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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. [ABSTRACT FROM AUTHOR]

In recent times, large-scale infrastructural projects are being constructed on varieties of soil, especially in highly compressible marine clays and soft soil. The coefficient of consolidation (cv) is one of the most important technical parameters used to estimate the consolidation characteristics of the soil. The experimental laboratory techniques used to obtain cv are time-consuming and possess different practical limitations. In this study, a reliable method for predicting cv is presented based on machine learning (ML). The study considered 11 inherent soil variables, among which the least significant variables are discarded using univariate feature selection technique. Different ML models were developed like the random forest, artificial neural network, and support vector machine for nonlinear mapping of the cv using dimensionally reduced independent variables. Verification against experimental data demonstrates that the Random Forest model accurately predicts the cv (with MAE = 0.0231, MSE= 0.00148, and RMSE = 0.03854). Further, a comparative study of the proposed model is presented with available empirical equations and numerically simulated data. Moreover, the strengths and shortcomings of different ML algorithms are also discussed in detail. [ABSTRACT FROM AUTHOR]

Suction bucket installation in pure clay or pure sand is well established. However, in layered soils, particularly in sand over clay soils, the soil plug uplift is considered a major installation risk and feasibility of installation is often questioned. In this paper, the experience from installation of two suction bucket jackets at two offshore wind farms in layered soils is reported. The installation at both sites was successful and no excess plug uplift was observed. The transfer of suction to the clay-sand interface is believed to have contributed to the success of the installations. The two cases presented in this paper provides confidence in suction bucket foundation installation in similar soil conditions. [ABSTRACT FROM AUTHOR]

This research investigates the shrinkage behaviour of clay specimens subjected to different hydraulic paths. The volume change and microstructure of desiccated clay specimen directly dried from reconstituted slurry and compacted states, and the desiccated clay specimens obtained by subjecting the as-compacted clay specimen to cyclic wetting and drying process were compared. The experimental results showed that the initial microstructural difference between reconstituted slurries and compacted specimens influences their shrinkage behaviour. The compacted clay specimens retained the bimodal structure even after subjecting to cyclic wetting and drying, unlike the reconstituted slurry, which showed a predominant unimodal structure at the end of drying process. This is due to the absence of large macropores in the desiccated clay specimen dried from reconstituted slurry state, which is evidenced from the mercury intrusion porosimetry studies, scanning electron microscopy and nano-focus X-ray-computed tomography imaging experiments. [ABSTRACT FROM AUTHOR]

Analysis and design with simple correlations are always of interest to engineers. Predicting the bearing capacity of a spudcan in a multi-layered clay soil is one of the challenges facing jack-up designers and the installation process. In this paper, simple correlations are presented for the prediction of the bearing capacity–penetration curve of the spudcan using numerical modeling results and analyzing the parameters affecting the bearing capacity of a spudcan in a multi-layered clay soil. Multivariate regression was used to obtain these correlations and their quality was evaluated by comparing the numerical modeling results to the prediction correlations. Moreover, some examples were solved using data obtained from previous research and the resultant curves were compared with the reference curves. The results showed that the presented correlations had good accuracy in predicting the bearing capacity of spudcans in various profiles of multi-layered clay soils. [ABSTRACT FROM AUTHOR]

The Yellow River Delta is one of the most abundant offshore energy areas in China, and the construction of offshore projects is rapidly developing. In this paper, four typical regions of the Yellow River Delta in different periods were selected as research objects. In-situ cone penetration tests (CPTs), geotechnical testing, electron microscope scanning testing, and soil type indexing (Ic) was used to classify and identify the soil layers. At the same time, a modified calculation model based on CPT for the shear wave velocity of fine-grained seabed soil was sought and verified with the measured values. The results showed that: (1) the obtained soil layers are mainly classified by clay and silty soil, which is in line with the conclusions of previous scholars on the classification of the Yellow River Delta soil layer. (2) The measured shear wave velocity is generally between 100 m/s and 250 m/s, and it gradually increases with depth. (3) The depth, cone resistance, and soil behavior index are directly related to the calculation of the shear wave velocity in this area. (4) Discrete analysis of measured and calculated shear wave velocity provides theoretical support for the change of shear wave velocity under different conditions. [ABSTRACT FROM AUTHOR]

