With the recent growth in coastal development, dredged clay has been increasingly used as a core reclamation material. However, marine clay may exhibit a consolidation behavior distinct from that of terrestrial clay owing to pore water salinity. In particular, salinity variations induced by environmental factors such as groundwater level fluctuations or seawater leaching can alter the compressibility and settlement behavior of clay deposits, thereby increasing uncertainty in settlement prediction. In this study, disturbed dredged clay was collected and remolded at different salinity levels (0%, 1%, 2%, and 3%) to investigate the effects of salinity variation on consistency and consolidation responses. The experimental results indicated that decreasing salinity increases the consistency indices (liquid limit and plastic limit) and clay compressibility. These trends are attributed to the expansion of the diffuse double layer and the consequent loosening of the clay microstructure under low-salinity conditions. These findings highlight the importance of considering pore water salinity for reliable settlement prediction and the rational design of dredged coastal reclamation grounds.

In urban areas, appropriate backfilling design is necessary to prevent surface subsidence and subsurface cavities after excavation. Expandable foam grout (EFG), a mixture of cement, water, and an admixture, can be used for cavity filling because of its high flowability and volume expansion. EFG volume expansion induces a porous structure that can be quantified by the entrapped air content. This study observed the unit weight variations in the EFG before and after expansion depending on the various admixture-cement and water-cement ratios. Subsequently, the air content before and after expansion and the gravimetric expansion ratios were estimated from the measured unit weights. The air content before expansion linearly increased with an increase in the admixture-cement ratio, resulting in a decrease in the unit weight. The air content after the expansion and the expansion ratio increased nonlinearly, and the curves stabilized at a relatively high admixture-cement ratio. In particular, a reduced water-cement ratio limits the air content generation and expansion ratio, primarily because of the short setting time, even at a high admixture-cement ratio. Based on the results, the relationship between the maximum expansion ratio of EFG and the mixture ingredients (water-cement and admixture-cement ratios) was introduced.

Collapsible soils pose significant challenges to engineering projects due to their instability and sudden changes in volume upon variations in water content. In this study, the collapse potentials of specimens with sand–clay mixtures are experimentally investigated by considering factors, such as initial water content and clay fraction. The specimens are subjected to vertical stress up to σˊv = 440 kPa in an instrumented oedometer cell, including the wetting process at σˊv = 220 kPa. The settlement and shear wave velocity (Vs) are continuously measured during loading and wetting to propose a geophysical approach based on shear wave velocity measurements for better understanding of collapse mechanisms. The results show that the collapse potential of sand–clay mixtures increases with increasing clay fraction at a specific water content. However, the variation in the collapse potential can be the sole function of the clay water content (= water content/clay fraction). As the suction pressure decreases upon wetting, the Vs shows a time-dependent decrease during wetting, and the decreasing is proportional to the collapse potential, indicating the loss of small-strain stiffness. However, when the settlement ceases, a portion of Vs can be recovered over time because of the formation of a stable soil structure, leading to the ratio of Vs after collapse to Vs before collapse ranges from 0.85 to 1.05. Additionally, this study reveals that a relatively higher initial degree of saturation (> 50

Expandable foam grout (EFG) is a cementitious mixture with relatively high flowability, high volume expansion, and low long-term strength. EFG mixtures typically contain water, cement, bentonite, aluminum powder, and an alkali-free accelerator. Aluminum powder induces volume expansion in EFG mixtures through chemical reactions with the cement paste, resulting in hydrogen gas generation in the cement paste. Subsequently, gas retention establishes a porous structure as the mixture loses its flowability through cement hydration (cement setting). The alkali-free accelerator plays a critical role in the activation of cement hydration, depending on the accelerator content. Therefore, it is important to evaluate the effects of the accelerator content on the volume expansion and strength of EFG mixtures because the hydration rates affect these characteristics. This study experimentally observed the evolution of the expansion ratio and compressive strength of EFG mixtures with various accelerator contents. The expansion ratio and compressive strength decreased with an increase in accelerator content, partly because of the shortened setting time. Based on these results, the relationship between the accelerator content of the EFG mixtures and their mechanical properties was established. Furthermore, the relationship between volume expansion and compressive strength was determined.

