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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 (ΔDt/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. [ABSTRACT FROM AUTHOR]

• The internal force analytical solution of lining structure under P-ware action was obtained by using the analytical method. • The influence of the hardness of surrounding rock and peak acceleration on the analytical solution were analyzed. • Through the engineering, the reasons for the large error between numerical solution and analytical solution was analyzed. • The most unfavorable position of lining structure under P-wave seismic load was proposed. In an earthquake, the strong interaction between the surrounding rock and the lining structure causes the lining structure susceptible to extrusion or shear damage, and predicting the internal force distribution trend of the lining structure by the analytical method was advantageous for the preliminary design of the tunnel structure. In this work, the quasi-static method was used to approximate the displacement and deformation caused by the P-wave seismic load as far-field compressive stress. The analytical solution of the internal force for the lining structure was obtained by the analytical method, and the reliability of the analytical method was further verified. The dynamic response law of the lining structure was analyzed using numerical solutions in conjunction with engineering examples. The results show that the analytical method can be used to predict the trend of internal force distribution in the lining structure under seismic action, which has important theoretical guiding significance for the preliminary design of the tunnel structure. With the decrease in the hardness of the loess surrounding, the relative deviation of the theoretical, numerical, and literature results gradually decreases. With the increase of ground motion intensity, the interaction between the loess surrounding and the lining structure becomes more intense, and the internal force of the lining structure gradually increases. The numerical results were greater than the analytical results due to the consideration of the influence of initial stress. Under the action of the P-wave earthquake, the extreme values of the internal force with the lining structure mainly occurred at the location of the vault, arch waist, and inverted, and the most unfavorable positions of circular loess tunnel lining structures under P-wave seismic load was proposed. [ABSTRACT FROM AUTHOR]

Reasonable support force is crucial for the stability of the excavation face in sandy pebble tunnels. By utilizing the existing failure mode of the logarithmic spiral curve, this study combined the collapse arch model with the limit analysis method to establish a failure model for the excavation face in sandy pebble tunnels. A calculation method for the ultimate supporting force applicable to the excavation face of sandy pebble tunnels was also proposed. Then, the theoretical analysis presented in this paper was compared with numerical simulation and existing theories to determine the failure areas under different internal friction angles and cohesion values. Finally, the excavation face stability of a shield tunnel in Beijing was analyzed using theoretical analysis and numerical simulation methods. The results showed that the analytical solution proposed in this paper was in good agreement with the limit supporting force derived from existing research, with convenient and accurate calculations. The limit supporting force decreased nonlinearly with the increase of the internal friction angle, and was more sensitive to changes in the friction angle when the angle was small. The limit supporting force decreased approximately linearly with the increase in cohesion. When the burial depth was small, it had a more significant impact on the limit supporting force. When the C / D ratio exceeded 1. 0, the increase of the burial depth of the tunnel had no obvious effect on the limit supporting force, and the friction angle had a very significant effect on the failure area. With the increase of internal friction angle, the failure area decreased significantly. Cohesion had little impact on the failure area, i. e., the size of the energy dissipation surface remained nearly unchanged under different cohesion values. For the shield tunnel in Beijing, the calculation based on the limit analysis method optimized the collapse range and shape, making the failure mode more reasonable while increasing the failure range, achieving excellent engineering application results. [ABSTRACT FROM AUTHOR]

Objective: The visual guiding system, as a tunnel traffic safety improvement method by using visual guiding facilities to actively guide driving safely, has been widely used in countries with many tunnels, in recent years. This paper aims to quantitatively study the comprehensive evaluation of traffic safety of the visual guiding system in tunnels, which has certain engineering application value and can provide support for the quantitative evaluation and optimal design of tunnel traffic safety. Methods: Based on the analysis of the relevant factors of urban tunnel traffic safety, a multi-factor comprehensive evaluation system with 5 upper-level indicators and 12 basic-level indicators was proposed. Considering the independent and incompatible indicators, a comprehensive evaluation method of traffic safety of the visual guiding system in urban tunnels was constructed by using the extension matter-element model. Taking the scene of 4 types of tunnel curves, such as no facilities, horizontal stripe, chevron alignment sign, and LED arch, as examples, the comprehensive evaluation of various schemes were carried out by using simulation tests. Results: The traffic safety comprehensive evaluation system of visual guiding system in urban tunnels can be analyzed from five aspects: perception reaction, guidance ability, driver factor, driving task, and facility appearance. The results demonstrated significant the comprehensive evaluation result of the target level of scene 1 was L4, scene 2 was L3, scene 3 was L2, and scene 4 was L1. That is, the final results of the comprehensive evaluation of the four scenes were poor, medium, good, and very good, respectively. Conclusions: In the scheme of visual guiding system for urban tunnel curves, the effectiveness of the three types of designs, from high to low, was the LED arch, chevron alignment sign, and horizontal stripe, and the safety of the scene without facilities was the lowest. Hence, setting the LED arch in the urban tunnel curve has a good effect in the aspects of guidance ability, sight distance, and sight zone, and is conducive to the driver's perception reaction and driving task. [ABSTRACT FROM AUTHOR]

In the process of tunnel construction, problems such as high-stress rockburst, large deformation of soft rock, water inrush and mud gushing, secondary cracking of linings, blasting interference, man-made damage, and mechanical damage are often encountered. These pose a great challenge to the installation of monitoring equipment and line protection. In order to solve these problems, the 2# inclined shaft of Muzhailing Tunnel in the Gansu Province of China, which exists under high stress, water bearing, and bias conditions, was taken as the research object in this paper. By assembling a string, drilling grouting and sealing, and introducing multiple modes of protection, new fiber grating sensor group installation and line protection methods were proposed. The automatic continuous monitoring of the deep deformation of surrounding rock and the automatic continuous monitoring of steel arch stress were realized. The field monitoring results showed that: (1) the fiber grating displacement sensor group could be used to verify the authenticity of the surface displacement results monitored by the total station; (2) the NPR anchor cable coupling support effectively limited the large deformation of soft rock and the expansion of surrounding rock in a loose circle, and the range of the loose circle was stable at about 1 m; and (3) the main influence range of blasting was at a depth of 0~5 m in surrounding rock, and about 25 m away from the working face. In addition, to secure weak links in the steel arch due to the hardening phenomenon, a locking tube was set at the arch foot. In the support design, the fatigue life of the steel was found to be useful as the selection index for the steel arch frame to ensure the stability of the surrounding rock and the long-term safety of the tunnel. The present research adopted a robust method and integrates a variety of sensor technologies to provide a multifaceted view of the stresses and deformations encountered during the tunneling process, and the effective application of the above results could have certain research and reference value for the design and monitoring of high stress, water-bearing, and surrounding rock supports in tunnels. [ABSTRACT FROM AUTHOR]

