Search Results (75)

The deformation characteristics of the surrounding rock in tunnel groups are considered critical for the design of support structures and the assurance of the long-term safety of deep-buried diversion tunnels. The deformation behavior of surrounding rock in tunnel groups was investigated to guide structural support design. Field tests and numerical simulations were performed to analyze the distribution of ground stress and the ground reaction curve under varying conditions, including rock type, tunnel spacing, and burial depth. A solid unit–structural unit coupled simulation approach was adopted to derive the two-liner support characteristic curve and to examine the propagation behavior of concrete cracks. The influences of surrounding rock strength, reinforcement ratio, and secondary lining thickness on the bearing capacity of the secondary lining were systematically evaluated. The following findings were obtained: (1) The tunnel group effect was found to be negligible when the spacing (D) was ≥65 m and the burial depth was 1600 m. (2) Both P_0.3 and P_max of the secondary lining increased linearly with reinforcement ratio and thickness. (3) For surrounding rock of grade III (IV), 95% u_lim and 90% u_lim were found to be optimal support timings, with secondary lining forces remaining well below the cracking stress during construction. (4) For surrounding rock of grade V in tunnels with a burial depth of 200 m, 90% u_lim is recommended as the initial support timing. Support timings for tunnels with burial depths between 400 m and 800 m are 40 cm, 50 cm, and 60 cm, respectively. Design parameters should be adjusted based on grouting effects and monitoring data. Additional reinforcement is recommended for tunnels with burial depths between 1000 m and 2000 m to improve bearing capacity, with measures to enhance impermeability and reduce external water pressure. These findings contribute to the safe and reliable design of support structures for deep-buried diversion tunnels, providing technical support for design optimization and long-term operation. Full article

To prevent the occurrence of excavation face instability incidents during shield tunneling, this study takes the Bailuyuan tunnel of the ‘Hanjiang-to-Weihe River Water Diversion Project’ as the engineering background. A three-dimensional discrete element method simulation was employed to analyze the tunneling process, revealing the displacement response of the excavation face to various tunneling parameters. This led to the development of a risk assessment method that considers both tunneling parameters and geological conditions for deep-buried shield tunnels. The above method effectively overcomes the limitations of finite element method (FEM) studies on shield tunneling parameters and, combined with the Analytic Hierarchy Process (AHP), enables rapid tunnel analysis and assessment. The results demonstrate that the displacement of the excavation face in shield tunnel engineering is significantly influenced by factors such as the chamber earth pressure ratio, cutterhead opening rate, cutterhead rotation speed, and tunneling speed. Specifically, variations in the chamber earth pressure ratio have the greatest impact on horizontal displacement, occurring predominantly near the upper center of the tunnel. As the chamber earth pressure ratio decreases, horizontal displacement increases sharply from 12.9 mm to 267.3 mm. Conversely, an increase in the cutterhead opening rate leads to displacement that first rises gradually and then rapidly, from 32.1 mm to 121.1 mm. A weighted index assessment model based on AHP yields a risk level of Grade II, whereas methods from other scholars result in Grade III. By implementing measures such as adjusting the grouting range, cutterhead rotation speed, and tunneling speed, field applications confirm that the risk level remains within acceptable limits, thereby verifying the feasibility of the constructed assessment method. Construction site strategies are proposed, including maintaining a chamber earth pressure ratio greater than 1, tunneling speed not exceeding 30 mm/min, cutterhead rotation speed not exceeding 1.5 rpm, and a synchronous grouting range of 0.15 m. Following implementation, the tunnel construction successfully passed the high-risk section without any incidents. This research offers a decision-making framework for shield TBM operation safety in complex geological environments. Full article

