Soft Marine Clay Research Articles

Vertical bearing capacity of HSCM pile groups in marine soft clay

Vertical bearing capacity of HSCM pile groups in marine soft clay

Salinity and oven-drying effects on the plasticity of a marine soft clay

Considering the extensive use of plasticity-based correlations in geotechnical practice to estimate soil parameters, this paper evaluates the influence of pore fluid salinity and soil drying on the plasticity of Ballina clay, an estuarine soft clay from northern New South Wales (Australia). A comprehensive experimental study, which includes controlled leaching/salinisation paths applied to natural (remoulded) as well as oven-dried clay, prior to the estimation of the Atterberg limits, is presented. Plasticity tests are complemented with chemical analysis of the pore fluid carried out to evaluate the processes involved in the leaching/salinisation mechanisms for remoulded and oven-dried clay. A strong dependency of liquid limit on pore fluid salinity and oven-drying is observed in Ballina clay. Leaching modifies the soil fabric from an initially saline–sodic flocculated towards a normal flocculated arrangement. The experimental results show that changes in soil plasticity upon leaching are largely reversible upon salinisation paths. Oven-drying promotes the stacking of clay minerals (aggregation), which in turn reduces the water absorption capacity of the clay. The consequences of neglecting both salinity and drying effects in practice when adopting well-established relationships between mechanical parameters and soil plasticity are also briefly discussed.

Experimental study on the thixotropic strength of the marine soft clay from the Yangtze River estuary

Soft clay in the offshore area of the Yangtze River estuary has been investigated considering its basic physical properties. Forty-five unconfined compressive strength tests were conducted on the remolded marine soft clay to investigate the impacts of curing time T, water content w, plasticity index IP, and clay particle content ρc on the thixotropic static shear strength ratio As of the marine soft clay from the Yangtze River estuary. Results show that the stress–strain curves were primarily strain hardening and strain softening curve types. Unconfined compressive strength qu increased with an increase in T. All specimens with different basic physical properties were capable of thixotropic strength recovery. When T = 0–28 days, As increased rapidly, while for T > 28 days, As of most specimens increased slightly or tended to stabilize. The impacts of w, IP and ρc on As do not follow a consistent pattern, but there is a strong correlation between As and w/wL (wL is the liquid-limit water content). For w/wL < 0.75, As increased with increasing w/wL, whereas for w/wL ≥0.75, As decreased with increasing w/wL. We proposed a simple and widely applicable power function prediction model for the As of the soft clay from the Yangtze River estuary.

Experimental study on the stabilization of marine soft clay as subgrade filler using binary blending of calcium carbide residue and fly ash

This study endeavors to realize the concurrent utilization of marine soft clay (MSC) and industrial waste, specifically calcium carbide residue (CCR) and fly ash (FA), through a series of experimental investigations. The optimal ratio between CCR and FA, as well as the efficacy of the composite agent (CF–1), were examined, and an empirical equation associating the unconfined compressive strength (qu) of stabilized MSC was developed through unconfined compressive strength (UCS) tests. Microscopic analyses, including X–ray diffraction (XRD), scanning electron microscopy (SEM), and energy–dispersive spectroscopy (EDS), were employed to unveil the intrinsic mechanisms underlying CF–1 stabilized MSC. Subsequently, the suitability of CF–1 solidified MSC as a roadbed filler was ascertained through laboratory tests. Results revealed the optimum CCR:FA ratio for CF–1 to be 4:1, demonstrating superior curing effects compared to individual components such as Portland cement (PC), CCR, and FA, with commendable environmental and economic benefits. The developed empirical equation exhibited effectiveness in predicting the qu of CF–1 solidified MSC under varying curing dates (T) and dosages (Wg) conditions. Characterization through XRD, SEM, and EDS identified the primary products formed within the stabilized MSC matrix with CF–1 as comprising calcium–silicate–hydrate (C–S–H) gel, calcium–aluminate–hydrate (C–A–H) gel, and a minor amount of calcite. As T and Wg increased, the reduction in pores between soil particles enhanced the structural integrity and macro–strength of the cured MSC. The failure pattern of CF–1–solidified MSC elementary samples depended on the CF–1 dosage and curing duration. The solidification mechanism of CF–1 on MSC involved pozzolanic, ion exchange, and carbonation reactions. CF–1 solidified MSC satisfied all the specified requirements for roadbed filler in the relevant code, demonstrating substantial potential for in–situ solidification projects involving MSC.

