Search Results (68)

During offshore operations of jack-up platforms, the spudcan may experience sudden punch-through failure when penetrating from an overlying stiff clay layer into the underlying soft clay, posing significant risks to platform safety. Conventional punch-through prediction methods, which rely on predetermined soil parameters, exhibit limited accuracy as they fail to account for uncertainties in seabed stratigraphy and soil properties. To address this limitation, based on a database of centrifuge model tests, a probabilistic prediction framework for the peak resistance and corresponding depth is developed by integrating empirical prediction formulas based on Bayes’ theorem. The proposed Bayesian methodology effectively refines prediction accuracy by quantifying uncertainties in soil parameters, spudcan geometry, and computational models. Specifically, it establishes prior probability distributions of peak resistance and depth through Monte Carlo simulations, then updates these distributions in real time using field monitoring data during spudcan penetration. The results demonstrate that both the recommended method specified in ISO 19905-1 and an existing deterministic model tend to yield conservative estimates. This approach can significantly improve the predicted accuracy of the peak resistance compared with deterministic methods. Additionally, it shows that the most probable failure zone converges toward the actual punch-through point as more monitoring data is incorporated. The enhanced prediction capability provides critical decision support for mitigating punch-through potential during offshore jack-up operations, thereby advancing the safety and reliability of marine engineering practices. Full article

Ground subsidence is a significant geotechnical hazard in urban areas, leading to property damage, casualties, and broader societal issues. This study investigates the mechanisms of cavity formation and ground subsidence through laboratory model tests using Korean standard sand and marine clay under controlled conditions. A transparent soil box apparatus was fabricated to simulate sewer pipe damage, with model grounds prepared at various relative densities, groundwater levels, and fines contents. The progression of cavity formation and surface collapse was observed and quantitatively analyzed by measuring the time to cavity formation and ground subsidence, as well as the mass of discharged soil. Results indicate that lower relative density accelerates ground subsidence, whereas higher density increases cavity volume due to greater frictional resistance. Notably, as the fines content increased, a tendency was observed for ground subsidence to be increasingly suppressed, suggesting that cohesive clay particles can limit soil loss under seepage conditions. These findings provide valuable insights for selecting backfill materials and managing subsurface conditions to mitigate ground subsidence risks in urban infrastructure. Full article

In situ testing is essential in geotechnical engineering, providing valuable insights into both soil stratification and material behaviour. This paper illustrates an automated framework for deriving constitutive model parameters from in situ test data. The framework employs a graph-based approach that enhances both transparency and adaptability—transparency by explicitly tracing the computation of each parameter and adaptability by allowing users to incorporate their expertise. The study applies this framework to a marine clay test site, demonstrating its ability to determine soil parameters efficiently. Additionally, the framework is directly integrated into a finite element software, enabling seamless parameter transfer for numerical modelling. A case study is presented in which a shallow foundation is simulated to illustrate the practical application of this approach. This framework is particularly valuable in the early stages of geotechnical projects, providing detailed soil characterisation when site data is limited. Validating the accuracy of the derived parameters and incorporating additional in situ test methods are part of ongoing research. Full article

Coastal marine soft clays subjected to long-term storm wave loading often exhibit inclined initial principal stress orientation (α₀) and subsequent cyclic principal stress rotation (PSR). These stress states critically influence soil mechanical behavior and failure mechanisms, threatening offshore structural stability. This study employs hollow cylinder apparatus testing to investigate the undrained cyclic loading behavior of reconstituted soft clay under controlled α₀ and PSR conditions, simulating storm wave-induced stress paths. Results demonstrate that α₀ governs permanent pore pressure and vertical strain accumulation with distinct mechanisms, e.g., a tension-dominated response with gradual pore pressure rise at α₀ < 45° transitions to a compression-driven rapid strain accumulation at α₀ > 45°. Rotational loading with PSR significantly intensifies permanent strain accumulation and stiffness degradation rates, exacerbating soil’s anisotropic behavior. Furthermore, the stiffness degradation index tends to uniquely correlate with the permanent axial or shear strain, which can be quantified by an exponential relationship that is independent of α₀ and PSR, providing a unified framework for normalizing stiffness evolution across diverse loading paths. These findings advance the understanding of storm wave-induced degradation behavior of soft clay and establish predictive tools for optimizing marine foundation design under cyclic loading. Full article

