rock under the coupling effect were studied. The study produced four primary sets of results. First, the principal stresses in the deeply buried tunnel with a high geothermal temperature could be characterized by the expression σ_H>σ_h>σ_Z , and the principal stresses generally exhibited linear increasing trends as the burial depth and geothermal temperature increased. Second, under the coupled action of high geothermal temperature and in-situ stress, as the geothermal temperature rose, the plastic zone of the surrounding rock gradually expanded. The shape of the plastic zone also changed from elliptical to annular, and finally to a “butterfly” shape, and dangerous expansion of the plastic zone occurred locally. Third, the irregularity of the plastic-zone expansion gradually increased as the lateral pressure coefficient decreased. The morphology of the plastic zone in the surrounding rock evolved from an elliptical shape to a “butterfly” shape, and the extension of the plastic zone significantly affected its deterioration in the surrounding rock. Fourth, in deep rock with a high geothermal temperature, a high deviatoric stress was likely to form in the surrounding rock, and the local distortion of the plastic zone caused by this stress could lead to dangerous expansion of the plastic zone, which could eventually produce instability in the rock surrounding the tunnel.

Accidental ground surcharge loads can induce adverse effects such as segment cracking in underlying shield tunnel structures, with particularly pronounced impacts on pre-damaged tunnel segments. Cracks represent one of the most common initial damage forms in shield tunnel structures. To investigate through-crack failure mechanisms in shield tunnel segments with initial cracks under surcharge loading, this study conducted 1:8 scaled indoor model tests, considering factors including initial crack length, quantity, morphology, and surcharge position. Research findings demonstrate that increased initial crack length and quantity significantly reduce the critical load required for through-crack formation. Specifically, segments with 9 cm longitudinal initial cracks required 50.9% less load to develop through-cracks compared to intact segments. Similarly, segments containing two 9 cm circumferential initial cracks exhibited a 22.1% reduction in critical load relative to those with single circumferential cracks. Initial cracks in pre-damaged segments substantially influence the propagation path of new cracks during subsequent loading failures. The detrimental effects of staggered longitudinal-circumferential initial cracks exceed those of purely longitudinal cracks, which themselves pose greater risks than circumferential cracks alone. Bilateral surcharge loading significantly increases the critical load threshold for through-crack formation compared to unilateral loading. This highlights the severe structural risks associated with uneven load distribution.

In this study, the calcium leaching behavior in hydraulic concrete under aggressive environments was systematically investigated. Concrete specimens with water-to-binder ratios of 0.45 were subjected to accelerated leaching in 6 mol/L NH4Cl solutions. Macro-properties, including the porosity, leaching depth, and cumulative calcium dissolution, were quantified over 360 days. Microstructural characterization via scanning electron microscopy and phase composition analysis through X-ray diffraction (XRD) revealed the dissolution mechanisms of calcium hydroxide (CH) and calcium silicate hydrate (C-S-H) gels. In addition, a novel two-dimensional reactive transport model was developed within the COMSOL Multiphysics framework that explicitly incorporated the pore structure evolution (tortuosity and clogging effects) and interfacial transition zone heterogeneity. Analysis of the calcium leaching model and experimental results indicated that CH dissolution dominated the early leaching stage (0–30 days), while C–S–H decalcification governed the intermediate stage (30–150 days). As the leaching depth approached approximately 15 mm after 360 days of exposure, the erosion process stabilized and entered a steady-state development phase, which was primarily attributed to pore-blocking effects and densification of the inner matrix. The SiO2 crystallinity index derived from the XRD analysis showed a strong correlation with the rate of C–S–H decomposition.

Infrastructure construction and resource exploitation in cold areas are of great significance to social development. The freeze–thaw cycle experiment, uniaxial compression, CT scanning and frost heave force monitoring were carried out on the precast fissure red sandstone of slope in Fugu area of northern Shaanxi Province. Utilising three-dimensional reconstruction techniques, we analysed the dynamic mechanical properties of rock samples, considering both frost heave force monitoring and the uniaxial compression and CT scanning. By introducing the fractal dimension, we established a freeze–thaw load damage model for fractured sandstone. Furthermore, we conducted a correlation analysis between the micro- and macro-scales, aiming to explore the effects of freeze–thaw process on rock samples. With the increasing number of freeze–thaw cycles, the quality and wave velocity of water-saturated sandstone decrease significantly, which is mainly due to the gradual penetration of internal defects, which makes the originally tight particle structure become loose, and the water-saturated sandstone is not able to be removed. The originally tight particle structure become loose, and at the same time, the internal pores and micro-cracks expand and connect with each other. By conducting frost heave force monitoring and performing dynamic mechanical testing on sandstone samples, it is observed that the fracture part of sandstone presents a positive micro-strain due to the participation of water in the state of saturated water, and its peak strain gradually increases with the increase in freeze–thaw cycle.