Soil liquefaction response is significantly affected by soil gradation (particle size, angularity, coefficient of uniformity) and density. However, the literature on the factors affecting liquefaction resistance with initial static shear stress (e.g., sloping ground) is more limited and primarily based on clean, poorly graded sands. As a result, the influence of particle size and gradation on the liquefaction potential of soils with initial shear stress is overlooked. In this study, 223 large-size cyclic simple shear tests were conducted on poorly and well-graded sands and gravels to evaluate the effects of soil gradation on the liquefaction resistance with the presence of initial static shear stress. Sandy and gravelly soils with coefficients of uniformity ranging from 1.6 to 42 were tested in a large-scale cyclic simple shear device under constant volume conditions, and the initial static shear stress correction factor K alpha values were obtained. The results show that poorly graded sand specimens exhibit flow liquefaction, have a more significant vertical effective stress reduction as the initial static shear stress increased, but also exhibit beneficial effects of initial static shear stress even if loosely packed, mainly due to their more dilative nature. Well-graded sandy soils, on the other hand, did not have as an abrupt loss of stiffness compared to poorly graded sand specimens, but due to their higher coefficient of uniformity may be more contractive, causing more pronounced shear strain development at the last few cycles. Gravel content also affected the void ratio of sand, which influenced the onset of strain softening or hardening during cyclic loading. Dense specimens with initial static shear stress exhibit cyclic mobility, but this may not necessarily provide beneficial effects of the K alpha correction factor, especially for higher coefficients of uniformity. The experimental results suggest that the widely used K alpha correction factor approaches that were originally suggested based on poorly graded sand may be overoptimistic for both loose and dense soils when considering a broader spectrum of soils such as those encountered in engineering practice. It is proposed that the K alpha correction factor should consider not only relative density and initial static shear stress but also particle size and gradation (i.e., determining the gravel content and the coefficient of uniformity), as well as angularity.

Highly porous cementitious materials have been utilized in various geotechnical applications, such as filling subsurface cavities, backfilling, and enhancing loose layers. In particular, expandable foam grout (EFG) has significant potential for cavity filling owing to its unique characteristics such as volume expansion and high flowability. Various EFG samples were prepared by mixing water, cement, aluminum powder, bentonite, and an accelerator at various ratios. Cementitious materials with various mixing ratios have different volume expansion and flowability, and each ingredient causes different impacts on their properties. This study investigated the effects of aluminum and bentonite contents on volume expansion and flowability. Expansion ratios and flow consistencies were estimated from expansion and flow tests. The results show that the expansion ratios increased with increasing aluminum content regardless of the water-cement ratio while slightly decreased with increasing bentonite content within a given range of ingredient contents. Moreover, the flow consistency increased with increasing water-cement ratio and decreasing aluminum and bentonite contents. The properties were evaluated using EFG mixtures containing relatively high bentonite contents to observe the effects of bentonite on a wide range of cementitious materials with varying bentonite contents. The expansion ratios and flow consistencies of the EFG mixtures containing relatively high bentonite contents decreased steeply with increasing bentonite content. Finally, the ingredient effects on volume expansion and flowability were discussed to design the mixture depending on its purpose.

Interfacial tension varies with temperature. This paper investigates the effects of temperature-dependent interfacial tension on shear wave velocity. We designed a nylon cell equipped with bender elements in a cross-hole configuration to measure the shear wave velocity of nine sand–silt mixtures with different degrees of saturation (S = 0%, 2.5%, 5%, 10%, and 100%). All specimens were subjected to a temperature change from 10 °C to 1 °C. The results demonstrate that shear wave velocity tends to be very sensitive to changes in temperature at a low degree of saturation. Particle-scale analyses overlapped with the experimental results and captured the critical role of temperature-dependent interfacial tension in small-strain skeletal stiffness. In fact, the temperature should be considered during laboratory and field shear modulus measurements of the long-term performance of energy geosystems subjected to thermally induced repetitive loads.

