Search Results (84)

Ultra-deep circular shafts are increasingly deployed in congested urban environments, yet their structural performance in highly sensitive soft clay remains susceptible to diaphragm wall panel joints, structural imperfections, and complex interactions with adjacent structures. This study presents a high-fidelity three-dimensional (3D) numerical investigation into the excavation behavior of an ultra-deep circular shaft with a diameter of 30 m and an excavation depth of 56.3 m in Shanghai soft clay by synthesizing high-resolution field monitoring with advanced finite element modeling. The numerical framework was established in PLAXIS 3D utilizing the Hardening Soil model with small-strain stiffness (HSS), explicitly incorporating an equivalent structural stiffness reduction scheme (0.8 vertically and 0.5 circumferentially) to capture panel segmentation, joint compliance, and concrete cracking. The reduced-stiffness model successfully reproduces the measured deep-seated bulging profiles and internal force distributions with high fidelity. The findings reveal exceptional deformation control capabilities of the circular geometry, yielding a maximum lateral wall deflection of merely 9.1 mm (0.016%H_e), which is significantly smaller than the normalized deformation ratio of 0.3%H_e observed in five analogous rectangular excavations in Shanghai. The numerical results indicate that circumferential compression governs the overall load transfer behavior, while vertical bending response remains relatively limited. Furthermore, a pronounced circumferential anisotropy in wall deformation is governed by asymmetric boundary conditions, where localized Metro Jet System (MJS) ground improvement significantly restrain movements, whereas the non-grouted area experience peak deflections. Crucially, interaction with the adjacent external diaphragm walls of ancillary structures induces a complex 3D stress redistribution rather than a beneficial shielding effect, amplifying the peak shaft wall displacement by nearly 62.8% (from 4.73 mm to 7.70 mm). These insights underscore the criticality of integrating small-strain soil mechanics, equivalent structural degradation, and adjacent structural boundaries into predictive design protocols for ultra-deep circular retaining systems. Full article

To address the challenge of deformation control in operating tunnel structures, this study investigates a novel reinforcement method for operating shield tunnels using a basalt-fiber-reinforced polymer-wrapped concrete-filled steel tube (BFRP-CFST) composite profile. Two primary study variables were considered. At the segment level, the reinforcement condition comprised two levels: unreinforced and BFRP-CFST-reinforced, with three replicate specimens at each level (US-1 to US-3 and RS-1 to RS-3, respectively). At the full-ring level, the number of installed composite profile frames comprised five levels (n = 0, 1, 2, 3, and 4), where n = 0 represented the unreinforced reference condition. A combined experimental and numerical framework was established, including full-scale four-point bending tests on individual tunnel segments and finite element simulations of full-ring linings. Experimental results demonstrate that the ultimate bearing capacity of reinforced segments increased from 534.4 kN to 921.3 kN, corresponding to a 72.4% improvement. The load level before visible cracking increased by 84.2%. At maximum crack widths of 0.2 mm and 2.0 mm, the mid-span displacement of the reinforced segments was reduced by 30.0% and 21.4%, respectively. The test observations indicate that the prefabricated composite profiles effectively delayed crack development and improved the post-cracking stiffness of the segment. Full-ring numerical simulations further showed that installing one to four composite profile frames increased the external load corresponding to a convergence displacement of approximately 10.5 cm by 12.4%, 21.1%, 28.5%, and 37.4%, respectively. Scientifically, the results reveal a staged load-transfer process in which adhesive bonding provides distributed load transfer during the initial response, while mechanical anchors maintain residual load transfer after local interface debonding; they also establish a quantitative relationship between the number of profile frames and full-ring convergence resistance. From an applied engineering perspective, the proposed profile increased the ultimate load and crack-initiation load of the segments by 72.4% and 84.2%, respectively, while its lightweight and prefabricated configuration provides a potentially rapid rehabilitation option for operating shield tunnels. Full article