Real-time and accurate assessment of the Uniaxial Compressive Strength (UCS) of surrounding rock during Tunnel Boring Machine (TBM) tunneling is crucial for adjusting control parameters. However, existing methods face challenges in achieving the timely and accurate acquisition of UCS. Furthermore, there has yet to be research utilizing interpretable artificial intelligence to explore the relationship between tunneling parameters and UCS, which could provide new insights. To address these issues, this study proposes an interpretable artificial intelligence model to predict UCS based on TBM tunneling parameters. The proposed model is called the Joint Denoising and Weighted Interpretable Ensemble Model (JD-WIEM), which comprises data Joint Denoising (JD), a performance-driven weighted ensemble framework, and model interpretation. The JD approach utilizes the multi-level decomposition and collaborative processing strategies of multiple denoising methods to separate noise from different frequency components of complex signals. The performance-driven weighted ensemble framework leverages adaptive weighting to enhance the complementary performance strengths of heterogeneous base models, capturing data characteristics from multiple dimensions. Accumulated Local Effects and SHapley Additive exPlanations are used to determine the key features that predict UCS and to reveal the sensitivity of features to changes in UCS. Moreover, a model transfer strategy is proposed to enhance JD-WIEM’s applicability under diverse geological conditions. The model was validated using data from six water conveyance tunnels. The results indicate that JD-WIEM achieved a coefficient of determination of 0.9834, outperforming state-of-the-art methods. Using JD to process the tunneling data significantly improved the model’s prediction accuracy. From a global perspective, thrust was the most critical feature for predicting UCS. In addition, the thrust and Field Penetration Index (FPI) exhibited greater sensitivity to rapid increases in UCS within high-strength surrounding rocks; revolutions per minute was more sensitive to UCS rapid increases in low-strength surrounding rocks, and penetration showed higher sensitivity to rapid decreases in UCS. This study is vital for ensuring efficient TBM tunneling. Highlights

This study aims to investigate the responses of shield tunnel structures subjected to disturbances caused by bilateral pit excavation, and it systematically reveals for the first time the impact mechanism of bilateral pit excavation on the distribution of perimeter pressure and deformation patterns of shield tunnels. Using a bilateral pit excavation project in Nanjing as a case study, this research establishes methods for calculating longitudinal displacement and circumferential pressure of tunnels under bilateral pit excavation conditions, employing the image source method for analysis. A refined three-ring segment model is developed, and the load structure method is used to analyze the impact of deep foundation excavation on the tunnel located between the two excavation sites. The results indicate that, compared to unilateral excavation, bilateral excavation significantly increases the perimeter pressure at the top and bottom of the tunnel, with a smaller increase in pressure at the arch waist. The deformation pattern is characterized by contraction at the top and bottom and expansion at the waist, forming a transverse elliptical deformation. The maximum vertical convergence values of the middle segment ring are 25.00 mm at the top and 25.88 mm at the bottom, with a vertical absolute convergence value of 44.5 mm and a convergence ratio (Delta Dt/Dt) of 0.72%. As the foundation coefficient increases, the perimeter pressure at the top and bottom of the tunnel also increases. When the tunnel is closer to the foundation pits (Sp decreases), the perimeter pressure at the bottom of the tunnel increases. Conversely, as the distance between the two foundation pits (S) increases, the impact of excavation on the tunnel shifts from the upper part to the lower part, resulting in decreased upper perimeter pressure and increased lower perimeter pressure. The research findings provide important references for similar engineering projects.

软弱围岩挤压大变形、支护结构变形失效、TBM护盾卡机等是复杂地质条件下跨流域调水超长深埋隧洞的关键技术问题,国内某深埋软岩输水隧洞在施工时出现软岩膨胀大变形,在隧洞TBM施工过程中顶管片在左、右侧管片上纵缝受偏压影响,其错台量较大,为了确保隧洞衬砌结构长期安全运行,本文通过TBM施工强膨胀围岩挤压大变形加固计算,对错台部分管片采用钢支撑纵环向加固、自进式中空锚杆化灌或水泥灌浆加固措施;选择不利断面对加固后的隧洞围岩进行长期稳定性仿真计算分析,并结合运行期6个监测断面的实测数据与监控指标进行对比分析,加固后管片裂缝错台不再继续扩展,表明该处置方案十分成功,研究成果可为其他类似工程提供借鉴与参考.

寒区水工隧洞在通风条件下产生的温度变化会影响衬砌结构力学性能,进而影响水工隧洞的安全运行.以新疆布伦口水电站水工隧洞为依托,基于现场监测数据,采用有限元法对在不同风温、风速下隧洞不同深度处衬砌结构的热学、力学耦合特性进行深入分析.结果表明:不同风温下水工隧洞洞口衬砌温度低于洞内衬砌温度,洞口衬砌温度变化幅度大于洞内衬砌温度变化幅度;随着通风时间增加,一次衬砌与二次衬砌压应力均先减小后增大,最大压应力均位于拱腰处;不同风速下一次衬砌与二次衬砌最大温差为 8.40℃,沿水工隧洞轴向与径向距离的增加,温度逐渐升高,风速、风温影响逐渐减小,最大温度拉应力位于拱腰,一次衬砌为0.12 MPa,二次衬砌为0.32 MPa;在不同风温和不同风速下,一次衬砌与二次衬砌位移均呈水平收缩、竖直隆起趋势.研究成果可为寒区水工隧洞衬砌优化设计提供理论参考.

