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The release of ground stress brought on by overlying excavation poses a significant threat to regular tunnel operation, especially when the foundation pit intersects the tunnel inclination, and the torsional deformation of the tunnel also needs to be considered. Based on the foundation pit intersecting with the subway tunnel at an angle, the U-shaped soil reinforcing (USR) technique was introduced to limit the tunnel heave produced by overlying excavation. The Topcon MS05A automated monitoring system was used to track the following: (1) the evolution of the tunnel heave over time and space; (2) the convergent deformation of the cross section; and (3) the torsional deformation. The reinforcement efficiency of the USR method was assessed with numerical simulations, and the effect of intersection angles and reinforcement dimensions on the deformation of the underlying tunnel was further discussed. In addition, an optimal design was suggested for the USR method that considers cost. Tunnel deformation utilizing the USR method was reduced by 63.40%, and the maximum heave was observed to be merely 6.5 mm. The influence zone on the tunnel by overlying excavation was up to 2.5 times the excavation widths, and the tunnel always produced clockwise rotation. Backfilling generates significant and sharp distortion, so the backfilling speed must be carefully controlled. The foundation pit spanning the tunnel at a small angle caused a bigger heave and torsion of the tunnel, which should be avoided. The proposed optimization approach can determine the cost based on the tunnel deformation control criteria. This study provided a valuable reference for the protection of adjacent excavations of subway tunnels in deep sandy strata. [ABSTRACT FROM AUTHOR]

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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 Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department 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 Beijing University of Technology is the property of Journal of Beijing University of Technology, Editorial Department 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 examine the impact of inner lining defects on the mechanical behavior of double-shell structures and validate the efficacy of the shield tunnel support system, similar model tests were employed to analyze the deformation characteristics, internal force distribution, damage progression, and interaction strength of double-shell lining structures with inner lining defects in three typical locations (crown, shoulder and waist) under ultimate loads. This study discloses how inner lining defects affect the load-bearing capacity of the double-shell structure and makes recommendations. The results show that (1) The existence of defects in the inner lining makes the deformation of the double-shell lining structure under the action of external loads uncoordinated. The overall load-bearing capacity of the structure decreases by 33% to 50%. (2) Local stress concentrations and increased eccentricity lead to a significant increase in the internal force proportion and failure of the defective inner lining, thus failing to limit the deformation of the segments and the early damage of the double-shell lining structure. (3) Of the three locations studied, the impact of inner lining defect position on the mechanical behavior of the double-shell structure follows this ranking: arch waist most impactful, crown weaker than arch waist, least impactful at shoulder. [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]

ABSTRACT When a shield tunnel passes through a karst area, the water‐filled cave can easily make the surrounding rock metamorphic, resulting in water inrush, ground collapse, and shield machine failure and other engineering hazards. Natural cavities have a significant degree of geometric irregularity due to groundwater alteration and soluble rock erosion. Considering the difficulties in describing the shape of a natural irregular cavity, circular, rectangular, and elliptical geometries have been simplified in most related studies. Based on the upper bound theorem of limit analysis, we established a three‐dimensional failure model including the karst caves located directly above and below the circumferential side of the tunnel. Then, we deduced the corresponding analytical solution of the critical safety distance (CSD). Furthermore, the effects of rock mass parameters, cave parameters, and geometric parameters on the CSD were analyzed. Then we designed the numerical simulation considering the irregular geometry shape at the circumferential side of tunnel using the Fourier descriptors. In addition, we estimated the CSDs for two failure models using the revised dichotomy and failure criterion. The findings demonstrated a quantifiable association between CSD and Fourier descriptors of irregular cave shape, resulting in the development of a CSD prediction model. These test results can provide a theoretical foundation and direction for predicting water inrush caused by the constrained irregular cave. [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]

With the rapid expansion of shield tunnel projects in China, precise accounting of CO2 emissions throughout the entire process is essential for advancing green and low-carbon construction practices. This paper introduces an innovative CO2 accounting methodology utilizing a cost-based carbon emission coding system. It adopts a multilevel approach to carbon emission accounting, aligned with this coding system, which facilitates a detailed examination of carbon emission ratios and characteristics across various construction techniques. The analysis includes six typical shield tunnel projects varying in diameter, focusing on sub-projects to scrutinize CO2 emissions and establish specific indicators. The findings indicate that CO2 emissions per 10,000 yuan of investment, approximately 30.25% (or 3025 kgCO2e/10,000 yuan), are more consistent than those per unit of length. Moreover, the study highlights differing CO2 emission trends among sub-projects compared to whole tunnel projects, assessing emission indicators and distribution patterns in four sub-projects: shield excavation, segmental lining, internal structure, and tunnel reinforcement. From these findings, the paper suggests more precise and tailored strategies for CO2 reduction. This research provides a theoretical basis for future construction planning and carbon management strategies. [ABSTRACT FROM AUTHOR]