Mobile laser scanning (MLS) has become an effective technique for deformation monitoring in subway shield tunnels. Among various deformation characteristics, segment dislocation is an important indicator of tunnel structural health because it reflects the relative deformation between adjacent segments and may affect the mechanical behavior and waterproof performance of segmental joints. However, existing MLS-based methods for dislocation detection still suffer from facility interference, inaccurate seam localization, and limited automation in quantitative analysis. To address these challenges, this study proposes an automated method for shield tunnel segment dislocation detection based on MLS point cloud processing. The proposed framework consists of three main steps. First, a point cloud filtering strategy integrating offset features and semantic segmentation is developed to remove facility-related noise while preserving tunnel wall information. Second, a tunnel segment segmentation method combining bolt hole extraction and moving template matching is introduced to achieve accurate localization of both horizontal and longitudinal seams, where bolt holes are identified using normal vector and distance constraints. Finally, automated segment dislocation analysis is performed based on the filtering and segmentation results. Experimental results demonstrate that the proposed filtering method improves accuracy by 8.7% and 5.6% compared with conventional ellipse fitting and cylinder fitting methods, respectively. Using manually interpreted reference values derived from the same MLS dataset as the evaluation reference, the proposed method achieves less than 2 mm deviation in both seam localization and dislocation analysis, demonstrating high consistency with manual interpretation. Compared with existing automatic approaches, the proposed method provides more accurate and reliable automated dislocation analysis, significantly reducing the need for manual inspection. The proposed method enhances the automation, consistency, and reliability of shield tunnel deformation assessment and provides an effective solution for structural health monitoring. Full article

Parallel shield tunneling in close proximity to existing metro tunnels induces additional settlement deformation of existing structures, which poses a challenge to operational safety. In this paper, a self-developed Φ200 mm model shield machine test system is adopted to carry out model test research on the settlement response of existing tunnels induced by parallel symmetric shield tunneling. A 1:30-scaled 3D-printed refined assembled segment model is fabricated based on similarity theory, and high-precision distributed optical fiber sensing technology is used for deformation monitoring. The influences of vertical spacing of tunnels, center spacing of new tunnels, axis angle and stratum loss rate on the settlement of existing tunnels are analyzed. The results show that the settlement curve of the existing tunnel arch presents a normal distribution shape, and the maximum settlement occurs near the new tunnel side. The settlement of existing tunnels decreases with the increase in vertical spacing between new and existing tunnels, and increases with the increase in stratum loss rate and center spacing of new tunnels. The research results can provide experimental support for safety control of parallel shield tunnel construction. Full article

During the construction of large-diameter shield tunnels, tunnel lining segments frequently experience uplift after exiting the shield tail, inducing structural defects such as dislocation, cracking, and water leakage. This issue threatens both construction safety and the long-term sustainable operation of large-diameter shield tunnels. Shield tail grouting slurry buoyancy is the primary cause of segment uplift. However, existing studies mainly rely on atmospheric pressure tests and simplified models, failing to capture the dynamic evolution of grout buoyancy under real confining pressures. This study optimized grout mix proportions through laboratory tests and developed a novel buoyancy testing apparatus. Systematic time-dependent buoyancy tests were conducted. Results show that cement-based grouts exhibit a distinct three-stage buoyancy dissipation pattern, which is strongly influenced by confining pressure, stratum conditions, and mix design, whereas inert grouts follow a single-stage exponential decay. The optimized mix YH1 reduced the complete buoyancy dissipation time by 20–35% compared with conventional cement-based grout S9. Based on field monitoring at the Yangcheng West Lake Third Channel project, approximately 90% of segment uplift deformation occurred during the grout buoyancy persistence stage. These findings provide reliable theoretical support for optimizing anti-floating grout design and contribute to the resilience and sustainability of urban underground infrastructure. Full article

Deformation monitoring is critical for structural health assessment of operational shield tunnels in urban rail transit. LiDAR point clouds in operating tunnels usually contain auxiliary facilities, occlusions, noise, and uneven point density. Conventional section-by-section ellipse fitting often leads to unstable parameter jumps between adjacent sections. This paper presents a high-precision method to extract lateral deformation from tunnel LiDAR point clouds. First, a point-wise attention Transformer network (PWAT) is proposed based on PointNet++ for lining segmentation, using k-NN adaptive sampling, geometric position encoding, and geometry-constrained multi-head self-attention. Second, a continuity-constrained RANSAC (CC-RANSAC) algorithm is developed to improve ellipse parameter stability by adding continuity penalties between neighboring sections. Experiments were carried out on a Shanghai metro shield tunnel. Results show that PWAT achieves 99.53% overall accuracy and 99.06% mIoU in six-class segmentation. CC-RANSAC reduces the mean residual to 2.0 mm and the center jump rate to 4.2%. Compared with total station data, the mean absolute error and root mean square error are 1.35 mm and 1.68 mm. The proposed method can automatically and accurately extract lateral deformation for operational shield tunnels. Full article