Drawing from the engineering context of a shallow-buried, biased-load, permeable ribbed double-arch tunnel, the strength reduction method was employed to determine the failure pattern of the surrounding rock at the tunnel's ultimate excavation state. According to the failure characteristics of surrounding rock and the basis of basic assumptions, a fractured sliding surface was hypothesized, and a structural load calculation model for the surrounding rock pressure in the permeable ribbed double-arch tunnel was derived. This model was compared and validated against the results obtained from the stratum structure model. An analysis of the sensitivity of the surrounding rock pressure was conducted. The findings indicated that the tunnel was subjected to asymmetric biased loads, with the vertical load on the side with large buried depth chamber being significantly greater than that on the side with small buried depth chamber. The horizontal load on the right sidewall of the side with large buried depth chamber was significantly greater than the horizontal load on the surface of the left and right lining segments above the central partition wall. The horizontal lateral pressure coefficient was influenced by the slope's biased angle and the internal friction angle of the surrounding rock's sliding surface, with the latter having a more substantial effect. The surrounding rock pressure was closely related to the horizontal lateral pressure coefficient and was influenced by the rock density, the slope's biased angle, and the internal friction angle of the sliding surface. The sensitivity of surrounding rock pressure was significantly impacted by the slope's biased angle and the internal friction angle. [ABSTRACT FROM AUTHOR]

After excavation of tunnels in interbedded surrounding rock, accidents such as rock peeling and arch crown collapse are prone to happen. In response to this issue, we first established an analysis model for the excavation of the interbedded surrounding rock tunnel through theoretical analysis, proposed corresponding failure criteria, and analyzed the reasons for the easy failure of the interbedded tunnel support structure based on the concept of principal stress difference. We also created interfaces in FLAC3D (version 6.0) software to restore the actual interbedded interface, verifying the effectiveness of principal stress difference in analyzing the deformation characteristics of the tunnel. Then, the instability forms of the interbedded surrounding rock tunnel were divided into two types, and effective support methods for the corresponding instability forms were proposed. Finally, based on the analysis results of the study, support was provided for the collapsed tunnel on site. A grouting large pipe shed was put to innovative use to support the tunnel arch waist, stabilizing the surrounding rock that is prone to shear slip and fracture at the upper part of the arch waist. The results indicate that the surrounding rock control effect is good. This study has a good reference value for on-site rapid construction and support design, and is of great significance for the instability prevention and control of interbedded surrounding rock tunnels. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the complexity of construction sequence and the extended duration required to construct super large section tunnels, the selection of excavation method critically influences the stability of the surrounding rock and support structures. In this work, the Xiaoyuan Tunnel project in Jiangxi Province serves as the research background for employing ABAQUS software to simulate the variations in displacement and stress within the rock and support structures under three different excavation methods. The simulated results are subsequently compared and verified against monitoring data. The findings indicate that the three-benching seven-step method releases more stress (maximum principal stress value reaches 0.621 MPa) from the surrounding rock and support structures than the other methods, resulting in stress concentrations. Therefore, it is of vital significance to complete the initial support in time and seal the tunnel opening quickly. The maximum principal stress values caused by three excavation methods all appear at the arch foot position, highlighting the need for prompt reinforcement of stability support there. Compared to the CRD method and the three-benching seven-step method, the tunnel vault's settlement value caused by the double-side drift method is reduced by 14% and 19%, respectively. Furthermore, the largest disturbance of the surrounding rock occurs under the CRD method, while the double-side drift method minimizes such disturbances, making it the preferred choice for the construction of super large section tunnels. These insights are invaluable for guiding the selection and optimization of construction methods for such tunnels. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Characterized by long spans, low aspect ratios, and intricate construction sequences, super-large cross-section tunnels present substantial construction risks. Therefore, the selection of the optimal excavation method and construction sequence is crucial for ensuring the safety of tunnel construction and minimizing project costs. This paper takes a super large transverse-section highway tunnel as a case study, employing field monitoring data combined with ABAQUS software to analyze the stress and deformation of surrounding rock and support structures under different excavation methods. The findings reveal that the deformation of surrounding rock and support structures excavated by the Double-Side Drift Method is smaller than those caused by the three-benching seven-step method and the CRD excavation method. Nevertheless, the significant stresses of surrounding rock and support structures are released by the Double-Side Drift Method, leading to potential stress concentrations. Thus, it is necessary to ensure the rapid completion of early support and quick sealing of the tunnel. Furthermore, the sixth process achieves smaller deformation (including arch displacement and surface settlement) of the tunnel, a shorter construction period, and lower economic costs when compared to other construction processes. Consequently, it can obviously be concluded that both the Double-Side Drift Method and the sixth construction process stand out as the most appropriate choices for excavating super large cross-section tunnels. The insights obtained from this study provide theoretical guidance for the design and construction of similar tunnel projects. [ABSTRACT FROM AUTHOR]

The steel rib and the lattice girder are two typical steel arch frames used in the primary lining of the New Austrian Tunnelling Method (NATM) highway tunnel. In the process of tunnel construction, it is necessary to choose the support method according to the mechanical properties, durability, construction difficulty, and economic benefits. In order to analyze the mechanical characteristics of steel arch frames, a loading and measurement test system for steel arch was designed, and destructive tests were carried out on a three-bar lattice girder, four-bar lattice girder, and I-beam steel rib. The steel utilization coefficient was introduced to compare the mechanical properties of the different types of steel frames. The results show that the I-beam steel rib has the largest steel utilization coefficient, but it is not well combined with concrete. Among the lattice girders, the three-bar W-shaped lattice girder uses the least amount of steel under the same load, which reduces the construction cost and is worth applying and popularizing. Additionally, the steel utilization coefficient of different types of lattice girders can be optimized through the ratio of steel bar diameters. It is proved that the steel utilization coefficient can provide a reference for the evaluation and selection of steel frames for the primary lining of highway tunnel engineering. [ABSTRACT FROM AUTHOR]