Effects of jet grouting on adjacent ground through numerical modelling

When using jet grouting for soil stabilisation, effects of the installation process need to be evaluated. This could be particularly important for applications in challenging ground conditions and low initial ground stability. This study investigates such effects in soft marine clays using numerical finite-element (FE) simulations for both flat and sloping terrains. Additionally, an analytical solution using the modified Hagen–Poiseuille equation was developed to (a) assess the pressure induced by the grout at any installed depth and (b) illustrate the importance of maintaining a proper amount of return flow to avoid build-up of excessive pressures in the ground during the jet-grouting process. Combining the analytical and the FE simulations, jet-grouting induced soil displacements, were determined. For flat terrain, the area affected by jet grouting was approximately three to four times the column radius. By contrast, for the studied slope (inclination of 1 : 3), the influenced area increased to about ten times the column radius. The obtained displacement magnitude was also considerably larger for sloping terrain than for flat terrain. The reported findings relate to jet grouting in marine clays (which is not the normal application of this technology) and cannot be extrapolated to other soils.

Undrained behavior of marine clay under one-way cyclic loading with variable confining pressure

Settlement of roads or railway caused by traffic loading has a serious effect on the safety and service performance of transport infrastructures constructed on soft marine clay. While simple cyclic triaxial test with constant confining pressure (CCP) were used in most of the previous studies, a series of cyclic triaxial tests with variable confining pressure (VCP) were carried out on normally consolidated (NC) and overconsolidated (OC) reconstituted Wenzhou soft clay in this paper to study the undrained behavior of soft marine clay due to surcharge preloading as well as cyclic traffic loading. VCP test is able to approximate the complicated stress path than CCP test caused by traffic loading. The test results indicate that NC specimens show significantly different pore water pressure (u) evolution compared with OC specimens. However, a change in the overconsolidation ratio (OCR) of OC specimens does not have a significant influence on variation of u with identical cyclic stress ratio (CSR) and total stress path (η). The slope of the effective stress path is dependent on the total stress path under which the specimen was loaded cyclically, regardless of the OCR and whether variable confining pressure was applied. The slope of the effective stress path is broadly in line with the slope of corresponding total stress path. In addition, the development of permanent axial strain (εpa) due to one-way cyclic loading was shown to depend significantly on the values of η and OCR. Both the variable confining pressure and OCR limited the strain accumulation of saturated marine clay under undrained one-way cyclic loading. Finally, the effects of η and OCR on the magnitude of εpa after 1000 loading cycles are quantified and incorporated in a power law function for the permanent deformation prediction of soft marine clay due to traffic loading.

Optimization of Geothermal Heat Pump Systems for Sustainable Urban Development in Southeast Asia

This study examines the optimization of ground source heat pump (GSHP) systems and energy piles for sustainable urban development, focusing on Southeast Asia. GSHPs, which utilize geothermal energy for indoor HVAC needs, offer a sustainable alternative to traditional systems by utilizing consistent subsurface temperatures for heating and cooling. The study highlights the importance of understanding thermal movement within the soil, especially in soft marine clays prevalent in Southeast Asia, to improve GSHP system efficiency. Using a one-dimensional finite difference model, the study examines the effects of soil thermal conductivity and density on system performance. The results show that GSHP systems, especially when integrated with energy piles, significantly reduce electricity consumption and greenhouse gas emissions, underscoring their potential to mitigate the urban heat island effect in densely populated areas. Despite challenges posed by the region’s hot and humid climate, which could affect long-term effectiveness, the study highlights the need for further study, including field experiments and advanced modeling techniques, to optimize GSHP configurations and fully exploit geothermal energy in urban environments. The study’s insights into soil thermal dynamics and system design optimization contribute to advancing sustainable urban infrastructure development.

Effects of Salt Content and Freeze-Thaw Conditions on Dynamic characteristics and its microscopic mechanism of Chloride Silty Clay

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Experiment and analysis on dynamic characteristics of marine soft clay

A series of cyclic triaxial tests were conducted on marine soft clay deposits to establish and validate a predictive model for cumulative plastic strain. Additionally, a numerical model of particle flow code in cyclic triaxial tests was developed. The effects of confining pressure, moisture content, and dynamic stress ratio on the dynamic properties of marine soft clay were examined, considering factors such as volume deformation and microscopic failure patterns. The results indicated that both the predictive model and numerical model showed strong consistency with the experimental data. The plastic strain of marine soft clay was influenced by moisture content, stress ratio, and confining pressure in a consistent manner, with moisture content being the primary factor. A predictive model for the cumulative plastic strain of marine soft clay was successfully established, allowing for the evaluation of dynamic properties from the perspective of cumulative plastic strain. During the loading process in the numerical model, microcracks within the soil structure gradually compacted, and the main displacement of the specimen extended from the vertical center axis to the sides, ultimately resulting in shear damage.