Cyclical footage, a fundamental parameter in tunnel construction, has received limited attention despite its critical role in ensuring excavation stability and safety. To investigate the underlying mechanisms by which different cyclical footage values influence the stability of deeply buried tunnels, the Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC^3D) was employed to simulate the spatiotemporal evolution of tunnel responses during excavation. The simulation results reveal that each cyclical footage scenario produces a “segmental decline” pattern in tunnel displacement. Unlike shallow tunnels, where peak displacement typically occurs near the tunnel face, in deep tunnels the maximum Y-direction displacement appears at the center of the excavation face. Furthermore, as cyclical footage increases, the displacement extent first expands and then contracts. The stress release process is found to be minimally affected by cyclical footage, with vertical strain in the tunnel roof nearly fully released within 1 m ahead of the excavation face. Therefore, deploying tunnel support structures beyond this 1 m zone may enhance their effectiveness. This study provides a theoretical reference for optimizing excavation parameters in deep tunnels and contributes to reducing the likelihood of support failure during underground construction. Full article

It has been found in engineering practice that the degree of rockburst risk increases when roadway excavation occurs near the stratigraphical boundary of different lithologies. This study uses the 1276 m deep-buried roadway of a lead–zinc mine in Yunnan, China, as its engineering background. Based on a numerical analysis of this case, it investigates the mechanical behavior of surrounding rocks in different lithological formations and explores the causes of excavation-induced rockburst. Additionally, by changing the excavation strategy in a numerical simulation, the influence of the direction of roadway excavation on the degree of rockburst risk in the construction of different lithological formations is assessed. The results are summarized as follows: (1) When the tunnel passes from the C₁b stratum (limestone) to the D₃zg stratum (dolomite), an abnormal stress zone forms in the roof rock strata of the D₃zg stratum (the lower plate of the stratum boundary). The rockburst risk level was evaluated by introducing the numerical rockburst index in this abnormal stress zone, which aligns closely with on-site rockburst investigation results. The rockburst risk is the greatest in the abnormal stress zone, which provides an external energy storage environment for the development of rockburst disasters. (2) Near the stratum boundary, the rockburst risk level when excavating from the D₃zg stratum to the C₁b stratum is greater than that when excavating from the C₁b stratum to the D₃zg stratum. The direction of tunnel excavation significantly affects the rockburst risk level during construction that crosses different lithological strata. These findings can provide a theoretical basis for the construction design of similar underground projects. Full article

When deep-buried tunnels are excavated using the drill-and-blast method, the surrounding rock is subjected to combined cyclic blasting loads and excavation-induced stress unloading. Understanding the distribution characteristics of rock damage zones under these conditions is crucial for the design and safety of building-integrated underground structures. This study investigates the relationship between surrounding rock damage and in situ stress conditions through numerical simulation methods. A constitutive model suitable for simulating rock mass damage was developed and implemented in the LS-DYNA (version R12) code via a user-defined material model, with parameters determined using the Hoek–Brown failure criterion. A finite element model was established to analyze surrounding rock damage under cyclic blasting loads, and the model was validated using field data. Simulations were then carried out to explore the evolution of the damage zone under various stress conditions. The results show that with increasing hydrostatic pressure, the extent of the damage zone first decreases and then increases, with blasting-induced damage dominating under lower pressure and unloading-induced shear failure prevailing at higher pressure. When the hydrostatic pressure is less than 20 MPa, the surrounding rock stabilizes at a distance greater than 12.6 m from the tunnel face, whereas at hydrostatic pressures of 30 MPa and 40 MPa, this distance increases to 29.4 m. When the lateral pressure coefficient is low, tensile failure occurs mainly at the vault and floor, while shear failure dominates at the arch waist. As the lateral pressure coefficient increases, the failure mode at the vault shifts from tensile to shear. Additionally, when the horizontal stress perpendicular to the tunnel axis (σ_H) is less than the vertical stress (σ_v), variations in the axial horizontal stress (σ_h) have a significant effect on shear failure. Conversely, when σ_H exceeds σ_v, changes in σ_h have little impact on the extent of rock damage. Full article