The elastic solutions of isotropic complex noncircular deep or shallow tunnels are obtained by the complex variable theory in this paper. In the solution procedure, the mapping function in the form of power series is adopted and Cauchy integral formulas are widely applied to simplify the calculation. The unified solutions expressions for the mapping function with any number of series terms (namely the solving accuracy) are presented. When the terms number of the mapping function is determined, the solutions are accurate for the tunnels considering the influence of local rock gravity, as they are derived by analysis without any approximation and numerical method. Compared to previous analytical method that maps tunnels and surface boundary to rings, the surface boundary conditions of this method are not fully satisfied but the coefficients of the mapping function used are easier to solve, requiring fewer series, and the solution process is simpler and faster. Therefore, it is more suitable for deep and shallow rock tunnels that are not near the surface. Semi-circle arch, three-centered arch, horseshoe shape, asymmetric trapezoid and 'C' shape tunnels are analyzed as examples, and the validity of the results is verified by comparing the analytical solution obtained with the FEM numerical solution calculated in ANSYS software. Highlights: Elastic analytical algorithm for shallow rock tunnels with complex shapes is proposed. Solutions proposed are valid for the mapping function in power series form with any number of terms. The impact of tunnel asymmetry is considered in this study. High-accuracy solutions for tunnels with complex shapes are obtained by controlling the number of mapping function terms [ABSTRACT FROM AUTHOR]

Proper design of special segments under cavity conditions is essential for successfully implementing the upward shield tunneling method. When constructing upward tunnels, the segment structure in the corresponding construction area of the horizontal tunnel is special. To study the internal force distribution on the structure under the worst possible conditions given by the upward shield tunneling method, MIDAS GTS NX software is used to numerically simulate the structure based on the condition of the cavity behind it to determine the most unfavorable radius of the cavity. Moreover, an analysis of the cavity location is conducted. The results demonstrate that when the cavity is located at the bottom of the arch with a radius of 1 m and near the top of the arch with a radius of 0.5 m, the special segment structure is under the most unfavorable combination of stresses. The most dangerous working condition occurs when there is a 0.5 m radius cavity on one side of the arch in the cross‐section of the special segment. [ABSTRACT FROM AUTHOR]

Shield tunneling processes can result in accidents like water inrush and collapse due to instability in the tunnel face. This paper conducts a systematic investigation of the deformation features and failure mechanism of subsea shield tunnels with different burial depths crossing fault zone. The research entails combing theoretical analysis, numerical simulation, and data mining with the second subsea tunnel in Jiaozhou Bay, Qingdao. The impact of the shallow and deep burial depths on the damage modes of the shield tunnel face is analyzed from the perspective of the pressure arch effect. When the tunnel burial depth exceeds the limit, the overlying rock of the tunnel will form a pressure arch that supports the overlying rock. The study investigates the impact of various factors on the tunnel face's failure modes using a fluid-structure interaction approach. Among them, as the thickness of the overlying bearing stratum increased, the displacement of the tunnel face initially decreased but later increased. The increase of cohesion and internal friction angle contributed to decreasing the displacement of the tunnel face, while seawater depth and tunnel diameter exhibited diverse effects. In the grey correlation analysis, the seawater depth exhibited the most sensitive impact on the pressure arch height. [ABSTRACT FROM AUTHOR]

To study the impact of blasting construction of double-layer superimposed primary support arch cover method, relying on the station construction project of Dalian Metro Line 5, the disturbance of blasting on high-rise buildings, surrounding strata, adjacent pilot tunnels and the arch structure is analyzed based on numerical simulation and field monitoring results. At the same time, research is carried out on the blasting excavation footage of pilot tunnels. The results show that there will be a certain "elevation amplification effect" (EAE) on high-rise buildings during the blasting construction using the method. The peak particle velocity (PPV) of adjacent tunnels decreases gradually with the increase of the distance from the explosion centers. For the adjacent pilot tunnel, the main influence area is within the range of − 5 to 5 m from the pilot tunnel face. For adjacent buildings, the main influence stage is within the range of − 2 to 2 m from the pilot tunnel face. Blasting operations significantly intensify the plastic yield of surrounding rocks around the station. Blasting excavation footage can be used as the optimization parameter in the construction process, and the blasting excavation footage of pilot tunnel 4 can be adjusted from 1.0 to 1.5 m. The formation of the arch structure composed of double-layer superimposed primary support and secondary lining effectively reduces the impact of rock blasting on the whole station and high-rise buildings. [ABSTRACT FROM AUTHOR]

To explore the stress state of lining structures in a tunnel traversing a water-rich fault zone, the long-term in-situ stress monitoring of surrounding rock, initial steel arch frames, and secondary lining concrete were conducted in a red-bed mudstone section of a tunnel under construction in Gansu. The force patterns of the tunnel structure were analyzed during the water and mud outburst control period in the water-rich fault. The results show that moisture seepage from the water-rich fault results in a maximum surrounding rock pressure of 498.28 kPa on the crown during construction. Following the application of the secondary lining, the pressure decreases gradually, but the pressure on the inverted arch continues to rise, reaching a peak of 352.75 kPa. The initial steel arch supports display a clear asymmetrical force distribution, with greater force on the upper outer side than the lower. Maximum compressive stress occurs at the crown and right waist, where the right waist experiences bending and breakage due to stress from fault activity. Inside the arch, stress distribution is lower at the top and higher at the bottom, with the greatest compressive stress on the left side of the inverted arch. Overall, the secondary lining concretes comply with the safety factor requirements of tunnel. The crown and right waist, being directly impacted by the water-rich fault, sustain the maximum concrete compressive stress. Continuous moisture penetration from the fault zone to the tunnel's base rock post-construction prolong the stress stabilization period for the inverted arch, increasing the risk of floor heave during long-term operation. It is crucial to monitor the deformation of the tunnel base during operation. These results offer valuable insights for optimizing reinforcement strategies and formulating drainage plans in similar tunnel projects. [ABSTRACT FROM AUTHOR]