The progression of marine resource exploration into deepwater and ultra-deepwater regions has intensified the requirement for precise quantification of the undrained shear strength of clay. Although diverse in situ testing methodologies—including the vane shear test (VST), cone penetration test (CPT), T-bar penetration test (TPT), and ball penetration test (BPT)—are widely utilized for the assessment of clay strength, systematic discrepancies and correlations between their derived measurements remain inadequately resolved. The aim of this work is to provide a systematic comparison of strength interpretations across different in situ testing methods, with emphasis on identifying method-specific biases under varying soil behaviors. To achieve this, a unified numerical simulation framework was developed to simulate these four prevalent testing techniques, employing large-deformation finite element analysis via the Coupled Eulerian–Lagrangian (CEL) approach. The model integrates critical constitutive behaviors of marine clays, specifically strain softening and strain rate dependency, to replicate in situ shear strength evolution. Rigorous sensitivity analyses confirm the model’s robustness. The results indicate that, when the stain rate and softening effects are neglected, the resistance factors from the CPT and VST remain largely insensitive to shear strength variations. However, T-bar and ball penetrometers tend to underestimate strength by up to 15% in high-strength soils due to the incomplete development of a full-flow failure mechanism. As a result, their application in high-strength soils is not recommended. With both the strain rate and softening effects considered, the interpreted strength value S_ut from the CPT increases by 13.5% compared to cases excluding these effects, while other methods exhibit marginal decreases of 4–5%. The isolated analysis of strain softening reveals that, under identical softening parameters, the CPT demonstrates the least sensitivity to strain softening among the four methods examined, with the factor reduction ratio N_s/N₀ ranging from 0.76 to 1.00, while the other three methods range from 0.65 to 0.88. The results indicate that the CPT is well suited for strength testing in soils exhibiting pronounced softening behavior, as it reduces the influence of strain softening on the measured results. These findings provide critical insights into method-specific biases in undrained shear strength assessments, supporting a more reliable interpretation of in situ test data for deepwater geotechnical applications. Full article

The salt concentration of the pore solution can alter the micro-pore and particle structure of soil, thereby affecting its engineering properties. To investigate the compression characteristics of marine soil under different salt concentrations, one-dimensional compression and SEM scanning tests were conducted on marine reconstituted clay from the Yellow Sea with varying NaCl concentrations (0–5%). The effects of NaCl concentration on the compression characteristics and microstructure of marine sedimentary clay were analyzed. The results indicate that: (1) Compressibility increases up to a NaCl concentration of 2.5%, after which it declines. At 2.5% NaCl threshold concentration, the coefficient of compression, compressibility index, and consolidation coefficient reach their peak values, and the response becomes more pronounced with increasing compression pressure. During the secondary compression stage, as pore water is expelled, the impact of NaCl concentration on compressibility diminishes, while the rebound characteristics remain unaffected by NaCl concentration; (2) SEM analysis reveals that at a NaCl threshold concentration of 2.5%, the pore fractal dimension, particle fractal dimension, pore anisotropy, and particle anisotropy reach their maximum values, with the most complex shape and pores and particles aligning in the same direction. When the concentration is less than 2.5%, the soil exhibits narrow pores and rounded particles upon compression. When the concentration exceeds 2.5%, the microstructure changes in the opposite direction, confirming the particle rearrangement mechanism driven by surface contact under moderate salinity. At the threshold concentration of 2.5%, a balance between electrostatic forces and attractive forces enables stable surface-to-surface contacts, maximizing compressibility. The findings of this study provide valuable references for the foundation design of marine geotechnical engineering in specific sea areas, thereby enhancing the safety and reliability of related projects. Full article

As the economy evolves, there has been an increasing interest in exploring oceanic resources. However, the complex marine environment poses several geological challenges for offshore engineering endeavors. The presence of gassy soil significantly influences the deformation properties and integrity of the soil, significantly impacting offshore engineering construction. Triaxial shear tests and creep tests were conducted on gassy clay with silt content, prepared using the laboratory “zeolite method”, to analyze its shear deformation characteristics and long-term resilience. We proposed a prediction model for calculating the long-term resilience of silt-containing clay, accounting for confining pressure and gas content, and verified its efficacy through experimentation. Our findings reveal the following: The stress–strain relationship curve of silt-containing gassy clay is a typical strain hardening curve. The greater the confining pressure or the smaller the gas content, the greater the stress under the same strain and the greater the yield stress; when the gas content is the same, the greater the confining pressure, the greater the long-term strength of the soil; and when the confining pressure is the same, the smaller the gas content, the greater the long-term strength of the soil. The research results can provide theoretical reference for actual complex engineering. Full article

