Search Results (57)

The complexity of the loading mode and action mechanism is demonstrated in the portal frame anti-uplift structure. The stress evolution process of the portal frame structure during the excavation of the upper foundation pit is revealed through in situ structural stress tests and numerical modeling analysis reflecting the small strain characteristics of stratum. The stress distribution of uplift piles and anti-floating plates is analyzed, with the axial force of piles and the development law of bending moment in plates being specifically examined. It is emphasized that the load of the uplift pile is generated by friction between the pile and soil caused by stratum floating, which is predominantly produced during the excavation of the upper block and the unloading of the surcharge. The pile 11# is observed to be under tension in the middle and compressed at both ends, with the extreme value of tensile stress of these 24 piles being located at 0.15 times the pile length below the top of the middle pile. The main loads of the anti-floating plate are identified as backfilling, foundation buoyancy, and lateral soil pressure. The lower part of the two pile spans is subjected to tension, while the upper part is under compression, with the bending moment extremes being located on the side where the frame is first formed. A significant increase in stiffness is exhibited by the frame structure after its formation, and the influence from the excavation of other blocks is markedly reduced. The most adverse condition is determined to occur during the integral removal of the upper surcharge. The reference value of these research results is confirmed for clarifying the stress mechanism of anti-uplift portal frame structures and optimizing key technical parameters in structural design and construction. Full article

This study numerically investigates the deformation and consolidation behavior of high-water-content river sediment improved by a combined vacuum preloading and internal air-bag pressurization (VPA) system. A 2D axisymmetric finite-element model in Abaqus 2021 with the Modified Cam-Clay constitutive law is established to simulate the treatment process. Key design parameters—air-bag pressure, pressurization timing, embedment depth, and staged loading—are systematically analyzed. Results show that: (1) Under a −80 kPa vacuum, an additional 20 kPa air-bag pressure reduces the maximum inward horizontal displacement by over 20%, while effective stress increases linearly with pressure; (2) Early pressurization (20 days) better controls lateral deformation and accelerates strength gain; (3) Staged pressurization (20 kPa upper, 40 kPa lower) outperforms uniform loading in both displacement control and cost-effectiveness; (4) Compared to 30 kPa surcharge preloading, VPA further reduces horizontal displacement by 10–18% under equivalent total load. The hybrid “vacuum–air-bag–surcharge” scheme yields the highest effective stress and smallest lateral deformation. The VPA method enhances sediment engineering properties, providing a viable approach for resource utilization of dredged materials. Full article

A series of centrifuge model tests was performed to investigate the influence of subgrade surcharge loading on adjacent bridge pile foundations in soft soils, based on the Mingu Road project in Zhongshan City, China. Four surcharge distances (1D, 2D, 3D, and 4D, where D is the pile diameter) were examined to clarify the spatial–temporal evolution of pile–soil interaction. The results show that horizontal displacement, bending moment, and lateral soil resistance of the pile increase over time, exhibiting significant time-dependent behavior characterized by rapid initial growth followed by stabilization. As the surcharge distance increases, these responses decrease markedly, indicating a strong spatial attenuation effect. The bending moment along the pile depth follows a unimodal pattern with a peak at the soft soil layer. In contrast, the lateral soil resistance exhibits a similar trend of increase and decrease with depth. When the surcharge distance exceeds approximately 4D, the additional influence on the pile response becomes small. This study provides physical evidence and theoretical support for the safe design and construction of bridge pile foundations adjacent to road embankments in areas with soft soil. Full article

This study investigates the displacement behavior of excavations under asymmetric loading conditions and proposes optimized support design strategies from the perspective of displacement control. Physical model tests reveal that, in excavation projects under eccentric loading conditions, the retaining structure as a whole tends to deform toward the non-surcharge side rather than following the conventional symmetric deformation pattern. Displacement increases nonlinearly with surcharge intensity, but the growth rate diminishes as the load further increases due to localized surcharge effects and structural restraints. Numerical analyses further demonstrate that increasing embedment depth and wall thickness effectively mitigates lateral displacement, although a marginal effect is observed beyond critical thresholds. For instance, at an embedment depth of 12 m (twice the excavation depth), maximum lateral displacement decreases by nearly 50%, and when combined with a wall thickness of 13 cm and a depth of 14 m, the reduction reaches approximately 90%. These findings establish a quantitative basis for deformation control in excavations subjected to asymmetric loading and guide the efficient optimization of retaining systems. They enhance design reliability and construction efficiency, offering practical value for improving safety, performance, and overall project economy. Full article