With the further implementation and development of the Western Development Strategy, studying the mechanical behavior and deformation characteristics of deep-buried tunnels in layered hard rock under high ground stress conditions holds considerable engineering significance. To study the mechanical properties and long-term deformation and failure characteristics of different bedding stratified rocks, this research employed an MTS815 electro-hydraulic servo rock testing system and a French TOP rheometer. Triaxial compression tests, rheological property tests, and long-term cyclic and unloading tests were conducted on shale samples under varying confining pressures and bedding angles. The results indicate that (1) under triaxial compression, shale demonstrates pronounced anisotropic behavior. When the confining pressure is constant, the peak strength of the rock sample exhibits a “U”-shaped variation with the bedding angle (its minimum value at 60°). For a fixed bedding angle, the peak strength of the rock sample progressively increases as the confining pressure rises. (2) The mode of shale failure varies with the angle: at 0°, shale exhibits conjugate shear failure; at 30°, shear slip failure along the bedding is controlled by the bedding weak plane; at 60° and 90°, failure occurs through the bedding. (3) During the creep process of layered shale, brittle failure characteristics are evident, with microcracks within the sample gradually failing at stress concentration points. The decelerated and stable creep stages are prominent; while the accelerated creep stage is less noticeable, the creep rate increases with increasing stress level. (4) Under low confining pressure, the peak strength during cyclic loading and unloading creep processes is lower than that of conventional triaxial tests when the bedding plane dip angles are 0° and 30°, which is the opposite at 60° and 90°. (5) In the cyclic loading and unloading process, Poisson’s ratio gradually increases, whereas the elastic modulus, shear modulus, and bulk modulus gradually decrease. Full article

Deep-buried soil tunnels in weak rock strata often face severe risks, such as collapse and large deformation, making the rational selection of construction methods critical. Using a tunnel project in Baotai District, Yan’an City as a case study, this research compares the three-step method, three-step temporary inverted arch method, double-side wall pilot tunnel method, and CD method. By combining a numerical simulation with field monitoring, the study evaluates surrounding rock deformation and support stress characteristics. Results show that while deformation differences among methods are small, the double-side wall pilot tunnel method offers optimal deformation control, and the three-step temporary inverted arch method provides the best stress distribution and meets the specification requirements. Notably, only the three-step method shows anchor bolt stress exceeding the design limits. Considering safety, efficiency, and cost, the three-step temporary inverted arch method is recommended. The strong agreement between simulation and monitoring data highlights the model’s reliability and its value in guiding tunnel design and construction optimization. Full article

In practical engineering, it is often necessary to constructed deep pits next to tunnels. So it is crucial to evaluate surrounding tunnels deformation and stress to ensure their safe operation. Pasternak soil model that considers soil nonlinear is adopted to solve tunnel beam’s differential equation to obtain longitudinal tunnel deformation and stress. The rationality of considering soil nonlinear methods was verified by contrasting measured with calculated results. On this basis, a comparative study was conducted on the calculation and analysis of various influencing factors based on engineering examples. It shows that the longitudinal tunnel deformation reduces with increase of soil modulus, tunnel axis and pit long side angle, tunnel stiffness reduction coefficient, tunnel axis and pit center horizontal distance. When discrete length of tunnel is less than 5 m, calculated value of longitudinal tunnel deformation changes little with discrete length. When pit depth increases, maximum longitudinal tunnel deformation also increases gradually. When tunnel buried depth gradually increases in the range of 1.5~3.9 times pit depth, maximum longitudinal tunnel deformation reduction rate becomes small. Similar pro-jects construction methods can refer to the results, and it have certain practical application value of engineering. Full article

