Search

The lining cavities in tunnels have strong concealment and pose significant risks, seriously affecting tunnel operational safety. Therefore, it is necessary to develop efficient and high-precision detection techniques for tunnel lining cavities. In this study, concrete slabs with different parameter cavities were selected as the research object, and experiments on remote detection using Laser Doppler Vibrometry were conducted. During the experiments, the vibration parameters of the concrete surface were measured for cavities of varying sizes and depths, filled with different materials, and under different detection distance conditions. The vibration differences between the defective and healthy parts were analyzed using the spatial spectral entropy algorithm. The results showed that for cavities with side lengths of 200mm, depths of 50mm, and filled with hollow wooden boxes, the maximum velocity amplitudes of the surface concrete were 10.68, 3.55, and 4.01 times higher than those of the healthy parts, respectively. Moreover, at the same frequency, larger cavity areas and shallower depths resulted in greater surface vibration amplitudes. The vibration amplitudes of the surface with hollow wooden box filling were higher than those with foam polystyrene board filling. With increasing detection distance, the overall surface vibration velocity of the cavities was higher at a distance of 3 m from the laser probe compared to 5 m, indicating the ability to quantitatively describe the apparent vibration characteristics of concrete cavities under different parameters. This study demonstrates the significant effectiveness of laser Doppler vibrometry in remote detection of lining cavities in tunnels. [ABSTRACT FROM AUTHOR]

The fully mechanized tunnelling method using an earth pressure balance tunnel boring machine (EPB-TBM) with a horseshoe-shaped cross section was first developed and applied to a loess mountain tunnel, along with the application of a horseshoe-shaped segmental tunnel lining. The mechanical behavior of this novel type of segmental tunnel lining still contained uncertainties, and full-scale ring tests were conducted for further investigation. During the loading process, the ring deformation, joint opening, and concrete strain were measured, and the occurrence and progression of structural damage were observed and documented. The experimental results demonstrate that the structural failure of the horseshoe-shaped segmental ring mainly occurred in the arch area, while the invert did not prove to be a weak area. The deformation and failure mechanisms of the horseshoe-shaped segmental ring were found to be similar to those of circular ones. Significantly, the specific characteristics of the ring convergence deformation and bending moment distribution were significantly affected by the distribution positions of segment joints. In addition, during the initial stages of TBM advancement, frequent segment damage was observed at inferior joints, and the elaboration on the causes and corresponding measures was provided. This study provides significant evidence for the design and optimization of horseshoe-shaped segmental tunnel linings. [ABSTRACT FROM AUTHOR]

Various diseases such as lining defects, structural cracking, and water leakage are common in tunnel operation. Therefore, this paper considers the research object of the highway tunnel with typical lining defects, namely voids behind the lining. The stress distribution and crack distribution of the void behind the lining were analyzed by numerical simulation based on XFEM, and the cracking mode of the lining was studied by model test. According to the results:(1) The voids behind the tunnel lining change the stress distribution characteristics of the lining, and the lining structure within is stretched, significantly reducing the overall safety of the lining structure. (2) With the expansion of the void range (i.e. the void toroidal range and radial length), the lining area corresponding to the void is easy to crack, and the expansion of the void range leads to the increase of the crack area, which is also verified by the model test results. (3) A safety factor analyzes the bearing capacity of the lining structure. The safety factor of the lining area corresponding to the void is reduced, which is consistent with the results obtained by the XFEM method for the calculation of lining cracking, which proves that the XFEM method can be applied to the safety calculation of tunnel lining structure. [ABSTRACT FROM AUTHOR]

This paper presents an analytical solution derived with force method for the internal forces in the ring lining of maglev train tunnels, which are typically in a circular section and shallowly buried with low vacuum air pressure in the lining. The model incorporates the vacuum pressure induced by the differences in air pressures outside and inside the lining, and the vacuum pressure is assumed to be the active load exerting to the outside of the lining. The model assumes the vertical overburden acting on the lining is proportional to the soil depth at every particular point along the tunnel lining circumference. The lining-ground interaction, represented by tangential and normal resistance to the lining, is combined into the model and is comprehensively evaluated. The Mohr-Coulomb theory is used to estimate the interaction between tangential and normal resistance. The comparison with other models and case histories implies that the proposed model fits well for the field measurement data and results predicted with other models. Analyses based on the proposed model indicated that the vacuum pressure has a negligible effect on the bending moments acting on the lining, but its effect on the normal forces is significant. Parametric studies show that a higher cohesion and internal angle of friction of soils can induce a lower maximum bending moment and higher normal force, indicating that the better the soil conditions the thinner the lining. The cover-to-diameter ratio C/D impacts the maximum bending moment and the optimum C/D is approximately 0.20 in this study, a generally soft soil case. [ABSTRACT FROM AUTHOR]

The lining interfaces of composite linings typically include two interfaces: the primary lining–secondary lining interface and the primary lining–waterproof layer–secondary lining interface. These interfaces are observed in Chinese highway tunnels with weak surrounding rock. In order to ascertain more effective measures to accommodate the deformations between tunnel linings, it is necessary to investigate the shear resistance performance of the interfaces and the factors that influence this performance. The samples are classified according to the presence or absence of waterproof layers, cohesive interfaces, and rough interfaces. Subsequently, direct shear tests are conducted under constant normal stress. The shear rate is 1 mm/min, and the normal stress is 0.5, 1.0, and 2.0 MPa, respectively. The results of the tests demonstrate that the shear properties are influenced by the normal stress, the waterproof layer, the cohesive interface and the rough interface. The shear resistance performance of the lining interface in the absence of a waterproof layer is observed to be superior to that observed with a waterproof layer. The normal compressive stiffness range for the primary lining‐secondary lining interface is observed to be between 0.69 and 3.17 GPa, with a pre‐peak shear stiffness range of 0.12–1.88 GPa. The effective cohesion range is found to be between 0 and 0.29 MPa, while the internal friction angle range is observed to be between 22.62° and 29.43°. In contrast, the normal compressive stiffness for the primary lining–waterproof layer–secondary lining interface is observed to be within the range of 1.24–9.78 GPa, the pre‐peak shear stiffness range is 0.45–39.68 GPa, the effective cohesion range is 0.07–1.98 MPa, and the internal friction angle range is 34.92°–52.24°. In conclusion, this investigation presents a number of potential measures that could be employed to enhance the shear resistance performance of tunnel lining interfaces. Furthermore, it furnishes a set of parameters derived from the test results that could serve as a foundation for subsequent research and design endeavors. [ABSTRACT FROM AUTHOR]