Rectangular shield tunnels demonstrate significant advantages in underground space utilization due to their optimal cross-section efficiency and enhanced spatial functionality. Furthermore, their shallow overburden construction capability minimizes environmental impact and preserves subsurface resources. However, compared with circular shield tunnels, rectangular configurations exhibit greater susceptibility to longitudinal differential torsional deformation under asymmetric external loading. This deformation mechanism may induce excessive stresses in segments and connecting bolts, potentially causing joint offsets at tunnel rings that compromise structural integrity. This paper proposes a computational method for determining the longitudinal equivalent torsional stiffness of rectangular shield tunnels under combined compression–bending–torsion loading based on an equivalent continuum model. The proposed novel theoretical solutions were systematically validated against numerical simulations through comparative analysis. Parametric studies revealed that the effective ratio of longitudinal torsional stiffness increases proportionally with segment width-to-height ratio and bolt quantity while exhibiting inverse correlations with segment thickness and bolt equivalent shear length. The effective ratio of longitudinal torsional stiffness is directly correlated with compression–torsion ratios and bending–torsion ratios, with different load combinations significantly influencing torsional performance. Consequently, design optimizations incorporating increased bolt pre-tension forces or pre-stressed segment structures are proposed to improve torsional performance in rectangular shield tunneling systems. Full article

To evaluate the coupled deformation of existing shield tunnels induced by multi-segment excavations with isolation piles, this study develops an integrated analytical framework combining a Kerr three-parameter foundation-plate model with a three-dimensional image-source solution. A closed-form expression for the soil displacement field is first derived by incorporating layered soil conditions, staged excavation, and associated spatial effects. The soil–pile interaction of isolation piles is then modeled using the Kerr foundation, and the flexural response is obtained through variational formulation and finite-difference discretization. These responses are sequentially propagated through the excavation stages, enabling the superposition of multi-pit effects on the final retaining-wall deformation. The image-source method and a volume-equivalent transformation are further used to convert wall deformation into an additional stress field acting on the tunnel, which is ultimately coupled with a tunnel–soil deformation–coordination model to compute horizontal tunnel displacements. This unified workflow establishes a continuous mechanical transfer chain—from excavation-induced soil loss to isolation-pile bending and finally tunnel deformation. Parametric analyses show that lateral displacement of the retaining structure is jointly governed by wall bending and pit-bottom uplift, producing a right-skewed “S-shaped” profile. The bending-moment peak shifts toward earlier-excavated zones, indicating a memory effect of excavation sequencing. Two engineering cases verify that the proposed method accurately reproduces the magnitude and depth of measured wall deflections, while predicted tunnel displacements show a near-Gaussian pattern with high accuracy near the peak. The analytical framework provides a robust theoretical basis for optimizing pit segmentation and excavation sequencing adjacent to shield tunnels. Full article

The mechanical method has become a new construction method for connected aisles in metro tunnels due to its advantages of fast construction speed, high safety, and minimal ground disturbance. During the tunneling process, the interaction mechanism between the composite segment and the shield cutterhead is complex. Taking Shenzhen Metro Line 8 No. 1 Connected Aisle as the research object, a 3D refined model of the shield cutterhead, composite segments and bolt system were built with Abaqus to investigate their dynamic response under cutting. The Drucker–Prager damage model and contact algorithm were introduced to describe the nonlinear behavior of the cutting process. The reliability of the numerical model was verified by concrete cutting tests and on-site Fiber Bragg Grating monitoring, and good agreements were observed. Results show cutterhead cutting first induces circumferential squeezing, then extends longitudinally with a notable time lag, and longitudinal dynamic response is much stronger than transverse. Affected by cutterhead thrust–rotation coupling, cuttable segments have larger displacement with maximum 0.07 mm, forming an asymmetric deformation zone. Ring joint opening follows “a distal attenuation of the opening amount” rule with maximum 0.018 mm, while bolt stress and displacement show “near-end concentration with gradient attenuation”, with longitudinal bolts being more responsive. Mechanical disturbance from small-shield cutting is minimal, with tunnel segment deformation, joint openings, and bolt stress all remaining well below code-specified allowable values. Numerical results show good agreement with field monitoring data of ring joint openings obtained using Fiber Bragg Grating (FBG) sensors, confirming the reliability of the simulation. The results can provide references for structural design and construction parameter optimization of composite segments in a connected aisle. Full article

