Search

Mechanical response of soils under simple shear conditions has long been a subject of significant interest in the field of geomechanics. When subjected to simple shear loading, soils experience rotations of the principal stress directions. To provide a unified description for the simple shear behavior of clay and sand, this paper proposes a novel critical state model that accounts for the influence of principal stress rotation (PSR), based on the unified critical state model for overconsolidated clay and sand with subloading surface (CASM-S). The novelty of the newly proposed model, which is named as CASM-SP, lies in its ability to consider the influence of direction of the stress increment when establishing the plastic flow rule that is suitable for both clay and sand. Therefore, the model can capture the mechanical response of soils resulting from the PSR loading mechanism, such as noncoaxial behaviors. Then, the newly proposed model is validated through the comparisons with a series of experimental data of clay and sand under both drained and undrained simple shear conditions. Results predicted by the CASM-SP model agree well with those from the experiments, demonstrating that CASM-SP can reasonably describe the simple shear behavior of both clay and sand. [ABSTRACT FROM AUTHOR]

ABSTRACT Contourites (contour‐current deposits) are commonly associated with deep‐water environments, but this study documents a shallow‐water, muddy contourite drift in the centre of Taiwan Strait. The drift body (water depths of 30 to 70 m, 220 km long, 50 to 70 km wide, 0 to 30 m thick), with its long axis approximately colinear with the Taiwan Strait Current, is flanked on both sides by moats. Compositional data show that the drift is composed of sediment carried northward by the Taiwan Strait Current from the Choshui River draining Taiwan. The coast‐normal Changyun Ridge directly offshore of the Choshui River splits the Taiwan Strait Current into two branches that occupy the moats. Oblique cross‐drift flow from west to east contributes to drift growth. The dispersal system shows a down‐current fining from sands on the Changyun Ridge (ca 100 km long, 25 to 45 km wide) to the fine‐grained elongate drift; these together represent the asymmetrical subaqueous portion of the Choshui delta. Cores show that the drift is <8 kyr old, with sedimentation rates up to 7.8 m/ka. It coarsens upward during the initial phase of drift growth, perhaps due to an increase in current strength, with smaller‐scale textural bedding attributed to fluctuating current strengths or variations in wave energy depending on the location. Seismic data show that the southern end of the drift is migrating westward, due to elongation of the Changyun Ridge, whereas the middle and distal end are migrating eastward because of cross‐drift flow. Erosion by the eastern branch of the Taiwan Strait Current detached the drift from the coeval coastal mud belt. The influence of tidal currents is small because of the destructive interference of tidal waves entering from the two ends, creating weak rotary tidal currents over the drift. Wave energy is small within the Strait but larger waves arriving from the East China Sea are thought to be responsible for upward coarsening of the more exposed northern end. Taiwan Strait serves as a starting point for developing a facies model for ocean‐current‐dominated straits and seaways. [ABSTRACT FROM AUTHOR]

The work studies scenarios of self-ignition of hydrogen-air mixtures after a shock wave reflects from a destructible barrier made of sand or a solid wall. The experiments were carried out using a shock tube. The transverse dimensions of the diagnostic section were 40 × 40 mm. The initial pressure of the hydrogen-air mixture varied from 10 kPa to 50 kPa. The molar excess of hydrogen (equivalence ratio) was 0.3, 0.4 and 0.5. Typical oscillograms of pressure, a photomultiplier tube, and the results of high-speed visualization using the Schlieren method are presented. When the shock wave interacted with the destructible barrier, a thermodynamic unloading of shock-compressed mixture occurred in the direction of the scattering of fragments of the barrier. It was shown that under certain conditions, self-ignition of hydrogen could be prevented by using a destructible barrier. In this case, the prevention was recorded in a narrow range of Mach numbers of the incident shock wave, which are characterized by the occurrence of the so-called "weak" (or "mild") ignition of the hydrogen-air mixture. The conditions for strong ignition behind the reflected shock wave, as well as during the interaction of the reflected shock wave with the flame front behind the incident shock wave, were determined. The results of the presented experimental work are aimed at ensuring explosion safety when working with hydrogen in a confined space. [Display omitted] • The interaction of a shock wave with a sand barrier was studied. • Scenarios for self-ignition behind a reflected shock wave were determined. • Self-ignition can be prevented by placing a sand barrier instead of a solid wall. • The pressure ratios were determined during self-ignition. [ABSTRACT FROM AUTHOR]

