Showing papers in "Marine Georesources & Geotechnology in 2023"
TL;DR: In this paper , a series of undrained cyclic shear tests was carried out on saturated coral sands, with different initial physical states, as they were subjected to rotations of 90° in the paths of cyclic stress with various initial orientations under isotropic conditions.
Abstract: A series of undrained cyclic shear tests was carried out on saturated coral sands, with different initial physical states, as they were subjected to rotations of 90° in the paths of cyclic stress with various initial orientations under isotropic conditions. An important finding is that the cumulative dissipated energy required for liquefaction (Ws) was significantly affected by their fines content (FC), relative density (Dr), and effective stress of consolidation (p′0), but was independent of the conditions of cyclic loading. Ws increased significantly with the increase in p′0. When FC was less than the threshold fines content, Ws increased with FC and decreased with an increase in Dr. The equivalent intergranular void ratio (e*) was introduced to reflect the effects of FC, physical states of the particles, and inter-particle contact on the physical properties of coral sand. The results revealed a unique relationship between e* and Ws at p′0 = 100 kPa. Furthermore, the unified model of the relation between the normalized cumulative dissipated energy and the ratio of excess pore water pressure (EPWP) followed an arc-tangent function. This model can be used to characterize the generation of EPWP with the cumulative dissipated energy of fine-grained sand under isotropic consolidation conditions.
5 citations
TL;DR: In this paper , undrained cyclic torsional shear tests and reconsolidation tests were carried out to compare the characteristics of saturated coral sand and siliceous sand (Nanjing fine sand and Ottawa sand).
Abstract: Reported here are undrained cyclic torsional shear tests and reconsolidation tests carried out to compare the characteristics of the undrained cyclic response and reconsolidation volumetric strain (εv) of saturated coral sand and siliceous sand (Nanjing fine sand and Ottawa sand). An important finding is that the cyclic resistance ratio of saturated coral sand increases with increasing relative density (Dr) and decreases with increasing consolidation confining pressure (p0′) under isotropic consolidation. For given Dr and p0′, the liquefaction resistance of saturated coral sand is higher than that of saturated siliceous sand. There is good correlation between εv and the excess pore water pressure (ue) of sand before liquefaction. For a given consolidation stress with increasing maximum shear strain (γmax), εv of saturated coral sand tends to stabilize at a value defined as the ultimate reconsolidation volumetric strain, which decreases with increasing Dr. Also, εv of saturated siliceous sand is less than that of saturated coral sand, and with increasing p0′ and Dr, the measured εv approaches the theoretical post-liquefaction maximum volumetric strain. Prediction models for εv of saturated coral sand are developed based on the liquefaction level and γmax, respectively.
3 citations
TL;DR: In this article , the authors used CT scanning and petrographic thin section observations to visually and quantitatively analyze crack morphological characteristics after triaxial shear failure at a microscopic scale.
Abstract: Coral reef limestone (CRL) is a marine sedimentary rock dominated by biogenesis, and its composition as well as internal structure characteristics are different from traditional terrigenous rocks. This article used CT scanning and petrographic thin section observations to visually and quantitatively analyze crack morphological characteristics after triaxial shear failure at a microscopic scale. The analysis revealed the mechanism of crack initiation and propagation from the perspectives of geological genesis and fracture mechanics. Results show that the crack propagation mechanism in the bio-cemented framework includes propagation along crystal boundaries and across crystals. Cracks can be classified as intergranular cracks, transgranular cracks, and bifurcation cracks based on crack morphology. The destruction mode of the specimen is controlled by the pore structure and cemented framework. Based on the pore distribution, the destruction mode can be divided into local tension failure and monoclinic shear failure. Understanding CRL crack propagation mechanisms has important scientific significance and practical engineering value for enriching rock damage theory and long-term stability analysis of island reef engineering foundations.
2 citations
TL;DR: In this article , a critical evaluation of the applicability of traditional methods and neural network-based methods in separating pore space from the matrix on computed tomography (CT) scanning images of two types of coral reef limestone specimens with coarse and fine pores was conducted.