The development of marine energy requires reliable foundations, which may be located near submarine slopes. This paper utilizes the lower bound limit analysis (LBLA) to analyze the undrained bearing capacity of foundations on slopes with anisotropy and linearly increasing strength with depth. The anisotropic undrained strength (AUS) model is employed to simulate the anisotropy of the slope soil. This study considers five variables that affect the bearing capacity: the normalized foundation setback (L/B), load angle (θ), strength ratio (s_uc/γB), heterogeneous index (ρB/s_uc), and anisotropy ratio (r_e). Here, s_uc represents the soil strength obtained from triaxial compression tests, while ρ denotes the strength gradient. The results indicate that the bearing capacity increases with the increase in L/B, s_uc/γB, ρB/s_uc, and r_e, while the maximum bearing capacity corresponds to a load angle ranging from 75° to 90°. The failure modes of foundations under different boundary conditions were presented and discussed. To establish the relationship between the foundation bearing capacity and each variable, the multivariate adaptive regression splines (MARS) is introduced. The MARS results indicate that θ is the most significant variable, while the relative importance of L/B is the lowest; neither can be neglected in practical engineering. The empirical equation based on the MARS algorithm can accurately predict the bearing capacity of foundations in non-homogeneous and anisotropic clay. These results offer critical guidance for engineering practice, enabling efficient design of marine foundations near slopes while accounting for soil anisotropy and heterogeneous strength gradients, thereby reducing risks of instability in offshore energy infrastructure. Full article

Seabed foundations consisting of interbedded layers of saturated soft clay and sand deposited during the Quaternary period are widely distributed in the coastal areas of Southeastern China. These soil foundations are prone to significant settlement under seismic loading. The study of the seismic dynamic response characteristics of saturated foundations with interbedded soft clay–sand and the development of rapid prediction models are essential for controlling settlement and ensuring the service safety of marine structures. A total of 4000 sets of seabed foundation models are randomly generated, with layers of saturated soft clay and sand and with a random distribution of layer thickness and burial depth. The mechanical behavior of saturated soft clay is described using the Soft Clay model based on the boundary surface theory, and the generalized elastoplastic constitutive model PZIII is used to characterize the mechanical behavior of sandy soil. The finite element platform FssiCAS is employed for a computational analysis to study the characteristics of seismic subsidence in saturated seabed foundations with interbedded soft clay–sand. A machine learning model is implemented based on the Random Forest algorithm, in which 3200 sets of numerical simulation results are used for model training, and 800 sets are used for validating the model’s reliability. The results show that under seismic excitation, the pore water pressure within the saturated seabed foundation with interbedded soft clay–sand accumulates, effective stress decreases, and the seabed foundation softens, to a certain extent. During the post-seismic consolidation phase, significant settlement of the seabed foundation occurs. The fast prediction model based on the Random Forest algorithm could reliably predict the settlement characteristics of submarine foundations. This research provides a new technological avenue for the rapid prediction of the seismic settlement of submarine foundations, which could be of use in engineering design, assessment, and prediction. Full article

The change in bound water content with temperature is a core issue in studying temperature effects in clayey soils. This study used nuclear magnetic resonance (NMR) techniques to measure pore water in three types of marine clay, ranging from inland to coastal areas. The T₂ cutoff values were proposed to distinguish between bulk water, capillary water, and bound water, and the curves of unfrozen water and bound water content with changing temperatures were obtained during the freezing process. Additionally, the impact of soil properties on bound water content was analyzed. The research findings indicated that the pore water in marine clay is dominated by bound water, and the change in bound water content with temperature in each soil layer can be divided into four stages: the trace phase change stage, the intense phase change stage, the transitional phase change stage, and the stabilizing stage. Further, the effect of soil properties such as organic matter content, soluble salt content, and cation exchange capacity on bound water content was illustrated, and clay content and bound water content were found not to be strictly positively correlated. Full article

With the development of the offshore wind industry in China, the amount of offshore wind turbines has increased rapidly. Large-diameter steel monopile foundations of offshore wind turbines have been widely adopted in China with lots of marine clay located. However, the conventional offshore wind monopile bearing capacity prediction from the American Petroleum Institute (API) based on the small-diameter flexible pile field test is inaccurate with the rigid mechanism of large-diameter monopile causing economically loss. The piezocone penetration test (CPTU) is a common marine in situ test to exactly acquire soil parameters. Therefore, a CPTU-based offshore wind monopile rigid mechanism inference method is proposed. A creative numerical offshore wind power monopile and CPTU combined model is established through COMSOL. A self-compiling parameter function is applied to soil modeling and an innovative mobile boundary function is created to simulate CPTU penetration. Through the model, real-time CPTU data can be acquired when monopile is applied with different horizontal loads. The peripile soil stress change can be timely detected by CPTU. Through CPTU data, the monopile rigid bearing mechanism is verified. A rigid rotation center is found at the 60% point of the inserted monopile. The method is an important foundation for the next step of monopile bearing capacity research. Full article