Movement of sediment along shallow continental shelves is a natural process with wide‐ranging environmental and economic implications, making it of high importance to marine spatial planning efforts in the offshore. Development of marine renewable energy, for instance, requires detailed understanding of the morphodynamics of mobile bedforms to select foundation types and ensure safe installation of infrastructure in shallow shelf environments. This study evaluates geomorphology and sediment mobility of Dogfish Bank (< 20 mbsl) in the Hecate Strait offshore British Columbia, Canada, using hydroacoustic and airborne bathymetric data combined with seismic profiles and grain‐size information. These data reveal current‐swept features ranging from sediment‐depleted lag to sediment‐abundant sand ridges and dunes, with sand ribbons and furrows in‐between. Seismic reflection data show up to 15 m of surficial sand concentrated beneath north‐aligned sand ridges that dominate the bathymetry of northwest Hecate Strait. Sand ribbons (typically understood sediment‐limited features in shallow marine environments) are notably maintained over seabed with comparable sand thickness to adjacent dunes (i.e. sediment‐abundant features), suggesting local spatial variability in hydrodynamics and sediment characteristics (principally grain size) influence expression of mobile bedforms. Repeat mapping between 2008 and 2019 shows dunes and ribbons both migrate northwards, with largest seafloor changes along northeast‐facing lee sides of dunes, matching closely with published models of sediment mobility which suggest northward bedform migration is largely driven by storms. Median total migration distance is 164 m (northward) for dunes (time‐averaged rate of 14.9 m/year). Sand ribbons show less migration (median northward distance of 73 m) and migrate in a depth‐dependent manner. Because sand ribbons are typically flow‐parallel features, their lateral migration likely results from varying current directions and flow acceleration over shallower seabed. Sand ribbon migration should therefore a consideration in studies examining seabed change, particularly when they are formed over unconsolidated sediment. [ABSTRACT FROM AUTHOR]

Shoreline position (e.g., beach width) is a critical component of flooding and overtopping forecasts but difficult to predict accurately. We model beach width changes with a supervised machine learning (ML) approach informed by equilibrium principles. The time history of wave energy anomalies that force equilibrium models is used as an ML input feature. The sweeping simplifying equilibrium model assumptions relating beach width change to anomalies are replaced with data‐based ML results. Supervised learning regression methods including linear, support vector, decision trees, and ensemble regressors are tested. Observations for model training and testing includes weekly to quarterly beach elevation surveys spanning approximately 500 m alongshore and 8 years at two beaches, each supplemented with several months of ∼100 sub‐weekly surveys. These beaches, with different sediment types (sand vs. sand‐cobble mix), both widen in summer in response to the seasonal wave climate, in agreement with a generic equilibrium model. Differences in backshore erodability contribute to differing beach responses in the stormiest (El Niño) year that are reproduced by a simple extra trees regression model but not by the equilibrium model. With sufficiently extensive training data, the ML model outperforms equilibrium by providing flexibility and complexity in the response to wave forcing. The present ML and equilibrium models both fail to simulate a uniquely stunted beach recovery unlike other recoveries in the training data. Plain Language Summary: Beach elevation surveys are compared at two beaches in San Diego County. Both beaches narrow during winter as large wave events transport sand offshore and widen during summer as gentle waves move sand onshore. The seasonality of such beaches has been characterized by simple models that primarily rely on wave energy relative to an average state to predict beach width changes, known as equilibrium models. Here, we highlight some of the limitations of equilibrium models, such as a tendency to over predict winter erosion at a beach backed by non‐erodible infrastructure. We demonstrate that machine learning models, when trained with sufficient observations, can predict beach width changes more accurately than equilibrium models. Key Points: The Equilibrium‐informed extra tree (ET) regression machine learning model uses input features of only wave history, inspired by equilibrium conceptsWith sufficient training, ET outperforms a widely used equilibrium model [ABSTRACT FROM AUTHOR]

Repeated surveys of vegetation plots offer a viable tool to detect fine‐scale responses of vegetation to environmental changes. In this study, our aim was to explore how the species composition and species richness of dry grasslands changed over a period of 17 years, how these changes relate to environmental changes and how the presence of spring ephemerals, which may react to short‐term weather fluctuations rather than long‐term climatic trends, may influence the results. A total of 95 plots was surveyed in 2005 and resurveyed in 2022 in dry grasslands of the Kiskunság Sand Ridge (Hungary, Eastern Central Europe), where there has been a significant increase in mean annual temperature during the last decades, while no trends in precipitation can be identified. Db‐RDA was performed to reveal compositional changes. The changes in environmental conditions and naturalness state were assessed using ecological and naturalness indicator values. We also compared per‐plot richness of all species, native species and non‐native species of the old and the new relevés. All analyses were repeated after removing all spring ephemerals. We found clear temporal changes in species composition. Mean temperature indicator values increased, while mean soil moisture indicator values decreased during the 17 years. Also, decreasing per‐plot richness was detected both for all species and for native species, while mean naturalness increased. After the removal of spring ephemerals, the compositional changes were less obvious although still significant. The increase in the temperature indicator values remained significant even without the spring ephemerals. However, the decrease in the moisture indicator values, the decrease in the number of all species and native species, as well as the increase in naturalness indicator values disappeared when spring ephemerals were excluded from the analyses. Our study demonstrates that between‐year weather differences and long‐term environmental trends both contribute to observed vegetation changes. [ABSTRACT FROM AUTHOR]