Abstract: This paper conducts a critical evaluation of the applicability of traditional methods and neural network-based methods in separating pore space from the matrix on computed tomography (CT) scanning images of two types of coral reef limestone specimens with coarse and fine pores. By comparing with the manually labelled “ground truth,” it is shown that the Otsu method and other traditional methods have good segmentation accuracy and high efficiency when subjected to specific image preprocessing schemes, but their robustness is poor. UNet neural networks with a mixed contrast training dataset have high accuracy and strong robustness, but they are complex and computationally expensive. The three-dimensional reconstruction and analysis of the spatial distribution of porosity shows that the coral reef limestone specimen with coarse pores has a clear pore structure, while the rock matrix and pores are interlaced in the specimen with fine pores. Last, the statistical analysis of porosity and the pore distributions prove that the segmentation accuracy has a significant influence on the subsequent pore analysis. The current study highlights the importance of using appropriate image segmentation schemes and provides useful guidance for future interpretation of pore structure features of coral reef limestone based on CT scanned images.
2 citations
TL;DR: In this article , a comprehensive review of researches conducted over the past four decades on the impact of pore water chemistry (including salt type, salinity, ion valence, pH) on soil properties such as the microstructure, settlement, Atterberg limits, shear strength, conductivity, unsaturated soil mechanics properties and thermal properties is presented.
Abstract: Three quarters of the world’s significant urban centers are located in coastal regions where clay minerals are prevalent. The microstructures and physico-mechanical properties of clay sediments are highly susceptible to alterations in pore water chemistry. The pore water chemistry in soil changes easily due to groundwater pollution, seawater erosion, degradation, etc. However, there are several inconsistencies in the literature on the change of physical and mechanical properties of clay soils caused by the change of pore water chemical properties, i.e., disparate experimental results were reported for the same soil property, or varying explanations were proposed for the identical experimental results. Currently, the research in this field mainly focuses on the macroscopic behavioral modifications while lacking the explanations of microscopic mechanism. Therefore, this paper presents a comprehensive review of researches conducted over the past four decades on the impact of pore water chemistry (including salt type, salinity, ion valence, pH) on soil properties such as the microstructure, settlement, Atterberg limits, shear strength, conductivity, unsaturated soil mechanics properties and thermal properties. The fundamental mechanisms underlying the varied experimental observations on clay sediments affected by salt and pH are systematically explored, and deficiencies in this field are identified. The observed dispersion in the literatures is attributed to the spatial variation and heterogeneity of soil compositions, different test methods, and insufficiency of the fundamental microscopic mechanisms of the observed soil behaviors, etc. Therefore, it is necessary to further explore the essential mechanisms of the test results in the future to establish a unified conclusion.
1 citations
TL;DR: In this paper , the authors examine the behavior of the helical pile groups embedded in soft clay subjected to combined uplift and lateral loading considering three different configurations (rectangular, triangular, and square) and different spacings between the piles (2 to 5 times the helix diameter).
Abstract: Helical piles have lately emerged as a viable alternative foundation solution in offshore geotechnical applications. The helical piles are typically installed in groups to resist large loads from the structures and may encounter combined loading due to some factor such as the waves from the water surrounding it. Recent research works on group helical piles focused mostly on piles embedded in sand and their response to individual loading regimes. This research has been carried out to examine the behaviour of the helical pile groups embedded in soft clay subjected to combined uplift and lateral loading considering three different configurations (rectangular, triangular, and square) and different spacings between the helical piles (2 to 5 times the helix diameter). A three-dimensional finite element model is developed to predict the load-displacement response of the group and is validated against the 1 g laboratory scale model test results. The findings from the analyses reveal that the influence of combined loading reduces the lateral capacity of the group helical pile. The spacing between the helical piles also has a substantial impact on the response to combined loading. The role of critical spacing ratio for various configurations has also been discussed in this paper.
1 citations
TL;DR: Wang et al. as discussed by the authors presented a case study using the conventional vacuum preloading combined with surcharge preloading method (vacuum pressure of 90 kPa, surcharge height of 3 m) to improve the thick clay-slurry ground for a subgrade engineering project in Zhuhai, China.