Marine soft soils are characterized by high compressibility, low strength, and low permeability, which often result in excessive settlement and stability problems. Drainage consolidation methods are widely regarded as effective solutions for improving such soils. This review summarizes recent progress from four perspectives: optimization of traditional techniques, combined applications of multiple methods, development of emerging innovative approaches, and advances in drainage element materials and structures. Traditional methods such as surcharge and vacuum preloading have been refined through innovations in loading schemes, drainage improvements, and design approaches, while hybrid combinations with electroosmosis, thermal treatment, and dynamic loading have further enhanced their efficiency and applicability. In parallel, novel techniques such as siphon drainage, aerosol-assisted consolidation, and osmosis-based drainage show promise for sustainable applications. Furthermore, biodegradable and multifunctional drainage elements provide new directions for environmentally friendly and efficient soft soil improvement. Looking ahead, drainage consolidation technology is expected to move toward greener, low-carbon, and intelligent solutions. This review offers a comprehensive reference for engineering practice and a useful basis for guiding future research in marine soft soil improvement. Full article

The calculation of internal forces is a critical aspect in the design of statically indeterminate structures. Local trapezoidal loads, as a common loading configuration in practical engineering (e.g., earth pressure, uneven surcharge), make it essential to investigate how to compute the internal forces of statically indeterminate structures under such loads by using the displacement method. The key to displacement-based analysis lies in deriving the fixed-end moment formulas for local trapezoidal loads. Traditional methods, such as the force method, virtual beam method, or integral method, often involve complex computations. Therefore, this study aims to derive a general formula for fixed-end moments in statically indeterminate beams subjected to local trapezoidal loads by using the integral method, providing a more efficient and clear theoretical tool for engineering practice while addressing the limitations of existing educational and applied methodologies. The integral method is employed to derive fixed-end moment expressions for three types of statically indeterminate beams: (1) a beam fixed at both ends, (2) an an-end-fixed another-end-simple-support beam, and (3) a beam fixed at one end and sliding at the other. This approach eliminates the redundant equations of the traditional force method or the indirect transformations of the virtual beam method, directly linking boundary conditions through integral operations on load distributions, thereby significantly simplifying the solving process. Three representative numerical examples validate the correctness and universality of the derived formulas. The results demonstrate that the solutions obtained via the integral method align with software-calculated results, yet the proposed method yields analytical expressions for structural internal forces. Comparative analysis shows that the integral method surpasses traditional approaches (e.g., force method, virtual beam method) in terms of conceptual clarity and computational efficiency, making it particularly suitable for instructional demonstrations and rapid engineering calculations. The proposed integral method provides a systematic analytical framework for the internal force analysis of statically indeterminate structures under local trapezoidal loads, combining mathematical rigor with engineering practicality. The derived formulas can be directly applied to real-world designs, substantially reducing computational complexity. Moreover, this method offers a more intuitive theoretical case for structural mechanics education, enhancing students’ understanding of the mathematical–mechanical relationship between loads and internal forces. The research outcomes hold both theoretical significance and practical engineering value, establishing a solving paradigm for the displacement-based analysis of statically indeterminate structures under complex local trapezoidal loading conditions. Full article

Asymmetric structures are widespread in deep excavation engineering and place heightened demands on the deformation control and safety of retaining systems. This study focuses on an asymmetric deep foundation pit project in a soft soil area, using PLAXIS 3D to model the entire excavation process, with model accuracy confirmed by measured values. The study systematically explores the impact of multiple factors—including surcharge loading, external groundwater level, soil internal friction angle and cohesion, and the elastic modulus and embedment ratio of the retaining structure—on the lateral displacement of retaining piles. Orthogonal experimental design is utilized to calculate lateral displacements for various factor combinations, with sensitivity analyzed using the range method and verified by grey relational analysis. The results demonstrate that all factors influence the maximum lateral displacement of retaining piles to varying degrees. Both the orthogonal tests and range analysis consistently identify the influence ranking as soil internal friction angle > soil cohesion > retaining structure elastic modulus > embedment ratio > external groundwater level > surcharge loading. The grey relational analysis yields identical rankings. These results offer theoretical support and practical guidance for the design and monitoring of retaining structures in asymmetric deep excavations within soft soil environments. Full article