Soil pressure in clay formation tunnels is closely related to soil arch effect and the development of slip surfaces. Firstly, numerical simulation software is used to simulate the actual situation of tunnel excavation, and the change rule of the slip-cracking surface of cohesive soil is analyzed. Secondly, based on the numerical simulation results and the ellipsoid theory, the pressure formula of Terzaghi loose Earth is modified considering that the principal stress trace is catenary. Finally, the calculation results are compared with the finite element calculation results to verify the rationality of the formula in this paper. The relationship between the internal friction angle, cohesion force c, eccentricity ε, looseness coefficient β, and the pressure of loose Earth is further studied. The results show that there is a gap between the sliding crack angles with or without dilatancy angle and it will affect the development form of soil arch. The slip angle decreases gradually with the increase of the buried depth ratio H/D and becomes stable when the buried depth ratio H/D≥3. Compared with deep-buried tunnels, the increase of internal friction angle in the shallow-buried tunnel is more conducive to reducing the overlying soil pressure. The loose soil pressure decreases with the increase of eccentricity ε and loose coefficient β, and the influence of eccentricity ε on loose soil pressure is significantly greater than that of loose coefficient β. Therefore, the change of eccentricity ε should be paid close attention in the project. [ABSTRACT FROM AUTHOR]

As yielding supports can deform without being damaged, the yielding principle has attracted significant attention for tunnelling in squeezing ground compared with the heavy support method. The deformation energy of surrounding rock can be managed using yielding supports that maintain the rock pressure within the bearing capacity of the supports. However, although the yielding principle has been often applied in practical scenarios, a design method for yielding supports has yet not been well developed. This study discusses interaction between the squeezing ground and yielding supports and investigates the influence of the time‐dependent behaviour of rock on the yielding supports. The yielding supports can be implemented by the movement of sliding joints of steel arches or by shortening the yielding elements inserted in shotcrete linings. The deforming process of yielding supports can be divided into three stages: elastic a, yielding, and elastic b. A three‐stage pressure‐displacement relationship of yielding supports is proposed and a method is provided for the calculation of the support stiffnesses of yielding supports in different stages. Furthermore, a unified design approach for the yielding supports is presented and the theoretical model is established after simplifying the asymmetry of problem. The analytical solution for tunnel displacement and support pressure in a tunnel supported by the yielding supports is obtained. The proposed design method for the yielding supports is successfully applied to the Saint Martin La Porte access tunnel, and the mean tunnel deformation in this tunnel is appropriately predicted by the analytical solution. Additionally, a parametric investigation is performed based on the analytical solution, and the effects of yielding path, yielding displacement, support thickness, and installation time of the yielding supports are discussed. Finally, certain highlights of the analytical model of yielding supports in this study are identified, compared with other researches, and recommendations for the design of the yielding supports are provided. The outcome of this research has potential applications in the preliminary design of deep tunnels in squeezing ground. [ABSTRACT FROM AUTHOR]

The field monitoring data showed that a small amount of main reinforcement bars of lattice girder at the arch of a tunnel were pulled, and the calculation showed that the initial support structure should be compressed. To find out the reason for the tension of the main reinforcement, the geological radar was used to detect the cavity in the sprayed concrete layer at the tension position. In order to clarify the tension mechanism of the main reinforcement and the influence of factors such as the position and size of the cavity on the main reinforcement, numerical simulations were carried out. The results show that the cavity causes the eccentric compression of the shotcrete layer, resulting in moment of the lattice girder and the change of the stress distribution of the main reinforcement. The main reinforcement experiences tensile stress when the cavity size surpasses 3 m × 0.2 m, reaching a tensile stress of 81 MPa at a cavity size of 6 m × 0.2 m. Notably, the cavity located at the foot of the arch is more likely to produce substantial tensile stress on the primary reinforcement compared to those at the arch crown and waist. The research results provide a theoretical basis for the interpretation and analysis of tunnel lattice girder monitoring data. [ABSTRACT FROM AUTHOR]

Water and sand leakage (WSL) disasters frequently occur in underground engineering such as tunnels and foundation pits. The appearance of leakage port destroys the stable soil structure and leads to the leakage of soil particles in large quantities under the action of water flow and gravity, especially in gap-graded sandy soil layer. Therefore, model experiments on the WSL of gap-graded sandy soil with different grain size distributions are conducted by self-designed WSL simulation device. Moreover, the applicability of Peck curve and ellipsoid theory in estimation of the volume loss rate and influence radius of WSL in sandy soils is explored. Results show that GGS1 containing 20% coarse particles fails to form soil arch with 80.7% of sand leaked. However, GGS2 and GGS3 containing 40% and 60% coarse particles form soil arches in WSL with 13.5% and 10.9% of sand particles leaked, respectively. Moreover, the soil surface settlement decreases, while the settlement influence radius increases, as the content of coarse particles increases. The natural filter channel formed in sandy soils with higher coarse particle content is longer and wider. Finally, theoretical results are consistent with experimental results, which verifies the applicability of Peck formula and ellipsoid theory in the evolution of WSL. [ABSTRACT FROM AUTHOR]

Sulfate corrosion is one of the main causes of tunnel lining deterioration. An accurate understanding of the damage characteristics and corrosion mechanism of sulfate-corroded tunnels is the basis for the anti-corrosion design and damage control of the tunnel lining. Based on a project concerning a sulfate-corroded tunnel in the mountainous area of Southwest China, this study conducted a field investigation and laboratory tests and, combined with existing research data, summarized the damage characteristics and corrosion mechanism of this type of tunnel and proposed the characteristic corrosion state of tunnel lining in a sulfate environment. The results show that 1) sulfate corrosion led to leakage, surface spalling crystallization, and strength loss, and the corrosion typically occurred at the arch waist and arch foot. 2) Physical and chemical corrosion occurred in the tunnel lining, and the corrosion products included sodium sulfate, calcium carbonate, gypsum, ettringite, and thaumasite. 3) In China, this type of tunnel is mainly located in the Southwest and Northwest, and its lining is in a special state of “one-sided accelerated corrosion.” [ABSTRACT FROM AUTHOR]