MgCl2 is widely used on roads for controlling dust and humidity, reducing the scattering of coarse particles, anti-icing, and improving the geotechnical properties of "problematic soils" by chemical stabilization. In this study, we initially induced the MgCl2 solution to electrokinetic stabilization. Six electrokinetic experiments were conducted on marine clayey soil, collected from Zhuhai, China, to investigate the feasibility using MgCl2 solution as a green stabilizer in the electrokinetic stabilization process. The dewatering efficiency, unconfined compressive strength (UCS), anode corrosion and power consumption due to electrokinetic treatment were analysed. Up to 600% increases in UCS taken from the anode zones was observed after 7-days of curing. The results revealed that injecting of 0.8% MgCl2 solution (by the dry wight of soil) at a constant concentration of 20% was the optimum amount for the electrokinetic stabilization of marine clayey soil from Zhuhai, and the higher concentration of MgCl2 solution reduced the degree of anode corrosion. [ABSTRACT FROM AUTHOR]

Geosynthetic-encased stone column (GESC) has been proved as an effective alternative to reinforcing soft marine clay soils with low undrained shear strength. In this paper, three-dimensional (3-D) coupled mechanical and hydraulic modeling based on centrifugal model test was carried out to investigate the performance of GESC-supported embankment over soft clay with two different stiffness of encasement (i.e., 450 kN/m and 3300 kN/m). The numerical modeling results agree well with the centrifugal model test recordings. This investigation reveals that with the increase in the geogrid stiffness the differential settlement between the GESC and the surrounding soft marine clay soil was found to increase. Under the embankment load, the encased columns located below the embankment slope have experienced significant vertical and lateral stress ratio. Moreover, columns below the embankment slope tend to experience significant hoop strain below the top of the column. [ABSTRACT FROM AUTHOR]

The organic matter within clay soil is one of the important factors affecting its engineering characteristics. In this study, the influence of organic matter on the strength evolution of cement-stabilized marine soft clay is evaluated by scanning electron microscopy (SEM) and unconfined compressive strength (UCS) testing. The experimental results show that the after-curing clay water content of the specimens increased with the organic matter content. However, the after-curing unit weight decreased with the organic matter content. The strength decreased with the increase in the amount of organic matter. The strength loss (SL) increased with the organic matter content. A new mathematical model was determined and then used to quantitatively analyze the strength of the investigated samples. A relationship between the strength and organic matter content was established. The evaluation of the accuracy of this new strength model was carried out by comparing the predicted values and measured values, and the results indicated that the deviation was mostly within 10%. Finally, the microscopic changes of the sample surface and influencing mechanism of the organic matter were revealed through SEM. A high soil strength is mainly due to a relatively low porosity, a dense microstructure and the formation of hydration products. [ABSTRACT FROM AUTHOR]

The jacked-in pile method provides a substitute procedure that permits the installation of pre-formed piles with negligible vibration in a noiseless manner, thereby reducing noise impacts in marine and urban environments. This research was carried out by using a small-scale physical modelling approach to examine the movement of soil during pile installation. The model soil was formulated from a mix of amorphous silica and mineral oils; the resulting mixture was subjected to consolidation in a transparent chamber. The model pile was driven vertically down the mid-point of the soil model at different vertical speeds using a strain control device. The array of soil displacement dispersal was obtained by utilising the close-range photogrammetry and particle image velocimetry techniques. The deformation of soil during pile installation was found to decrease with progressive increase of the penetration rate. This result can be employed in the assessment of the disturbance effects of pile installation on underground services and archaeological relics beneath the ground in both urban and marine environments. [ABSTRACT FROM AUTHOR]

In the design of reclamation, long-term settlement is seriously concerned. This paper presents a case study on the ground settlement of a reclamation project in Nansha, China. Fourteen undisturbed soil samples were taken at different depths from this site. Both oedometer tests on fourteen specimens and triaxial hydraulic conductivity tests on nine specimens were conducted. Finite element (FE) modelings using soft soil creep (SSC) model or soft soil (SS) model for modeling clayey soils with or without creep and the calculation using a new simplified method were performed to analyze the consolidation settlement of clay deposits subjected to filled loadings. The FE simulated results and calculated results from the new simplified method were compared with the monitored data in the field. Results show that the curves of the FE modeling using SSC model and the calculation from new simplified method have the same trends as those of the measured settlements. The creep contributes to excess pore pressure dissipation during the consolidation. Furthermore, ground settlements of the reclamation are predicted with the aid of the FE and new simplified method analysis. These predictions can provide the essential information for engineers to control or reduce the settlement in future. [ABSTRACT FROM AUTHOR]