In this study, a refined numerical model, which contains the detailed geometric construction of the longitudinal joints, is established to investigate the bearing performance of the segmental ring based on the horizontal convergence. Firstly, the model is verified by comparing it with the reported results of a documented full‐scale model test. Then, according to the load‐structure method, this numerical model is employed to investigate the deformation behavior and bearing capacity of the segmental ring. Moreover, the effects of the coefficient of lateral pressure and subgrade reaction are extensively taken into consideration through comprehensive numerical analyses. According to the numerical results, a bilinear model is proposed to describe the relation between the convergent displacement and the stratum pressure, which could be used to preliminarily estimate the convergence after the completion of tunnel construction. Otherwise, the development of structural defects, such as the joint opening and the water leakage, has close association with the horizontal convergence. Therefore, a simple evaluation method for tunnel structure safety assessment is proposed using horizontal convergence deformation as an indicator to predict the tunnel service state. Since this indicator is easy to obtain during the tunnel operation, it is convenient for the engineers to assess the bearing capacity of the segmental ring and the service state of the tunnel structure quickly. [ABSTRACT FROM AUTHOR]

Synchronous grouting technology is a crucial aspect of shield tunnel construction. However, understanding the mechanism of slurry diffusion during this process is challenging due to its complexity and invisibility. Existing theoretical models often oversimplify the grouting process and do not account for multi‐stage diffusion mechanisms. By considering the radial penetration of slurry and viewing the diffusion process as the formation of annular pancakes through circumferential filling, a 3D diffusion numerical model is established using the volume of fluid (VOF)‐multiphase flow model in Fluent software. The model's validity is confirmed through calculations based on theoretical formulas and monitoring data from engineering examples. This study uncovers the patterns of slurry diffusion and examines how factors like porosity, grouting pressure, and slurry density impact diffusion radius and segment stress. The findings of this research provide a crucial theoretical foundation for shield synchronous grouting construction. [ABSTRACT FROM AUTHOR]

Fabric anisotropy significantly influences the mechanical behavior of sandy soils, potentially resulting in diverse failure patterns during shield tunneling owing to insufficient support pressure. In this paper, a set of specimens with bedding angles (α ) and an isotropic specimen are well generated to simulate active failure at the tunnel face using DEM. The evolving failure of the soil in distinct α are scrutinized, and ground settlement is further explored. Furthermore, microscopic information is juxtaposed to systematically elucidate the influence of α on failure patterns at a microscopic level. Macroscopic findings reveal that, aside from specimens with α = 0° and 90°, particle displacement experiences deflection as it extends toward the ground surface in other specimens. However, this deflection behavior is only noticeable under conditions of large deformation. Additionally, across all specimens, the maximum displacement of the ground surface is observed in those with α = 90°, while the minimum value is noted in specimens with α = 45°. Notably, considerable particle rotation occurs within the shear face. However, the deflection behavior has not been found in specimens with α = 0° and 90°. Similarly, in specimens with these two specimens, there is no noteworthy deflection observed in the principal direction of contact normal. [ABSTRACT FROM AUTHOR]

Aiming at the condition of shield tunnel undercrossing the foundation of a pile group directly, using the settlement and inclination of the pile caps as the evaluation index, the reinforcing effect of the pregrouting of the soil around the pile foundation, the deep hole grouting behind the tunnel segment, and the combination of the two reinforcement methods are analyzed through three-dimensional numerical simulation. A reasonable reinforcement scheme is found and applied to practical engineering. The results show that for the pregrouting reinforcement of the soil around the pile, the optimal reinforcement scheme is to extend 0.5 m around the pile cap in the plane and vertically from the surroundings of the pile cap to 1/3 of the pile length below the bottom of the cap. When deep hole grouting reinforcement is adopted, larger reinforcement range and a certain range of radial reinforcement radius of tunnel section will result in a better effect of reinforcement. The combination of the two schemes is better than the single use of one. The practical application results show that the combined reinforcement scheme can effectively control the influence of shield tunnel excavation on the pile foundation of an elevated waiting hall. [ABSTRACT FROM AUTHOR]