Abstract: A reclamation project was undertaken in Zhuhai, China, covering an area of 11.35 km2 with a clay-slurry thickness of 30 m. It is interesting to find a good reinforcement method, which is more suitable for strengthening such a large-scale dredged clay-slurry ground. Evidence from engineering practice shows that vacuum preloading or vacuum preloading combined with surcharge preloading method technology has certain advantages. However, further data is required to verify their performance in the field. This paper presents a case study using the conventional vacuum preloading and vacuum preloading combined with surcharge preloading method (vacuum pressure of 90 kPa, surcharge height of 3 m) to improve the thick clay-slurry ground for a subgrade engineering project in Zhuhai, China. A series of field monitoring, in-situ tests, and laboratory tests were performed to evaluate their treatment effect by analysis of vacuum degree, ground surface settlement, layered settlement, consolidation degree, lateral displacement, excess pore water pressure dissipation, and vane shear strength. The results showed that the ground treated via vacuum preloading combined with surcharge preloading method was more effective than conventional vacuum preloading. The vacuum degree of vacuum preloading combined with surcharge preloading method was slightly lower than that of conventional vacuum preloading, decreasing with depth. The settlement is increased by 55.56%, average consolidation degree is enlarged by 40.9%, lateral displacement can be augmented by 2.4 times, pore water pressure coefficient is less than 0.6, and undrained shear strength is amplified by 22.2%. These findings can be used to guide the design of the combined preloading method of the subgrade engineering project along the east coast of China.
1 citations
TL;DR: In this paper , a series of undrained cyclic torsional shear tests on saturated coral sand are carried out to further explore the liquefaction characteristics of coral sand.
Abstract: The liquefaction of saturated marine coral sand is of a great issue for the safety of ocean engineering. A series of undrained cyclic torsional shear tests on saturated coral sand are carried out to further explore the liquefaction characteristics of coral sand. Based on the energy method, the effects of relative density (Dr), effective mean principal stress (p′0), and cyclic stress ratio (CSR) on undrained responses of saturated coral sand are investigated. Two failure criteria are discussed to evaluate the dissipated energy required to cause initial liquefaction (Wl). The test results show that the Wl is significantly affected by Dr and p′0. The generation patterns of excess pore water pressure (EPWP) and single amplitude torsional strain amplitude (γSA) along with cumulative dissipated energy (Wc) are described, and the unified generation model of both ue and γSA along with Wc are established. The liquefaction resistance curves for various Dr and p′0 are strongly related to Wl. Analyzing the cumulative dissipated energy required to trigger liquefaction, a modified stress level index termed CSRe is proposed to normalize the liquefaction resistance curves of saturated coral sand under different Dr and p′0. The test data in literature also verify the applicability of CSRe.
1 citations
TL;DR: In this paper , the authors investigated the geomechanical performances of geocell-reinforced soil (GRS) backfilled with magnesia-based cement-stabilized marine fill using the nonlinear stress-strain relationship and 3D FEM models as an alternative to the traditional earth GRS walls.
Abstract: Cement-stabilized soil retaining wall structures are becoming increasingly popular for high-speed railway lines. However, the widely used Portland cement is heavily associated with carbon dioxide (CO2) emissions. Additionally, the rising cost and scarcity of sand traditionally used as fill material is becoming a concern. Besides, the geomechanical performances of the cement-stabilized soil retaining walls using three-dimensional (3-D) finite element method (FEM) numerical analysis have seldom been investigated. To address these issues, this study investigates the geomechanical performances of geocell-reinforced soil (GRS) backfilled with magnesia-based cement-stabilized marine fill using the nonlinear stress-strain relationship and 3-D FEM models as an alternative to the traditional earth GRS walls. The study finds satisfactory results regarding stability, deformation, and settlement. Only nominal facing reinforcements may be required as the magnesia cement mechanically stabilizes the fill. Moreover, the strength and stiffness properties improve with increased curing duration. The safety factors and observed displacements were within acceptable limits. However, the critical region for the cement-stabilized marine fill GRS wall showing a rupture zone was identified at the toe of the structure. Finally, the study developed a load-displacement model for settlement predictions and uncertainty interpretations, and explained the strength development and deformation mechanisms. The results suggest that cement-stabilized soil retaining walls using magnesia-based cement could be a viable alternative to traditional earth GRS walls, while mitigating environmental concerns and reducing costs.
1 citations
TL;DR: In this paper , the microstructural probability entropy and corresponding quantification criterion were introduced to examine the effects of grain size distribution, grain orientation on monotonic, and post-cyclic moment capacities of suction caissons.