A novel corrugated steel-reinforced concrete pipe that enhances electromagnetic shielding performance compared to the conventional reinforced concrete power pipes is developed and presented in this paper. In order to investigate the pipe’s behaviour under jacking and service conditions, the critical axial compression and flexural moment distributions were represented by two separate flat segments of a circular pipe cross-section, respectively. A total of six column specimens were designed for axial compression testing, while another four beam specimens were prepared for four-point bending tests to examine the bending behaviour. Prior to testing, all specimens were subjected to standard curing, and the material properties of steel and concrete were determined via standard tests. The load versus deformation curves of column specimens, the moment versus deflection curves of beam specimens, and the corresponding failure modes were obtained from the tested specimens. It was revealed that the load-carrying capacities of the corrugated steel-reinforced concrete cross-sections were comparable to those of the conventional reinforced concrete counterparts. Advanced finite element (FE) models incorporating the mechanical properties of encased corrugated steel plates (CSPs) and the damage development of concrete were developed and were validated against the experimental failure modes and load-carrying capacities. Based on both experimental and numerical results, the load-carrying capacity of corrugated steel-reinforced concrete cross-sections was evaluated by referring to Chinese standard GB/T 11836 and American standard ASTM C76. The experimental and numerical finding can pave the way for further research and applications of this novel type of corrugated steel-reinforced concrete pipe. Full article

The behavior of shield tunnel lining structures is known to be influenced by segmental joints. Most studies conducted in this area use simplified models, which may not properly simulate the behavior of the segmental joints. This study utilizes a full-reinforced concrete segment model to rigorously investigate the seismic behavior of joints in a segmental tunnel lining, explicitly accounting for segment–segment contact, interaction, and joint bolts. Specifically, a comprehensive full dynamic analysis of a two-dimensional (2D) lining–soil model, incorporating nonlinear constitutive models for both concrete (CDPM) and soil (Mohr–Coulomb), was conducted to investigate the effects of joint bolt type, seismic intensity, and vertical excitation component on the seismic response. The lining–soil model was excited using three ground motions. The results indicate that the joint rotation is significantly influenced by the amplitude and frequency content of ground motions, which has implications for the watertightness of the gasketed joint. In particular, including the vertical component of the excitations was found to increase the diametral deformation by at least 150% and tended to increase other structural responses. Moreover, the bolt tension increased significantly by over 400% with only a 150% increase in seismic intensity, highlighting the strong nonlinear sensitivity. However, due to the inherent constraints of the 2D plane-strain assumption, the influence of the bolt type remains inconclusive. Full article

The rapid urbanization of coastal regions has intensified the demand for durable underground infrastructure like shield tunnels, where reinforced concrete (RC) structures are critical yet susceptible to long-term degradation in marine environments. This study develops an integrated machine vision-based framework for assessing the long-term durability of RC in marine shield tunnels by synergistically combining point cloud analysis and deep learning-based damage recognition. The methodology involves preprocessing tunnel point clouds to extract the centerline and cross-sections, enabling the quantification of geometric deformations, including segment misalignment and elliptical distortion. Concurrently, an advanced YOLOv8 model is employed to automatically identify and classify surface corrosion damages—specifically water leakage, cracks, and spalling—from images, achieving high detection accuracies (e.g., 95.6% for leakage). By fusing the geometric indicators with damage metrics, a quantitative risk scoring system is established to evaluate structural durability. Experimental results on a real-world tunnel segment demonstrate the framework’s effectiveness in correlating surface defects with underlying geometric irregularities. This integrated approach offers a data-driven solution for the continuous health monitoring and residual life prediction of RC tunnel linings in marine conditions, bridging the gap between visual inspection and structural performance assessment. Full article