Visual inspection and hammering tests are the standard methods for inspecting shield tunnels. They can provide a comprehensive judgment based on the engineer's past experience and conditions, such as cracking, water leakage, and structural details. However, one problem with this method is that the inspection results are highly dependent on the skills of the inspector. To overcome this limitation, it is necessary to develop an easy and quantitative inspection method for shield tunnels. The influence line (IL), which is the response at a specific point due to a unit load that is moved along the target structure, can be used for evaluating the soundness of the infrastructure. Therefore, in this study, we propose a method for determining the IL that can be applied when the speed of a passing train changes. The IL is determined by measuring the displacement due to the train load using a MEMS accelerometer. Finally, to verify the validity of the determined IL, a finite element analysis is performed. Good agreement is found between the ILs determined experimentally and analytically when the soil spring constant is 18 times higher than the nominal value, with a correlation coefficient of 0.98. [ABSTRACT FROM AUTHOR]

With the growing prevalence of lithium battery electric vehicles, the incidence of fires resulting from thermal runaway in lithium batteries is also on the rise. In contrast to conventional fuel vehicle fires, fires involving lithium battery electric vehicles exhibit distinct differences in fire dynamics, fire loads, and smoke characteristics. These variations impose more stringent requirements on the design of passive fire protection systems within tunnels. To evaluate the fire resistance performance of existing passive fire protection systems under electric vehicle fire conditions, this study first used PyroSim software 2022 (integrating FDS 6.7.9) to establish fire models for combustion engine trucks and electric trucks, comparing the combustion characteristics of both types of fires without insulation lining materials. Based on the electric truck fire model, different insulation lining materials were added. The analysis of the simulation results focused on the impact of the thermal conductivity and emissivity of each lining material on peak tunnel temperatures, aiming to identify the insulation lining material with the best fire resistance performance. The results indicate that the heat release rate, temperature distribution, toxic gas concentration, and smoke propagation of lithium battery combustion engine truck fires are all higher than those of combustion engine truck fires. Among the five insulation lining materials studied, SiO2 gel material demonstrated superior fire resistance compared to the others. This research provides a scientific and rational basis for tunnel fire protection design and fire response strategies, aiming to mitigate the damage caused by lithium battery electric vehicle fires to tunnel lining structures. [ABSTRACT FROM AUTHOR]

Rapid acquisition of rock structure information during tunnel construction is crucial for optimizing subsequent construction strategies and avoiding engineering rock disasters. In this regard, this study proposes the best time to obtain rock structure information on the tunnel face during the construction period. By summarizing relevant studies on rock information acquisition locally and abroad and combining them with the actual situation during the construction of the Lushan Tunnel, this study analyzed the factors affecting the quality of rock information acquisition during the construction period and the approximate range of the optimal timing of acquisition. We also conducted experiments on the concentration of respiratory dust and the concentration of total dust on each section of the Lushan Tunnel construction site and explored the optimal timing of acquiring rock information on the tunnel face by conducting several dust experiments at the construction site. The results showed that the best time to obtain information was before the erection of the steel arch, which was also the best time for the engineers to conduct mechanical characterization of the tunnel face and the lining inspection of the tunnel. The optimal acquisition timing identified in this study is crucial for improving the accuracy of rock information acquisition and guiding subsequent construction programs. [ABSTRACT FROM AUTHOR]

Excess pore water pressure (EPWP) induced by shield tunneling has a significant influence on the stability of the tunnel face, post-construction settlement, and the mechanical behavior of the tunnel lining. However, the three-dimensional and unsaturated property of the soil field is seldom considered in current research. Considering the non-uniform radial convergence model, a modified three-dimensional displacement solution induced by shield tunneling was established first. Then based on unsaturated EPWP elastic theory, a reliable and efficient method is developed to expedite the evaluation of EPWP distribution in three-dimensional saturated and unsaturated clay soil. The validity of the method is confirmed through comparison with field test and numerical outcomes. The analysis examples demonstrate that negative and positive EPWP are generated above the tunnel crown and beneath the tunnel invert, respectively. In the vertical direction, the negative EPWP exhibits a decreasing trend ahead of the heading face and an increasing trend behind it. Along the longitudinal direction, the influence zone of EPWP extends to 1D ahead of and 6D behind the heading face. With the decrease of soil saturation, the EPWP values tend to diminish. The maximum EPWP values observed in saturated conditions can be 16.13 times higher than those under unsaturated conditions. [ABSTRACT FROM AUTHOR]

The capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity. [ABSTRACT FROM AUTHOR]

Passive confinement provided by transverse reinforcement is taken into account in the design of reinforced concrete structures subjected to high compressive loading such as columns, piers, or tunnel lining segments. In current guidelines, several models exist to account for this beneficial effect. However, these approaches lack mechanical consistency regarding the three‐dimensional load dispersion of the confining forces. The article addresses this knowledge gap by introducing a new model based on a lower‐bound solution according to the theory of plasticity, along with a simplification regarding the governing confined concrete area. The proposed model and its simplified version are compared to the design approaches proposed by current guidelines, and both are successfully validated against experimental data. The simplified new model is a valuable alternative to existing models in current guidelines, as (i) it is mechanically more consistent, (ii) its application is more straightforward, and (iii) it allows the comprehensive treatment of rectangular and circular cross‐sections using the same equations. [ABSTRACT FROM AUTHOR]

This paper proposes a simplified analytical solution for longitudinal seismic responses of a circular tunnel crossing a fault zone under longitudinally propagating shear waves. The transmissions and reflections of shear waves at two geological interfaces between the fault zone and intact rock are considered when calculating the free‐field displacement. An improved elastic foundation beam model considering different tangential contact conditions at the tunnel‒rock interface is also adopted. According to the continuous conditions at the two geological interfaces, explicit expressions for the tunnel displacement, bending moment, and shearing force are given. The effectiveness of the proposed analytical solution is validated via numerical simulations, and the importance of accounting for tangential contact conditions at the tunnel‒rock interface is emphasized. Moreover, parametric studies are performed to investigate the effects of the fault zone width, rock conditions, tunnel lining stiffness, tangential contact conditions, and earthquake frequency on the deformation and internal forces of tunnels subjected to seismic waves. This novel analytical solution can be utilized to quickly estimate the longitudinal seismic responses of circular tunnels crossing fault zones subjected to longitudinally propagating shear waves, particularly in the preliminary engineering design, and can be extended to geological conditions with multiple interfaces. [ABSTRACT FROM AUTHOR]

Similar to the deep-buried tunnel, the lining of the cut-and-cover tunnel (CCT) exhibits varying degrees of cracking failure during ultrahigh backfill. To explore the whole progressive failure process of a high-filled cut-and-cover tunnel lining structure from the mesodamage to the macrolocal failure and then to the overall instability during backfill, based on the discrete-element program PFC2D, we simulated the mechanical behavior and fracture characteristics of the CCTs with rectangular, circular, and arch lining section features with the backfill height. Two load-reduction measures—load-reduction material (LRM) and the interaction of LRM and concrete walls—were then further proposed, and the impact of load-reduction measures on the progressive failure of CCT lining was analyzed. The simulation results show that the various lining section features indicate differences in the distribution and value of lining stress and fracture. But the CCT lining with features of the three sections exhibits a progressive failure process from cracking to local collapse and falling and finally to overall instability as the backfill height increases. Furthermore, the LRM and concrete walls can effectively reduce the vertical stress of the lining vault and the horizontal stress of the haunch, respectively, to ensure the stability and integrity of the CCT. [ABSTRACT FROM AUTHOR]