To consider the influence of the interaction of each clayey layer in the interbedded soils of a foundation on the soil consolidation, a two-dimensional calculation model based on the overall analysis is proposed and the controlling equations of each layer are established. A semianalytic solution for the excess pore-water pressure in the frequency domain is derived by combining the Laplace transform with the Fourier cosine transform and introducing the boundary transformation method. The theoretical solution is compared with numerical simulations for verification, and the relevant parameters are also analyzed to further explore the consolidation characteristics of the foundation. The results show that the proposed theoretical solution can effectively reflect the distribution of excess pore-water pressure in each soil layer under the given foundation conditions; the deviation of the average degree of consolidation from the numerical results is less than 2.0%. When only one sandy layer is laid out in the foundation, it is most conducive to the consolidation to arrange the sandy layer in the middle-lower part of the soil layer. When the total thickness of the sandy layer is the same, the maximum consolidation rate that can be achieved by arranging two sandy layers in the lower part of the foundation is slightly faster than that achieved by arranging a single sandy layer. When the ratio of the horizontal permeability coefficient of the sand to the permeability coefficient of the adjacent clay is greater than or equal to 20, the excess pore-water pressure in the sandy layer can be considered to be evenly distributed along the vertical direction. [ABSTRACT FROM AUTHOR]

Sediment transport to the sea by rivers is crucial for the stability of estuaries and coasts. The Yangtze River, the largest river in China, like many large rivers worldwide, is experiencing a decrease in sediment load reaching the coast. However, the tidal flat around Qidong Cape, located at the entrance of the North Branch of the Yangtze Estuary, is undergoing extensive siltation. The source of this sediment is unclear. In this study, a sediment core was collected and the geochemical characteristics of rare earth elements (REE) were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The results indicate the following: (1) The average content of REE is 178.57 μg/g, and the average ratio between LREE and HREE is 8.66, which is comparable to sediments from the South Yellow Sea. The chondrite-normalized and UCC-normalized patterns resemble those of the Yangtze River and the South Yellow Sea, indicating a negative gradient, a weak Ce-negative anomaly, and a distinct Eu-negative anomaly. (2) The continental shelf deposits in eastern China are primarily derived from sediment flux delivered by rivers. The sediments in the South Yellow Sea mainly originate from the Yangtze River and the Yellow River, exhibiting characteristics of a mixed source due to long-term geological processes, namely geochemical processes. The REEs in the tidal flat around Qidong Cape inherit the source area's characteristics and originate from the weathering of upper continental rock in mainland China. Moreover, the tidal flat around Qidong Cape is influenced by both runoff and tidal actions, leading to strong land–sea interactions and reducing the environment, explaining the Eu-negative anomaly. (3) Hydrodynamic forces in the North Branch of the Yangtze River have shifted from runoff to tidal dominance since the 1930s. However, marine hydrodynamics outside the estuary have remained unchanged. Consequently, the Subei coastal current plays a key role in sediment transport and diffusion. Sediments from the south wing of the Radiative Sand Ridge in the South Yellow Sea are transported southward by the Subei coastal current, and under tidal influence, suspended sediment is deposited in the tidal flat around Qidong Cape. Therefore, the sediment source has gradually shifted from the Yangtze River to the South Yellow Sea. [ABSTRACT FROM AUTHOR]

Dynamic compaction is a method of ground reinforcement that uses the huge impact energy of a free-falling hammer to compact the soil. This study presents a DC method for strengthening coral reef foundations in the reclamation area of remote sea islands. Pilot tests were performed to obtain the design parameters before official DC operation. The standard penetration test (SPT), shallow plate-load test (PLT), and deformation investigation were conducted in two improvement regions (A1 and A2) with varying tamping energies. During the deformation test, the depth of the tamping crater for the first two points' tamping and the third full tamping was observed at two distinct sites. The allowable ground bearing capacity at two disparate field sites was at least 360 kPa. The reinforcement depths were 3.5 and 3.2 m in the A1 and A2 zones, respectively. The DC process was numerically analyzed by the two-dimensional particle flow code, PFC2D. It indicated that the reinforcement effect and effective reinforcement depth were consistent with the field data. The coral sand particles at the bottom of the crater were primarily broken down in the initial stage, and the particle-crushing zone gradually developed toward both sides of the crater. The force chain developed similarly at the three tamping energies (800, 1500, and 2000 kJ), and the impact stress wave propagated along the sand particles primarily in the vertical direction. [ABSTRACT FROM AUTHOR]

