Search Results (236)

Ensuring the safe landing of deep-sea mining vehicles (DSMVs) on soft seabed sediments is critical for the stability and operational reliability of subsea mineral extraction. However, deep-sea sediments, particularly in polymetallic nodule regions, are characterized by low shear strength, high compressibility, and rate-dependent behavior, posing significant challenges for full-scale experimental investigation and predictive modeling. To address these limitations, this study develops a high-fidelity finite element simulation framework based on the Coupled Eulerian–Lagrangian (CEL) method to model the landing and penetration process of full-scale DSMVs under various geotechnical conditions. To overcome the high computational cost of FEM simulations, a data-driven surrogate model using the random forest algorithm is constructed to predict the normalized penetration depth based on key soil and operational parameters. The proposed hybrid FEM–ML approach enables efficient multiparameter analysis and provides actionable insights into the complex soil–structure interactions involved in DSMV landings. This methodology offers a practical foundation for engineering design, safety assessment, and descent planning in deep-sea mining operations. Full article

To address the critical challenge of ensuring bottom water-inrush stability during the excavation of ultra-deep foundation pits for riverside suspension-bridge anchorages under complex geological conditions involving high-pressure confined groundwater, we investigate the application of D-RJP high-pressure rotary jet grouting pile technology for ground improvement. Its effectiveness is systematically validated through a case study of the South Anchorage Foundation Pit for the North Channel Bridge of the Zhangjinggao Yangtze River Bridge. The D-RJP method led to the successful construction of a composite foundation within the soft soil that satisfies the permeability coefficient, interface friction coefficient, bearing capacity, and shear strength requirements, significantly improving the geotechnical performance of the anchorage foundation. A series of field experiments were conducted to optimize the critical construction parameters, including the lifting speed, water–cement ratio, and stroke spacing. Core sampling and laboratory testing revealed the grout columns to have good structural integrity. The unconfined compressive strength of the high-pressure jet grout columns reached 5.45 MPa in silty clay layers and 8.21 MPa in silty sand layers. The average permeability coefficient ranged from 1.67 × 10⁻⁷ to 2.52 × 10⁻⁷ cm/s. The average density of the columns was 1.66 g/cm³ in the silty clay layer and 2.08 g/cm³ in the silty sand layer. The cement content in the return slurry varied between 18% and 27%, with no significant soil squeezing effect observed. The foundation interface friction coefficient ranged from 0.44 to 0.52. After excavation, the composite foundation formed by D-RJP columns was subjected to static load and direct shear testing. The results showed a characteristic bearing capacity value of 1200 kPa, the internal friction angle exceeded 24.23°, and the cohesion exceeded 180 kPa. This study successfully verifies the feasibility of applying D-RJP technology to construct high-performance artificial composite foundations in complex strata characterized by deep soft soils and high-pressure confined groundwater, providing valuable technical references and practical insights for similar ultra-deep foundation pit projects involving suspension bridge anchorages. 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

Cement–Soil Mixing (CSM) Pile is an important technology for soft ground reinforcement, and its as-formed compressive strength directly affects engineering design and construction quality. To address the significant discrepancy between laboratory-tested strength and field as-formed strength arising from differing environmental conditions, this study conducted modified laboratory experiments simulating key field formation characteristics. A cement–soil preparation system considering actual immersion conditions was established, based on controlling the initial water content state of the foundation soil before pile formation and applying submerged conditions post-formation. Utilizing data mining on 84 sets of experimental data with various preparation parameter combinations, a prediction model for the as-formed strength of CSM Pile was developed based on the Particle Swarm Optimization-Extreme Gradient Boosting (PSO-XGBoost) algorithm. Engineering validation demonstrated that the model achieved an RMSE of 0.138, an MAE of 0.112, and an R² of 0.961. It effectively addresses the issue of large prediction deviations caused by insufficient environmental simulation in traditional mix proportion tests. The research findings establish a quantitative relationship between as-formed strength and preparation parameters, providing an effective experimental improvement and strength prediction method for the engineering design of CSM Pile. Full article