Abstract: Suction caissons are being widely employed as a reliable and economic foundation to offshore wind farm. Previous studies are inconclusive in soil microstructural evolution around soil–structure. This article describes a half-caisson subjected lateral cyclic loading with the macro photography device (MPD). The microstructural probability entropy and corresponding quantification criterion are introduced to examine the effects of grain size distribution, grain orientation on monotonic, and post-cyclic moment capacities of suction caissons. The image-based results provide evidence of significant particle rearrangement occurred adjacent to the caisson wall. The variations of the grain size entropy and the orientation entropy with cycles were obviously affected by loading amplitudes, sand gradations, and position of the caisson interface, but less dependent with the loading frequency. Experimental results reveal the dominance of the grain size entropy over the moment capacity of suction caissons under different loading characteristics and sand samples. The half-model tests together with the MPD shed light on soil–structure behaviors with the microstructural evolution at the suction caisson interface.
1 citations
TL;DR: In this paper , the authors present an approach to increase image size by increasing image size and decreasing image size, without generating new experimental data, and no potential conflict of interest to disclose.
Abstract: Click to increase image sizeClick to decrease image size Disclosure statementNo potential conflict of interest to disclose.Data availability statementThis study has not generated new experimental data.
TL;DR: In this paper , the effect of single and dual voids on the lateral bearing capacity of nearshore large-diameter monopiles in marine clay by the finite element limit analysis (FELA) method is numerically examined.
Abstract: This study numerically examines the effect of single and dual voids on the lateral bearing capacity of nearshore large-diameter monopiles in marine clay by the finite element limit analysis (FELA) method. The ability of the numerical model to accurately predict the pile-void system behavior is evaluated by performing degenerated verification analyses on existing studies. Based on numerous numerical results, several design charts for capacity reduction coefficients are produced to provide a quick and straightforward assessment of the pile capacity with single and dual voids by multiplying that without voids by coefficients. Particularly, the coupling coefficient is further proposed to quantify the coupling effect between dual voids, and the corresponding design charts are also given. The subsequent parametric studies indicate that the void effect gets aggravated as the void is enlarged and close to piles but would be weakened as the soil around the pile gets strengthened; the void effect is positively and negatively associated with the void depth in the cases of low and great shear strength, respectively. The effect of single and dual voids (inc. coupling effect between dual voids) on the pile capacity and failure mode is further graphically explained by the plastic multiplier contour maps.
TL;DR: In this article , the effects of particle size distribution, initial relative density and impact load on the permeability of calcareous sand were investigated with a seepage test device equipped with an impact loading system.
Abstract: Due to the characteristics of geographical environment and many complicated factors, the seepage properties of calcareous sand are quite different from those of common continental and marine sediments. To investigate the change of permeability coefficient of calcareous sand under external load, a seepage test device equipped with an impact loading system was developed. The effects of particle size distribution, initial relative density and impact load on the permeability of calcareous sand were investigated with this device. The results showed that the larger the curvature coefficient and uniformity coefficient, the smaller the initial relative density lead to the greater the permeability coefficient of calcareous sand and the more obvious the change of permeability coefficient before and after loading. The permeability change of calcareous sand under impact load was greater than that of quartz sand.
TL;DR: In this article , the bearing capacity of expandable anchors with different shapes and plate numbers was evaluated using the coupled Eulerian-Lagrangian, discrete element, and finite element methods.
Abstract: Advancements in industry and increased energy demands have led to the construction of onshore and offshore platforms. The stability of these platforms is a major challenge for geotechnical engineers. Expandable anchors have recently been proposed to address this issue. Researchers have investigated the bearing capacity of anchors with different shapes and plate numbers using experimental and numerical methods. The use of a suitable method for numerical modeling of expandable anchors is necessary to determine their performance. The current study evaluated the bearing capacity of multi-plate anchors using the coupled Eulerian-Lagrangian, discrete element, and finite element methods and compares their results. The effect of an increase in the number of plates (to three), the distance between plates, the plate shape (square or circular), and the soil density (80% or 60%) on the bearing capacity of the anchors was determined. The results showed that the Eulerian model was in very good agreement with the experimental results and that the square anchor exhibited a higher bearing capacity than the circular anchor. An equation is proposed for the calculation of the bearing capacity of expandable anchors.