With the completions of large-scale construction projects such as Qitai embankment, Xuwei embankment and Guanhekou guide dike, the seabed evolution in the Lianyungang-Xuwei sea area has changed from natural evolution to the evolution under engineering conditions. In particular, the stability of the Guanhekou sand spit is very important to the Xuwei Channel. Based on the analysis of terrain comparison and tidal mathematical model by topographic data from the sea area of Lianyungang to Xuwei, the seabed evolution analysis in Xuwei sea area under the comprehensive influence of large-scale engineering was carried out. The results show that since the construction of large-scale engineering, the terrain of the sea area near the engineering has been significantly adjusted. The seabed near shallow beach at the constructions has silted up and the area of 2 m-shoal continues expanding to the open sea, and the seabed at the outer edge and head of the embankment and guide dike was scouring. Especially during the period from 2013 to 2018, the amplitude of terrain erosion and sedimentation reached its maximum. After 2018, the seabed in the engineering sea area is still in the process of adjustment, but the amplitude of terrain erosion and sedimentation and the change rate of isobath have slowed down. The outward rate of sedimentation in Guanhekou sand spit has increased compared with the natural evolution period, but since 2018, the frequency of large waves near the sand spit has been low, and the sand spit has remained stable overall. The results provide important reference and inspiration for the evaluation of large-scale coastal engineering in the surrounding sea areas. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive three-dimensional numerical investigation of horizontal square anchors embedded in geogrid-reinforced sand. Prior experimental studies have demonstrated notable enhancements in anchor uplift capacity when placed below geogrid reinforcement in soil. However, these results are limited to small anchor plates tested in laboratory conditions with over-reinforced sand. In contrast, this study focuses on large field-scale anchors and explores the influence of anchor width, embedment depth, reinforcement size, stiffness, and tensile strength on uplift capacity. The findings reveal that the optimal size for geogrid reinforcement is three times the anchor width. A diminishing improvement in uplift capacity with increasing anchor width was observed. Additionally, deeper anchor embedment reduces the uplift capacity improvement in geogrid-reinforced sand. The geogrid reinforcement is found to be more efficient in the case of shallow anchors placed in loose sand. The major contribution of this paper lies in the response analysis of large anchors and providing a better understanding of the uplift mechanism in geogrid-reinforced sand. • This paper presents a three-dimensional numerical investigation of large field-scale horizontal square anchors embedded in geogrid-reinforced sand. • The findings reveal that the optimal size for geogrid reinforcement is three times the anchor width (B) in contrary to the 5B value reported in the previous literature. • A diminishing improvement in uplift capacity with increasing anchor width was observed. • Deeper anchor embedment reduced the uplift capacity improvement in geogrid-reinforced sand. • The geogrid reinforcement is found to be more efficient in the case of shallow anchors. [ABSTRACT FROM AUTHOR]

Soil nails and tieback anchors are used extensively for excavation support and slope stabilization; however, their performance can be complicated by limited pullout capacity or installation challenges. This paper presents the results of field load tests performed on anchorage elements with snakeskin-inspired surfaces that do not require grout and that can reduce the force required for installation. These tests evaluated the effects of the asperity geometry, soil type, and embedment depth on the anchor load transfer behavior and pullout capacity. The tests consisted of jacked installation and pullout loading in sites consisting of dense sand and structured silt. The test results in sand indicate that the installation force and pullout skin friction increase as the asperity height is increased and the asperity length is decreased. The pullout capacity of the snakeskin-inspired anchors in sand was between 1.2 and 4.2 times greater than the capacity of a reference rough anchor. In the structured silt site, disturbance during installation influenced the pullout behavior, resulting in a decrease in anchor capacity as the asperity height was increased. However, the anchor capacity with small asperity heights was greater than that of the reference rough anchor. The snakeskin-inspired anchors mobilized direction-dependent skin friction, resulting in pullout skin friction values that were as much as 3.0 and 4.5 times greater than those generated during installation in the sand and silt sites, respectively, due to mobilized passive resistances during pullout. The results indicate that the snakeskin-inspired anchors can outperform conventional driven anchors in sands. However, the possible effects of installation disturbance should be evaluated carefully in sensitive, structured soils. [ABSTRACT FROM AUTHOR]

Microbially induced calcite precipitation is an environment-friendly method for improving stiffness, strength, and dilatancy of loose or weak soils. Although many experimental studies have been performed on biocemented sands, few efforts have been devoted to establishing constitutive models for such materials. A critical-state-based bounding-surface model for biocemented sands was proposed in this research. An exponential equation of the plastic deviatoric strain was used to describe the degradation in a biocemented bond. The established model was applied to predict the drained triaxial test results of biocemented calcareous sands at different confining pressures and biocementation levels. We found that the current proposed biocemented model can well predict the softening and dilation of biocemented calcareous sands. [ABSTRACT FROM AUTHOR]

The bearing capacity of shallow foundations on geocell-reinforced sand (GRS) depends not only on the soil characteristics but also on the geometries and properties of geocell. The geometry characteristics of GRS comprise height, length and cell aperture size of geocell as well as the sand layer thickness engaged between footing and GRS layer. Using the design-of-experiments (DOE) method the trends of bearing capacity ratio (BCR) as a function of selected geometry parameters of geocell are systematically visualized. Furthermore, trends of BCR as a function of geocell-selected geometry parameters are analysed. To this end, the study deploys the response surface methodology (RSM) to identify several configurations of geocell by conducting only twenty-seven laboratory tests. The results show that the DOE-RSM method gives an efficient interpretation of the variable's interaction while it lessens the number of tests. In addition, it has been found that the geocell height is the most influential parameter on BCR of footings on GRS. Moreover, an interaction between geocell aperture size and geocell height is recognised. The results are formulated and compared with the literature, resulting in good agreement. [ABSTRACT FROM AUTHOR]