The service performance of tunnel lining is affected by crack properties and development states. In this paper, numerical simulation models were established to investigate the mechanics characteristics and safety performance for lining structures under different cracks based on the extended finite element method (XFEM). Analyze multiple quantitative factors in simulation, including changes in crack location, crack length, and crack distribution range in the lining structure. The axial force and bending moment of the preset cracks in the lining structures were first studied. The maximum safety factor attenuation rate ( D k m a x ) was proposed to analyze the impact of longitudinal and annular cracks on the safety performance. The axial force at the vault of the lining arch is the most significantly affected by the combined longitudinal cracks at multiple locations. When the length of a longitudinal crack increases from 1 m to 6 m, the axial force value at the crack point decreases by 33.77%, 36.15%, and 11.32%. However, the bending moment value increases by 4.47 times, 2.50 times, and 1.69 times. Under the influence of longitudinal cracks in an "arch crown + arch shoulder", "arch crown + arch waist", and "arch crown + arch shoulder + arch waist", the axial force in the arch vault increased by 21.55%, decreased by 17.52%, and decreased by 13.45%. The distribution pattern of the bending moment under the influence of circumferential cracks shows convexity at the arch shoulder and arch foot, and concavity at the arch waist and side walls. The safety factor scatter curve with longitudinal cracks shows a gradual transition from a "W" shape to a "U" shape. The safety factor curve with circumferential cracks presents an approximately symmetrical wave-shaped distribution. [ABSTRACT FROM AUTHOR]

The control of surrounding rock is a challenge faced during large-section tunnel construction, resulting in insufficient strength of the traditional support. Confined concrete arches with high strength and rigidity are suitable for controlling large-section tunnel surrounding rocks. To effectively control the soft surrounding rock of large cross-section tunnels, it is necessary to study the bearing characteristics and influencing mechanisms of confined concrete arches. A mechanical test on large-scale arch in traffic tunnels is conducted. The deformation mode and ultimate bearing capacity of the arch are analysed. The test results show that the deformation mode of the confined concrete arch is "the vault and bottom converge inwards, and the whole arch becomes flat". The maximum bearing capacity of the arch in the stable bearing stage is 830.7 kN, and the ultimate bearing capacity is 1157.2 kN. On the basis of laboratory tests, numerical simulations are conducted on different arch dimensions and cross-section parameters. The influence mechanisms of the section dimension and arch design parameters on the bearing capacity are clarified. As the section dimension increases, the load-bearing capacity of the arch decreases continuously. The ultimate bearing capacity of the arch with an on-site size is 784.5 kN, which is 32.2% lower than that of the arch in the laboratory test. A comprehensive evaluation index considering cost and bearing capacity has been established to select reasonable design parameters for confined concrete arches. Based on the above research results, engineering suggestions are put forwards, and the arch is applied in the Letuan tunnel, which effectively controls surrounding rocks. [ABSTRACT FROM AUTHOR]

Floor heave is a typical tunnel issue in tunnelling engineering. To gain deep insights into the deformation mechanism and failure processes of floor heave at the bottom of a tunnel in layered rock, biaxial step-loading tests were conducted on rock samples (including schist and sandstone) with and without prefabricated invert arches. The failure processes of the samples were observed by the three-dimensional digital image correlation technique (3D-DIC) during the test. The test results showed that the deformation evolution processes of the floor heave of the sample included the following steps: (1) crack initiation at the interlayer weak planes; (2) separation of the rock matrix into platy structures along the bedding planes and flexures; and (3) fracture and uplift of the platy structures in the middle part. As the stress redistributes on the bottom plate of the sample, and stress concentration zones shift toward locations far away from the arching surface, the deformation evolution shows a similar variation trend with the stress. Continuous buckling fracturing takes place progressively from the vicinity of the arch surface to certain distant regions. Based on the test results, the key location of internal surrounding rock deformation was determined, and the mechanism of floor heave was clarified. The schist sample SC-BI-10 began to experience floor heave at 1064.4 s, and the deformation curve (the relationship between Y and U) showed a convex shape in the range of 0–20 mm in the Y-coordinate. The displacement reached its maximum value at y = 11.7 mm, corresponding to the position where the rock slab was broken. In addition, the influence of the interlayer properties and cover depth of rocks on bottom uplift was also studied. The design of tunnel supports and the monitoring and prevention of floor heave can benefit from this study. [ABSTRACT FROM AUTHOR]

The complex distribution of synchronous grouting pressure results in excessive tunnel deformation and various structural diseases, especially for ultra-large-diameter shield tunnels. In this study, to reduce the risk of tunnel failure, a three-dimensional refined finite element model was established for the Wuhan Lianghu highway tunnel project, taking into account the non-uniform distribution of synchronous grouting pressure. This study focuses on investigating the development patterns of internal forces, deformations, and damages in segment structures under varying grouting pressure ratios. The results indicate that the primary failure mode of a segment is tensile failure occurring at the outer edge of the arch. Moreover, an increased ratio of grouting pressure between the arch bottom and top leads to a higher positive bending moment value and greater tensile damage at the arch waist. The tunnel ring gradually exhibits distinct "horizontal duck egg" shape deformation. When the grouting pressure ratio is 2.8, there is a risk of tensile cracking at the outer edge of the arch waist. At this time, the segment convergence deformation is 39.71 mm, and the overall floating amount reaches 43.12 mm. This research offers engineering reference for the prediction of internal forces and deformations in ultra-large-diameter shield tunnels during grouting construction, thereby facilitating their application in the development of resilient cities. [ABSTRACT FROM AUTHOR]

The foundation of a seismic safety assessment of cross-fault hydraulic tunnels is an acceptable and accurate seismic response. A dynamic contact force algorithm that may take into consideration the interaction between the fault–surrounding rock–lining structure was devised in light of the contact characteristics of various media in cross-fault hydraulic tunnels under seismic activity. A quantitative instability criterion using a relative displacement ratio as the criterion was devised based on the cusp catastrophe model. By using the cross-fault hydraulic tunnel of the Lawa Hydropower Station as an example, it was possible to evaluate and assess the impacts of four working circumstances on the seismic response of the tunnel lining structure. The findings demonstrated that the lining haunch exhibited stronger stress and displacement responses when subjected to seismic activity. The consideration of fault–surrounding rock–lining interaction exacerbated the displacement and stress seismic responses of the lining structure. The haunch, bottom arch, and top arch of the lining's characteristic parts—which ranged in size from large to small—responded more seismically as peak ground acceleration rose. Applying the aforementioned instability criterion, the haunch, bottom arch, and top arch of the liner structure could withstand maximum peak ground accelerations of 0.10 g, 0.20 g, and 0.35 g, respectively. The aforementioned technique offers a fresh perspective on how to evaluate the seismic response and seismic safety of the tunnel's lining structure, and the study's findings can serve as a guide for seismic design. [ABSTRACT FROM AUTHOR]