TL;DR: In this article , a group of in-situ Cone Penetration Tests (CPT) was conducted to evaluate the seabed soil properties and liquefaction potential of the Yellow River Subaquatic Delta.
Abstract: This paper aims to provide a design basis for engineering disaster prevention and mitigation by accurately describing the spatial distribution of soil liquefaction. A group of in-situ Cone Penetration Tests (CPT) was conducted to evaluate the seabed soil properties and liquefaction potential of the Yellow River Subaquatic Delta. The factor of safety against liquefaction (FSL) and liquefaction potential index (LPI) were utilized to investigate the liquefaction characteristics of seabed soils. The findings are as follows: (1) The delta is "near coarse and far fine," with sand and silt dominating the onshore direction and silt and silty clay dominating the offshore direction; (2) Silt, as a structured soil, has a maximum sensitivity of 10, and there are local liquefaction phenomena. The size of a Soil behavior type index can be used as the limit value of liquefaction discrimination in the region; (3) The FSL of the shallow layer is smaller, while that of the deep layer is generally larger. The FSL near the coast is smaller than that far from the coast, but its variation range is large, indicating that the shallow soil layer near the coast is more prone to liquefaction; (4) The LPI of the delta is less than 5, which is significantly affected by the wave cycle loads and geographical environment. Liquefaction can occur, but the probability of large-scale liquefaction is low.
TL;DR: In this paper , an anti-washout grout using marine soft clay to stabilize the wind power pile foundations was proposed. But the results showed that high cement content, HPMC, and sodium silicate decreased the workability of grout while enhancing the washout resistance.
Abstract: This study aims to prepare an anti-washout grout using marine soft clay to stabilize the wind power pile foundations. The cement, hydroxypropyl-methyl cellulose ether (HPMC), and sodium silicate were chosen as the main materials to modify the marine soft clay, and the fluidity, bleeding rate, setting time, rheology, anti-washout characteristics, and compressive strength were investigated. The results showed that high cement content, HPMC, and sodium silicate decreased the workability of grout while enhancing the washout resistance. The addition of HPMC and sodium silicate would increase the yield stress and plastic viscosity of the grout. The sodium silicate content was the key factor influencing the early strength, while the cement content and HPMC affect the later strength. The microstructures including the morphology of C-S-H gels and the content of ettringite and calcium hydroxide significantly changed with the addition of sodium silicate, and Friedel’s salt was observed through the microstructure analysis. This study can provide effective guidance for the utilization of marine soft clay, the preparation of anti-washout grout, and the control of pile foundation stability.
TL;DR: In this paper , the authors investigated the degree and efficiency of sand resource extraction based on a hydro-cyclone separation principle via a series of experiments and found that appropriately increasing the water content will have a positive effect on the separation degree, which can achieve a maximum value of 73.26%.
Abstract: For engineering waste soils with a large proportion of sand resources, an effective technique for sand extraction from waste soils still needs to be developed. This study investigates the degree and efficiency of sand resource extraction based on a hydro-cyclone separation principle via a series of experiments. The soil samples in the experiments contained a sand content ranging from 12.56% to 52.75% and a water content ranging from 155.96% to 597.04%. The results show that the water contents of test samples should reach a certain threshold to perform hydro-cyclone separation, and appropriately increasing the water content will have a positive effect on the separation degree, which can achieve a maximum value of 73.26%. However, the separation degree reaches an upper limit value when the water content is greater than approximately 400%, which is revealed by the characteristics of soil viscosity varying with water content, and high-water content for the separation efficiency is not beneficial. To balance the separation degree and efficiency, optimum sample water contents for sand extraction and an evaluation approach for different sand content samples are proposed. Through application of the proposed approach, an average sand extraction efficiency of 135.88 g/s can be achieved.
TL;DR: In this article , a particle swarm optimization (PSO) algorithm is used to optimize the drainage system of subsea tunnels, in which hydraulic boundary conditions, including size of the tunnel, number of sump pits and pumps, and pump operation plans, are allocated section-by-section and simulated to achieve economic optimization.