In this study, centrifuge model tests were carried out to investigate the lateral response of single pile in coral sand foundation. The load–displacement relationships, pile deflections, bending moments, the changes in horizontal soil pressure, the predicted particle crushing behaviors, and p-y curves were compared and discussed in detail to study the influence of pile diameter and vertical load. Test results show that increasing diameter is the most direct and effective method to improve the horizontal bearing capacity of pile; the presence of vertical load would lead to an increase of bending moment and lateral displacement of the pile due to P-Δ effect and an improvement in soil resistance due to the vertical compression effect; the influence of particle breakage behavior of coral sand was not significant. In addition, the applicability of the existing p-y models for the coral sand foundation was systematically evaluated. According to the comprehensive analysis of the stress state of sand around pile, the evolution of soil resistance with depth was determined, which can be simulated by a power function. Based on the centrifuge test results, a modified p-y model for coral sand was proposed, and its rationality and applicability in predicting pile–soil responses were validated systematically. [ABSTRACT FROM AUTHOR]

A series of strain-controlled cyclic triaxial tests were performed on Firoozkuh sand‒silt mixtures with wide ranges of fines content (FC), relative density (Dr), and effective confining stress (σc′) to investigate their liquefaction resistance in terms of capacity energy (Wliq). Also, several cyclic test results from previous studies were collected and reanalyzed. The results showed that Dr could be used as a proper parameter to define soil density state for predicting Wliq of clean sands and sand‒silt mixtures when FC is greater than dispersing fines content (FCdis). However, due to the complicated role of FC in coarse‒fine assemblies, no universal relationship between Wliq and FC has been reported for the soil mixtures when FC is less than the threshold fines content (FCth). Therefore, the concept of equivalent granular void ratio (e∗) was used to capture the coarse‒fine interactions in such mixtures. It was also found that the fines contribution factor (b), which is the fraction of fines participating in load transfer, is dependent on Dr, as well as particle size disparity ratio (χ) and FC, neglected in previous studies. Finally, a new model was proposed for the prediction of the b value and also a unique relationship between e∗ and Wliq was obtained for all mixtures of specified sand and silt where FC ≤ FCth. [ABSTRACT FROM AUTHOR]

In arid regions, the use of ridge cover as a traditional agricultural strategy has been effective in mitigating soil wind erosion. However, few studies have focused on the sand transport characteristics of different micro‐ridge spacings and heights. This study aimed to identify the mechanism by which ridges change the near‐surface sand transport. In a controlled wind tunnel environment, the aeolian sand flux structure and sand transport flux (qz) at heights from 0 to 0.7 m were measured. The results showed that, compared with no ridges, ridge covering could significantly modify the structure of aeolian sand flux near the surface, yielding a substantial reduction in the proportion of sand transport to the total sand transport in the 0‐ to 0.1‐m height layer. In the absence of ridges, blown sand was mainly concentrated in the 0‐ to 0.1‐m height layer, and qz decreased exponentially as the height increased. With various micro‐ridge spacings and heights, when H was less than 0.1 m and L was more than 15H, the blown sand also remained concentrated in the 0‐ to 0.1‐m height layer, and qz decreased exponentially as the height increased. When H increased to 0.15 m from 0.1 m and L decreased from 15H to 5H, the height of the blown sand was concentrated in the 0.3‐ to 0.4‐m layer. The blown sand layer of most ridge structures was concentrated at a height of 0.1–0.4 m, and the structure of the aeolian sand flux resembled an 'elephant nose effect'. The total sand transport rate of all ridge structures was significantly lower than that with no ridges, indicating that a reasonable ridge structure can effectively prevent wind erosion. [ABSTRACT FROM AUTHOR]

Copyright of Revista Fotocinema is the property of Revista Fotocinema and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bioerosion traces are a powerful tool for reconstructing benthic paleo-communities through the geological record. The late Quaternary marine deposits of Patagonia (Argentina) are elongated ridges parallel to the present coast, rich in sand, gravel and shells, the latter being the main substrate for bioerosion traces. However, the ichnological studies in the Quaternary are scarce in high latitudes of the Southern Hemisphere. This work describes for the first time the bioerosion traces recorded in shells belonging to diverse taxa of mollusc from Quaternary deposits in Puerto Lobos, Southern of San Matias Gulf (Patagonia, Argentina). This study complements the scarce information on bioerosion traces in the Southern Hemisphere. A total of 710 mollusc shells were obtained from four Quaternary beach ridges at Puerto Lobos. As a result, 15 ichnotaxa were recorded for the first time in the site, 13 of them for the first time in the Holocene of San Matías Gulf. Through qualitative analysis, bioerosion patterns were observed in the late Quaternary of Puerto Lobos. The abundance of worm and sponge borings in the Pleistocene could be related to warm and sediment-free waters. On the contrary, the results of the bioerosion study in the Holocene and recent samples were very similar. This could indicate that the same environmental factor controlled both bioerosion patterns. For the Holocene, it was observed that the bioerosion pattern is mainly represented by trace produced by suspension and filter-feeding organisms, such as bryozoans, among others. Together with the increase in ichnodiversity, this could indicate an increase in nutrient availability in the San Matías Gulf associated with upwelling events. Therefore, our results reinforce the hypothesis proposed by previous authors that the upwelling events currently observed in the study area began during the mid-Holocene. [ABSTRACT FROM AUTHOR]