The Maowusu Desert is still suffering from serious ecological and environmental security issues such as wind erosion and desertification, influenced by both natural and human factors. The amendment of aeolian sandy soil with soft rock material presents an effective erosion control strategy, leveraging the complementary structural and compositional properties of both materials to enhance soil stability and rehabilitate degraded environments. However, there are few studies that investigate the effect of soil surface electrochemical properties and particle interaction forces on the structural stability of compound soils with soft rock and sandy soil. This decade-long field study quantified the electrochemical properties and interparticle forces and their synergistic effects on structural stability across five soft rock-to-aeolian sandy soil blend volume ratios (0:1, 1:5, 1:2, 1:1, 1:0) within the 0–30 cm soil profile. The results showed that the soil organic matter (SOM), specific surface area (SSA), and cation exchange capacity (CEC) significantly increased with the incorporation of soft rock material. For five different proportions, with the addition of soft rock and the extension of planting years, the content of SOM increased from 5.65 g·kg⁻¹ to 11.36 g·kg⁻¹, the CEC varied from 4.68 cmol kg⁻¹ to 17.91 cmol kg⁻¹, while the σ₀ importantly decreased from 1.8 to 0.47 c m⁻² (p < 0.05). For the interaction force at 2.4 nm between soil particles, the absolute value of van der Waals attractive force increased from 0.10 atm to 0.38 atm, and the net force decreased from 0.09 atm to −0.30 atm after the incorporation ratios of soft rock from 0:1 to 1:1. There was a significant negative correlation between the resultant net force between the particles of compound soil and the SSA and CEC. These results indicate that the addition of soft rock material positively improves the surface electrochemical properties and internal forces between aeolian sandy soil particles, further enhancing its structural stability. This study establishes a foundational theoretical framework for advancing our mechanistic understanding of aeolian sand stabilization and ecosystem rehabilitation in the Mu Us Desert. Full article

This study investigates the effect of pile diameter on the seismic performance of single piles using the kinematic interaction framework outlined in Method III of the Turkish Building Earthquake Code TBEC-2018. Pile diameters of 65 cm, 80 cm, and 100 cm were analyzed under four different soil profiles—soft clay, stiff clay, very loose sand-A, and very loose sand-B. The methodology integrated nonlinear spring modeling (P-y, T-z, Q-z) for soil behavior, one-dimensional site response analysis using DEEPSOIL, and structural analysis with SAP2000. The simulation results showed that increasing the pile diameter led to a significant rise in internal forces: the maximum bending moment increased up to 4.0 times, and the maximum shear force increased 4.5 times from the smallest to the largest pile diameter. Horizontal displacements remained nearly constant, whereas vertical displacements decreased by almost 50%, indicating improved pile–soil stiffness interaction. The depth of the maximum moment shifted according to the soil stiffness, and stress concentrations were observed at the interfaces of stratified layers. The findings underline the importance of considering pile geometry and soil layering in seismic design. This study provides quantitative insights into the trade-off between displacement control and force demand in seismic pile design, contributing to safer foundation strategies in earthquake-prone regions. Full article

The implantable capsule grouting pile is a novel pile foundation technology in which a capsule is affixed to the side of the implanted pile to facilitate grouting and achieve extrusion-based reinforcement. This technique is designed to improve the bearing capacity of implanted piles in coastal areas with deep, soft soil. This study conducted model tests involving multiple grouting positions across different foundation types to refine the construction process and validate the enhancement of bearing capacity. Systematic measurements and quantitative analyses were performed to evaluate the earth pressure distribution around the pile, the resistance characteristics of the pile end, the evolution of side friction resistance, and the overall bearing performance. Special attention was given to variations in the lateral friction resistance adjustment coefficient under different working conditions. Furthermore, an actual case analysis was conducted based on typical soft soil geological conditions. The results indicated that the post-grouting process formed a dense soil ring through the expansion and extrusion of the capsule, resulting in increased soil strength around the pile due to increased lateral earth pressure. Compared to conventional piles, the grouted piles exhibited a synergistic improvement characterized by reduced pile end resistance, enhanced side friction resistance, and improved overall bearing capacity. The ultimate bearing capacity of model piles at different grouting depths across different foundation types increased by 6.8–22.3% compared with that of ordinary piles. In silty clay and clayey silt foundations, the adjustment coefficient η_s of lateral friction resistance of post-grouting piles ranged from 1.097 to 1.318 and increased with grouting depth. The findings contribute to the development of green pile foundation technology in coastal areas. Full article

To address the issue of structural tilting caused by uneven foundation settlement in soft soil areas, this study combined a specific engineering case to conduct numerical simulations of the rectification process for an inclined reinforced concrete building using ABAQUS finite element software. Micropile-raft combined jacking technology was employed, applying staged jacking forces (2400 kN for Axis A, 2200 kN for Axis B, and 1700 kN for Axis C) with precise control through 20 incremental steps. The results demonstrate that this technology effectively halted structural tilting, reducing the maximum inclination rate from 0.51% to 0.05%, significantly below the standard limit. Post-rectification, the peak structural stress decreased by 42%, and displacements were markedly reduced. However, the jacking process led to a notable increase in the column axial forces and directional changes in beam bending moments, reflecting the dynamic redistribution of internal forces. The study confirms that micropile-raft combined jacking technology offers both controllability and safety, while optimized counterforce pile layouts enhance the long-term stability of the rectification system. Based on stress and displacement cloud analysis, a monitoring scheme is proposed, forming an integrated “rectification-monitoring-reinforcement” solution, which provides a technical framework for building rectification in soft soil regions. Full article