This article presents the performance of the short-term bearing capacity on soft clay soil treated by Kenaf geotextile under vertical loading via a small-scale modelling test at unit gravity. The ground model was formulated by consolidating kaolin in a rigid testing compartment. In the loading test, the strip footing was represented by a rigid footing. For the treated case, a series of tests were performed to examine the effects of the burial depth of the Kenaf geotextile on the bearing capacity of the soft soil. The Kenaf geotextile was laid beneath the rigid footing (at the ground surface) and at 50, 75 and 100 mm depth from the soil surface. All the measured results of the Kenaf geotextile treated ground were compared with the untreated ground. The incorporation of Kenaf fibre geotextile was observed to enhance the bearing capacity of soft cohesive clay up to 281% depending upon the depth of the installed geotextile. The geotextile at the surface provided the highest bearing capacity and sustained the highest displacement at failure. The outcome of this research will promote the use of natural fibre geotextiles as sustainable earth reinforcement in temporary earthwork applications. [ABSTRACT FROM AUTHOR]

This study established a Couple Eulerian–Lagrange model to simulate monopile vibratory penetration for the investigation of soil plugging effect during high-frequency penetration of monopiles for wind turbine. Simulation analysis is focused particularly on soil plugging effect of a large diameter monopile during vibratory penetration into sand, clay, or layered soil. The results of the numerical simulation show that soil plugging effect is unlikely to occur during monopile penetration into the clay soil, while partial soil plugging may occur during the sand penetration. Penetration resistance at the pile toe is transferred to the radial stress around the pile wall. At a critical point penetration process, internal shaft friction becomes larger than external shaft friction. Moreover, radial pressure factors increase during partial soil plugging effect. For layered soil, the topsoil not only has great influence on the soil plugging effect, but also affects shaft friction in the subsoil during monopile penetration. [ABSTRACT FROM AUTHOR]

An experimental investigation was undertaken in order to assess the effect of sodium (Na2SO4) and calcium (CaSO4·2H2O) sulphates and curing period on stress–strain curves and failure modes of grey (GS) and red (RS) clayey soils stabilised by lime (L), natural pozzolana (NP) and their combinations (L–NP). Several soil–L–NP mixtures were studied to be used as subgrade soils for road pavements. Stress–strain curves were obtained from unconfined compressive strength (UCS) test made on several soil–L–NP specimens after curing for 7 and 120 days. Tests results showed that the use of L or L–NP without sulphates produced a significant increase in peaks stress of both clayey soils and then modified their stress–strain curves from nonlinear to linear behaviour almost up to 70% of peak stress after a longer curing period. However, the presence of 2% Na2SO4 or any CaSO4·2H2O content provided beneficial effects on peaks stress and stress–strain curves of both stabilised clayey soils and then improved their linearity almost up to 95% of peak stress after curing for 120 days. In contrast, the presence of 6% Na2SO4 caused undesirable effects. In addition, both sulphates greatly affected the failure modes of soil–L–NP specimens, particularly at a later stage. [ABSTRACT FROM AUTHOR]

The effect of pH on the physical and mechanical properties of a sediment was investigated through a set of experimental tests. The sediment was formed from deposition of suspended particles in a fluid. Two different types of clay soil were suspended in fluids with different pH (2, 4, 7, 9 and 11) in cylindrical tubes with volume of 1 liter and also in special cylindrical reservoirs. The height of the sediment was measured in the cylindrical tube until equilibrium was achieved. The sediment deposited in the reservoirs was dried in air and then Atterberg limit, compaction and unconfined compressive strength (UCS) tests were conducted on samples prepared from each sediment. The results showed that the final height of the settled sediment is a function of pH; the height of sediment is increased with increasing the pH. Also, the Atterberg limits increased with increasing the pH. The maximum dry unit weight and optimum water content decreased and increased with increasing the pH. The final strength of the sediment decreased with increasing pH. Based on the SEM analysis, it was found that the values of pH influence the properties of the formed sediments. [ABSTRACT FROM AUTHOR]