This study aims to clarify the mechanism of slurry support and its effect at different stages of slurry infiltration in shield construction. The analysis of various expressions of slurry support throughout the entire excavation cycle is based on the theories of slurry infiltration effects and the cutting action of the cutters. Furthermore, the limit support pressure calculation method at the tunnel face is modified considering the slurry support mechanism observed during different slurry infiltration stages. Some of the main conclusions drawn are as follows. (1) When slurry deep infiltration occurs, the main form of slurry support is the seepage force acting on the soil skeleton. At this stage, the limit support pressure from the filter cake model will not be sufficient to meet the tunnel face stability requirements. (2) The effectiveness of slurry support is influenced by both the slurry infiltration state and the cutting action of the cutterhead. Slurry infiltration and shield tunneling together create a quasi-static equilibrium state, in which slurry support is effective only when the infiltration velocity corresponding to this state is greater than the critical velocity. (3) And the influence of shield tunneling parameters on the slurry support mechanism is significant. Compared with the cutter's penetration degree, the cutter's rotational speed has a more pronounced effect on the conversion rate of slurry support pressure at the shield tunnel face. [ABSTRACT FROM AUTHOR]

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.)

As shield tunnels increase, managing shield muck strains construction and the environment. To mitigate this problem, shield muck replaced bentonite in silty clay to improve synchronous grouting slurry. Initially, the physical attributes and microstructural composition of shield muck were obtained, alongside an analysis of the effects of the muck content, particle size, and general influencing factors on the slurry properties through standardized tests and regression models. Subsequently, leveraging three-dimensional response surface methodology, admixture interactions and multiple factor impacts on the slurry were explored. Finally, utilizing the SQP optimization technique, an optimal slurry blend ratio tailored for actual project needs was derived for improved muck slurry. The findings reveal with the decreasing bleeding rates as the muck content rises, the particle size diminishes. An inverse relationship exists between the muck content and slurry fluidity. At soil–binder ratios below 0.6, a decrease in the soil–binder ratio intensifies the influence of the water–binder ratio on the slurry density, bleeding rate, and setting time. The fly flash–cement ratio inversely correlates with the slurry bleeding rate, while the ratio greater than 0.6 is positively correlated. For muck particle sizes under 0.2 mm, the fly flash–cement ratio inversely impacts the density, while over 0.2 mm, it correlates positively. The optimal proportion for silty clay stratum synchronous grouting slurry, substituting muck for bentonite, includes a water–binder ratio of 0.559, binder–sand ratio of 0.684, fly flash–cement ratio of 2.080, soil–binder ratio of 0.253, particle size under 0.075 mm, and water-reducing admixture of 0.06. [ABSTRACT FROM AUTHOR]

When an earth pressure balance shield passes through soft-upper and hard-lower composite strata, it faces challenges such as cutterhead "mud cake" formation, inefficient muck removal, and tool wear. To address these issues, this study focused on silty clay-completely weathered granite composite strata and conducted laboratory tests on ground conditioning in different strata based on the adaptability and performance of soil conditioners. The study explored the effects of soil conditioners, such as foam agent and bentonite slurry, as well as their improvement methods on soft-upper and hard-lower strata, to determine an optimal ground conditioning scheme and the appropriate addition ratios for shield tunneling in composite strata. The results showed that: (1)Combining a 3% concentration foam agent solution with bentonite slurry at a 1 : 8 ratio yielded good results. (2)The silty clay strata were improved by foam agent. The slump of the muck increased with the foam addition ratio, while the shear strength, cohesion, internal friction angle, and permeability coefficient decreased. The optimal addition ratio of the soil conditioners was between 19. 7% and 22. 8%. ( 3) The completely weathered granite strata were improved using a combination of foam agent and bentonite slurry, which effectively enhanced the flow plasticity and impermeability of the muck. When using only foam, the optimal addition ratio was between 22. 2% and 28. 7%, while the combined foam and bentonite slurry method required a ratio of 24. 3% to 31. 5%. Field application and construction feedback showed that the above improvement scheme effectively enhanced the flow plasticity of the muck, and significantly improved the shield thrust, cutterhead torque and tool wear. [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.)

The deformation of the Yangtze River embankment on soft and water-rich strata is greatly affected by the disturbance of the construction of the shallow buried super-large diameter shield tunnel. Based on on-site monitoring data, under the background of a large double-line shield tunneling project with a diameter of 15. 07 m, the spatiotemporal evolution law of the settlement of the Wuwei Yangtze River embankment was studied and the rationality of excavation parameters and embankment reinforcement measures were analyzed. The research results indicate that the amplitude of surface settlement of embankments can be effectively reduced by the reinforcement treatment of compacted grouting. When the right tunneling passed through the embankment, the overall settlement deformation of the embankment above the central axis increased with the number of days the shield tail leaves. The maximum settlement was located in the front section of the embankment, which was 20. 37mm, and there was generally a slight uplift far from the central axis. After the left tunneling passed through the embankment, the overall vertical deformation of the embankment followed a distribution pattern of “ uplift of the front and back sections of the left embankment, settlement of the embankment section, and overall settlement of the right line, with a decrease in amplitude from the front section to the back section of embankment” . Thus, it is concluded that when shield tunneling passes through the Yangtze River embankment, the adjustment of excavation parameters such as incision pressure, thrust, and torque is affected by the overload effect of the embankment. [ABSTRACT FROM AUTHOR]