This study investigates the behavior and performance of a newly proposed cone-top pile foundation designed to improve stability in layered, deformable, or strain-sensitive soils. Traditional shallow and uniform conical foundations often suffer from excessive settlement and reduced capacity when subjected to vertical loads and horizontal soil deformations. To address these limitations, a hybrid foundation was developed that integrates an inverted conical base with a central pile shaft and a rolling joint interface between the foundation and the superstructure. Laboratory model tests, full-scale field loading experiments, and axisymmetric numerical simulations using Plaxis 2D (Version 8.2) were conducted to evaluate the foundation’s bearing capacity, settlement behavior, and load transfer mechanisms. Results showed that the cone-top pile foundation exhibited lower settlements and higher load resistance than columnar foundations under similar loading conditions, particularly in the presence of horizontal tensile strains. The load was effectively distributed through the conical base and transferred into deeper soil layers via the pile shaft, while the rolling joint reduced stress transmission to the structure. The findings support the use of cone-top pile foundations in soft soils, seismic areas and areas affected by underground mining, where conventional designs may be inadequate. This study provides a validated and practical design alternative for challenging geotechnical environments. Full article

As a key transportation infrastructure, it is of great significance to ensure the seismic safety of the high-speed railway hub station. Taking Changde high-speed railway hub station as background, a comprehensive 3D numerical model of the high-speed railway station structure is proposed to consider the engineering geological characteristics of the site, soil nonlinearity, and pile-soil interactions. The results show that the hub station structural system, considering pile-soil interaction, presents the ‘soft-upper-rigid-down’ characteristics as a whole, and the natural vibration is lower than that of the station structure with a rigid foundation assumption. Under the action of three strong seismic motions, the nonlinear site seismic effect is significant, the surface acceleration is significantly enlarged, and decreases with the buried depth. The interaction between pile and soil is related to the nonlinear seismic effect of the site, which deforms together to resist the foundation deformation caused by the strong earthquake motions, and the depth range affected by the interaction between the two increases with the increase of the intensity of earthquake motion. Among the three kinds of input earthquake motions, the predominant frequency of the Kobe earthquake is the closest to the natural vibration of the station structure system, followed by the El Centro earthquake. Moreover, the structures above the foundation of the high-speed railway hub station structural system are more sensitive to the spectral characteristics of Taft waves and El Centro waves compared to the site soil. This is also the main innovation point of this study. The existence of the roof leads to the gradual amplification of the seismic response of the station frame structure with height, and the seismic response amplification at the connection between the roof and the frame structure is the largest. The maximum story drift angle at the top floor of the station structure is also greater than that at the bottom floor. Full article

Xanthan gum (XG) has potential application prospects as a biopolymer in soil reinforcement engineering. However, there remains a lack of relevant research on its influence on the mechanical properties, microscopic mechanism, and pH value changes in clay. In this study, the effects of different XG dosages (0%, 5%, 10%, 15%, and 20%) on the microscopic mechanism, pH value, and mechanical strength of clay at the 7-day curing age were investigated through tests including Zeta potential, infrared spectroscopy, scanning electron microscopy (SEM), pH value, unconfined compressive strength, and triaxial shear strength. The results show that the addition of XG can not only promote charge exchange to generate hydrogen bonds and increase the bonding force between clays but can also form flocculent aggregates between the matrices, cementing the clay, filling the pores, and reducing the porosity of the samples. It can significantly increase the mechanical strength of the sample. When the content of XG is 20%, the unconfined compressive strength (UCS) and cohesion of the sample reach their maximum, increasing by 296% and 806%, respectively, compared with the reference group without XG. The conclusions drawn from this research can not only provide a theoretical reference for improving soft clay foundations but also expand the application research of XG in clay. Full article

Taking the shield construction of Xiamen Metro Line 2 tunnel side-crossing the Tianzhushan overpass and under-crossing the Shen-Hai Expressway as the engineering background, FLAC3D 6.0 software was used to examine the deformation of adjacent structures based on shield construction parameters in upper-soft and lower-hard strata. The reliability of the numerical simulation results was verified by comparing measured and predicted deformations. The study results indicate that deformation of the pile will occur during the construction of the tunnel shield next to the pile foundation. The shape of the pile deformation curve in the horizontal direction is significantly influenced by the distance from the pile foundation to the adjacent tunnel’s centerline, as well as by soil bin pressure, grouting layer thickness, and stress release coefficient. During the tunnel shield construction beneath the expressway, increasing the soil bin pressure, the grouting layer thickness, and reducing the stress release coefficient can effectively minimize surface deformation and differential settlement on both sides of the deformation joints between the bridge and the roadbed. The practice shows that, by optimizing shield construction parameters in upper-soft and lower-hard strata, the deformation of nearby bridges and pavements can be kept within allowable limits. This is significant for reducing construction time and costs. The findings offer useful references for similar projects. Full article