Levees are geologically complex earthen structures that vary laterally and vertically. Current levee inspection practices consist of mainly visual inspections of the surface with limited instrumentation that measures data at discrete locations. To better characterize and monitor the subsurface of these highly complex and spatially distributed systems, non-invasive geophysical methods, such as the multichannel analysis of surface waves (MASW) and electromagnetic induction (EMI), can be used to map the geophysical properties, i.e., shear wave velocity and apparent electric resistivity, respectively. This study focuses on investigating the effect of soil grain size on shear wave velocity and electric resistivity measurements conducted in the laboratory for a range of relative density, water content, and confining stress values. The testing program involved two types of sand: Ottawa C109 sand and Nevada sand, which have different grain sizes, with a D50 of 0.36 mm and 0.18 mm, respectively. It is shown that both shear wave velocity and electric resistivity measurements were affected by grain size and can therefore be used to distinguish between different types of sands at depth. Laboratory testing showed that the coarser sand has higher shear wave velocity at lower water contents and that shear wave velocity decreases with increasing water content. Finer sand particles exhibited lower electrical resistivity for all soil densities and water contents compared to the coarser sand specimens, but the relationship was more pronounced at lower water contents.

In the 2016 Kaikoura earthquake, liquefaction of gravelly soils from reclaimed fills occurred in CentrePort, Wellington, New Zealand. This study presents constant volume monotonic and cyclic simple shear tests on well-graded gravel with sand collected from CentrePort. A large-scale cyclic simple shear device is utilized to evaluate the monotonic, cyclic, and postcyclic responses of the sandy gravel soils. Specimens prepared at various relative densities were subjected to a vertical effective stress of 100 kPa and then monotonically and cyclically sheared. After the cyclic loading, the postcyclic response was evaluated, including volumetric compression or monotonic shear with or without dissipation of excess pore water pressure. Shear wave velocity was measured before and after the cyclic loading. The results show that the well-graded sandy gravel has a high potential for liquefaction, with higher relative density specimens having higher liquefaction resistance. Postcyclic volumetric strain is primarily correlated with density and maximum shear strain during cyclic loading. Postcyclic reconsolidation causes densification of the liquefied specimens, resulting in higher monotonic shear resistance, while postcyclic monotonic shear without dissipation of excess pore water pressure reveals that substantial shear strain is required to develop the shear resistance. Shear wave velocity was significantly reduced after liquefaction, but recovered to slightly higher than its precyclic shear values after reconsolidation. Compared to other gravelly and sandy soils, the well-graded sandy gravel showed a similar or slightly higher liquefaction resistance than gap-graded and uniform gravels. Moreover, the well-graded sandy gravel had a relatively lower ultimate postcyclic volumetric strain due to a small variation between its maximum and minimum void ratios. The results advance our understanding of the liquefaction resistance and subsequent postcyclic responses of the well-graded sandy gravel soils.

A field velocity resistivity probe (FVRP) can measure compressional waves, shear waves and electrical resistivity in boreholes. The objective of this study is to perform the soil classification through a machine learning technique through elastic wave velocity and electrical resistivity measured by FVRP. Field and laboratory tests are performed, and the measured values are used as input variables to classify silt sand, sand, silty clay, and clay-sand mixture layers. The accuracy of k-nearest neighbors (KNN), naive Bayes (NB), random forest (RF), and support vector machine (SVM), selected to perform classification and optimize the hyperparameters, is evaluated. The accuracies are calculated as 0.76, 0.91, 0.94, and 0.88 for KNN, NB, RF, and SVM algorithms, respectively. To increase the amount of data at each soil layer, the synthetic minority oversampling technique (SMOTE) and conditional tabular generative adversarial network (CTGAN) are applied to overcome imbalance in the dataset. The CTGAN provides improved accuracy in the KNN, NB, RF and SVM algorithms. The results demonstrate that the measured values by FVRP can classify soil layers through three kinds of data with machine learning algorithms.

Understanding dynamic mechanical properties of hydrate reservoirs is essential for ensuring safety and economic hydrate production. The modulus, damping ratio, and Poisson's ratio are critical parameters in interpreting seismic surveys and well logging data and the stability prediction of hydrate reservoirs during production or under earthquake conditions. In this paper, the shear and Young's moduli and damping ratios were evaluated by conducting resonant column tests on the synthetic hydrate-bearing specimens with respect to hydrate saturation, stress state, strain range, void ratio, pore pressure, and stress history. Regardless of the test conditions, a distinct increase in the damping ratio with an increase in the modulus of hydrate-bearing specimens could be used to identify the hydrate occurrence. The stress and hydrate improve the modulus of hydrate-bearing specimens; however, the exponent enhancement of stress on the modulus of hydrate-bearing specimens is suppressed by high hydrate saturation. In addition, a rapid nonlinear decrease in the normalized modulus of hydrate-bearing specimens with high hydrate saturation occurred under identical strain increments, and the corresponding damping ratio also increased rapidly. Along with the modulus data of other synthetic and natural hydrate-bearing specimens determined using various methods, a definite exponential relationship between E-h = E-0* e(n)*(Sh) and different parameter settings was established to satisfy various application conditions. In contrast, the Poisson's ratio of hydrate-bearing sediments should be determined with caution because of its relationship with specimen deformation or damage.