This study investigates the prediction of ground loss rate during soft-soil shield tunneling using Peck’s back analysis method and XGBoost model. Bayesian optimization is employed to determine optimal hyperparameters, ensuring comprehensive and efficient model tuning. The XGBoost model is compared with Random Forest (RF) and Support Vector Machine (SVM) models to benchmark its performance. The results demonstrate the superior accuracy and robustness of the XGBoost model. Also, the results show that the soil properties and the grouting factors of the excavation face affect the duration of the instantaneous settlement of the ground surface. There is a specific correlation between the depth-to-diameter ratio, the coefficient of variation in the advancing speed of the shield machine, the maximum surface subsidence, and the ground loss rate. The prediction model of the ground loss rate based on the combined approach of Peck back analysis and eXtreme Gradient Boosting and Bayesian optimization has high reliability in soft-soil layers, and this method can provide a specific reference for predicting construction risk in related projects. [ABSTRACT FROM AUTHOR]

Excavation of subway tunnels in hard rock generates strong vibration waves that pose potential risks to the stability of surrounding structures. In this study, the discrete element method-finite difference method (DEM-FDM) coupling was adopted to build the model of tunnel structure-rock-pile, which was validated by field monitoring data. Then, the vibration response of piles under various pile-tunnel spacings was analyzed, revealing the occurrence of vibration peak rebound phenomena within certain distance ranges. The range of vibration effects was categorized. Furthermore, in shield tunneling construction, the energy induced by vibrations was mainly concentrated within the 50 Hz range. Low-frequency vibrations result in a wider effect range. The study also demonstrated that within a 1d (tunnel diameter) range of the pile-tunnel spacing, the vibration induced by shield tunneling construction had a more significant effect. As the pile-tunnel spacing increased, the piles transitioned from being subjected to bending forces to experiencing bending-shear forces. Finally, the vibration effects on the existing piles were evaluated under field working conditions. It also provided suggestions for construction based on the effects and laws of the pile dynamic response. [ABSTRACT FROM AUTHOR]

In this article, the influence of soil condition on the dynamic response of a tunnel and the surrounding soil was studied by both experimental model tests and numerical simulations. We tested a 1/20‐scale tunnel model with three different soil conditions: upper soft soil and lower hard soil, homogeneous soft soil and homogeneous hard soil. We also applied dynamic loads, sweep loads and train loads on the model tunnel for time domain and frequency domain analysis. The experimental and numerical results revealed that the interface between the soft and hard soil strata has an obvious amplification effect on the vibration wave. With the propagation of the vibration wave to the surface, the damping effect of the soil above the tunnel becomes the main factor affecting the dynamic response of soil. The internal force response of the tunnel structure is for the most part concentrated in the section under the excitation load, which is mainly affected by the soil properties beneath the tunnel. [ABSTRACT FROM AUTHOR]

In response to the problem of deformation caused by surrounding construction disturbances in existing shield tunnels in soft soil areas, lateral horizontal grouting is often used. Based on an independently designed and developed lateral grouting experimental device, the mechanism of horizontal lateral grouting on the convergence deformation of the tunnel was determined. A three-dimensional finite-element analysis model was established to study the force and deformation characteristics of the tunnel tube sheet, and to verify the correctness of the model test results. The grouting remediation efficiency, η, was introduced to establish the relationship between the grouting volume and the convergent deformation. The results show that the tunnel tube sheet was subjected to asymmetric additional soil pressure along the ring direction, and asymmetric displacement occurred, which was most obvious on the grouting side. The additional moment distribution was symmetrical and spindle-shaped, and the peak bending moments mostly appeared in the arch roof, the arch bottom, and the arch whist. With a continuous increase in grouting volume, the efficiency of the grouting remediation decreased, and the two were negatively correlated. [ABSTRACT FROM AUTHOR]