The development of transportation in large cities requires the construction of new structures subterranean in close proximity to existed structures subterranean. Finding the best appropriate position of the new structure subterranean will help to minimize the magnitude of movement there will be in soil surrounding the existing one. The purpose of this study is to involve assessing the immediate influences that will result from the new tunnel excavation in close proximity to existed tunnel at different angular positions ß (0° to 180°) relative to existing one, especially destabilization of the soil surrounding, including movements, displacements of soil mass and surface settlement, in addition to internal efforts generated in lining of old tunnel, and to provide a solution by selecting an ideal angular position for the tunnel that will be excavated relative to the existing one. This is a crucial factor when searching for a full solution to the problem of interactions between subterranean structures. This study uses numerical analysis to examine the movements and displacements of soil mass surrounding, the settlement and the internal efforts induced in the old tunnel's lining impacted by the new tunnel excavation. Several factors, such as the excavation technique, tunnel spacing, liner thickness, etc., had a favorable impact on diminishing the extreme values acquired at the critical angle position (ß =135°). A parametric study was conducted to minimize the maximum values obtained. As a result, these elements could affect planning and security objectives. [ABSTRACT FROM AUTHOR]

The external water pressure of lining is of great significance to the determination of lining thickness and drainage scheme of water-rich deep buried tunnel. The existing research often ignores the analysis of the influence of macroscopic geological conditions on the seepage field, which leads to the lack of reliability evaluation of the external water pressure estimation results and lining design schemes of deep buried tunnels. Based on the Qinling Water Conveyance Tunnel Project of Hanjiang-to-Weihe River Diversion Project, this paper generalizes the deep-buried tunnel in the water-rich area into three representative macro-geological environment models under the watershed, the mountainside area and the river, and studies the influence law and mechanism of geological conditions and engineering measures on the seepage field of surrounding rock and the external water pressure of lining. The results show that: (X) The seepage direction of groundwater around the watershed tunnel is mainly vertical under the condition of the same height of groundwater at the top of the tunnel and impermeable lining. The seepage direction of groundwater around the tunnel under the river is mainly horizontal. The external water pressure reduction coefficient of the watershed tunnel, the tunnel near the mountain area and the tunnel under the river increases in turn. The reduction coefficient of external water pressure of tunnel under watershed increases with the increase of buried depth, which is 0.72,0.77 and 0.84 respectively. The reduction coefficients of the external water pressure of the mountain tunnel and the river tunnel are almost unchanged, which are 0.91, 0.91, 0.93 and 0.95, 0.96, 0.96, respectively. (2) After the same drainage measures are taken, with the increase of buried depth, the reduction coefficients of external water pressure of watershed tunnel are 0.15,0.42,0.64 respectively, and the pressure reduction effect is the best. The external water pressure reduction coefficients of the tunnel near the mountain and the tunnel under the river are 0.48, 0.67, 0.77 and 0.63, 0.80,0.83, respectively, and the pressure reduction effect gradually deteriorates. (3) When the buried depth of the tunnel is 1 200 m, the reduction coefficients of external water pressure of the watershed, mountainside and river tunnel are 0.43~0.73, 0.67~0.89 and 0.80~0.95 respectively with the increase of the permeability coefficient of the surrounding rock, which shows the regularity that the external water pressure increases with the increase of the buried depth of the tunnel. The research results are universal, and the rationality of water pressure resistance design of tunnel lining in water-rich area can be evaluated from the regularity of macroscopic hydrogeological conditions of tunnel and reduction coefficient of external water pressure. [ABSTRACT FROM AUTHOR]

A shaking table model test of the tunnel was carried out to compare the damping effects of polyurethane foam aluminum(AF/PU) and sponge rubber. The test shows that the damping effect of polyurethane foam aluminum is better, and the dynamic earth pressure and strain values of each measuring point of the tunnel lining are relatively smaller. The ANSYS software was used for the ground motion simulation. The first principal stress and first principal strain of the lining were compared and analysed between the two types of damping layers. It was found that the damping effect of AF/PU was better, which is consistent with the test results. The damping effects of AF/PU with thicknesses of 10, 20, and 30 cm were 22.3%, 29.03%, and 31.41%, respectively. The damping effect increases with an increase in thickness, but the growth rate slows. [ABSTRACT FROM AUTHOR]

Intelligent detection of the apparent defects of tunnel linings on the basis of deep learning has become a mainstream trend, and how to objectively diagnose the hazard level of tunnel defects via semantic segmentation images is the key to intelligent control of tunnel health. In this study, a tunnel lining defect image diagnosis method that uses graph neural networks is proposed. First, the binary images obtained by semantic segmentation are used as the data set, and quantitative parameters, such as crack length, maximum width, box dimension, and area density, are calculated according to the crack orientation and employed as graph node attributes. Second, the construction of graph data is based on the similarity of defect attributes. Third, clustering is completed using graph neural networks and K-means, and the number of clusters and danger levels of crack defects are reasonably determined. Last, a tunnel crack risk index is developed via partial least squares regression analysis, and the grading criteria for defect levels are established. Results show that the method is effective in extracting the key attributes of crack images and clustering them into different hazard levels, which is important for maintaining tunnel health. [ABSTRACT FROM AUTHOR]

The detachment of railway tunnel lining constitutes a grave danger to train operation safety and drastically curtails the tunnel's service life. This study endeavors to efficiently detect the void defects in railway tunnel lining by creating a finite element model of tunnel lining structures. Utilizing this model, the study simulates the nonlinear acoustic wave propagation cloud maps for three representative tunnel lining structures: void-free, air void, and water void. This facilitates a thorough examination of the acoustic signal characteristics in the wavefield, time domain, and frequency domain. To satisfy the precision and efficiency demands of tunnel lining void detection, this study has devised and developed a portable acoustic detector that incorporates automatic analysis and processing capabilities and is furnished with a high-performance rare-earth magneto-strictive acoustic excitation device. This detection system can swiftly detect and assess typical void defects in tunnel lining. To further validate the effectiveness of this system, this study conducted lining defect detection in the Pingdao Railway Tunnel in the eastern Qinling Mountains. The test results show that the detection rate of this system for both air-filled and water-filled voids with a width of 1 m reached 100%, demonstrating its extremely high application value. [ABSTRACT FROM AUTHOR]