Performance of incineration bottom ash amended marine soft clay stabilized by cement in seawater

Incineration serves as an effective waste management method driven by its ability to reduce mass and volume of municipal solid waste. However, this process generates incineration bottom ash (IBA), which is commonly disposed of in landfills in many countries, especially when dealing with fine IBA. To address this issue, recycling fine IBA for soft marine clay (MC) stabilization is a sustainable option compared to landfilling. Previous studies revealed that aggregate-like and weak hydration properties of fine IBA may increase the strength and decrease compressibility of MC. Nevertheless, when using IBA-MC in land reclamation or coastal protection, the performance may deteriorate, particularly in the presence of seawater. Therefore, this study employed chemical stabilization method combined with ordinary Portland cement (OPC), to solidify/stabilize IBA-MC (OPC-IBA-MC). The aim was to improve the performance of IBA-MC in seawater. The appearance, water content, strength, mineralogy, and microstructure of IBA-MC and OPC-IBA-MC soaked in seawater were investigated. The results showed that the strength of OPC-IBA-MC (4075 kPa) cured in air for three months was significantly higher than that of IBA-MC (983 kPa). Nevertheless, after soaking in seawater, OPC-IBA-MC was dismantled, rendering its strength untestable. The mineralogy and microstructure of OPC-IBA-MC revealed that the formation and growth of ettringite caused instability in OPC-IBA-MC in seawater.

Effect of salinity on geotechnical properties of soft marine clay

ABSTRACT Marine clays are soft clays with low shear strength and high compressibility. These soils are prone to seawater intrusion, due to which their engineering properties may be altered. Therefore, the effect of salinity on engineering properties of marine clay has to be investigated prior to any engineering activity in those areas. In this paper, an attempt has been made to study the effect of salinity on various geotechnical properties of Cochin marine clay. As sodium chloride is the most abundant mineral salt in seawater, the effect of 0%, 0.5%, 1%, 2%, 3% and 4% sodium chloride on marine clay for different curing periods were studied. The results of the study show that liquid limit decreases whereas the strength and compressibility characteristics improve as the concentration of salinity increases. Leaching, however, reverses these improvements, amplifying compressibility by 30% and decreasing pre-consolidation pressure by almost 50%. ITherefore, prior to design of any foundation structures on coastal areas prone to salt water intrusion, the behaviour of clay with variation in salinity should be investigated.

An elastoplastic model with egg-shaped yield surface for coastal soft clay

A novel elastoplastic constitutive model with an egg-shaped yield surface (ESE model) is proposed herein to elucidate the strength-deformation characteristics of marine soft clay. One of the key improvements offered by this model is its ability to address the singularity associated with plastic strain increments at yield surface corners—a limitation commonly encountered in traditional elastoplastic models. Additionally, the proposed model demonstrates flexibility, as it can transform into various forms under different conditions. Subsequently, to evaluate the efficacy of this egg-shaped elastoplastic model, numerical simulations are performed within the finite element software ABAQUS using an implicit integration algorithm through the user material subroutine interface (UMAT). The simulations encompass standard triaxial consolidation tests involving saturated soft clay sourced from the Itsukaichi marine clay as well as two types of saturated kaolin clays. The outcomes derived from these simulations by the ESE model are compared with both empirical data and numerical simulations originating from the widely employed Modified Cam-Clay (MCC) model. The simulations of the ESE model for three conventional triaxial tests on clay demonstrate superior concordance with experimental measurements in comparison to the MCC model. This underscores the efficacy of the proposed ESE model in predicting the strength and deformation characteristics manifested by coastal soft clays under undrained conditions. Finally, the predictions for deformation in an adjacent tunnel according to the ESE model closely align with experimental measurements and prior to the simulations conducted using the MCC model and advanced models such as the bounding surface model and the unified model, thereby affirming its practical utility in engineering applications.