To investigate the arching effect of shallow buried hard rock tunnels under overlying load, the engineering scenario of a subway station on Qingdao Metro Line 6 is utilized. A large-scale tunnel loading model test is conducted, in conjunction with finite element numerical simulations, to analyze the impact of various overburden ratios on strata arching. The results show that: when the tunnel excavation span is certain, with an increase in the overlying rock mass, the stress diffusion process of the surrounding rock can be better accomplished to form the arch effect. This means that the thickness of the overburden of the tunnel determines whether or not the surrounding rock appears to have a stratified arch effect. When the tunnel overlying rock thickness is certain, the span of the tunnel determines the shape of the formation into an arch, that is, the curvature of the arch. The joint surface is an important factor in tunnel stability. When the overlying load increases to a certain value, the rock mass at the joint plane slips relatively, leading to the displacement phenomenon of the surrounding rock, which then affects the formation and shape of the formation arch. [ABSTRACT FROM AUTHOR]

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A small clear-distance, double-arch tunnel under an asymmetrical load combines the characteristics of small clear-distance, tunnels and double-arch tunnels, and the influence of an asymmetrical terrain must be considered. Its construction stability is a problem worth studying. This paper used the Wengcun tunnel as the engineering background. Midas/GTS finite element analysis software was used to study the effects of eight excavation sequences and two excavation methods on tunnel stability. The results showed that the deformation and force of the tunnel were asymmetric under the asymmetrical terrain. Both middle partition walls were deformed towards the shallowly buried side, and the shallowly buried side was deformed to a greater extent. Excavating shallow side tunnels first can effectively mitigate the impact of asymmetric terrain. The arch settlement of the Center Diaphragm Excavation Method is 1.33 cm, which is smaller than the three-step excavation method of 1.48 cm; however, this difference is not significant. The Three-bench Excavation Method was more efficient. Based on the conclusion of a numerical simulation, the construction site adopted the construction sequence of excavating the shallowly buried side tunnel first and adjusted the excavation method to the Three-bench Excavation Method. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To meet the operational requirements of a new metro line in Guangzhou, China, a complex tunneling project was undertaken in a business area surrounded by high-rise buildings and underground utility pipelines. Two large-section mine tunnels, with a maximum excavation span of 15.6 m, were constructed, crossing beneath the existing metro line 7 in close proximity. To ensure construction safety, extensive field monitoring was conducted, investigating the deformation and stress characteristics of the newly built tunnel lining structures and settlement of existing tunnels during various construction stages. The findings indicate that the structural integrity of the newly built tunnels may be compromised by the ground pressure resulting from deep-hole grouting, which is aimed at protecting the existing metro line above. The primary lining of the new tunnels is particularly susceptible to stress at the arch waist, where it experiences significantly higher stress compared to the arch crown and arch foot. While constructing the secondary lining before removing temporary diaphragm supports can be advantageous in controlling ground settlement, the stress levels within the secondary lining can fluctuate significantly once the temporary supports are removed. Once the tunnels are completed as closed loops, the stress conditions in both the primary and secondary lining tend to stabilize. The secondary lining primarily undergoes flexural stress, with internal force diagrams roughly symmetrical to the cross-section center line, and the most vulnerable position being at the left arch waist or invert. This investigation provides valuable insights for the design and construction of similar engineering projects in the future. [ABSTRACT FROM AUTHOR]

To study the stress distribution characteristics of surrounding rock and the spalling mechanism of deep hard rock tunnels with different arch heights, the complex variable function and angle-preserving transformation method in elasticity theory were applied to the analytic solution of tangential stress distribution of arch tunnels during stress adjustment. In addition, true triaxial tests were conducted on granite cube specimens (100 mm × 100 mm × 100 mm) containing holes with three arch heights (including the 25 mm semi-circular arch, 16.7 mm three-centered arch, 12.5 mm three-centered arch) to simulate the spalling process under different initial ground stresses. The stress distribution solution and experimental results show that the initial failure stress of arch holes is 0.39–0.48 times the uniaxial compressive strength (UCS) of the rock. The initial failure location occurs at the arch foot, where tangential stress maximizes. When the lateral pressure coefficient is in the range of 0.38–0.50, the tangential stress is 3.2–3.5 times the UCS. The rock debris of the hole wall are in thin flake shapes. Symmetrical V-shaped or curved failure zones occurred on hole sidewalls. The stress distribution resolution of the surrounding rock of tunnels with different arch heights shows that with the increasing burial depth, the bearing performance of the semi-circular arch tunnel is optimal. In addition, the maximum tangential stress increases as the height of the arch decreases or the lateral stress increases, making it easier for the initial failure to occur at the foot of the arch. [ABSTRACT FROM AUTHOR]

The Gaoloushan Tunnel in Longnan City, Gansu Province, China, frequently experiences rockburst disasters due to high in-situ stress. Managing rockburst in deep-buried tunnels remains a challenging issue. This paper employs RFPA (Rock Failure Process Analysis) software to establish a calculation model of constant resistance and large deformation (CRLD) anchorages and analyzes the effects of different support methods and pre-stress levels on rockburst. We simulate the process of tunnel rockburst disasters and find that ordinary anchor support incurs rockburst on the right arch waist and arch top, forming a V-shaped explosion pit. CRLD anchor support has several advantages in rockburst control, such as more uniform stress distribution in the surrounding rock, a uniform distribution of plastic zones, less noticeable damage to the tunnel, and effective control of the arch top displacement. The effectiveness of the CRLD anchor support under varying pre-stress conditions shows that a higher pre-stress results in a smaller plastic zone of the surrounding rock and arch top displacement and a lower number of acoustic emission signals, which better explains the excavation compensation effect. Moreover, adding long anchorages in the deep surrounding rock area can better control rockburst and reduce surrounding rock deformation. Based on these findings, we propose a comprehensive control system that combines long and short anchorages and provides the optimal scheme based on calculations. Therefore, by using high-prestress CRLD anchor support and the combination of long and short anchorages at critical positions, we can enhance the integrity of the surrounding rock, effectively absorb the energy released by the surrounding rock deformation, and reduce the incidence of rockburst disasters. [ABSTRACT FROM AUTHOR]