During the assembly of concrete segments into a tunnel lining, small geometric imperfections are unavoidable. In the longitudinal joints, they lead to contact deficiencies, which affect the eccentricities of the forces transferred through them. This influences the development of internal forces along the lining's circumference. However, it is often not realistically considered in structural calculations. In this paper, the effects of longitudinal joints assembly imperfections on the lining's internal forces were investigated by employing finite element models for various lining configurations. The results show that assembly imperfections have an unfavorable effect on the internal forces in most cases. Depending on the loading situation, this can lead to more required reinforcement and higher utilization ratios in the segments field and joints compared to perfectly assembled linings. Stiffer and less deformable configurations are at higher risk of experiencing more severe effects. In systems at risk, an individual assessment is recommendable. Therefore, a simplified method is introduced that requires a significantly reduced modeling effort and calculation time and lower software capabilities. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of the tiny soil arch effect generated by the soil between the steel tubes in the ring direction of the tunnel overrun tube shed on the force deformation of the steel tubes during the working period. By assuming the arch effect axis between the steel tubes is circular and intercepting any three adjacent steel tubes on the tunnel contour line to establish a vertical coordinate system, the equation of the arch axis and the coordinates of the arch top were derived. Referring to the calculation theory of the peripheral rock pressure of the Taishaki tunnel, the peripheral rock pressure borne by the steel tubes of the pipe shed under the consideration of the micro‐arch effect was derived. Assuming the pipe shed acts as a semi‐infinite long beam on Pasternak's two‐parameter elastic foundation, the pipe shed was divided into four sections axially based on the initial support application status and the tunneling position of the working surface. The controlling equations for each section were analyzed and solved. The theoretical deflection curves of the pipe shed were obtained using actual engineering construction parameters and were validated by monitoring the settlement values of the soil layer above the tunnel using multipoint displacement meters. The study shows that the initial support application status and the tunneling position of the working surface significantly affect the functioning mechanism of the pipe shed, causing it to play different roles at different stages. When the working surface advances to the target section, the pipe shed exerts a beam arch effect; when the working surface tunnels beyond the target section, the pipe shed exerts a combined beam effect. The deflection change trend of the pipe shed with the advancement of the working surface is characterized by rapidly increasing, rapidly decreasing, and slowly decreasing stages, with the maximum deflection change occurring above the working surface position. Considering the micro‐arch effect, the theoretical deflection changes are larger and closer to the actual engineering situation compared to the existing theory that does not consider the micro‐arch effect. The results provide theoretical references for the design and implementation of tunnel overrun pipe sheds, moving beyond mere engineering experience and validating new methods for monitoring the deformation of surrounding rock during tunnel construction, effectively ensuring construction safety during tunnel excavation. [ABSTRACT FROM AUTHOR]

Mobile laser scanning (MLS) has emerged as a pivotal tool for accurately collecting tunnel point cloud data and enabling the detection of tunnel deformation. This study introduces a novel approach for the precise monitoring of tunnel cross-section deformation, a critical factor in assessing stability and lining safety. The MLS system used in this study is the Self-mobile Intelligent Laser Scanning System (SILSS) for data acquisition. A comparison with corresponding data acquired by Leica P16 demonstrates that the data collected by SILSS are accurate. The methodology developed utilizes ellipticity parameters and deformation analysis indices based on the ellipse-fitting analysis of circular shield tunnel deformation. A key innovation is the robust denoising of data using the Random Sample Consensus (RANSAC) method, ensuring accurate ellipse fitting and extraction of tunnel lining. Subsequently, an algorithm segmented the tunnel cross-section lining into individual shield tunnels, enabling the calculation of ellipticity parameters for shield tunnels, which are the objects for deformation analysis. The experimental results underscore the novelty and effectiveness of this approach in monitoring deformation across different indices. The method proves to be a reliable tool for assessing tunnel health, providing a detailed evaluation of the cross-section's condition through statistical and graphical visualization. This study significantly advances shield tunnel monitoring, offering a practical and precise methodology for tunnel deformation analysis based on MLS point cloud data. [ABSTRACT FROM AUTHOR]

Using digital twin models of tunnels has become critical to their efficient maintenance and management. A high-precision 3D tunnel model is the prerequisite for a successful digital twin model of tunnel applications. However, constructing high-precision 3D tunnel models with high-quality textures and structural integrity based on mobile laser scanning data remains a challenge, particularly for tunnels of different shapes. This study addresses this problem by developing a novel method for the 3D reconstruction of multi-shaped tunnels based on mobile laser scanning data. This method does not require any predefined mathematical models or projection parameters to convert point clouds into 2D intensity images that conform to the geometric features of tunnel linings. This method also improves the accuracy of 3D tunnel mesh models by applying an adaptive threshold approach that reduces the number of pseudo-surfaces generated during the Poisson surface reconstruction of tunnels. This method was experimentally verified by conducting 3D reconstruction tasks involving tunnel point clouds of four different shapes. The superiority of this method was further confirmed through qualitative and quantitative comparisons with related approaches. By automatically and efficiently constructing a high-precision 3D tunnel model, the proposed method offers an important model foundation for digital twin engineering and a valuable reference for future tunnel model construction projects. [ABSTRACT FROM AUTHOR]

The accurate detection of tunnel lining cracks and prompt identification of their primary causes are critical for maintaining tunnel availability. The advancement of deep learning, particularly in the domain of convolutional neural network (CNN) for image segmentation, has made tunnel lining crack detection more feasible. However, the CNN-based technique for tunnel lining crack detection commonly prioritizes increasing algorithmic complexity to enhance detection accuracy, posing a challenge in balancing the accuracy of detection and the efficiency of the algorithm. Motivated by the superior performance of Unet in image segmentation, this paper proposes a lightweight tunnel lining crack detection model named Mini-Unet, which refined the Unet architecture and utilized depthwise separable convolutions (DSConv) to replace some standard convolution layers. In the optimization of the proposed model parameters, applying a hybrid loss function that integrated dice loss and cross-entropy loss effectively tackled the imbalance between crack and background categories. Several models were set up to contrast with Mini-Unet and the experimental results were analyzed. Mini-Unet achieves a mean intersection over union (MIoU) of 60.76%, a mean precision of 84.18%, and a frame per second (FPS) of 5.635, respectively. Mini-Unet outperforms several mainstream models, enabling rapid detection while maintaining identified accuracy and facilitating the practical application of AI power for real-time tunnel lining crack detection. [ABSTRACT FROM AUTHOR]