Application of ANN in Construction: Comprehensive Study on Identifying Optimal Modifier and Dosage for Stabilizing Marine Clay of Qingdao Coastal Region of China

Nowadays, the use of new compound chemical stabilizers to treat marine clay has gained significant attention. However, the complex non-linear relationship between the influencing factors and the unconfined compressive strength of chemically treated marine clay is not clear. In order to study the influence of various factors (dosage, type of stabilizer, curing age) on the unconfined compressive strength of solidified soil during chemical treatment, experiments were performed to determine the unconfined compressive strength of soft marine clay modified with various types of stabilizers. Further, an artificial neural network (ANN) model was used to establish a prediction model based on the unconfined compressive strength test data and to verify the performance. Sensitivity and optimization analyses were further conducted to explore the relative significance of parameters as well as the optimal dosage amount. Research has found that when the content of aluminate cement is 89.5% and the content of curing agent is 30%, the unconfined compressive strength significantly increases after 28 days of solidification, and the change in quicklime content has the greatest effect on the improvement in the unconfined compressive strength. The influence of modifiers on the unconfined compressive strength is in the order: potassium hydroxide > kingsilica > quick lime > bassanite. The values of each factor were obtained when the unconfined compressive strength was the maximum, which provided support for the optimization of the treatment scheme. The analysis of chemical treatment is no longer limited to the linear relationship according to the test results, which proves the feasibility of non-linear relationship analysis based on the artificial neural network.

Influence of Cross-Correlation on the Modelled Uncertainty in Stress–Strain Behavior of Soft Clays

Reliability-based design is increasingly being applied to geotechnical problems because it allows the robust consideration of various sources of uncertainty, such as the inherent variability of soil properties. Some soil properties, however, are mutually dependent, and ignoring this cross-correlation may lead to biased estimates of the probability of unsatisfactory performance. Hence, in this study, the Gaussian copula was used to evaluate how the applied cross-correlation or independence between the compressibility properties affects the uncertainty in the stress–strain response of two marine soft clays. Two settlement calculation methods were considered: the compression index and Janbu tangential stiffness methods. The correlation coefficients were defined from the site-specific oedometer data at two extensively studied clay sites, and from a database. The simulated oedometer curves were compared to the observed variability in the site-specific data. The settlements in the clay sublayers were then computed, and different cases were compared by means of boxplots. It is concluded that the Janbu method leads to a significant overestimation of uncertainty in settlement if the cross-correlation between the compressibility parameters is ignored. On contrary, the compression index method seems less sensitive to the assumed correlation structure, and as such, the parameters can be treated as independent in most cases.

Mechanical Characteristics and Damage Constitutive Model of Fiber-Reinforced Cement-Stabilized Soft Clay

Marine soft clays are prevalent in coastal regions of China, giving rise to engineering challenges such as salt swelling, corrosion, and load bearing in foundations with soft soil. This study is dedicated to enhancing the mechanical properties of fiber-reinforced cement-stabilized soft clay (FCSSC) and revealing its strengthening mechanism. Uniaxial compression tests are performed to explore the impact of fiber length, fiber amount, and curing ages on mechanical behavior. The stabilization mechanisms of cement and glass fibers are explored through damage analyses and microscopy. Based on the experimental results, a damage constitutive model is formulated for FCSSC, and its validity is established by comparing fitting curves with testing curves. The results demonstrate a significant improvement in the mechanical properties of the stabilized soil, attributed to the synergistic effects of the cement and glass fibers. The growth rate of the unconfined compressive strength decreased with increasing curing ages. Notably, the fiber length significantly impacted the strength index, with short-chopped fibers playing a crucial role in strength enhancement. The compressive strength exhibited an initial increase followed by a decrease with rising fiber content, reaching a maximum between 0.3% and 0.4%. The bridging effect of the glass fibers proved effective in inhibiting compression crack expansion and mitigating structural damage of the soil sample. However, excessive fiber content or length led to improved local porosity, resulting in the deterioration of strength and deformation properties. The stress–strain curves fitted using the proposed damage constitutive model accurately reflected the stress–strain relationship and deformation characteristics of the FCSSC.

Experimental investigation on strength characteristics of marine soft clay under monotonic and cyclic loading

Sea areas with an average water depth of 5-15 m in the East China Sea are mostly muddy soft-foundation seabed. The wind power infrastructure built on them must fully consider the mechanical properties of marine soft clay during design process. In this study, monotonic and cyclic tests were conducted to study the strength characteristics of soft clay at various strain rates, cyclic stresses and initial effective vertical stresses using a simple shear apparatus. The test results showed that, as the strain rate increased, the peak shear stress of the samples under different confining pressures increased. However, the failure lines of the effective stress path of samples under different strain rates and vertical stresses are uniform. Compared to the traditional cyclic failure criteria, the failure criterion based on the inflection point of double amplitude strain can reflect the deformation characteristics of the specimen more accurately. The peak shear strength obtained from the monotonic tests was used to normalize the cyclic stress. Subsequently, the relationship between the number of failure cycles and normalized cyclic stress level of the soft clay specimens was established.