AbstractOne of the main problems of carbonate sands is the fragile nature of particles and their susceptibility to breakage. Carbonate sands are affected by volumetric strain even at low stress levels, which is not the case with silicate sands. By defining a simple breakage model, the current study develops an elastoplastic critical state constitutive model that considers the impact of particle breakage on the mechanical behavior of carbonate sands. The particle breakage model depends on mean effective stress and critical breakage stress, which is assumed to correspond with the precompression pressure of soil in the oedometer test. In the proposed model, critical state line movement with the breakage parameter (α) considers the particle breakage effect. Based on the unified clay and sand model (CASM), a novel dynamic yield surface with a shape parameter affected by particle breaking has been created. Certain modifications are made to the modified Cam-Clay stress dilatancy to predict the behavior of carbonate sand. The current model has only ten parameters that simulate the carbonate sands’ behavior even at high-stress levels without any breakage test. Experimental data with different soil densities, loading stress paths, and stress levels were compared with the model, and the results demonstrated satisfactory conformance. [ABSTRACT FROM AUTHOR]

AbstractMultiple studies confirm that determining the liquefaction resistance of sand-silt mixtures is more intricate compared to pure sand. Furthermore, it has been observed that the global void ratio fails to accurately predict the behavior of silty sand soils due to the fines particles, which can occupy voids between sand grains without significantly contributing to resisting external forces. To address this, a new parameter called equivalent void ratio (e*) has been proposed to better forecast the response of medium sand-fines mixtures. To investigate this further, a series of compression triaxial tests were conducted on mixtures comprising medium sand with low plastic fines. These mixtures were prepared in the laboratory with an initial relative density and subjected to varying confining pressures. The test results were utilized to assess the undrained shear strength of medium sand-silt mixtures based on the equivalent void ratio (e*) and to establish the equivalent granular steady-state line, which serves as a reference for calculating the equivalent state parameter (ψ*). Analysis of the obtained data suggests a correlation between the equivalent void ratio (e*) and the equivalent state parameter (ψ*) with the grading characteristics (such as D10, D50, Cu, D10R, D50R, and CUR) of the medium silty sand. [ABSTRACT FROM AUTHOR]

As escalating environmental pressures threaten the world's beaches, understanding the driving factors influencing their geomorphological changes is of critical global importance. This study focuses on the morphological changes of Sigeng beach adjacent to Changhua River Mouth in Hainan Island, China through decadal monitoring of shoreline and profile topography and tries to illuminate the natural and anthropogenic factors that drove geomorphological changes. The results showed that Sigeng beach undergone significant changes between 2008 and 2024, with notable accretion at the northernmost and southernmost and general erosion at other sections. The shoreline change rates ranged between -18.4 m/yr and 13.0 m/yr, with the average rate of -1.9 m/yr, indicating overall erosion. The net longshore sediment transport (LST) rates along Sigeng beach was estimated through the combination of the cross-shore (profile) and longshore (shoreline) changes. The overall direction of net LST along the beach were southward, except for the northern section where the direction was northward due to the diffraction of NE waves by the long sand spit at the northernmost. The net LST rates at each profile varied from 0.8×104 m³/yr to 3.5×104 m³/yr. The main factors controlling Sigeng beach evolution, including seasonal wave action and reduction in fluvial sediment load, followed by sand spit and coastal structures, typhoon events, aeolian transport, and sea level rise, were discussed. Subsequently, adaptive protection measures, including beach nourishment, accompanied with groin system or multiple detached breakwaters were proposed to combat with beach erosion. The analysis presented in this study is helpful to understand the morphodynamics and to predict the future change of beaches. [ABSTRACT FROM AUTHOR]