Considering the effect of surrounding rock on lining in the design of tunnel lining within fractured rock masses is challenging, particularly in accurately predicting the reserved deformation of the tunnel. This study bases a rock mass classification method and the established Hoek–Brown (H-B) strength criterion to assess the deformation characteristics of the surrounding rock. It establishes a more scientifically rigorous theoretical calculation method for the reserved deformation of tunnel linings that accounts for the rock–lining interaction. An optimization design approach for the lining structure, based on the synergistic effect and considering the stress safety of the concrete lining and the rock's displacement release rate, is proposed. Case analysis is utilized to validate the safety of the lining design in the study section through computational verification. The recommended optimized lining parameters are identified: the support time is initiated when the tunnel wall's surrounding rock deforms by 9 mm, and the lining thickness is optimized to 47 cm, which is approximately 36.5% less than the pre-optimization thickness. This precise optimization of support timing and lining thickness enhances both the safety and economic efficiency of the Wufengshan Tunnel. The method allows for the calculation of the optimal combination of support time and lining thickness tailored to different surrounding rock conditions, offering significant reference value for tunnel lining optimization. [ABSTRACT FROM AUTHOR]

Existing concrete specifications limit the crack width in order to fulfill the limits of serviceability and durability. The crack width calculation results differ depending on the influences of the variability of the used materials, the geometry, the actions and the uncertainty of the used calculation model itself. In this contribution, the influence of the variability of the input parameters on the calculated crack width is investigated using probabilistic methods in a real case study of a highly loaded tunnel lining cross‐section. The primary objective of this study is a sensitivity analysis to identify the geometric and material‐related input parameters with the most significant influence, which must be particularly controlled during execution for quality control purposes. The study in this article is based on the Eurocode deterministic model for calculating crack width for a stabilized cracking stage in late concrete age. [ABSTRACT FROM AUTHOR]

This paper presents a novel displacement–performance design method for the shield tunnel based on the mobilized strength design (MSD) theory. First, the nonlinear relationship between the ground volume loss caused by tunnel excavation and the earth pressure was constructed to obtain the real earth pressure on the tunnel lining. Second, the nonlinear relationship between the convergence displacement of the lining and the ground resistance was established to acquire the subgrade reaction acting on the tunnel lining. Finally, the proposed method was verified by orthogonal numerical experiments and compared with the finite element method (FEM) results. Compared with the FEM, the average deviation of the bending moment and the axial force is about 9% and 1%. The average variation of the bending moment can be reduced to 1% after calibration. The results calculated by this developed method are better than the traditional beam–spring model. Its accuracy is close to the FEM based on the strata–structure concept. Therefore, the proposed method based on MSD theory in this paper has the characteristics of high efficiency and simplicity, which provides a new auxiliary design approach for the structural design of shield tunnels in clay areas. [ABSTRACT FROM AUTHOR]

The paper introduces a new model of compressive membrane action (CMA) for a conical fan failure mechanism around a patch load in a reinforced concrete plate with in-plane restraint. The new model is based on a concept of 3-dimensional wedging and it is fundamentally different from conventional arching models of CMA. The new model accounts for the effects of CMA on the bending resistance at yield lines and the complementary wedging effect of compressive membrane forces at the yield lines, considering the interaction between the radial and tangential forces acting on the wedgelike segments in a restrained fan. The model was developed in the context of an investigation of the strength of fiber reinforced shotcrete (FRS) tunnel linings, but it is readily adaptable for conventional reinforced concrete plates and slabs. The paper compares the wedging model results (predicted load-deflection curves) with field test results for FRS tunnel linings. It is shown that the wedging model provides a good approximation to the available test results. [ABSTRACT FROM AUTHOR]

Water seepage in tunnel lining cracks considerably influences the structural safety of a tunnel. In this study, chitosan was introduced in the enzyme-induced carbonate precipitation (EICP) to repair the cracks in in-service tunnel linings. The influence of chitosan incorporation on the Ca2+ precipitation ratio during EICP was analyzed by aqueous solution experiments, and the optimal content of added chitosan was obtained. Moreover, in terms of specimen scale and field tests, the determination of permeability characteristics, and mass loss, scanning electron microscopy and ground penetrating radar technology were used to analyze the changes in permeability coefficient and mass loss of cracked concrete repaired by chitosan-combined EICP under normal temperature (25°C±2°C) and freeze–thaw (FT) cycling conditions. The effect, feasibility, and action mechanism of chitosan-combined EICP for tunnel crack repair in extreme environments were explored. The results showed that the incorporation of an appropriate amount of chitosan in traditional EICP could accelerate Ca2+ precipitation, provide nucleation sites for the precipitation of CaCO3 , promote the existence of the deposited CaCO3 crystals in the form of calcite with higher strength, and reduce mass loss in extreme circumstances. The combination of hydrogel and CaCO3 makes the impermeable layer more compact and reduces the permeability coefficient of repair concrete. The permeability coefficient descends exponentially with the decrease of mass loss under FT conditions. Chitosan-combined EICP represents an environmentally friendly and feasible method for crack repair in in-service tunnel linings. [ABSTRACT FROM AUTHOR]

Hydraulic tunnels are prone to pass through faults and high-intensity earthquake areas, which will cause serious damage under fault dislocation and earthquake action. Fault dislocation and seismic excitation are often considered separately in previous studies. For tectonic earthquakes with higher frequency in seismic phenomena, fault dislocation and ground motion are often associated, and fault dislocation is usually the cause of earthquake occurrence, so it is limiting to consider the two separately. Moreover, strong earthquake records show that there will be significant differences in the mainland vibration within 50 m. The uniform ground motion inputs in previous studies are not suitable for long hydraulic tunnels. This paper begins with the simulation of non-uniform stochastic seismic excitations that consider spatial correlation. Based on stochastic vibration theory, multiple multi-point acceleration time-history curves that can reflect traveling wave effects, coherence effects, attenuation effects, and non-stationary characteristics are synthesized. Furthermore, a fault velocity function is introduced to account for the velocity effect of fault dislocation. Finally, numerical analyses of the response patterns of the tunnel lining under four different conditions are conducted based on an actual engineering project. The results indicate the following: (a) the maximum lining response values occur under the combined effects of fault dislocation and non-uniform seismic excitation, indicating its importance in the seismic resistance of the tunnel. (b) Compared to uniform seismic excitation, the peak displacement of the tunnel under non-uniform seismic excitation increases by up to 6.42%, and the peak maximum principal stress increases by up to 28%. Additionally, longer tunnels exhibit a noticeable delay effect in axial deformation during an earthquake. (c) Under non-uniform seismic excitation, the larger the fault dislocation magnitude, the greater the peak displacement and peak maximum principal stress at the monitoring points of the lining. The simulation results show that the extreme response values primarily occur at the crown and haunches of the tunnel, which require special attention. The research can provide valuable references for the seismic design of cross-fault tunnels. [ABSTRACT FROM AUTHOR]