The existence of giant karst cave can cause collapse and water inrush hazards during the excavation of the karst tunnel, causing serious economic losses. In this paper, based on the FEA software MIDAS, a numerical simulation model for the backfilling of a large karst cave through a large cross-section tunnel was established. The distribution characteristics and change rules of the displacement field, stress field, horizontal support stress, and plastic zone of the tunnel surrounding rock and backfill were explored. The first stage of tunnel excavation leads to a sharp increase in the displacement of the tunnel's surrounding rock and the deterioration of the plastic zone, which should be strengthened and monitored. The tunnel arch, waist, and wall footing areas were prone to stress concentration. The two layers of horizontal support force show a certain regularity, showing a sharp increase and a gradually smooth growth trend. Meanwhile, the site monitoring results for arch settlement and horizontal convergence of the mega cavern tunnel were analyzed. The results show that the numerical calculation results were in good agreement with the values of site monitoring data. The average errors of final crown settlement and horizontal convergence were 8.6% and 15.9%, respectively, which verified the correctness of the numerical modeling method. This project can provide reliable experience for the construction of similar large cavern tunnels. [ABSTRACT FROM AUTHOR]

In order to study the dynamic stress distribution and the fracture area of rock around the tunnel under different orientations of blasting disturbance, AUTODYN finite difference method software was used to conduct numerical simulation research. Gauge monitoring points were set around the numerical model of the tunnel to conduct real-time monitoring of the stress distribution, displacement and fracture area of the tunnel. Based on the analysis of the stress wave propagation law, the following conclusions are obtained: (1) under the condition of the same blasting loads, the stress and displacement of the tunnel is relatively small when the blasting disturbance source is located above the roof, i.e., the stress state of the tunnel is relatively stable and the fracture area around the tunnel is minimal; (2) from the uniaxial stress around the tunnel and the tunnel peripheral displacement, it can be seen that the displacement caused by horizontal direction stress of the tunnel is the largest, and the deformation is mainly concentrated above the floor and at the shoulder, while the vertical wall part has almost no deformation; (3) for brittle materials such as rock, the arch-shaped stress-bearing surface is more likely to disperse stress, while the straight wall and flat floor of the tunnel cannot well disperse stress, resulting in uneven stress on the stress-bearing surface, uncoordinated deformation and ultimately, failure. [ABSTRACT FROM AUTHOR]

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock. [ABSTRACT FROM AUTHOR]

In order to study the damage mechanism of shield segment structure of shield tunnel with small curvature radius, based on practical engineering cases, a fine lining segment model considering segment joints and inter-ring joints was established to reveal the segment damage mechanism in the construction stage of shield tunnels with small curvature radius. The results showed that the axial force, shear force, positive bending moment and Mises stress of the segment all peaked at the inner and outer arch waists when the shield tunnel with small curvature radius was constructed in the turning section. The arch waist position of segments were more likely to be damaged during the excavation process. When the rectification angle of the jack thrust increased, the overall tunnel deviated to the outside. The outer side of the shield tunnel waist was more obviously affected, since the offset of outer arch waist was significantly larger than that of inner arch waist. The numerical simulation was consistent with the field observation of segment damage, which could provide reference for practical engineering. [ABSTRACT FROM AUTHOR]

Compared with single or twin tunnels, the pressure arch effect of deeply buried, symmetrically distributed triple tunnels are more complex and less studied. In this paper, the arching responses are in-situ measured in the deeply buried, symmetrically distributed triple tunnels of Badaling Great Wall station. Numerical research is subsequently conducted to investigate the formation and development of the pressure arch of triple tunnels. Then, the influencing law of buried depth on pressure arch behavior is systematically studied. Based on monitoring data, the rock pressure distribution is asymmetric about the axis of the triple tunnels, and the arching response of the middle tunnels is more significant than that of the left and right tunnels. According to numerical analysis, a combined large pressure arch may be easily formed across the triple tunnels. The pre-arching and double-arching effects are also numerically observed during triple tunnel excavations. The inner boundary of the pressure arch of the middle tunnel is 14.0 m, nearly two times higher than those of the left and right tunnels. This simulation result indicates that the mechanical state of the middle tunnel is the least desirable. Moreover, the critical arching depth of closely spaced tunnels is 1.75 times that of a single tunnel. Compared with a single tunnel, the support of triple tunnels should be additionally strengthened. [ABSTRACT FROM AUTHOR]