针对寒旱区渠道膨胀土浅层失稳特点,以伊犁河北岸干渠膨胀土为对象,设计了模拟复杂气候环境下的干湿和湿干冻融循环试验以及低应力条件下的直剪试验,探讨了渠道膨胀土抗剪强度、黏聚力、内摩擦角等抗剪特性随循环模式和干密度的衰减规律.结果表明:随法向应力增加,试样抗剪强度的衰减程度减小,试样干密度的降低对抗剪强度劣化效果减弱;试样抗剪强度在初次湿干冻融循环后的衰减率占总衰减程度的40%以上,试样历经5次循环后,在湿干冻融循环作用下黏聚力衰减程度较干湿循环增大20%左右;在一定压实范围内,无论是湿干冻融循环还是单一的干湿循环,试样的干密度越大,其黏聚力衰减程度越小,内摩擦角衰减程度越大,分析抗剪强度指标增减规律应同时考虑"挤缩"和"裂隙"效应的叠加作用;将S1WDFT和S2WDFT设为渠基土建造初和运行中的危险工况,拟合出其抗剪强度指标随湿干冻融循环次数变化的函数式.

In this study, the mechanical behavior of fully grouted rock bolts in hydraulic tunnels subjected to elevated ground temperatures was investigated. A differential equation for axial displacement of the rock bolt was formulated, which considers the force equilibrium of infinitesimal bolt segments and the stress transfer mechanism at the anchor–rock interface. The distribution functions for axial stress within the bolt and the interfacial shear stress were obtained by solving the differential equation, which incorporated the displacement of the surrounding rock mass as a parameter. This study showed that the effectiveness of the bolt–shotcrete support system decreases over time, considering the displacement relaxation rate of the surrounding rock mass. The mechanical model’s variation laws at 20 °C, 50 °C, and 80 °C were summarized by integrating the thermal deformation equation for material parameters, and the numerical simulation results were compared and analyzed. The findings revealed that the bond strength between the rock bolt and the rock mass diminishes as the temperature of the surrounding rock increases, leading to a reduction of interfacial shear stress at both extremities of the bolt. Moreover, the maximum axial force within the bolt escalates as the neutral point migrates farther from the tunnel wall.

The evolution characteristics and the extent of the plastic zone in rock mass can reflect the failure characteristics and destruction degree of a hydraulic tunnel. In this research, we derived the equation of a plastic zone range based on a gateway-like structure high-temperature tunnel through a theoretical analysis. On-site monitoring and discrete element model simulation were combined to analyze the temperature field law and plastic zone evolution characteristics of the jointed rock mass at high temperatures. The results show that the joints affect the temperature field variation in rock mass, and the vertical and horizontal joint groups pose significantly greater influence than the inclined joint group on temperature field. The sensitivity of the joint internal friction angle and thermal expansion coefficient to the range of the plastic zone is relatively small. Under various joint spacings, the influence of horizontal and inclined joint groups on the plastic zone morphology decreases, while the vertical joint group exhibits an incremental influence on the plastic zone morphology. Similar to the influence of the temperature field, the vertical and horizontal joint groups have a significantly greater influence on the plastic zone range than the inclined joint group. Under various rock mass temperatures, the plastic zone in rock mass results in the occurrence of uneven expansions along the direction of the joint dip angle, which changes the potential failure direction of rock mass and increases the potential destruction degree of rock mass, whereas it exhibits a smaller uniform expansion perpendicular to the joint dip angle, and the boundary of the plastic zone coincides with the joint surface, relatively hindering the potential destruction degree of rock mass. The research results of this study have certain reference values for the stability control of jointed rock mass in high-temperature hydraulic tunnels.

This paper investigates the impact of surcharge/unloading at both sides of the ground surface on an existing underground shield tunnel at varying burial depths. A large-scale indoor model experiment was conducted to study the vertical convergence deformation, tunnel settlement, and additional surrounding pressure of the tunnel at different burial depths when surcharge/unloading occurred at both sides of the ground surface. The effect of tunnel burial depth, surcharge mass, and uneven surcharge at both sides of the ground surface on the additional surrounding pressure of the existing underground shield tunnel was further investigated by theoretical calculation. The results indicate that under the same conditions, greater tunnel burial depth leads to reduced vertical convergence deformation, tunnel settlement, and additional surrounding pressure. Unloading can partially reduce the vertical convergence deformation and tunnel settlement, but it does not completely counteract the effect of the preceding surcharge. In cases of a symmetrical surcharge at both sides of the ground surface above the tunnel, the additional surrounding pressure of the tunnel is symmetrically distributed, with higher pressures at the arch top and arch bottom of the tunnel and lower pressures at the arch waist. This suggests that the arch top and arch bottom of the tunnel are vulnerable points under surcharge and require special attention. The surcharge above the tunnel has the most pronounced effect on the tunnel, followed by the surcharge at both sides of the ground surface, and, finally, the smallest effect from the bias load.