Shield tunneling adjacent to existing piles is common occurrence in subway construction. This study proposes a novel tunnel model capable of simultaneously simulating ground loss, unloading effects, and void grouting under in-flight conditions. Several three-dimensional (3D) centrifugal scale model tests are implemented in a silty-silty clay composite to investigate the response of a single pile (Test SP) and pile group (Test GP) with a sinking low cap subject to adjacent tunneling. The results indicate a critical influence area, i.e., 0.75D in front and 0.25D behind the centerline of the existing piles, is observed for the pile head settlement, in each test, and the induced bending moment in the piles above the tunnel spring line is more sensitive to tunneling than that below it. A decreasing trend in axial force along the pile shaft is observed in Test SP, whereas Test GP shows the opposite behavior. The maximum variations in axial force and bending moment occur near the tunnel invert and crown in Test SP, respectively, however, they all appear near the tunnel spring line in Test GP. There is a law of load transfer for downward migration in Test SP. In Test GP, however, the load on the upper part of pile P1 decreases and shifts to the lower section of pile P1 and the whole pile P2. Subsequently, the load on the upper part of pile P2 reduces and transfers to the lower part of pile P2 and the whole pile P1. A significant increment in the earth pressure near the pile toe is observed. The pore water pressure increases slightly at first and then dissipates. Digital image correlation (DIC) has been preliminarily demonstrated as a valuable tool for visually capturing the progressive behavior of pile-soil interactions during in-flight tunneling, proving advantageous for analyzing tunnel-soil-pile interaction issues under centrifugation conditions. [ABSTRACT FROM AUTHOR]

The study investigates the application of shotcrete as a temporary support during tunnel excavation, emphasizing its role in stabilizing rock fragments by understanding the load-transfer mechanism. Current research problems include a lack of standardized methodologies for designing primary shotcrete linings and insufficient understanding of shotcrete behavior under varying stress conditions, particularly in squeezing ground conditions. The proposed method utilizes the convergence-confinement method and support capacity plots to design shotcrete linings. This approach is demonstrated through a non-linear, finite element analysis of four tunnel sections of the Atal tunnel, India. Initially, empirical approaches were used to analyze the squeezing effects using geological data, followed by 2D plane strain and axisymmetric analysis to establish ground reaction curves (GRC) and longitudinal deformation profiles (LDP). Subsequently, analytical solutions were used to construct support characteristic curve (SCC), and rock-support interaction curves were generated using these three components (GRC, LDP, and SCC). Further, the study examined the effects of parameters such as age, grade, thickness of the shotcrete, disturbance factor, and anisotropic stress on axial force, bending moment, and shear forces in the shotcrete. Additionally, the shear capacity and bending capacity plots were constructed to evaluate shotcrete stability. Findings indicate that C40 shotcrete with a thickness of 0.35 m provides adequate structural resilience against shearing and bending forces. However, this design is deemed unsafe for both shearing and bending when disturbance factors and anisotropic stress ratios were considered. Specifically, increasing the disturbance factor from 0 to 1 result in a substantial increase in axial force by 64.4%. Under the isotropic stress conditions (ko = 1), shotcrete exhibits uniform axial force distribution; however, when ko = 0.5, axial forces at the springline increase by 6%, and when ko = 1.5, axial forces at the crown and invert increases by 67%. These findings underscore the importance of selecting appropriate shotcrete grade and thickness to ensure the safety and stability of tunnel linings under various stress conditions. This comprehensive analysis offers a novel approach by integrating empirical, analytical, and numerical methods to evaluate shotcrete performance, providing valuable insights for engineers dealing with similar geological conditions. The study offers a realistic and practical method for shotcrete lining design in circular excavations subjected to anisotropic stresses and disturbances in squeezing ground conditions. [ABSTRACT FROM AUTHOR]

The increasing problem of urban traffic congestion has led to the extensive use of underground tunnels. However, tunnel lining cracks pose a major threat to the integrity and safety of the structure. Although the traditional repair method is effective, it often requires higher construction technology and higher cost, and may cause damage to the concrete structure. In this study, microbial-induced calcium carbonate precipitation (MICP) was combined with basalt fiber cloth to repair and reinforce tunnel lining cracks. Bacillus pasteurii was used to optimize the microbial mineralization process, and the effectiveness of the method on cracks with different widths was evaluated using a water seepage test. In addition, the mechanical properties of the reinforced tunnel lining were tested. The microbial mineralization process effectively repaired cracks with widths of 1 mm, 2 mm, and 3 mm. The use of unidirectional basalt fiber cloth increased the bearing capacity of the strengthened member by 12.5%. The combined reinforcement method also enhances the deflection performance and alleviates the influence of water seepage on the bonding performance. This innovative and sustainable approach not only provides an effective solution for the repair of tunnel lining cracks, but also contributes to the broader field of eco-friendly building materials. This study highlights the potential of using this combination approach to improve the durability and performance of underground infrastructure. [ABSTRACT FROM AUTHOR]

Currently, research on employing finite difference method and discrete element method (FDM-DEM) coupling to assess the stability of tunnel lining structures is limited. This study utilized the FDM-DEM coupling approach, with the F2 fault of the East Tianshan Tunnel as a case study, to develop a numerical model in conjunction with PFC3D 6.0 and FLAC3D 6.0 software. We conducted a comprehensive analysis of the displacement deformation and crack progression of the tunnel lining structure under varying dislocation momentum conditions, unveiling the underlying mechanisms. The findings indicated that as the dislocation increased, the extent of damage to the vault intensified, and the particle contact force within the tunnel lining shifted from compression to tension, significantly contributing to the crack formation. Fault dislocation influenced the gradual expansion of cracks from the vault to the spandrel and arch waist, with the crack width increasing alongside the rising dislocation momentum. In particular, under substantial dislocation momentum, the overall stability of the tunnel lining was markedly diminished. The safety factor at the tunnel section declined progressively as the dislocation momentum escalated, with values of 2.53, 2.49, 2.43, 2.39, and 2.32 corresponding to dislocation momenta of 0.01 m, 0.05 m, 0.1 m, 0.15 m, and 0.2 m, respectively. This research offers valuable insights and a reference framework for investigating the stability of tunnel lining structures in proximity to fault dislocations, pinpointing potential failure points, and bolstering the structural integrity of tunnels. [ABSTRACT FROM AUTHOR]

This paper presents an IoT-based solution for detecting grouting voids in tunnel construction using the Raspberry Pi microcomputer. Voids between the primary and secondary tunnel linings can compromise structural integrity, and traditional methods like GPR lack continuous feedback. The proposed system uses embedded electrical wires in the secondary lining to measure conductivity, with disruptions indicating unfilled voids. The Raspberry Pi monitors this in real time, uploading data to a cloud platform for engineer access via smartphone. Field tests were conducted in a full-scale, 600 m long tunnel to evaluate the system's effectiveness. The tests demonstrated the system's accuracy in detecting voids in various tunnel geometries, including straight sections, curves, and intersections. Using only the proposed void detection system, the largest void detected post-grouting was 1.8 cm, which is within acceptable limits and does not compromise the tunnel's structural integrity or safety. The system proved to be a cost-effective and scalable solution for real-time monitoring during the grouting process, eliminating the need for continuous manual inspections. This study highlights the potential of IoT-based solutions in smart construction, providing a reliable and practical method for improving tunnel safety and operational efficiency during grouting operations. [ABSTRACT FROM AUTHOR]