Offshore wind power is a hot spot in the field of new energy, with foundation construction costs representing approximately 30% of the total investment in wind farm construction. Offshore wind turbines are subjected to long-term cyclic loads, and seabed materials are prone to causing stiffness degradation. The accurate disclosure of the mechanical properties of marine soil is critical to the safety and stability of the foundation structure of offshore wind turbines. The stiffness degradation laws of mucky clay and silt clay from offshore wind turbines were firstly investigated in the study. Experiments found that the variations in the elastic modulus presented “L-type” attenuation under small cyclic loads, and the degradation coefficient fleetingly decayed to the strength progressive line under large cyclic loads. Based on the experimental results, a random forest prediction model for the elastic modulus of the submarine soil was established, which had high prediction accuracy. The influence of testing the loading parameters of the submarine soil on the prediction results was greater than that of the soil’s physical property parameters. In criticality, the CSR had the greatest impact on the prediction results. This study provides a more efficient method for the stiffness degradation assessment of submarine soil materials in offshore wind farms. Full article

Offshore wind power is a new type of clean energy with broad development prospects. Accurate analysis of the uplift capacity of offshore wind turbine foundations is a crucial prerequisite for ensuring the safe operation of wind turbines under complex hydrodynamic conditions. However, current research on the uplift capacity of suction caissons often neglects the high-sensitivity characteristics of marine soils. Therefore, this paper first employs the freeze–thaw cycling procedure to prepare high-sensitivity saturated clay. Subsequently, a single−tube foundation for wind turbines is constructed within a centrifuge through a penetration approach. Ten sets of centrifuge model tests with vertical cyclic pullout are conducted. Through comparative analysis, this study explores the pullout capacity and its variation patterns of suction caisson foundations in clay with different sensitivities under cyclic loading. This research indicates the following: (1) The preparation of high-sensitivity soil through the freeze−thaw procedure is reliable; (2) the uplift capacity of suction caissons in high−sensitivity soil rapidly decreases with increasing numbers of cyclic loads and then tends to stabilize. The cumulative displacement rate of suction caissons in high-sensitivity soil is fast, and the total number of pressure–pullout cycles required to reach non-cumulative displacement is significantly smaller than that in low-sensitivity soil; (3) the vertical cyclic loading times and stiffness evolution patterns of single-tube foundations, considering the influence of sensitivity, have been analyzed. It was found that the secant stiffness exhibits a logarithmic function relationship with both the number of cycles and sensitivity. The findings of this study provide assistance and support for the design of suction caissons in high-sensitivity soils. Full article

Prefabricated vertical drains combined with heating is a new approach to improving the mechanical properties of soft clay foundations. Rising temperatures cause the formation of concentric and radially aligned soil regions with distinct heterogeneous characteristics. This results in incomplete contact between adjacent soil layers, with the water in the interstices impeding heat transfer and manifesting as a thermal resistance effect. Based on the theory of thermo-hydro-mechanical coupling, a two-dimensional dual-zone axisymmetric marine soft soil model improved by a prefabricated vertical thermo-drain has been established. A generalized incomplete thermal contact model has been proposed to describe the thermal resistance effect at the interface of concentric soil regions. The effectiveness of the numerical solution presented in this paper is verified by comparison with semi-analytical solutions and model experiments. The thermal consolidation characteristics of concentric regions of soil at various depths under different thermal contact models were discussed by comprehensively analyzing the effects of different parameters under various thermal contact models. The outcomes indicate that the generalized incomplete thermal contact model provides a more accurate description of the radial thermal consolidation characteristics of concentric regions of soil. The influence of the thermal conductivity coefficient on the consolidation characteristics of the concentric regions soil is related to the thermal resistance effect. Full article

Oil spills occur during different operations in the energy sector, such as crude oil transport, tank filling and cleaning, and fueling. Such spills are one of the major causes of the accumulation of oil derivatives in the environment, requiring the remediation of soil and marine environments. The production of a biosurfactant by Starmerella bombicola ATCC 222214 was maximized by investigating the effect of different carbon/nitrogen sources and culture conditions. The mineral medium selected for its production was supplemented with 2.0% potato peel flour, 5.0% waste canola frying oil, and 0.20% urea. The culture conditions were a 200 rpm shaking speed, a fermentation time of 180 h, and a 4.0% inoculum size. The yield of isolated biosurfactant was 7.72 g/L. The emulsification rates of heavy oil and motor oil were 65.55 and 95.00%, respectively, indicating an affinity for complex hydrocarbons. In stability tests performed at different pH values, temperatures, and NaCl concentrations, the surface tension ranged from 27.14 to 31.08 mN/m. The critical micelle concentration was 2.0 g/L, at which the surface tension was 33.26 mN/m. The biosurfactant was composed of 6,6-dimethoxy-octanoic acid and azelaic acid, and it exhibited low toxicity to Brassica oleracea and Solanum lycopersicum. In the kinetic test, the biosurfactant allowed for the removal of 82.30%, 96.65%, and 98.25% of exhaust motor oil from sand, silty soil, and clay soil, while in the static test in packed columns, the removal yields were 66.62%, 63.03%, and 58.45%, respectively. The biosurfactant produced in this study is promising for environmental remediation applications in the energy sector. Full article