Uneven settlement of the strata induced by ground fissure activity trigger great damage to a shield tunnel crossing a ground fissure zone. It is of great significance for the safe maintenance of tunnels to accurately predict the mechanical response of the tunnel structure under the dislocation of a ground fissure. In this paper, an analytical solution of mechanical behaviors of a shield tunnel crossing an active ground fissure zone is proposed. The shield tunnel-strata interaction in a ground fissure site is simplified as a Timoshenko beam placed on a Vlasov foundation. The governing differential equation and the closed-form solution for an equivalent shield tunnel subjected to additional load induced by the dislocation of ground fissure are derived. The proposed solution is adopted to analyze the mechanical behaviors of a shield tunnel, including tunnel displacement, rotation, bending moment, and shear force. The results of a model test and a numerical model are provided to verify the rationality of the proposed analytical solutions. Finally, a parameter sensitivity analysis about the additional load forms, the compression and shear modulus of the foundation, and the shear stiffness coefficients of the tunnel are conducted. The result shows that the form and value of the additional load has a large impact on the deformation and a slight impact on the internal forces of the tunnel. The foundation compression modulus determines the constraint effect of the strata, and the deformation and internal force response of a tunnel decrease with the increasing foundation shear modulus. In addition, the increase of shear coefficient enhances the shear stiffness of a tunnel, but largely increases the internal force as well. [ABSTRACT FROM AUTHOR]

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Copyright of Urban Mass Transit is the property of Urban Mass Transit 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 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 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 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.)

With the rapid development of urban rail transit networks, constructing shield tunnels often requires passing underneath existing buildings, which can potentially impact their safety. This study examined the impact of constructing a double-line shield tunnel underneath a railway bridge on the adjacent pile foundation via numerical simulation. Protective measures, including construction parameter control, grouting methods, monitoring, and early warning systems, were implemented to mitigate impacts. The results indicated that the bridge deformation fell within acceptable limits, with maximum horizontal and longitudinal displacements of 0.06 mm and a maximum vertical displacement of −0.31 mm. The railway bridge pile foundation experienced maximum horizontal and longitudinal displacements of 0.47 mm and vertical displacements of −0.23 mm during construction. Enhanced construction quality control and monitoring effectively controlled deformation to ensure the railway safety. This study provides valuable guidance for similar projects and future urban rail transit developments. [ABSTRACT FROM AUTHOR]

When shield tunnels are under complex geological conditions, tunnel damage, decreased structural performance, and shield tunnel deformation and destruction may occur. Therefore, a new type of composite segment and combined splicing joint were suggested and experimentally investigated in this study. According to the test results, the new composite segment effectively enhanced the load capacity of the segment, and the yield and ultimate loads of the segment were increased. Compared with the reference specimen, the ultimate load capacities of the proposed segments with different numbers were 23.8%, 50.0%, and 64.3% greater. Moreover, the combined splicing joint enhanced the initial bending stiffness and load capacity of the segment joint, reduced the opening displacement, and improved the rotational stiffness of the segment joint. The addition of a plug-in joint at the segment joint increased its load capacity by approximately 25%. A parametric study showed that the number and posit ion of the plug-in joint clearly affected the load capacity of the segment joint. In addition to the above test results, reasonable theoretical formulas for the new composite segment and combined splicing joint are given in this paper. [ABSTRACT FROM AUTHOR]

Shield tunnels' structural stability is challenged due to the fact that they are often built under rivers, lakes, and oceans. It is crucial to execute the structural deformation perception of the shield tunnel. Fiber Bragg grating (FBG) sensing technology is sensitive to deformation information, making it one of the greatest options for shield tunnels to perceive structural deformation. In this study, a 1:20 scale model test was carried out to investigate the deformation perception of the shield tunnel structure under three different layouts of surface-mounted FBG sensors. The deformation law of the tunnel is discussed, under the condition of two-factor cross fusion and especially under the condition of constant water pressure and soil pressure change. The results indicate that, under the combined action of water and soil pressure, the uniform water pressure of 0.33 MPa has a stabilizing effect on the segment strain under the vertical load of 0.4 MPa. The traditional four-point layout and the 18° uniform layout are more effective in detecting changes in local tunnel curvature and strain, respectively, compared to the 36° uniform layout mode. It is advised that the traditional four-point layout be used to collect information for other sections' monitoring and that the 18° uniform layout is for harsh terrain conditions. [ABSTRACT FROM AUTHOR]

To guarantee the safety of tunnel construction and the continued use of nearby structures, it is crucial to accurately forecast the size and extent of the plastic region that may occur due to tunnel excavation, as well as examine the impact on resilience. In this paper, the influence mechanism of tunnel construction on adjacent pile foundation and resilience assessment is investigated. Firstly, the stratum deformation and stress induced by tunnel construction are derived based on the thin-walled theory considering the influence of tunnel structure stiffness. Moreover, the resilience assessment based on the characteristics of the stratum plastic region is proposed to describe the degree of disturbance caused by tunnel construction to the adjacent pile foundation. Then, a comparison with a numerical simulation is conducted to verify the correctness of the prediction method of the stratum plastic region proposed in this paper. Finally, parameter sensitivity analysis is carried out, which indicates that pile parameters, soil parameters, and different tunnel outline conditions have a great influence on the prediction results. In order to reasonably control the impact of tunnel construction on the surrounding environment, safety control techniques, including advance grouting reinforcement and grouting uplift, need to be carefully designed. [ABSTRACT FROM AUTHOR]