In deeply buried, small-clearance tunnels, the failure of the surrounding rock is profoundly influenced by the superposition of stresses and the cumulative disturbance effects from multiple blasting events. Consequently, the failure characteristics and mechanisms of the surrounding rock are highly complex. Through a comprehensive analysis encompassing failure investigations, geological assessments, and surrounding rock pressure monitoring, this study systematically examines the spatio-temporal failure characteristics and geological discrepancies across 3 parallel tunnels (namely, a pilot tunnel, a left tunnel, and a right tunnel). The analysis reveals the asymmetric failure behavior of the surrounding rock and offers a detailed discussion of the underlying mechanisms. The temporal and spatial evolution of the surrounding rock pressure in these tunnels is carefully analyzed, with an emphasis on uncovering the asymmetric failure mechanisms during the excavation of deep, small-clearance tunnels. The results demonstrate that the failure of the surrounding rock exhibits significant asymmetry during excavation, with the damage being more pronounced on the valley side compared to the mountain side. Furthermore, the degree of damage in the advance tunnel is substantially greater than that in the backward tunnel, particularly in sections following the excavation of the backward tunnel. Additionally, the distribution of the surrounding rock pressure in the advance tunnel also exhibits pronounced asymmetry. The asymmetric failure of the surrounding rock is primarily attributed to the stress concentration in the deep valley and the disturbances introduced by the excavation process, which induces tangential stress concentrations in the surrounding rock mass. The findings of this study hold considerable significance for the design and optimization of tunnel support systems, as well as for disaster prevention strategies in deeply buried, small-clearance tunnels. Full article

Deep-buried subsea tunnels are often under high water pressure conditions, and the influence of the seepage field on the tunnel cannot be ignored. Existing studies generally assume that the surrounding rock exhibits permeability isotropy; this study developed a model of deep-buried subsea tunnel that considers the permeability anisotropy of surrounding rock and investigated the effects of permeability differences between the surrounding rock and lining structure on tunnel seepage flow and plastic zone extent. By employing coordinate transformation and conformal mapping methods, the hydraulic head and the seepage discharge for each region are determined for each section of the tunnel. Based on the analytical solution of the seepage field, the seepage force is treated as a body force, and using the Mohr–Coulomb criterion, an elastoplastic analytical solution for the lining and surrounding rock under anisotropic seepage is derived. Using the Shenzhen MaWan Sea-Crossing Passage as a case study, numerical simulations are conducted using Abaqus2021, and the results are compared with the analytical solution to verify the accuracy of the study. The research shows that the permeability anisotropy of surrounding rock increases the seepage discharge, and this effect becomes more significant with increasing burial depth. If the anisotropy is 10 times greater than its previous value, the tunnel seepage volume will increase by 35.6%. When the surrounding rock permeability is sufficiently large, the impact of permeability anisotropy on the seepage discharge is relatively weak, with the seepage discharge primarily dominated by the permeability of the lining. In the tunnel stress field, due to the significant difference in stiffness between the lining and the surrounding rock, the hoop stress in the lining is much larger than that in the surrounding rock, and there is a stress discontinuity at their interface. When the permeability of the elastic zone of the surrounding rock is 100 times greater than that of the plastic zone, the plastic radius of the tunnel will increase by 2 to 3 times compared to the previous value. Reducing the permeability of the plastic zone in the surrounding rock effectively limits the seepage body force acting on the lining, thereby enhancing the stability of the lining structure and reducing the risk of damage to the tunnel. Full article

In terms of rockburst control technology, it is generally believed that optimizing the section design and adopting the step method can effectively suppress the occurrence of rockburst, but there is no literature to explain the reasons for adopting this method from the experimental point of view. In addition, compared with the application of support, this method can achieve the effect of not increasing the construction process, not affecting the progress of the project and reducing the project cost. In view of this, the Gaoloushan deep-buried tunnel with rockburst was taken as the research object in this paper. Firstly, the excavation scheme based on the step method was proposed, and its explosion-proof effect was verified again. The experimental results showed that the step method could be essentially regarded as the transformation of surrounding rock by reasonably distributing explosives and reducing the working section. The beneficial effects of this method were as follows: the release intensity of absolute energy was slowed down, the way of energy release was changed; the stress condition of surrounding rock was improved; the path of the continuous supplement of strain energy in the original rockburst area was cut off; and the energy accumulation degree of surrounding rock was reduced, so that the accumulated energy in the rock mass did not exceed its energy storage limit at the location where the rockburst should have occurred. The reduced high energy was released in an orderly manner and induced the rock failure process, forming a fracture zone and a plastic zone. In the process of expansion, the fracture zone and plastic zone further reduced the stress concentration of the surrounding rock and deteriorated the mechanical properties of the surrounding rock. The stress concentration zone was transferred to the deeper surrounding rock outside the unloading relaxation zone, and part of the elastic energy accumulated in the surrounding rock was released. The strain energy could be distributed and dissipated, and the effect of energy safety and slow release was achieved. Full article