Abstract: In recent years, subsea tunnels have been constructed at greater depths, higher groundwater tables, and longer drives than those built previously. Controlling the water pressure and inflow rate of groundwater, i.e., the design of the drainage system, is a major challenge in subsea tunnels in terms of achieving hydraulic stability and ensuring economical operations. This has significant cost implications during construction and operation for long and deep subsea tunnels. In this study, the drainage system of subsea tunnels is optimized using the particle swarm optimization (PSO) algorithm, in which hydraulic boundary conditions, including size of the tunnel, number of sump pits and pumps, and pump operation plans, are allocated section-by-section and simulated to achieve economic optimization. Additionally, parametric studies are conducted to evaluate the influencing factors, including the drainage condition, hydrostatic pressure, radius of the tunnel, and initial stress. It is shown that optimal drainage is established under full drainage, nondrainage, and sometimes partial drainage systems depending on the hydraulic conditions. A tentative application of the proposed simulation method to a specific subsea tunnel illustrated that the construction cost can be significantly reduced through the optimization of the tunnel drainage system.
TL;DR: In this paper , a new settlement prediction model, which can synthetically reflect the effects of vacuum pressure, alternating criterion, and improvement time, was proposed to predict the ultimate settlement of high water content dredger fill improved by vacuum preloading method.
Abstract: To investigate the settlement behaviour under alternate vacuum preloading, a series of laboratory tests considering different influencing factors, such as vacuum pressure and alternating criterion, were conducted. Based on experimental data, a new settlement prediction model, which can synthetically reflect the effects of vacuum pressure, alternating criterion, and improvement time, was proposed. The prediction model took into account the influence of improvement depth and variations in vacuum pressure. The model was validated using several case studies and laboratory tests. Comparisons between the proposed model and layer-wise summation method results indicate that the calculated results of the proposed model are closer to the actual settlement with errors consistently less than 10%. The proposed model can conveniently and accurately predict the ultimate settlement of high water content dredger fill improved by vacuum preloading method.
TL;DR: In this article , the influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated.
Abstract: The present study provides insight into the cyclic behavior of unreinforced and geogrid-reinforced coral sand. To achieve these goals, stress-controlled undrained cyclic triaxial tests were conducted on medium-dense coral sand with and without geogrid reinforcements. The influence of geogrid reinforcement, cyclic stress ratios, and confining pressure on the deformation, pore pressure, liquefaction resistance, stiffness degradation, and particle breakage characteristics of saturated coral sand was investigated. The results indicated that coral sand reinforced with geogrid increased the liquefaction resistance and decreased the rate of pore pressure accumulation. The effectiveness of the geogrid inclusion on coral sand’s liquefaction resistance was found to be more pronounced under large effective confining pressure and a smaller cyclic stress ratio. Increasing the effective confining pressure increases the liquefaction resistance for both unreinforced and geogrid-reinforced coral sand, whereas increasing the cyclic stress ratios decreases the liquefaction resistance of the unreinforced and reinforced coral sand. The particle breakage was observed to be increased with increasing the effective confining pressure and cyclic stress ratio, and the breakage was more in the reinforced coral sand than the unreinforced coral sand.
TL;DR: In this paper , 1 g model tests are used to investigate the behavior of the monopile-friction wheel hybrid foundation under independent horizontal load (H) or torsional load (T), and combined loads (H-T) in sand soil.
Abstract: The monopile-friction wheel hybrid foundation withstands various loads in the marine environment, such as the vertical load (V) transmitted from the superstructure, horizontal loads (H) caused by wind or wave, torsional loads (T) caused by rotating structures. In this article, 1 g model tests are used to investigate the behavior of the monopile-friction wheel hybrid foundation under independent horizontal load (H) or torsional load (T), and combined loads (H-T) in sand soil, respectively. The failure envelopes of H-T loading plane are obtained from the measured load–displacement data with the simplified calculation equations presented as well. Finally, we also discuss quantitatively the influences of the pre-vertical loads, foundation geometry and loading eccentricity on the bearing capacity of the hybrid foundation via the three-dimensional finite element method. The results indicate that the displacement response of the hybrid foundation under independent loading is significantly different from that subjected to combined loads (H-T). The torsional bearing capacity of the hybrid foundation can be significantly improved by 6.6–33.34% under pre-horizontal load. The horizontal bearing capacity of the hybrid foundation decreases sharply after the pre-torsional load reaches a certain value, which decreases by about 20%. The presence of a friction wheel improves the torsional/bending moment distribution of pile shaft.
TL;DR: In this paper , an innovative winged caisson foundation for offshore wind turbine (OWT) is proposed, which adapts the conventional caisson to produce higher overturning capacities.