The aim of this experimental study is to estimate the maximum shear modulus (Gmax) of normally consolidated clayey soils using the results of a dilatometer test (DMT). A series of DMTs was conducted at the Busan New Port and Noksan sites in South Korea. In addition, basic index tests, bender element tests (i.e., shear wave velocity (Vs) measurements), and standard 1-D consolidation tests were performed using the undisturbed specimens. The results demonstrate that the Gmax of normally consolidated Busan clays cannot be adequately captured by the horizontal stress index (KD)-based empirical formula. Therefore, a Gmax estimating formula for normally consolidated clayey soils is newly suggested in this study using the dilatometer constrained modulus (MDMT) and stress-normalized material index (ID). Most notably, the estimated Gmax values using the suggested formula are comparable with the measured Gmax of both this study and the previous study on normally consolidated clayey soils. [ABSTRACT FROM AUTHOR]

The exploration and exploitation of marine georesources ordinarily disturbs the submarine soft clay surrounding construction areas and leads to a significant decrease in the shear strength of structured and sensitive clayey soils in submarine slopes. Under wave action, local slides can even trigger large-scale submarine landslides, which pose a serious threat to offshore infrastructure such as pipelines and footings. Therefore, accurately evaluating the stability of submarine sensitive clay slopes under wave-induced pressure is one of the core issues of marine geotechnical engineering. In this paper, a kinematic approach of limit analysis combined with strength reduction technique is presented to accurately evaluate the real-time stability of submarine sensitive clay slopes based on the log-spiral failure mechanism, where external work rates produced by wave-induced pressure on slopes are obtained by the numerical integration technique and then are applied to the work-energy balance equations. The mathematical optimization method is employed to achieve the safety factors and the critical sliding surfaces of submarine slopes at different time in a wave cycle. On this basis, the stability of submarine sensitive clay slopes under various wave parameters is systematically investigated. In particular, extreme wave conditions and special cases of slope lengths no more than one wavelength are also discussed. The results indicate that waves have some negative effects on the stability of submarine sensitive clay slopes. [ABSTRACT FROM AUTHOR]

To accurately characterize sound speed dispersion of shallow sediments in the Southern Yellow Sea, three types of sediments, i.e., silt, clayey silt, and silty clay, were selected to measure the sound speeds at 25-250 kHz. Over the frequency range, the sound speeds vary approximately from 1,536 to 1,565 m s−1 in silt sediment, from 1,511 to 1,527 m s−1 in clayey silt sediment, and from 1,456 to 1,466 m s−1 in silty clay sediment. The sound speed exhibits a slow increase with frequency in a nearly linear gradient, but these three types of sediments have different sound speed dispersion characteristics. The silt sediment with relatively coarse grains has the most significant sound speed dispersion, while the sound speed dispersions of the two others are relatively weak. Comparison between the measured dispersions and the model predictions shows that the grain-shearing model can match the measured data at most of frequencies. Nevertheless, when the grain bulk modulus was assigned 3.2 × 1010 Pa according to relevant references, the Biot-Stoll model predictions were higher than the measured values at high frequencies; when it was assigned a relatively small value of 2.8 × 1010 Pa, the model predictions achieved optimal matching with the measured values. [ABSTRACT FROM AUTHOR]

An angle exists between the initial static shear stress and cyclic shear stress when embankment and retaining walls are subjected to cyclic loadings. To investigate the influence of this angle on the dynamic properties of marine soft clay, tests were performed on Wenzhou soft clay. When the angle was varied from 0° to 90°, the shear strain and excess pore pressure decreased as θ increased while increased as θ increased from 120° to 180°. Shear strain developed more rapidly when θ was 120°, 150°, or 180° than that when θ was 0°, 30°, or 60°. These results indicate that the number of cycles to failure at the larger angles was greater than at the smaller angles. When θ was 90°, the strain in the x-axis direction increased as the number of cycles increased. The development of the excess pore pressure associated with specimen failure was different for different cyclic shear stress ratios and shearing angles. The effect of θ on the strain and excess pore pressure increased as the cyclic shear stress ratio increased. [ABSTRACT FROM AUTHOR]