Accidental surface surcharge will generate additional load in the stratum, which then leads to unfavorable impacts on the underlying shield tunnel. This paper proposes a probabilistic analysis method to address this problem. In this framework, an improved soil–tunnel interaction model considering the nonlinearity of the subgrade is established at first, and the Newton–Raphson iterative solution algorithm is employed to acquire tunnel responses. Then, the random field models of the initial stiffness and the ultimate reaction of the subgrade are constructed to realize the spatial variability of soil properties. Finally, with the aid of the Monte Carlo Simulation method, the probabilistic analyses on tunnel responses are performed by combining the improved soil–tunnel interaction model and the random field model of subgrade parameters. The applicability and the superiority of the improved soil–tunnel interaction model are validated by a historical case from Shanghai Metro Line 9. The results prove that the traditional linear foundation model will overestimate the bearing capacity of the subgrade, thereby leading to overly optimistic assessments of surcharge-induced tunnel responses. This shortcoming could be addressed by the improved nonlinear soil–tunnel interaction model. The influences of spatial variability of soil properties on tunnel responses are nonnegligible. The stronger the uncertainties of subgrade parameters, in terms of the initial stiffness and the ultimate reaction concerned in this work, the higher the failure risk of the shield tunnel subjected to the surcharge. The failure modes of the tunnel subjected to the surcharge are controlled by the longitudinal curvature radius of the tunnel within the current assessment criteria, which means if this evaluation indicator can be restricted within the allowable value, then the opening of the circumferential joint and the longitudinal settlement can also meet the requirements. Compared with the influences of the uncertainty of the subgrade ultimate reaction, the spatial variability of the subgrade initial stiffness has greater influences on tunnel failure risk under the same conditions. An increase in the range of surcharge will raise the risk of tunnel failure, while the influence of tunnel burial depth is just the opposite. Full article

Large-diameter rock-socketed monopiles supporting offshore wind turbines in soft clay strata face significant geotechnical risks from negative skin friction (NFS) induced by construction surcharges. While the effects of NFS on axial drag loads are documented, the critical interaction between horizontal pile loading and NFS development remains poorly understood. This research bridges this gap using a rigorously validated 3D finite element model that simulates the complex coupling of vertical substructure loads (5 MN), horizontal loading, and surcharge-induced consolidation. The model’s accuracy was confirmed through comprehensive verification against field data for both NFS evolution under surcharge and horizontal load–displacement behavior. The initial analysis under representative conditions (10 MN horizontal load, 100 kPa surcharge, 3600 days consolidation) revealed that horizontal loading fundamentally distorts NFS distribution in the upper pile segment (0 to −24 m), transforming smooth profiles into distinct dual-peak morphologies while increasing the maximum NFS magnitude by 57% (from −45.4 kPa to −71.5 kPa) and relocating its position 21 m upward. This redistribution was mechanistically linked to horizontal soil displacement patterns. Crucially, the NFS neutral plane remained invariant at the clay–rock interface (−39 m), demonstrating complete independence from horizontal loading effects. A systematic parametric study evaluated key operational factors: (1) consolidation time progressively increased NFS magnitude throughout the clay layer, evolving from near-linear to dual-peaked distributions in the upper clay (0 to −18 m); NFS stabilized in the upper clay after 720 days while continuing to increase in the lower clay (−18 to −39 m) due to downward surcharge transfer, accompanied by neutral plane deepening (from −36.5 m to −39.5 m) and 84% maximum axial force escalation (12.5 MN to 23 MN); (2) horizontal load magnitude amplified upper clay NFS peaks at −3.2 m and −9.3 m, with the shallow peak magnitude increasing linearly with load intensity, though it neither altered lower clay NFS nor neutral plane position; (3) surcharge magnitude increased overall NFS, but upper clay NFS (0 to −18 m) stabilized beyond 100 kPa, while lower clay NFS continued rising with higher surcharges, and the neutral plane descended progressively (from −38 m to −39.5 m). These findings demonstrate that horizontal loading critically exacerbates peak NFS values and redistributes friction in upper pile segments without influencing the neutral plane, whereas surcharge magnitude and consolidation time govern neutral plane depth, total NFS magnitude, and maximum drag load. This research delivers essential theoretical insights and practical guidelines for predicting NFS-induced drag loads and ensuring the long-term safety of offshore wind foundations in soft clays under complex multi-directional loading scenarios. Full article