Abstract: The foundation of an offshore wind turbine (OWT) accounts for up to 20% of the total cost; therefore, investigations into reliable and efficient foundations are important for the offshore wind energy industry. This article describes an innovative winged caisson foundation for OWTs, which adapts the conventional caisson foundation to produce higher overturning capacities. The behaviour of this proposed novel foundation in the sand was investigated through experimental and numerical modelling using a series of 1g tests (1/70th scale), centrifuge model tests (70g), and finite element (FE) simulations. Models with various wing sizes installed in different sand densities were tested in the laboratory by applying an overturning load. In this article, the moment–rotation performance of the foundation under monotonic loading is compared against that of conventional caissons to assess the potential benefits of adding wings to caisson foundations. Results show that there is a significant increase in overturning capacity provided by the novel foundation. FE models were first validated against experimental results, then, used to conduct a parametric study to better understand the behaviour of the winged caissons beyond the scaled model tests. In addition, the FE models were used to evaluate the drained response of the proposed foundation under combined loading.
TL;DR: In this article , the effect of the eccentric uplift of a mat foundation was experimentally and numerically investigated and the effects of eccentric distance, eccentric position, and foundation shape on the suction force of the mat foundation were discussed.
Abstract: The mat foundation is a new type of jack-up wind power installation platform suitable for clay seabed. Because of the large size of the mat foundation, a large suction force must be overcome during the uplift process. In this study, the eccentric uplift of a mat foundation was experimentally and numerically investigated. The effects of the eccentric distance, eccentric position, and foundation shape on the suction force of the mat foundation were discussed. The results revealed that the breakout force of the mat foundation mainly comprised the foundation weight and suction force. Both the uplift position and eccentric distance affected the suction force; however, the effect of the uplift position was considerably smaller than that of the eccentric distance. The dimensionless suction force for the eccentric uplift tended to decrease linearly as the eccentric distance increased. When the dimensionless eccentric distance was 0.5, the suction force was 0.35–0.5 times that in the case of central uplift.
TL;DR: In this paper , a probabilistic stability analysis for reinforced slope considering the spatial variability of soil strength is developed to guarantee the stability of the cofferdam slope during and after construction.
Abstract: How to guarantee the stability of the cofferdam slope during and after construction is a difficult problem. In this article, a practical procedure is developed to implement probabilistic stability analysis for reinforced slope considering the spatial variability of soil strength. In the proposed procedure, the improved random limit equilibrium method is adopted to calculate the safety factor and particle swarm optimization is adopted to search critical sliding surface of slope. The influence of different reinforcement positions, lengths, and number of layers on the reliability of reinforced slope and critical sliding surface is studied. The results show the variability of soil, the length, location, and the number of layers of geosynthetics are important factors affecting probability of failure (Pf) of reinforced slope. The location and the number of layers of geosynthetic reinforcement play an important role in the statistical characteristics of FOS and slip mass volume. The reinforcement length has a greater impact on the safety factor.
TL;DR: In this article , the rheological characteristics of diatomite with different diatom and water contents were assessed and compared using the Herschel-Bulkley model and Cheng's model.
Abstract: Diatomites, or natural soils containing diatoms are found in the marine environment all over the world. Diatomites tend to have skeleton microstructures, resulting in unique rheological behaviors. In marine areas, the rheological behavior of diatomite significantly contributes to geohazards, especially submarine landslides. Predicting and preventing submarine landslides require a profound understanding of the rheological characteristics of diatomites. Therefore, to assess the rheological characteristics of diatomite with different diatom and water contents, we prepared different diatom–kaolin mixtures (diatom contents ranging from 0 to 100 % and water contents from 66.8 % to 640 %) and subjected them to rheological shearing tests. The Herschel–Bulkley model and the Cheng's model were used to analyze the critical rheological parameters (i.e., dynamic and static yield stresses) and the flow behaviors of the samples. The results show that kaolin mixed with 20 % diatoms exhibits the highest value in yield stress. Also, the addition of diatoms alters the microstructure of kaolin which may lead to static yield at low water content and shear thickening at high water content. This study offers valuable references regarding critical rheological parameters and flow regimes for simulating submarine landslides in regions covered by natural sediments containing diatoms.