With the development of large-diameter shield tunnels, how to realize effective security and stability control of shield tunnel lining has become a significant research topic. This paper investigates the deformation and failure mechanism of lining large diameter shield tunnels in depth and discusses the deformation characteristics and influencing factors of the lining of the shield tunnel with various diameters through the software of finite element analysis ABACUS. A set of models with varying diameters is built under identical stress conditions in order to maintain control over the variable. The utilization of the elastic–plastic model is observed in the application of bolts and rebar. The utilization of the Concrete Damage Plasticity model has been taken into account for the concrete lining. For the sake of comparison, the crown displacement of the shield tunnel, strain in tension and compressive zones, bolt stress and strain, deformation and intemal force distribution around the shield tunnel, and cracks in the tension zone, are carefully studied. An in-depth analysis is conducted to elucidate the variations in damage evolution mechanisms across linings of different sizes, within the framework of plastic hinge theory. The results indicate that the convergence deformation of large-diameter tunnel lining increases significantly during loading compared with that of small-diameter tunnel. Moreover, the probability of brittle failure is higher in big-diameter shield tunnels compared to small-diameter tunnels, indicating that these larger tunnel structures are more prone to suffering geometric instability. [ABSTRACT FROM AUTHOR]

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In this paper, the methods of theoretical analysis, numerical simulation and fuzzy comprehensive evaluation are used to investigate the force and wear behavior of disc cutter in the process of rock breaking, and the accurate prediction of wear degree is realized. First, this paper proposes an accurate calculation method of the rock failure area. Based on this method, a new model suitable for a constant cross-section disc cutter to predict the normal and rolling forces is then proposed. Furthermore, analysis and comparison of the wear of a single disc cutter and a double disc cutter under varying penetration conditions were conducted by a numerical simulation method, the simulation results showed that the wear amount of the single disc cutter between different penetration shows an obvious aggregation trend. In contrast, the wear of the double disc cutter demonstrated a linear increase as the penetration increased. Finally, the analytic hierarchy process, fuzzy comprehensive evaluation method, and variable-weight theory were used to evaluate the wear degree. The evaluation model was validated by a field case in a metro section. [ABSTRACT FROM AUTHOR]

During shield tunneling construction, the buoyancy of segments occasionally occurs due to the influence of complex factors such as stratum excavation and simultaneous grouting at the shield tail. Referencing the construction of the tunnel section from Guangfu Avenue Station to Chongqing East Station of Chongqing Rail Transit Line 27 crossing the Kuxi River, a shield tunnel construction period segment buoyancy prediction model based on ISSA-XGBoost-GRU-SVM is proposed. First, the principal component analysis method is employed to consider the influence of shield excavation parameters on segment buoyancy, and a set of new features highly correlated with the principal components is selected as input. Second, to address the difficulty in manually configuring parameters and the randomness of the XGBoost model, an improved sparrow algorithm is used to optimize the model hyperparameters. Finally, leveraging the advantages of SVM in feature extraction and GRU neural networks in time series prediction, the ISSA-XGBoost-GRU-SVM hybrid neural network model is constructed by updating the weights of the prediction results using the reciprocal of the errors. The results show that the mean regression values at the top and bottom measurement points of the proposed model are 0.9, and the root mean square errors at the top and bottom measurement points decrease significantly compared to those of traditional algorithms. Compared to the numerical simulation results, the proposed model can better describe the changing characteristics of segment buoyancy during the accelerated uplift phase. Therefore, the algorithm of the proposed model in this paper has greater predictive effectiveness and accuracy. [ABSTRACT FROM AUTHOR]

A self-designed device for testing the waterproof performance of double-sealing gaskets is applied in a superlarge diameter shield tunnel to conduct water pressure resistance experiments on the inner and outer double-sealing gaskets considering bolt holes. Through these experiments, the waterproof performance of bolt-hole on double-sealing gasket systems is investigated. The results demonstrate the following: (1) The bolt holes control the overall waterproof performance of the double-sealing gaskets fixed on the inner and outer sides of the segmental joint. When they leak under insufficient waterproof capacity, the improvement in waterproof performance of double-sealing gaskets is less, compared to that when a single-sealing gasket is used. (2) The waterproof performance of double-sealing gaskets is considerably enhanced with sufficient waterproof performance of the bolt holes. (3) The waterproof performance of bolt holes should meet the collaborative waterproof requirements of double-sealing gaskets when applying them in superlarge diameter shield tunnels. [ABSTRACT FROM AUTHOR]