Karst hillslopes are generally characterized by different land uses. Land use and slope position impact soil erosion seriously, which in turn impacts the process of soil development and the patterns of soil properties. However, the impact of land use on soil physicochemical properties and the spatial variations and correlations between them are not fully understood on karst hillslopes. Therefore, nine sites had similar soil types, slope gradients, elevations, slope aspects and previous tillage practices were selected to conduct further research. This study was conducted to quantify the spatial distribution, variability and correlation of soil physical and chemical properties and stoichiometries as impacted by different land uses on a karst hillslope in Southwest China. Soil physical properties were significantly affected by slope position and soil depth. The soil bulk density and clay content increased with soil depth, while the opposite was true for the sand content. For the three land uses, the soil bulk density varied the most at the lower slope position, while clay and sand particles varied the most at the middle slope position. The mean spatial coefficient of variation (CV) of soil physical properties was ranked as sand (11.08%) > clay (7.77%) > bulk density (6.85%) > silt (3.81%). The mean spatial CV of soil chemical properties was ranked as available K (44.49%) > total P (16.77%) > total C (16.31%) > total N (13.09%) > available P (8.45%) > total K (7.51%). Overall, soil physicochemical properties exhibited significant spatial differences with slope location and land use on karst hillslopes. Soil chemical properties had greater spatial variation than physical properties, moreover, there were significant correlations between them. The results not only contribute to a deeper understanding of the impact of land use on the erosion process and mechanism on karst hillslopes but also provide a scientific understanding of the sustainable restoration of karst ecosystems. [ABSTRACT FROM AUTHOR]

In the western South China Sea, the diversity and complex genesis of sand waves lead to difficulties in measuring the actual scour depth of offshore wind turbine foundations. The present study employs methods such as insitu multibeam echo sounding along with numerical simulation techniques, combined with regional hydrological and geological data, to reveal the scour depth of pile foundations under seabed sand wave migration conditions (SPFSWM). Unlike previous studies, this study examines pile foundation scour depth from both macroscopic and microscopic perspectives, and proposes a method for risk assessment and safety zoning during the service life of pile foundations (RASZ). Our findings demonstrate that the dominant flow directions in the modern hydrodynamic environment play a crucial role in shaping and migrating sand waves, providing guidance for macro-level offshore wind project siting. Moreover, the study quantifies the changes in pile foundation elevations during sand wave migration and assesses their impact on safety throughout the service life of various pile foundations. Additionally, by utilizing Flow3D's numerical model and combining it with sampling data, the maximum scour depth likely to be experienced by pile foundations was calculated, establishing a microperspective on the range of pile foundation scour and analytically examining the coupling mechanism between sand wave migration and pile foundation scour in stages. By considering SPF-SWM, we estimated the actual depth variations of pile foundations in the study area, enabling effective assessment of scour conditions during their service life. This also provides ideas for delineating safety and risk zones, thereby offering precise locational analysis for the construction planning of offshore wind farm pile foundations. [ABSTRACT FROM AUTHOR]

The site characterization process is vital for the engineering structures and earthworks. In the current study, a Multi-Channel Analysis of Surface Waves (MASW) was carried out in western Riyadh City, Saudi Arabia. This aimed to determine subsurface geology, material stiffness, and potential weak zones approximately down to a depth of 30 m, and to propose the suitable seismic site characterization for precise foundation design. A total of 30 MASW lines were executed utilizing the Geode digital seismograph equipped with a 24geophone array of 4.5 Hz. The data acquisition, processing, and inversion were meticulously calibrated to derive shear velocities representing subsurface geological conditions. The Vs30 map, based on estimated values ranging from 443.71 m/s to 639.78 m/s for soil, was prepared for the area. The results of the 1D and 2D Vs profiles tinted small Vs values at shallow depths. The resulting geological model is composed of sand, gravel, moderately weathered limestone, and hard limestone sequence. Analysis of shear wave velocities shows variations, indicating low shear velocity (representing sediments or rocks of low stiffness) juxtaposed with higher velocity layers (indicating rocks of higher stiffness) at depths greater than 10 m. This could imply the presence of a cavity or weak zone. The topmost shear wave velocity zone indicated materials with low Vs values (ranging from 180 m/s to 360 m/s), predominantly associated with stiff materials such as silty sand, gravel, and sandy deposits. The subsequent zone, with 3 to about 10 m depth, was characterized by medium to very dense soil with shear wave velocity values ranging from 360 m/s to 760 m/s, attributed to layers of silty clay and silty sand. At approximately 12 m, a high shear velocity layer (ranging from 760 m/s to 1,500 m/s) was identified, extending to a maximum depth of 22 m, potentially indicative of less weathered or fractured bedrock associated with limestone. While the deepest layer, with very high shear velocity (exceeding 1,500 m/s) beyond 22 m, indicated bedrock associated with hard limestone. The average Shear-wave velocity of soil for the whole study area (Vs30 = 551.2 m/s) suggests that the site can be classified as Class C (Very Dense Soil and Soft Rock) according to the National Earthquake Hazard Reeducation Program NEHRP (National earthquake hazards reduction program, 2001). These results will support, to a great extent, the design of engineering structures in the area of study. [ABSTRACT FROM AUTHOR]