Groundwater is an important factor for the stability of the subway station pit constructed in the offshore area. To reflect the effects of groundwater drawdown on the stability of the station pit, this work uses a surface settlement formula based on Rayleigh distribution to construct a continuous deformation velocity field based on Terzaghi’s mechanism, so as to derive a theoretical calculation method for the safety factor of the deep station pit anti-uplift considering the effect of seepage force. Taking the seepage force as an external load acting on the soil skeleton, a simplified calculation method is proposed to describe the variation in shear strength with depth. Substituting the external work rate induced by self-weight, surface surcharge, seepage force, and plastic shear energy into the energy equilibrium equation, an explicit expression of the safety factor of the station pit is obtained. According to the parameter study and engineering application analysis, the validity and applicability of the proposed procedure are discussed. The parameter study indicated that deep excavation pits are significantly affected by construction drawdown and seepage force; the presence of seepage, to some extent, reduces the anti-uplift stability of the station pit. The calculation method in this work helps to compensate for the shortcomings of existing methods and has a higher accuracy in predicting the safety and stability of station pits under seepage situations. Full article

Circular deep excavations, characterized by their symmetrical geometry, are commonly employed in constructing foundations for large-span suspension bridges and as launching shafts for shield tunneling. However, the mechanical behavior of such excavations under asymmetric surface surcharge remains inadequately understood due to a paucity of relevant investigations. This study addresses this knowledge gap by establishing a three-dimensional finite element model (3D-FEA) based on the anchor deep excavation project of a specific bridge. The model is utilized to investigate the influence of asymmetric surcharge on the forces and deformations within the supporting structure. The results show that both the internal force and displacement cloud diagrams of the support structure exhibit asymmetric characteristics. The distribution of displacement and internal forces has spatial effects, and the maximum values all occur in the areas where asymmetric loads are applied. The maximum values of the displacement, axial force, and shear force of underground continuous walls increase with the increase in the excavation depth. The total displacement curves all show the feature of a “bulging belly”. The maximum displacement is 13.3 mm. The axial force is mainly compression, with a maximum value of −9514 kN/m. The maximum positive and negative values of the shear force are 333 kN/m and −705 kN/m, respectively. The bending moment diagram of different monitoring points shows the characteristics of “bow knot”. The maximum values of the positive bending moment and negative bending moment are 1509.4 kN·m/m and −2394.3 kN·m/m, respectively. The axial force of the ring beam is mainly compression, with a maximum value of −5360 kN, which occurs in ring beams 3, 4, and 5. The displacement cloud diagram of the support structure under symmetrical loads shows symmetrical characteristics. Under different load conditions, the displacement curve of the diaphragm wall shows the characteristics of “bulge belly”. The forms of loads with displacements from largest to smallest at the same position are as follows: asymmetric loads, symmetrical loads, and no loads. These findings provide valuable insights for optimizing the structural design of similar deep excavation projects and contribute to promoting sustainable urban underground development. Full article

Cylindrical retaining structures are widely adopted in intercity railway tunnel engineering due to their exceptional load-bearing performance, no need for internal support, and efficient utilization of concrete compressive strength. Measured deformation data not only comprehensively reflect the influence of construction and hydrogeological conditions but also directly and clearly indicate the safety and stability status of structure. Therefore, based on two geometrically similar cylindrical shield tunnel shafts in Shenzhen, the surface deformation, structure deformation, and changes in groundwater outside the shafts during excavation were analyzed, and the deformation characteristics under the soil–rock composite stratum were summarized. Results indicate that the uneven distribution of surface surcharge and groundwater level are key factors causing differential deformations. The maximum horizontal deformation of the shafts wall is less than 0.05% of the current excavation depth (H), occurring primarily in two zones: from H − 20 m to H + 20 m and in the shallow 0–10 m range. Vertical deformations at the wall top are mostly within ±0.2% H. Localized groundwater leakage in joints may lead to groundwater redistribution and seepage-induced fine particle migration, exacerbating uneven deformations. Timely grouting when leakage occurs and selecting joints with superior waterproof sealing performance are essential measures to ensure effective sealing. Compared with general polygonal foundation pits, cylindrical retaining structures can achieve low environmental disturbances while possessing high structural stability. Full article