Accurate settlement prediction for high-speed railway (HSR) soft foundations remains challenging due to the irregular and dynamic nature of real-world monitoring data, often represented as non-equidistant and non-stationary time series (NENSTS). Existing empirical models lack clear applicability criteria under such conditions, resulting in subjective model selection. This study introduces a Monte Carlo-based evaluation framework that integrates data-driven simulation with geotechnical principles, embedding the concept of symmetry across both modeling and assessment stages. Equivalent permeability coefficients (EPCs) are used to normalize soil consolidation behavior, enabling the generation of a large, statistically robust dataset. Four empirical settlement prediction models—Hyperbolic, Exponential, Asaoka, and Hoshino—are systematically analyzed for sensitivity to temporal features and resistance to stochastic noise. A symmetry-aware comprehensive evaluation index (CEI), constructed via a robust entropy weight method (REWM), balances multiple performance metrics to ensure objective comparison. Results reveal that while settlement behavior evolves asymmetrically with respect to EPCs over time, a symmetrical structure emerges in model suitability across distinct EPC intervals: the Asaoka method performs best under low-permeability conditions (EPC ≤ 0.03 m/d), Hoshino excels in intermediate ranges (0.03 < EPC ≤ 0.7 m/d), and the Exponential model dominates in highly permeable soils (EPC > 0.7 m/d). This framework not only quantifies model robustness under complex data conditions but also formalizes the notion of symmetrical applicability, offering a structured path toward intelligent, adaptive settlement prediction in HSR subgrade engineering. Full article

The rapid increase in population and the corresponding increase in developments have necessitated the stabilization of areas with poor soil conditions. Due to consolidation settlement, the soft grounds available are deemed unsuitable for such structures. This paper presents the use of cement additives to build sand–cement columns in saturated clayey soils. The approach significantly reduces consolidation settlement and increases the bearing capacity, providing a viable solution to foundation problems. Consolidation tests were conducted on saturated clay specimens and sand–cement columns arranged in various patterns. A 5% cement content by the dry weight of the sand was used in building sand–cement columns. The results showed that the consolidation settlement rate was high due to the extra drainage formed by the widened pores in the sand–cement columns. The extra drainage caused more water to leave the specimen in a given time. However, after full contact between the loading platen and sand–cement columns, the rate of consolidation settlement decreased. At this stage, sand–cement participated in carrying the load. Additionally, the effect of vertical drainage on speeding up consolidation at higher stress levels was minimal, as the widened pores in the sand–cement columns began to close. Full article

Collar monopile foundation is a new type of offshore wind power foundation. This paper explores the horizontal bearing performance of collar monopile foundation in saturated cohesive soil through a combination of physical experiments and numerical simulations. After analyzing the deformation characteristics of the pile–soil system under horizontal load through static load tests, horizontal cyclic loading tests were conducted at different cycles to study the cumulative deformation law of the collar monopile. Based on a stiffness degradation model for soft clay, a USDFLD subroutine was developed in Fortran and embedded in ABAQUS. Coupled with the Mohr–Coulomb criterion, it was used to simulate the deformation behavior of the collar monopile under horizontal cyclic loading. The numerical model employed the same geometric dimensions and boundary conditions as the physical test, and the simulated cumulative pile–head displacement under 4000 load cycles showed good agreement with the experimental results, thereby verifying the rationality and reliability of the proposed simulation method. Through numerical simulation, the distribution characteristics of bending moment and the shear force of collar monopile foundation were studied, and the influence of pile shaft and collar on the horizontal bearing capacity of collar monopile foundation at different loading stages was analyzed. The results show that as the horizontal load increases, cracks gradually appear at the bottom of the collar and in the surrounding soil. The soil disturbance caused by the sliding and rotation of the collar will gradually increase, leading to plastic failure of the surrounding soil and reducing the bearing capacity. The excess pore water pressure in shallow soil increases rapidly in the early cycle and then gradually decreases with the formation of drainage channels. Deep soil may experience negative pore pressure, indicating the presence of a suction effect. This paper can provide theoretical support for the design optimization and performance evaluation of collar monopile foundations in offshore wind power engineering applications. Full article