TL;DR: In this article , the physical properties of polymetallic nodules were analyzed and modeled to evaluate the harvesting performance of a nodule-lifting apparatus in a seabed mining electric vehicle.
Abstract: Seabed mining is a potential solution for diversifying the supply chains of various raw materials required for zero-emission industrial products. The design of a nodule-lifting apparatus in a seabed mining electric vehicle is a crucial step because it significantly affects the mining efficiency of the entire system. Although the physical properties of polymetallic nodules are vital external parameters, little attention has been paid to their effect on the design of nodule-lifting apparatuses. This study aims to analyze and model the physical properties of the polymetallic nodules, expand the conventional numerical model to deal with more diverse physical properties of the nodules, apply probabilistic analysis to evaluate the harvesting rate, and establish a design methodology to efficiently determine the best feasible design. The advantages of the proposed framework are that it enables: (1) quantification of the physical properties of the seabed polymetallic nodules, (2) consideration of these physical properties in the computational simulation of the nodule-lifting apparatus, (3) efficient evaluation of the harvesting performance of the nodule-lifting apparatus through an information criterion-based probabilistic analysis, and (4) effective design of the nodule-lifting apparatus with an orthogonal array and rule-based decision-making strategy.
TL;DR: Saeed et al. as mentioned in this paper detail the main theme of the published paper in the journal of Marine Georesources and Geotechnology; entitled "Liquefaction susceptibility of beach sand containing plastic fines" for enhancing the content integrity.
Abstract: This paper has been prepared to detail the main theme of the published paper in the journal of Marine Georesources and Geotechnology; entitled “Liquefaction susceptibility of beach sand containing plastic fines” for enhancing the content integrity to be considered as a discussion paper of Hamza Saeed, Zalihe Nalbantoglu & Eris Uygar (2021).
TL;DR: In this paper , the textural characteristics of foreshore sediment along the central Kerala coast were investigated using statistical parameters such as mean (M), standard deviation (SD), skewness (Sk), and kurtosis (K).
Abstract: The study investigates textural characteristics of foreshore sediment along the central Kerala coast. The selected beaches extend from Ponnani in the north to Alleppey in the south along the west coast of India. Samples were collected from foreshore zone at 22 selected locations to assess sediment grain size distribution and its seasonality. Statistical parameters such as mean (M), standard deviation (SD), skewness (Sk), and kurtosis (K) were used to evaluate the textural characteristics. The purpose of the present study was to examine the textural behaviour of coastal sediments in different seasons from November 2014 to October 2015. Textural characteristics show that the sediment samples are unimodal and bimodal with medium and fine grain sand. The standard deviation (sorting) reveals the sediment samples are very well sorted to moderately sorted with a range of 0.24 phi to 1.03 phi, while the skewness values of the sediment samples range from −0.55 phi to 0.32 phi. The CM plot depicts that the foreshore sediments are transported by tractive currents and transporting the sediments by rolling, bottom suspension with rolling. The analysis of Linear Discriminant Function (LDF) illustrates that the sediment samples are accumulated by aeolian or coastal and shallow turbulent environments.
TL;DR: In this article , the effects of anionic polyacrylamide (APAM) and inorganic flocculant ferric chloride (FeCl3) on the electrical conductivity and permeability coefficient of dredged sludge were obtained in tests.
Abstract: The application of electrokinetic geosynthetics in electroosmotic vacuum preloading treatment of dredged sludge suffers the problems of severe clogging and uneven reinforcement effects. The effects of organic flocculant anionic polyacrylamide (APAM) and inorganic flocculant ferric chloride (FeCl3) on the electrical conductivity and permeability coefficient of dredged sludge were obtained in tests, and the optimal flocculant dosage was determined accordingly. A series of electroosmotic vacuum preloading model tests were performed by adding organic and inorganic flocculants to dredged sludge. Slight variations of the discharge rate and settlement amount were noticed between the sludge samples mixed with FeCl3 and APAM at the vacuum preloading stage, but after electroosmosis initiation, the discharge rate of the sludge with APAM became higher, as well as the final settlement. The shear strength and uniformity of sludge with APAM after treatment were better than those of sludge with FeCl3. Compared to FeCl3, electroosmotic vacuum preloading with APAM help increase the effective electric potential of sludge and benefit the discharging of heavy metals.