Classification of fine-grained soils is typically conducted using plasticity charts. The typically used plasticity chart proposed by Casagrande was questioned by Polidori proposing different classification criterion in separating clayey and silty soils. Using natural clayey and silty soils sampled from four different coastal sites in Korea, applicability of both Casagrande’s and Polidori’s plasticity charts was evaluated. Classification results of Korean natural soils based on the Casagrande’s and Polidori’s plasticity charts did not match well with those based on the soils’ behavior reported in the previous publication. The disagreement in classification of Korean natural fine-grained soils may result from disregard of considerable silt fraction effect on plastic and liquid limits for Polidori’s chart. Consequently, revised proposal of Polidori’s plasticity chart was tentatively made for further classification of fine-grained soils suitable for Korean natural soils by accounting the effect of silt fraction on soil classification. [ABSTRACT FROM AUTHOR]

Granular piles are frequently used as a method of improving soft grounds as they provide increased bearing capacity and reduce foundation settlements. However, in very soft clayey soils, they may not derive their load-carrying capacity by low confining pressure provided by the surrounding soil. In such circumstances, granular piles may be reinforced with suitable geosynthetic to increase its load-carrying capacity and to reduce excessive bulging. In this study, the performance of small group of geosynthetic-reinforced granular piles (GRGPs) is examined in terms of load-carrying capacity, settlement, and modulus by laboratory model tests. The parameters investigated include modulus of reinforcement material, area replacement ratio (ARR) based on the column diameter and reinforcement length. The results indicated that increasing the modulus of the reinforcement and the ARR based on the column diameter enhances the overall performance of the GRGP group. It was also observed that reinforcement on top portion of the granular pile is sufficient to substantially increase the load-carrying capacity of granular pile group. [ABSTRACT FROM AUTHOR]

To study the effect and mechanism of carbon fiber reinforced clay, a series of unconfined compression tests for clay reinforced with carbon fiber have been performed under the conditions of controlled water content and dry density. The carbon fiber is mixed into soil with the quality percentage of 0.01, 0.02, 0.03, 0.05, 0.1, 0.15, 0.25, 0.35, and 0.5%, then a certain quality of water was added in the soil to achieve the optimum soil water content. Ten groups of samples were tested by the unconfined compression experiment. The results showed that the incorporation of carbon fiber elements can effectively improve the unconfined compressive strength and brittle failure mode of soil. The soil is strengthened at the beginning and then weakened with the increased incorporation of carbon fiber, the effect is especially significant when the mix percentage becomes 0.1%. The interaction at the interface between carbon fiber surface and soil matrix is analyzed by using scanning electron microscopy (SEM). It is found that the enhancement mechanisms of carbon fiber reinforced soil are one-dimensional reinforcement of a single carbon fiber thread and three-dimensional reinforcement caused by fiber network respectively. [ABSTRACT FROM AUTHOR]

For decades, various well-known empirical correlations have been established and commonly used to estimate the undrained shear strength of normally consolidated clays in geotechnical practice. However, there are still many contradictory cases regarding the validity of these correlations, so their applicability and reliability are questionable. In this study, an extensive geotechnical database for normally consolidated clays has been compiled. Next, a Bayesian nonparametric method is exploited to identify the most critical soil index properties in inferring the undrained shear strength and a new predictive model is proposed. Finally, the performance of the proposed predictive model is assessed and compared with two well-known correlations using an independent testing database. It confirms that the proposed model not only possesses high predictability, but also provides superior performance over other existing empirical correlations. [ABSTRACT FROM PUBLISHER]

The present study examines the suction characteristics and swelling behavior of clayey soils when exposed to natural seawater with respect to distilled water. The effects of saline waters on the engineering behavior of soils need to be determined since the salinity of the pore fluid of soils near coastal areas increases continuously. Six clayey soil samples with different mineralogy and characteristics were gathered and tested to determine the suction and swelling characteristics in the presence of natural seawater and distilled water. The results show that the total suction values of the samples are higher in the presence of seawater than in distilled water. The samples with high swelling potential have lower matric suction values than nonswelling soils. Moreover, in contrast to swelling-type soils, the matric suction values of the nonswelling soils remain similar in the presence both distilled water and seawater. The modified free swell index (MFSI) of the samples is well correlated with the liquid limit (LL), plasticity index (PI), and cation exchange capacity (CEC) in distilled water. However, coefficients of determination decreased in the presence of seawater. Also, there is no significant correlation existing between total and matric suction values and the MFSI values of the samples. [ABSTRACT FROM AUTHOR]