During shield tunneling, failing to replace worn cutters in a timely manner can decrease tunneling efficiency. To address this, an accurate prediction model for cutter wear is established, which aims to improve the utilization rate of disc cutters and overall construction efficiency. This model analyzes the relationship between cumulative wear and tunneling parameters with the aid of equivalent wear, and the database is extended to predict cumulative wear. By examining disc cutter wear data from the large-diameter shield tunnel project on the Xingye express line in Zhuhai, China, the wear types and patterns are studied through sectional statistics. The concept of equivalent wear amount is introduced, and its variation characteristics across different strata are analyzed. The relationship between wear amount and excavation parameters is fitted and a wear prediction model is established. The results show the following: (1) The disc cutter wear mainly manifests as uniform and partial wear, with partial wear being more prevalent in uneven soft and hard strata. (2) Disc cutter wear correlates positively with factors such as installation radius, blade width, formation type, and driving distance. (3) In a soft soil layer, equivalent wear changes smoothly, whereas in uneven strata, it progresses through adaptation, stability, and intensification stages. Fitting analysis shows that equivalent wear positively correlates with thrust and torque. The feasibility of the wear prediction model is validated using field measurement data. [ABSTRACT FROM AUTHOR]

In current engineering and research, the indices of cross-sectional deformation extracted from point clouds are primarily convergent deformation, which can hardly reflect the deformation characteristics of sectionally continuous deformation properties of shield tunnel linings under the action of a joint. To fully extract the cross-sectional deformation characteristics from point clouds, a deformation characterization method, which takes joints as boundary to fit each segment separately in a polar coordinate system using Fourier functions, is proposed. The fitted curves of each segment are then meshed based on the same density, and the node coordinates are tracked to derive the displacement field of each segment. Full-scale experiments and numerical models are used to validate the reliability of this method. In addition, theoretical analysis and numerical experiments are conducted to examine the influence of key factors (such as the types of fitting functions, influence of measurement errors, and selection of reference system) on deformation extraction results. The findings reveal the following: (1) The higher the order of the Fourier function used for fitting, the more detailed the fitting of the segment lining profile. (2) Under the effect of measurement errors, the application of high-order Fourier functions is susceptible to overfitting, which results in an increase in the deformation extraction error. (3) The proposed method shows its effect and feasibility in actual shield tunnel engineering. [ABSTRACT FROM AUTHOR]

In order to study the long-term settlement and its variation law for shield tunnel under combined action of surface load, train load, and consolidation settlement of under-consolidated soft soil, a finite element model is established by PLAXIS to calculate the long-term settlement of shield tunnel under external action based on the Nansha-Zhuhai (Zhongshan) intercity line in Guangzhou. The effect of each influencing factor on long-term settlement is analyzed by single factor sensitivity analysis and nonlinear fitting method, and five key influencing factors are identified. The calculation method of long-term settlement and optimal tunnel depth is proposed. The results show that: (1) The overconsolidation ratio and tunnel depth have the greatest influence on long-term settlement, followed by the load magnitude, load width, and train load, while the effects of load distance, train speed, and permeability coefficient on long-term settlement can be neglected. (2) In order to solve the long-term settlement of shield tunnel, a calculation method is proposed for shield tunnel in under-consolidated soft soil under static and dynamic load, and the calculation result is in good agreement with the simulation result. (3) By taking the control value of 20 mm for shield tunnel deformation specified in the national standard as the tunnel settlement control value, and substituting it into the equation for longterm settlement, the equation for optimal tunnel depth is obtained. The under-consolidation characteristics of soft soil have the greatest influence on the optimal tunnel depth. In order to effectively control the long-term settlement, it is suggested that the entire tunnel should be constructed in soil with better quality. If a tunnel has to be constructed in mud and mucky soil strata, foundation treatment should be carried out, and drainage consolidation should be performed to improve the consolidation degree of soil. [ABSTRACT FROM AUTHOR]

Abstract Excavation of subway tunnels in hard rock generates strong vibration waves that pose potential risks to the stability of surrounding structures. In this study, the discrete element method-finite difference method (DEM-FDM) coupling was adopted to build the model of tunnel structure-rock-pile, which was validated by field monitoring data. Then, the vibration response of piles under various pile-tunnel spacings was analyzed, revealing the occurrence of vibration peak rebound phenomena within certain distance ranges. The range of vibration effects was categorized. Furthermore, in shield tunneling construction, the energy induced by vibrations was mainly concentrated within the 50 Hz range. Low-frequency vibrations result in a wider effect range. The study also demonstrated that within a 1d (tunnel diameter) range of the pile-tunnel spacing, the vibration induced by shield tunneling construction had a more significant effect. As the pile-tunnel spacing increased, the piles transitioned from being subjected to bending forces to experiencing bending-shear forces. Finally, the vibration effects on the existing piles were evaluated under field working conditions. It also provided suggestions for construction based on the effects and laws of the pile dynamic response.