Under blasting load, a series of safety problems, such as lining cracking and surrounding rock instability, are prone to occur in deep-buried tunnels with a small net distance. It is significant to understand the dynamic response and failure mechanism of tunnels under blasting. The blasting attenuation formula is optimized through theoretical analysis and field experiments. The measuring point vibration is monitored in real time and the tunnel blasting model is established by ANSYS/LS-DYNA software. The model was set as having no reflective boundary and an uncoupled charge structure was used. The attenuation law of blasting seismic waves is studied from the adjacent tunnel lining and the direction of the tunnel cross-section and length. The inner and outer sides of the tunnel lining are investigated, respectively. The displacement and acceleration of lining measuring point are also analyzed. The dynamic response of the tunnel lining under blasting excavation is analyzed from multiple angles. The results show that the arch foot on the inner side of the lining (the side in contact with the tunnel headroom) is the first to generate vibration. On the outside of the lining (the side in contact with the rock),the peak vibration velocity is reached after blasting load unloading. There is little difference in the vibration velocity at different positions of the transverse section, but great difference in the vibration velocity of the longitudinal section. The influence of the horizontal displacement was greater than that of the vertical displacement. The vibration acceleration of the measuring point at the arch foot of the section is the largest and the detonation is also the largest. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Railway Science & Engineering is the property of Journal of Railway Science & Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• The large-span double-arch tunnel in proximity to existing track. • Independently developed a non-contact surface settlement scanning device. • Obtained the deformation characteristics of stratum and existing track during tunnel excavation. • Identified the failure mechanism of double-arch tunnel undercrossing existing track. This paper aims to study the influence mechanism of the large-span double-arch tunnels in proximity to existing tracks using 1 g model test. A novel non-contact device able to measure settlements automatically is developed to improve the test accuracy. During the test, the strata settlement, surrounding rock stress and track deformation induced by tunnel excavation are measured simultaneously. The results show that: (1) The excavation of the double-arch tunnel induces an asymmetric "W"-shaped horizontal surface settlement. The horizontal surface settlement near the centerline of the first excavation side is the largest. (2) The U-shaped groove structure exhibits an "M"-shaped deformation, while its structure produces bulges near the maximum horizontal surface settlement. (3) After excavation, the longitudinal surface settlement gradually decreases along the excavation direction, which causes the tilting or bottom voids of the U-shaped groove structure. The U-shaped groove structure may experience torsional shear damage under the load imposed by the train. [ABSTRACT FROM AUTHOR]

The position of seal roof block may greatly affect the overall performance of the segmental tunnel. However, a few investigations have been dedicated to evaluating this effect. In the present study, finite element models are established to simulate the ring structure-soil model in order to evaluate the capacity curve of the universal ring structure during progressive failure. Nineteen universal ring structures configurations were analyzed considering different locations of the adjacent seal roof blocks. The models accurately simulated the structural details of the typical handhole for curved bolt in the circumferential and longitudinal joints. The seismic performance of the universal ring structure with different configurations is evaluated and discussed in terms of the moment curve, plastic zone distribution, joint opening angle curve and capacity curve of the universal ring. The results indicate that there are significant differences in the maximum positive and negative moment, plastic zone, and tensile angle of the universal ring structure when the seal roof block is in different positions. At the same time, the development of the performance curve of the ring will also show significant differences, especially in the elastic stage. The structure exhibits best seismic performance when the seal roof block is located at arch shoulder and waist (−67.5° ± 22.5°) because it is less likely to reach the normal function, immediate operational, rectifiable or irreparable damage stages compared to other configurations. • The pushover simulation of the refined segmental tunnel model with different seal roof block positions is analyzed. • The position of the seal roof block with the best seismic performance was optimized. • When the seal roof block is in different positions, there is a significant difference in the capacity curve of the ring. • When the seal roof block is located at arch shoulder and waist (-67.5°± 22.5°), it has the best seismic performance. • This paper provides a reference for improving the seismic performance of segmental tunnels. [ABSTRACT FROM AUTHOR]

Fault fracture zones represent challenging geological conditions commonly faced during tunnel excavation, critically impacting the safety of both construction and operation phases. This study focuses on the deformation and failure characteristics of the surrounding rock and support structures within the fault fracture zone of the Tabaiyi Tunnel. A novel NPR anchor cable-truss active–passive coupling support system is introduced. A physical model experimental study is conducted to evaluate the effectiveness of this system in mitigating significant deformation and failure at the tunnel's initial branch within the fault fracture zone. A comparative analysis is performed between the model test and the engineering measurement results under the original support condition, followed by the NPR anchor cable-truss model test implementation to ensure the experiment's precision. Subsequently, the efficacy of the NPR anchor cable-truss coupling support system is examined through a field test. The results revealed that conventional anchor cables, commonly known as PR anchor cables, lack the mechanical properties necessary for high constant resistance and substantial deformation. This deficiency leads to the shear slip of the surrounding rock, distorting the anchor cable's broken arch, thereby rendering the tunnel unstable. In contrast, the tunnel maintains its integrity under the NPR anchor cable-truss coupling support system. The NPR anchor cable exerts prestress on the surrounding rock, compacting the loose and fragmented rock mass to form an arch structure, which enhances its bending stiffness. By adjusting nodes and implementing reinforcement measures, the truss absorbs and equalizes the pressure exerted by the surrounding rock due to the constant resistance deformation of the NPR anchor cable. This process stabilizes the primary support structure. In practical applications, the NPR anchor cable-truss coupling support system significantly reduced the deformation of the surrounding rock in the fault fracture zone from 1400 mm to less than 250 mm and can support approximately 87 % of the load from the surrounding rock. The findings from this research offer valuable insights for controlling the deformation of surrounding rock in tunnels traversing fault fracture zones. [ABSTRACT FROM AUTHOR]

• Large-scale model test of failure behavior of large cross-section tunnel under high geostress. • Load-bearing arch mechanism is investigated by model test and numerical simulations. • Stress transfer effect related with progressive rock failure is revealed. • Determination method of load-bearing arch boundaries is proposed. • Relationship between load-bearing arch position and tunnel wall displacement is illustrated. Understanding the failure process and the load-bearing arch effect of the surrounding rock is crucial for the stability control and support design of tunnels under high geostresses. In this study, the progressive collapse behavior and the formation mechanism of the load-bearing arch of a soft rock tunnel under high geostress were investigated by a model test and numerical simulations. First, a large-scale model test was conducted to study the stress redistribution rules and the failure process of the soft rock under different overloads. According to the model test results, the formation of the final load-bearing arch was divided into four stages including initial local load-bearing arch formation, rock failure inside the local arch, overall load-bearing arch formation and load-bearing arch outward transition. Both the progressive failure and arch mechanism were related to the stress transfer effect. Then, numerical simulations were carried out to verify the stress response results from the model test. The determination method for the inner and outer boundaries of the load-bearing arch was put forward based on the circumferential stress distribution, which was validated by the model test results. Furthermore, the relationship between the radial displacement of the tunnel boundary and the arch position was illustrated. It was found that the load-bearing arch showed an oval shape with a big top and a small bottom. The arch position was linearly correlated with the radial displacement at the tunnel wall. This study provides a comprehensive understanding of the load-bearing arch characteristics of large cross-section tunnels in soft rocks under high geostress conditions, which can be referred to in construction control and support design during tunnel construction. [ABSTRACT FROM AUTHOR]