The purpose of this study is to investigate the role of the degree of saturation and water distribution patterns on small strain soil properties. First, we measure P- and S-wave velocities of fine sands mixed with varying degrees of water saturation S-w = 0, 5, 30, 60, and 100% during the vertical loading under zero-lateral strain conditions. Next, we use a simple geometry analysis combined together with soil index properties to provide the first-order approximation of capillary pressure. Then, we consider the effect of capillarity on soil skeleton stiffness to analyze the data in the context of Gassmann's framework. Finally, we investigate the effect of water distribution patterns on small strain soil properties. Results show that water distribution pattern is a critical factor to control the low perturbation soil properties. Furthermore, a specific surface appears to be a good indicator to predict the effective stress- and pore size-dependent capillary pressure in the determination of small strain geophysical properties. (C) 2021 Elsevier B.V. All rights reserved.

This paper describes a method to form methane hydrate shells on water droplets. In addition, it provides blueprints for a pressure cell rated to 10 MPa working pressure, containing a stage for sessile droplets, a sapphire window for visualization, and temperature and pressure transducers. A pressure pump connected to a methane gas cylinder is used to pressurize the cell to 5 MPa. The cooling system is a 10 gallon (37.85 L) tank containing a 50% ethanol solution cooled via ethylene glycol through copper coils. This setup enables the observation of the temperature change associated with hydrate formation and dissociation during cooling and depressurization, respectively, as well as visualization and photography of the morphologic changes of the droplet. With this method, rapid hydrate shell formation was observed at ~-6 °C to -9 °C. During depressurization, a 0.2 °C to 0.5 °C temperature drop was observed at the pressure/temperature (P/T) stability curve due to exothermic hydrate dissociation, confirmed by visual observation of melting at the start of the temperature drop. The "memory effect" was observed after repressurizing to 5 MPa from 2 MPa. This experimental design allows the monitoring of pressure, temperature, and morphology of the droplet over time, making this a suitable method for testing various additives and substrates on hydrate morphology.

Undisturbed frozen samples can be efficiently obtained using the artificial ground freezing method. Thereafter, the restoration of in situ conditions, such as stress and density after thawing, is critical for laboratory testing. This study aims to experimentally explore the effects of thawing and the in situ stress restoration process on the geomechanical properties of sandy soils. Specimens were prepared at a relative density of 60% and frozen at −20 °C under the vertical stress of 100 kPa. After freezing, the specimens placed in the triaxial cell underwent thawing and consolidation phases with various drainage and confining stress conditions, followed by the shear phase. The elastic wave signals and axial deformation were measured during the entire protocol; the shear strength was evaluated from the triaxial compression test. Monotonic and cyclic simple shear tests were conducted to determine the packing density effect on liquefaction resistance. The results show that axial deformation, stiffness, and strength are minimized for a specimen undergoing drained thawing, restoring the initial stress during the consolidation phase, and that denser specimens are less susceptible to liquefaction. Results highlight that the thawing and stress restoration process should be considered to prevent the overestimation of stiffness, strength, and liquefaction resistance of sandy soils.

Abstract Unsaturated soils in vadose zones often experience periodic phase changes during seasonal temperature fluctuations. The liquid in partially saturated soils significantly affects the physical and chemical processes associated with the phase transformations. This study examined the role of water distribution patterns on the activation energy of unsaturated soils. The results revealed that the homogeneously mixed and evaporation‐driven specimens exhibited higher activation energy than the horizontally layered specimen, which exhibited the lowest activation energy. In addition, the activation energy results indicated that the induction time, increased with an increase in the water saturation, requires a longer induction time and results in a more significant difference in the final products, such as elastic wave velocities, during the freezing process. In addition, the activation energy and soil stiffness results revealed that the homogeneous system required a higher activation energy than the heterogeneous system. The higher heterogeneity degree of the vertically and horizontally layered water specimens delayed the primary water‐to‐ice phase change. This study recognizes the significance of heterogeneity in activation energy for phase transformation in unsaturated particulate media.