Though a comprehensive in situ measurement project, the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined. The measured excavation responses included the displacement of capping beam and retaining pile, settlement of ground surface, and deformation of metro lines. Based on the analyses of field data, some major findings were obtained: 1) the deformations of retaining structures fluctuated along with the increase of temperature, 2) the deformation variation of retaining structures after the occurrence of thawing of seasonal frozen soil was greater than that in winter, although the excavation depth was smaller than before, 3) the influence area of ground settlement was much smaller because of the features of seasonal frozen sandy soil, 4) the displacement of metro line showed a significant spatial effect, and the tunnel lining had an obviously hogging displacement pattern, and 5) earth pressure redistribution occurred due to the combined effects of freezing-thawing of seasonal frozen soil and excavation, leading to the deformation of metro line. The influence area of ground settlement was obviously smaller than that of Shanghai soft clay or other cases reported in literatures because of special geological conditions of Shenyang. However, the deformation of metro lines was significantly lager after the thawing of the frozen soil, the stress in deep soil was redistributed, and the metro lines were forced to deform to meet a new state of equilibrium. [ABSTRACT FROM AUTHOR]

Using the complex variable method, an elastic analytical solution of the ground displacement caused by a shallow circular tunneling is derived. Non-symmetric deformation relative to the horizontal center line of the tunnel cross-section is used as a boundary condition. A comparison between the proposed analytical method and the Finite Element Method is carried out to validate the rationality of the obtained analytical solution. Two parameters in the Peck formula, namely the maximum settlement of the ground surface center and the width coefficient of settlement curve, are fitted and determined. We propose a modified Peck formula by considering three input parameters, namely the tunnel depth, tunnel radius, and the tunnel gap. The influence of these three parameters on the modified Peck formula is analyzed. The applicability of the modified Peck formula is further investigated by reference to six engineering projects. The ground surface displacement obtained by the explicit Peck formula is in good agreement with the field data, and the maximum error is only 1.3 cm. The proposed formula can quickly and reasonably predict the ground surface settlement caused by tunnelling. [ABSTRACT FROM AUTHOR]

When a fire occurs in an underground shield tunnel, it can result in substantial property damage and cause permanent harm to the tunnel lining structure. This is especially true for large-diameter shield tunnels that have numerous segments and joints, and are exposed to specific fire conditions in certain areas. This paper constructs a full-scale shield tunnel fire test platform and conducts a non-uniform fire test using the lining system of a three-ring large-diameter shield tunnel with an inner diameter of 10.5 m. Based on the tests, the temperature field distribution, high-temperature bursting, cracking phenomena, and deformation under fire conditions are observed. Furthermore, the post-fire damage forms of tunnel lining structures are obtained through the post-fire ultimate loading test, and the corresponding mechanism is explained. The test results illustrate that the radial and circumferential distribution of internal temperature within the tunnel lining, as well as the radial temperature gradient distribution on the inner surface of the lining, have non-uniform distribution characteristics. As a result, the macroscopic phenomena of lining concrete bursting and crack development during the fire test mainly occur near the fire source, where the temperature rise gradient is the highest. In addition, the lining structure has a deformation characteristic of local outward expansion and cannot recover after the fire load is removed. The ultimate form of damage after the fire is dominated by crush damage from the inside out of the lining joints in the fire-exposed area. The above results serve as a foundation for future tunnel fire safety design and evaluation. [ABSTRACT FROM AUTHOR]

High-resolution line scan cameras with wide-angle lenses are highly accurate and efficient for tunnel detection. However, due to the curvature of the tunnel, there are variations in object distance that exceed the depth of field of the lens, resulting in uneven defocus blur in the captured images. This can significantly affect the accuracy of defect recognition. While existing deblurring algorithms can improve image quality, they often prioritize results over inference time, which is not ideal for high-speed tunnel image acquisition. To address this issue, we developed a lightweight tunnel structure defect deblurring network (TSDDNet) for curved-tunnel line scanning with wide-angle lenses. Our method employs an innovative progressive structure that balances network depth and feature breadth to simultaneously achieve good performance and short inference time. The proposed depthwise ResBlocks significantly improves the parameter efficiency of the network. Additionally, the proposed feature refinement block captures the structurally similar features to enhance the image details, increasing the peak signal-to-noise ratio (PSNR). A raw dataset containing tunnel blur images was created using a high-resolution line scan camera and used to train and test our model. TSDDNet achieved a PSNR of 26.82 dB and a structural similarity index measure of 0.888, while using one-third of the parameters of comparable alternatives. Moreover, our method exhibited a higher computational speed than that of conventional methods, with inference times of 8.82 ms for a single 512 × 512 pixel image patch and 227.22 ms for completely processing a 2048 × 2560 pixel image. The test results indicated that the structural scalability of the network allows it to accommodate large inputs, making it effective for high-resolution images. [ABSTRACT FROM AUTHOR]

To explore the load-bearing performance and the failure patterns of the lining structures, a full-scale loading test on the three-ring staggered assembled shield tunnel segments is carried out through a hydraulic loading system. In the experimental study, the segments’ internal force, convergence deformation, and displacement, and the bolts’ internal force, are analyzed. According to the experimental results, the relationship between internal force and deformation is obtained to determine the residual bearing capacity of the shield tunnel at each stage. Three stages are specified for the evolution of the segment’s maximum bending moment during the loading process, in which, the elastic stage is the main and longest stage, in which the bending moment of the segment increases the most. There are two stages for convergence deformation development and segment misalignment development. At the end of loading, the segment’s maximum positive and negative convergence values reach 61.22 and −57.69 mm, respectively. Besides, the maximum segment misalignment is 3.67 mm, which occurs in the direction of 90°. The segment cracks when its maximum convergence value reaches 25.03 mm. Moreover, there are signs of fracturing on the waist joint of the segment when its maximum convergence value reaches 32.73 mm. The concrete at the waist joint starts fracturing in pieces when the segment’s maximum convergence value reaches 38.93 mm, which is defined as the type of shear failure. Finally, the bearing capacity of shield tunnels during segment failure period can be evaluated by using the corresponding relationship between deformation and internal force. [ABSTRACT FROM AUTHOR]