Abstract This study investigates the prediction of ground loss rate during soft-soil shield tunneling using Peck’s back analysis method and XGBoost model. Bayesian optimization is employed to determine optimal hyperparameters, ensuring comprehensive and efficient model tuning. The XGBoost model is compared with Random Forest (RF) and Support Vector Machine (SVM) models to benchmark its performance. The results demonstrate the superior accuracy and robustness of the XGBoost model. Also, the results show that the soil properties and the grouting factors of the excavation face affect the duration of the instantaneous settlement of the ground surface. There is a specific correlation between the depth-to-diameter ratio, the coefficient of variation in the advancing speed of the shield machine, the maximum surface subsidence, and the ground loss rate. The prediction model of the ground loss rate based on the combined approach of Peck back analysis and eXtreme Gradient Boosting and Bayesian optimization has high reliability in soft-soil layers, and this method can provide a specific reference for predicting construction risk in related projects.

Objective Shield tunneling may cause displacement and deformation of the nearby viaduct foundation and reduce its bearing capacity. Therefore, the deformation effect caused by shield tunnel closely side-passing viaduct foundation is studied based on an actual project. Method Relying on the project of Hefei Metro Line 5 in which the shield tunnel passes the pile foundation of the viaduct on the side, a three-dimensional numerical model is established to analyze the horizontal displacement,the longitudinal displacement and the settlement pattern of the pile foundation caused by shield construction. Result & Conclusion The research results show that the horizontal displacement at the pile bottom presents dynamic changes of leaving, approaching and leaving the tunnel. The horizontal displacement of the pile body is similar to a C shape flexture curve. The displacement increases first and then decreases along with the pile depths, and the extreme value is located at the pile depth of 9~10 m. The longitudinal displacement at the pile bottom （parallel to the tunnel axis） shows a bimodal curve. After the shield passing the pile foundation, the pile body undergoes longitudinal deformation in the opposite direction of the excavation. After the shield passing through the pile foundation for 12m and further, the horizontal displacement of the pile body in longitudinal direction rebounds, indicating that the influence of shield tunneling on the longitudinal deformation of the pile foundation is reversible to a certain extent. The settlement of the pile foundation presents a steep trend. The closer the pile foundation at the same side is to the tunnel, the greater the settlement. Moreover, the excavation of the far side tunnel will cause secondary settlement of the pile top. The maximum settlement occurs at the bottom of the No.4 pile foundation, and the settlement value is 4.94 mm.

The mechanical properties of the steel-plate-reinforced segmental lining are generally determined by the load-bearing capacity of reinforced joints. However, there is a lack of valid calculation methods for compression-bending bearing capacity, and researchers mainly rely on experience and analogy for the design of reinforced joints. This paper proposes an analytical model based on the deformation and stress characteristics of the joint surface to calculate the compression-bending capacity of the steel-plate-reinforced joint. After verifying the applicability of this analytical model through finite element simulations, the evalution rules of the load-bearing capacity of the reinforced joint were attained, followed by a quantitative investigation into the influence of joint parameters on it. The results show that: (1) the bearing capacity curve of the reinforced joint under different axial forces can be separated into two parts, with the maximum ultimate bending moment found at the demarcation point, where the steel plate yielding and joint failure occur simultaneously; (2) the steel plate strength and cross-sectional area have a strong influence on the bearing capacity of the reinforced joint when the axial force is under 0.15RFF, where RFF is the axial force at pure-compression failure); (3) the concrete strength and segment width have a prominent influence on the curve when the axial force is over 0.30RFF; (4) the impact of the fictitious strain, bolt strength, bolt diameter, and bolt location on the bearing capacity is minimal in range and amplitude.

Shield tail grouting is an important measure to control tunnelling-induced ground deformation by injecting prepared grouting materials to fill the tail gap. The working performance of grout is usually invisible and hard to obtain in construction. This paper carries out an experimental study to investigate the tail grout behavior in ground. In the current research, a testing device is developed to explore the grout behavior in varying soils. The grout working performance is evaluated not only by the liquid grout properties such as fluidity, consistency, bleeding rate, stone rate and compressed deformation but also solid grout properties such as unconfined compressive strength and permeability. Three typical grouts are chosen and their behaviors in the various soils are observed. To take an insight on the behaviors, scanning electron microscopy and mercury intrusion porosimetry analysis are employed. The microstructure of solid grout is a sign of its working performance. The observation shows that the solid grout micro-structure is influenced by grout proportions, pressure, and ground permeabilities. The experimental results are applied in the case of Beijing Metro Line 12 for validation and as a result, the ground movement is inhibited due to high performance of tail grout.