Freeze-thaw cycles caused by seasonal temperature fluctuations significantly affect the geotechnical engineering properties. This study investigated the crucial role of water distribution patterns in the characterization of elastic wave properties for the fine F-110 sand during a freeze-thaw cycle. Sand specimens with four different water distribution patterns were prepared, namely homogeneously-mixed, evaporation-driven, vertically-, and horizontally-layered specimens. The P- and S-wave signatures of the specimens were monitored using piezo crystal sensors. Results indicated the criticality of water distribution patterns in the determination of small-strain soil properties even though the specimens had identical global water saturation. The nuclear magnetic resonance-based water volume depth profiles indicated that the evaporation-driven specimens had more heterogeneous pore-invasive ice-bonding layers at a high water saturation region; by contrast, the drying process facilitated uniform meniscuses around the particle contacts near the air percolation threshold. Elastic wave measurements for laboratory-prepared specimens might over/underestimate the small-strain soil stiffness of sediments in nature, wherein the drying processes prevailed to control the water saturation. This study highlighted a clear transition from capillary-controlled to cementation-controlled elastic wave properties during temperature oscillations.

Gas clathrates are both a resource and a hindrance. They store massive quantities of natural gas but also can clog natural gas pipelines, with disastrous consequences. Eco-friendly technologies for controlling and modulating gas clathrate growth are needed. Type I Antifreeze Proteins (AFPs) from cold-water fish have been shown to bind to gas clathrates via repeating motifs of threonine and alanine. We tested whether proteins encoded in the genomes of bacteria native to natural gas clathrates bind to and alter clathrate morphology. We identified putative clathrate-binding proteins (CBPs) with multiple threonine/alanine motifs in a putative operon (cbp) in metagenomes from natural clathrate deposits. We recombinantly expressed and purified five CbpA proteins, four of which were stable, and experimentally confirmed that CbpAs bound to tetrahydrofuran (THF) clathrate, a low-pressure analogue for structure II gas clathrate. When grown in the presence of CbpAs, the THF clathrate was polycrystalline and platelike instead of forming single, octahedral crystals. Two CbpAs yielded branching clathrate crystals, similar to the effect of Type I AFP, while the other two produced hexagonal crystals parallel to the [1 1 1] plane, suggesting two distinct binding modes. Bacterial CBPs may find future utility in industry, such as maintaining a platelike structure during gas clathrate transportation.

The prediction of soil response under repetitive mechanical loadings remains challenging in geotechnical engineering applications. Modeling the cyclic soil response requires a robust model validation with an experimental dataset. This study proposes a unique method adopting linearity of model constant with the number of cycles. The model allows the prediction of the terminal density of sediments when subjected to repetitive changes in pore-fluid pressure based on the two-surface plasticity. Model simulations are analyzed in combination with an experimental dataset of sandy sediments when subjected to repetitive changes in pore fluid pressure under constant deviatoric stress conditions. The results show that the modified plastic moduli in the two-surface plasticity model appear to be critical for determining the terminal density. The methodology introduced in this study is expected to contribute to the prediction of the terminal density and the evolution of shear strain at given repetitive loading conditions.

The ratio between the horizontal and the vertical effective stresses is defined as the coefficient of earth pressure at rest Ko. Ko in hydrate-bearing sediments is critical in understanding the stress states in hydrate-bearing sediments, yet has not been previously understood. An oedometer cell equipped with vertical and horizontal stress measurement sensors is used to measure the evolution of Ko in tetrahydrofuran hydrate- bearing sands during hydrate formation and dissociation and vertical stress changes. The results show that the response of Ko in hydrate-bearing specimens reflects the combined effects of hydrate cementation, the viscous nature of hydrate crystals, and the stress levels. These results can enhance the understanding of stress anisotropy and geomechanical behaviors of hydrate reservoirs during gas production.