Medusa SDMT testing at the Onsøy Geo-Test Site, Norway

The Medusa SDMT is the last-generation, fully automated version of the seismic dilatometer (SDMT). An extensive in situ testing campaign with the Medusa SDMT was carried out in June 2022 in different soil types at four well-known benchmark test sites in Norway, part of the Geo-Test Sites (NGTS) research infrastructure managed by the Norwegian Geotechnical Institute. The experimental campaign was conducted as part of the Transnational Access project – JELLYFISh funded by H2020-GEOLAB. This paper presents a preliminary assessment of significant results obtained by Medusa SDMT at the Onsoy test site, a soft marine clay. The data is compared to available in situ and laboratory data previously published at the Onsøy test site. The results show that the Medusa SDMT data are consistent with traditional (pneumatic) SDMT results. Furthermore, the parameters obtained from the interpretation of Medusa SDMT data, in particular the overconsolidation ratio OCR, the coefficient of earth pressure at rest K0, and the undrained shear strength su agree generally well with the corresponding parameters obtained in past investigations from other in situ and laboratory tests.

Load Test on Combined Pile and Cap / Pad Foundation System on Compressible Calcareous Sand and Comparison with FEM Modelling

An optimum type of foundation is expected to support 2 – 3 stories residential house on reclamation area to avoid deep foundation. The foundation will sit on engineering fill that constructed with calcareous sand which is classified as compressible sand. Below that part, at the original ground medium density sand and very soft marine clay is found stratified. Typical column in the residential building will have about 100 tons load intensity and based on this project, the design load for a single pile is 32 ton. Since no additional compression on soft clay layer is expected after building construction, than combine cap/pad foundation with short pile 6.5 m length is proposed. Load test with stress cell for this combine pile and cap/pad foundation was performed. The load test result show that interpretation using Chin’s and Mazurkiewicz’s Method obtained that the combined pile and cap/pad foundation’s ultimate bearing capacity of 112 – 119 tons. Analysis using stress cell data shows that the cap/pad carry about 31.8 % of the total load. Finite element analysis with axisymmetric condition conducted to study load distribution on combine pile and cap/pad foundation system. Analysis result was show that the cap or pad can carried about 38.1% of design load during testing. The 6.3% deviation between the stress cell and FEM results could be attribute by the assumption when calculating the load acting on cap/pad foundation. The stress cell analysis used the assumption that the load carried by the cap/pad foundation was uniform while the FEM results showed a non-uniform load.

Numerical Study on the Responses of Suction Pile Foundations under Horizontal Cyclic Loading Considering the Soil Stiffness Degradation

This paper analyzes the deformation responses of single-cylinder and four-cylinder suction pile foundations in soft clay under horizontal cyclic loading. Based on the existing stiffness degradation model of soft clay, a more suitable model for marine soft clay is proposed by carrying out dynamic triaxial experiments under different stress levels. The stiffness degradation and cumulative displacement of soil under cyclic loading are implemented in ABAQUS by compiling a USDFLD subroutine. The rationality is verified by comparison with the displacement response of the pile measured by the centrifugal model test and the scaled model test reported in the literature. With the aid of the current model, the stress state and deformation of suction pile foundations under horizontal cyclic load are further analyzed. The numerical results reveal the path of soil stiffness degradation and the deformation response of foundations during horizontal cycling. The cumulative displacement generated by the cyclic load is quantitatively displayed. It is proved that this model has the capability to reflect the cumulative displacement under cyclic loading and shows promise in analyzing the long-term deformation response of offshore foundations.

Post-cyclic undrained behavior of marine soft clay subjected to partially drained cyclic loading

Under long-term cyclic loading, marine soft clay in coastal areas is more likely to exhibit partially drained behavior than undrained behavior. The partially drained dynamic behavior of marine soft clay tends to exert a significant effect on the post-cyclic characteristics. Thus, this study conducted two series of monotonic shearing tests to investigate the mechanical behavior of marine soft clay after long-term (50,000 cycles) traffic loading in terms of variable confining pressure (VCP). The post-cyclic stress path, pore water pressure, and shear strength were discussed through comparison of the results with those of the standard monotonic shearing test (without cyclic loading history). Partially drained cyclic loading enhanced the post-cyclic shear strength and increased the brittleness of the specimen. The behavior of the pore water pressure and void ratio of post-cyclic soft clay were similar to those of clay during undrained cyclic loading to the reconsolidation process, that is, the specimen exhibited quasi-overconsolidation performance after partially drained cyclic loading. Subsequently, the relationships between the quasi-overconsolidation ratio (QOCR) and the total cyclic stress and strength ratios were developed, and the strength-dependent parameter of the latter relationship was determined through the standard undrained monotonic shearing test of overconsolidation soil.