Multi-layer linings have been widely used in deep rheological soft rock tunnels for the excellent performance in preventing large-deformation hazards. Previous studies have focused on the bearing capability of multi-layer lining, however, its failure characteristics and synergistic load-bearing mechanisms under high geo-stress are still unclear. To fill the gap, three-dimensional geomechanical model tests were conducted and synergistic mechanisms were analysed in this study. The model test was divided into normal loading, excavating, and overloading stages. The surrounding rock deformation was monitored by using an improved high-precise extensometer measurement system. Results show that the largest radial deformation appears on the sidewall, followed by the floor and vault during the excavating stage. The relative convergence deformation of sidewalls springing reaches 1.32 mm. The failure characteristics of the multi-layer linings during the overloading stage undergo an evolution of stability, crack initiation, local failure, and collapse, with a safety factor of 1.0–1.6, 1.6–2.0, and 2.0–2.2, respectively. The synergistic load-bearing mechanism analysis results suggest that the early stiffness and late yielding deformation capacity of large deformation support measures play important roles in stability maintenance both in the construction and operation of deep soft rock tunnels. Therefore, the combination of yielding support or a compressible layer with reinforced support is recommended to mitigate the effect of the high geo-stress. [ABSTRACT FROM AUTHOR]

An internal explosion may cause severe damage to an underground and surface ground structures. The intensity of the blast plays a substantial role in the damage to the structures, the configuration of the structure, material properties, and geometry of materials. There are several ways for a structure to be protect against blast loads. A tunnel could be protected employing the protective layer, directly located on the top of the structure. The influence of utilizing a protective layer, made of geofoam could appease the adverse effects of an internal explosion and decline vibrations when it comes to the surface ground. The modeling procedure used the coupled Eulerian–Lagrangian in Abaqus/Explicit. Lagrangian elements have been used for modeling soil and reinforced tunnel and trinitrotoluene as Eulerian elements. Drucker–Prager plasticity, Holmquist–Johnson and Johnson–Cook plasticity models were simulated for the stress–strain response of soil, concrete, and reinforcement, respectively. In addition, Jones–Wilkins–Lee equation of state used for the pressure-volume relation of TNT. As the results show, while explosion waves scatter inside tunnel and penetrate among top layers of soil, soil and lining without a protective layer experienced severe deformation and blast waves influenced surface ground structures negatively. Indeed, the more charge weight, the more deformation on tunnel lining and structures. It is observed that increasing geofoam thickness worked up to a certain thickness and semi-circular geofoam section on top of the structure fulfilled expectations. [ABSTRACT FROM AUTHOR]

The influence of underground excavation on urban areas constitutes a critical issue in tunnel engineering. This paper strives to establish a machine learning algorithm to predict maximum tunnel induced surface displacement. The algorithm was developed using FLAC3D and validated under actual conditions in the twin tunnel of the Seville metro line. A dataset of 526 simulations of underground excavation with Earth Pressure Balance (EPB) was used to predict the maximum surface displacement using machine learning techniques. Five machine learning methods to evaluate the significance of input data variables, as soil properties, tunnel depth, face pressure or grout pressure of EPB, proving the most accurate models, were Gradient Boost and XGBoost. Additionally, the feature importance analysis conducted using Random Forest indicated that soil properties play a crucial role in the prediction process. The XGBoost model's effectiveness in predicting surface displacement has been confirmed through validation on real monitored data from Seville metro tunnel Line 1. The percentage error of the calculated values was compared with the real vertical surface movements obtained, and it varied from 3.24 to 10.66%. This study develops a practical approach to improving construction planning for future excavations in Seville, making them safer and more efficient. [ABSTRACT FROM AUTHOR]

The prefabricated assembled cover arch reinforcement method offers rapid construction and high quality, effectively addressing the challenges of cast-in-place cover arch reinforcement used in tunnel linings in mountainous areas of China. This study investigated the mechanical performance of prefabricated assembled arches in tunnels through model tests and numerical simulations. The results indicate that joint opening and deflection, as well as their change rates, increase with eccentric distance. There is a roughly linear relationship between joint opening and deflection with increasing load. At an eccentric distance of + 0.2 m, the peak stress appears on the outside of the joint, with a valley on the inside, and stress concentration at bolt holes. The application of bolt preloading enhances the joint's stress performance. Furthermore, the stiffness of the lining and soil significantly impacts the mechanical response of the cover arch, with peak stress mainly observed at the foot of the cover arch and the handhole of the joint. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion in shield tunnel segments has an important impact on the structure's bearing capacity and failure mode. Generally, a shield tunnel structure is under small eccentric compression, but if the reinforcement corrosion develops sufficiently, then a transition occurs from small to large eccentric load state, thereby lowering the structural bearing capacity and endangering the safety of tunnel operation. In the study reported here, based on the compressive bending load characteristics of the shield lining structure, corrosion test columns with small eccentric loading were designed to simulate the actual force state of the tunnel lining, and the whole evolution process of their mid‐span strain, ultimate bearing capacity, and cracks under different corrosion degrees was analyzed. With increasing corrosion, the bearing capacity, concrete strain, and depth of the compressive zone of a test column decrease more and more rapidly, and at the maximum corrosion degree of 68.32%, the maximum reduction of bearing capacity is 53.23%. The tests show that the failure mode of a test column with high corrosion degree (≥46.25%) is transformed from small to large eccentric failure. Based on theoretical analysis of the normal section bearing capacity of reinforced concrete flexural members, a theoretical method is proposed for calculating the critical corrosion degree for the tunnel lining structure to transform from small to large eccentric failure. The theoretical calculation method is verified against finite‐element calculations, and the present research results offer theoretical support for the durability design and safety evaluation of shield tunnel lining structures. [ABSTRACT FROM AUTHOR]

Voids behind tunnel linings can be formed either during or after the construction phase, occurring due to inadequate backfilling, substandard workmanship, water erosion, or gravitational forces. Investigations into numerous tunnels in which collapses occurred while in operation have indicated that voids behind the liner constitute the primary contributors to these failures. Consequently, it is imperative to devise lining reinforcement strategies tailored to the specific conditions encountered in the field. Fiber-reinforced plastic (FRP) represents a viable alternative construction material that has been widely utilized in the reinforcement of concrete structures. It is essential to quantitatively assess the reinforcing effect of FRP grids when they are employed in the restoration of deteriorated tunnel linings, thereby facilitating the development of effective maintenance designs. In this study, we aimed to enhance the sensitivity analysis of the reinforcement method by evaluating the impact of voids through the analysis of bending moments and axial forces within the tunnel lining. The effects of voids based on the different locations in which they occur were explored numerically through an Elastoplast finite element analysis. The study involved simulating tunnel linings that had been reinforced with FRP grids and assessing the effects of such reinforcement in tunnels afflicted with various structural problems. Based on the outcomes of these simulations, the internal forces within the lining are scrutinized, and the efficacy of the reinforcement is appraised. [ABSTRACT FROM AUTHOR]