Accidental ground surcharge loads can induce adverse effects such as segment cracking in underlying shield tunnel structures, with particularly pronounced impacts on pre-damaged tunnel segments. Cracks represent one of the most common initial damage forms in shield tunnel structures. To investigate through-crack failure mechanisms in shield tunnel segments with initial cracks under surcharge loading, this study conducted 1:8 scaled indoor model tests, considering factors including initial crack length, quantity, morphology, and surcharge position. Research findings demonstrate that increased initial crack length and quantity significantly reduce the critical load required for through-crack formation. Specifically, segments with 9 cm longitudinal initial cracks required 50.9% less load to develop through-cracks compared to intact segments. Similarly, segments containing two 9 cm circumferential initial cracks exhibited a 22.1% reduction in critical load relative to those with single circumferential cracks. Initial cracks in pre-damaged segments substantially influence the propagation path of new cracks during subsequent loading failures. The detrimental effects of staggered longitudinal-circumferential initial cracks exceed those of purely longitudinal cracks, which themselves pose greater risks than circumferential cracks alone. Bilateral surcharge loading significantly increases the critical load threshold for through-crack formation compared to unilateral loading. This highlights the severe structural risks associated with uneven load distribution. Full article

The excavation of upper shallow foundation pits may cause the uneven deformation of existing tunnels buried below a shallow depth. Improper control measures may lead to a series of diseases, such as local cracking or breakage of the tunnel lining, which threaten the safety of tunnel operations. Regarding the safety of the existing tunnel affected by the construction of the foundation pit, cases of the application of portal frame anti-heave structures in upper foundation pit projects of existing tunnels in Shenzhen have been documented, and the main influencing factors have been analyzed and summarized. Taking the Qianhai Ring Water Corridor Project as an example, numerical orthogonal experiments were conducted to analyze the deformation response patterns in the depth of existing tunnels and the effectiveness of control measures in the upper shallow of foundation pit engineering. The roles of portal frame anti-heave structures are analyzed in detail using measured data. Studies indicate that the deformation of the existing tunnels mainly occurs during the top and immediately adjacent block excavation stages, and stabilizes after the uplift-resisting piles and anti-floating slabs form an effective frame structure. The portal frame anti-heave structures, combined with measures such as block excavation, jet grouting interlocking reinforcement, backfilling, and surcharge loading, have extremely strong deformation control capabilities. However, the construction costs are relatively high, leaving room for optimization. Full article

In coastal regions with thick, soft soil deposits, bridge pile foundations are susceptible to lateral displacements induced by the construction of adjacent seawalls. This study employs a three-dimensional nonlinear finite element framework to investigate the lateral deformation mechanisms of rock-socketed bridge piles under seawall surcharge loading in soft soils, considering the effects of both immediate construction and long-term consolidation. A parametric analysis is performed to evaluate the effectiveness of deep cement mixing (DCM) piles in mitigating pile displacements, focusing on key design parameters, including DCM pile length, area replacement ratio, and elastic modulus. The results reveal that horizontal pile displacements peak at the pile head post-construction (25 days: 25 mm) and progressively decrease during consolidation, shifting the critical displacement zone to mid-pile depths (20 years: 12 mm). Bending moment analysis identifies persistent positive moments at the rock-socketed interface. Increasing pile stiffness marginally reduces displacements (a < 1 mm reduction for a 22% diameter increase), while expanding the seawall–pile distance to 110 m decreases displacements by 72–84%. DCM pile implementation significantly mitigates short-term (48% reduction) and long-term (54% reduction) displacements, with optimal thresholds at a 30% area replacement ratio and a 40.5 MPa elastic modulus. This study provides critical insights into time-dependent soil–pile interaction mechanisms and practical guidelines for optimizing coastal infrastructure design to minimize surcharge-induced impacts on adjacent pile foundations. Full article