To investigate the influence of segmental lining width on ground and tunnel deformation during shield tunneling beneath residential buildings, a numerical analysis model was established using Midas GTS NX based on the engineering context of the Guangzhou Metro Guanggang Xincheng depot tunnel underpassing residential structures. The simulation results were validated through comparison with field monitoring data, and a gray relational analysis was employed to quantitatively assess the sensitivity of various deformation indicators to segment width. The findings indicate that, under the engineering scenario of a shield tunnel crossing beneath residential buildings, the use of 1.2 m-wide segments is more effective in controlling ground settlement and structural deformation of the tunnel compared with 1.5 m-wide segments. The deformation process associated with the 1.2 m segments exhibits a more stable settlement pattern, whereas the 1.5 m segments tend to induce repeated settlement–heave cycles in the surrounding ground, with a potential risk of segmental displacement exceeding warning thresholds. Sensitivity analysis shows that different deformation indicators respond unevenly to changes in segment width. From most to least sensitive, the indicators rank as follows: maximum ground deformation, maximum displacement during the post-excavation stage, and maximum displacement during the excavation stage. The results of this study provide theoretical support and reference for selecting segmental lining width in shield tunnels constructed beneath residential buildings. Full article

To reduce downtime of the Tunnel Boring Machine and improve construction efficiency of subway tunnels, the tunnel–station synchronous construction method was implemented in the Qingdao metro. In this method, the TBM advanced continuously through the station, while the upper station was excavated in stages using the primary support arch covering technique. Focusing on a construction scheme with low-grade temporary segments, this study develops a three-dimensional numerical model to investigate the mechanical response of shield lining during the simultaneous construction of a subway station and tunnel. The Mohr–Coulomb model and the Elastic model were employed to represent the mechanical behavior of the surrounding rock and support structure, respectively. The deformation, bending moment, axial force, and residual bearing capacity coefficients of the shield lining were systematically examined across six distinct construction stages. The results showed that asymmetric gradual unloading of the surrounding rock at the arch part caused the vertical displacement of the shield lining to be predominantly upward, with a maximum heave of 1.51 mm. Horizontal displacement exhibited significant asymmetry. During station arch excavation, asymmetric unloading led to an increase and clockwise shift in the bending moments of the shield lining. The axial forces transitioned from compression to tension at specific locations (40° and 240°), whereas the removal of temporary supports had only a minor influence. The maximum tensile stress of the shield lining increased by 3.35 times in Stage III and reached 0.69 MPa in Stage V, representing a 1.65-fold increase compared to the previous stage. Although the residual bearing capacity coefficient generally satisfied safety requirements throughout the construction process, it decreased to a minimum of 0.88 in Stage V, a 7% reduction relative to Stage IV, necessitating close monitoring. This study not only confirmed the safety of using temporary segments made of lower-grade concrete (C30) in tunnel–station synchronous construction but also provided valuable insights for optimizing construction schemes and controlling key risks, such as structural deformation, in similarly complex urban environments. Full article

Steel fiber reinforced concrete (SFRC) has become a feasible alternative material for traditional reinforced concrete (RC) segments in shield tunnel engineering due to its excellent crack resistance, toughness, and durability. However, its design parameters have not yet been standardized, and research at the material and structural scales remains relatively fragmented, lacking a unified design framework, which limits the widespread application of SFRC segments. This paper provides a comprehensive review of the mechanical performance and design methods of SFRC segments, focusing on four aspects: (1) research methods for mechanical performance, including experimental analysis, numerical simulation, and artificial intelligence algorithms; (2) theoretical calculation methods for flexural and shear bearing capacity and crack width; (3) mechanical response characteristics, including deformation modes and crack propagation patterns; (4) key influencing factors, such as matrix strength, steel fiber types, dosages, and aspect ratios. The study systematically reviews relevant research methods on the mechanical performance of SFRC segments, evaluates the applicability and limitations of existing theoretical calculation methods, and ranks the factors affecting the mechanical performance of SFRC segments from the perspective of material composition. Finally, based on the review, future research directions for SFRC segments are proposed, providing a systematic reference for the development of design standards, improvement of mechanical performance, and full-lifecycle reliability assurance of SFRC segments. Full article