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

As tunnel engineering advances towards greater depths, larger scales, and longer distances, high rock temperatures and tunnel thermal damage frequently occur, constituting some of the main geological hazards faced by transportation, water conservancy, and other tunnel engineering projects. In this study, we take the alternative option to the No.1 deep-buried water diversion tunnel of the “Diversion of Yellow River to Jining” project as the study area, combined with the geological data of the field investigation, to comprehensively consider the thermodynamic properties of the rocks along the tunnel and the logging data along the tunnel, and we use the least squares method to fit the temperature of the logging wells to obtain the thermal background parameters of the earth’s heat flow as well as other regional heat background parameters to obtain the thermal background parameters of the tunnel. The COMSOL Multiphysics software established a two-dimensional steady-state geothermal field numerical model to predict the rock temperature along the tunnel. The results show that the maximum temperature along the tunnel is 51.1 °C, the length of the tunnel with thermal damage class I is 45.9 km, the length of the tunnel with thermal damage class II is 18.4 km, the length of the tunnel with thermal damage class III is 8.0 km, and the length of the tunnel with thermal damage class IV is predicted to be 0.18 km. Compared with the on-site temperature measurement data, the model prediction error is within ±1.5 °C, which validates the accuracy of the model. This study adopts numerical simulation combined with field geological and logging data to provide a theoretical basis for tunnel heat hazard prevention. Meanwhile, it offers technical support for the design and construction of similar deep-buried high-temperature tunnels. Full article

The relationship between slabbing failure and rockburst has become a hot issue in rockburst research. In this paper, the experimental system of impact rockburst is used to conduct a simulation experiment of rockburst induced by slab failure on metamorphic sandstone samples taken from the deep-buried horseshoe-shaped tunnel in Gaoloushan, with “pan-shaped” rockburst pits on site and laboratory simulation experiments, which prove the rationality of the experimental results of rockburst. The quantitative analysis of the displacement field in the process of the slab buckling rockburst is carried out, which shows that the slab structure will undergo a long period of gestation before its formation, and the formation of the slab structure will accelerate the occurrence of rockburst. This type of rockburst has attenuation characteristics in the process of rockburst; in addition, the phenomenon of “slab buckling circle” is found. The generation of the “slab buckling circle” and the formation of slab buckling cracks are inconsistent, which is a time-lagged fracture in engineering. The relationship between the rupture parameters of rockburst disaster rock mass and time shows a compound exponential growth relationship, revealing that the mechanism of the slab buckling rockburst can be regarded as the result of the combined action of shear crack and tension crack, which plays a leading role, reflecting the characteristic of progressive fracture development. It is a typical progressive fracture-induced instability rockburst model, which is a strain-lag rockburst. Full article

Research on the calculation method of deep-buried surrounding rock pressure is an important subject in engineering mathematics. The existing calculation methods are mainly the two-hole closely spaced tunnel, double-arch tunnel, three-hole closely spaced tunnel, and three-arch tunnel. The four-hole closely spaced double-arch tunnel has the characteristics of both the double-arch tunnel and closely spaced tunnel, and its surrounding rock pressure distribution is more complicated. In this paper, the research is carried out based on Protodyakonov’s theory and the concept of process load. The influence of the post-construction tunnel on the supporting structure of the pre-construction tunnel is also considered. The calculation model of the surrounding rock pressure of the deep-buried four-hole closely spaced double-arch tunnel is established, and the calculation formula of the surrounding rock pressure is deduced and verified. Finally, the influences of the rock column parameters, excavation procedure, tunnel span, and middle partition wall on the surrounding rock pressure are analyzed. Full article