A submarine landslide on the edge of the Norwegian shelf that occurred around 8150 ± 30 cal. years BP triggered a major ocean-wide tsunami, the deposits of which are recorded around the North Atlantic, including Scotland. Ground-penetrating radar (GPR) was used here to investigate tsunami sediments within estuaries on the coast of northeastern Scotland where the tsunami waves were funnelled inland. Around the Dornoch Firth, the tsunami deposits are up to 1.6 m thickness, which is exceptionally thick for tsunami deposits and about twice the thickness of the 2004 IOT or 2011 Tohoku-oki tsunami deposits. The exceptional thickness is attributed to a high sediment supply within the Dornoch Firth. At Ardmore, the tsunami appears to have overtopped a beach ridge with a thick sand layer deposited inland at Dounie and partly infilled a valley. Later, fluvial activity eroded the tsunami sediments locally, removing the sand layer. At Creich, on the north side of the Dornoch Firth, the sand layer varies in thickness; mapping of the sand layer with GPR shows lateral thickness changes of over 1 m attributed to a combination of infilling an underlying topography, differential compaction, and later reworking by tidal inlets. Interpretation of the GPR profiles at Wick suggests that there has been a miscorrelation of Holocene stratigraphy based on boreholes. Changes in the stratigraphy of spits at Ardmore are attributed to the balance between sediment supply and sea-level change with washovers dominating a spit formed during the early Holocene transgression, while spits formed during the subsequent mid-Holocene high-stand are dominated by progradation. [ABSTRACT FROM AUTHOR]

Compound clinoforms are well‐recognized in modern large muddy deltas and in some ancient deltas, but there is still a lack of understanding regarding their lithology variations and the process by which sand from the shoreline clinothem reaches the subaqueous clinothem foresets that are sometimes 100 km away. Net‐to‐gross, thickness and facies association evaluation show overall coarsening‐upward through a 191 m thick exposure of the late Pliocene Orinoco, Lower Morne L'Enfer Formation, with a distinct tripartite lithology distribution. The subaqueous clinothem records a lower, relatively muddy coarsening‐upward interval, 112 m thick, with net‐to‐gross increasing from zero to 60%. On the lower delta front, zero net sand units show graded beds of silt and mud with occasional spring–neap rhythmites, strongly suggesting gravity flows influenced by tidal currents. These foreset beds are overlain by structureless very fine sand, interbedded with deformed wavy to lenticular, grey fluid mud layers that rapidly accumulated near the subaqueous clinoform rollover point. The tidally dominated subaqueous platform (subaqueous delta topset), 1 to 4 m thick, shows zero net sand units with anomalously high mud content, >70%, due to the high near‐bed suspended sediment concentration of externally derived fluid mud that migrated littorally alongshore from the Amazon Delta. The interaction of freshwater river flood discharge with fluid‐mud banks gave rise to density stratification with fine sand hypopycnally dispersing as a turbulent layer above the denser fluid‐mud carpet. The shoreline clinothem (<8 m thick) has high net‐to‐gross, >85%, attributed to winnowing of sediment by waves and tides. Utilizing net‐to‐gross trends and facies changes provide useful criteria to identify compound clinoforms in the rock record. The Orinoco Delta deposits, however, are unusual, since fluid mud hinders sand deposition on the platform, allowing for easy identification of platform facies and a clear distinction between the subaqueous and shoreline clinothem in outcrop. [ABSTRACT FROM AUTHOR]

Songkhla Lagoon has been studied for decades, but there is no clear evidence of its origin. As a barrier to the lagoon, the Satingpra Peninsula plays a crucial role in understanding its formation. Eleven sediment samples from sand ridges and tidal flats on the Satingpra Peninsular were collected and analysed for granulometry and geochronology. Both coarse-grained and fine-grained quartz-rich fractions were utilised to prepare samples of aliquots. The optically stimulated luminescence (OSL) dating was performed using the single-aliquot regenerative dose method for a determined (deposited) age. In addition, previous research, geological surveys and geochronological data were combined to explain their formation in this region. The OSL ages in the present study indicated that the late Holocene regression occurred between 0.36 and 3.27 ka (ka stands for 1,000 years). Integrated with previous studies, recorded ages dating back to the mid-Holocene sea level rise (ca. 6.5 ka) and the subsequent late-Holocene decline, indicate that both the old lagoon and middle beach ridge exhibit a sand ridge formation that runs parallel to the shoreline, extending from the south to the north. The middle sand, in this study, formed from about 3.02 to 1.5 ka ago resulting in the lagoon being isolated from the sea during that time. The lagoonal tide led the deposition as the present tidal flat from 3.3 to 1.7 ka. About 2.19 ka ago, the inner and middle ridges formed due to winddriven processes influenced by a dry climate. This was followed by a continued sea level regression, leading to the formation of the outer ridge around 1.5 ka ago when the sea level was 1.4 m below the present sea level. However, it's essential to consider this sea level data in relation to the tectonic and human-induced land motions in the surrounding area. [ABSTRACT FROM AUTHOR]

AbstractAccurate characterization of mechanical perturbations on the seabed is essential for developing models assessing the environmental impacts from physical disturbances. Furthermore, understanding the relationship between (1) seabed resistance and (2) penetration depth, can also facilitate the development of more efficient and less impactful fishing gears. This study examines these two aspects of tickler chain rigged beam trawling via large-scale physical experiments. Three scaled down models (“light,” “medium,” and “heavy” designs) were developed to represent the impacts from typical beam trawl configurations used in the North Sea and were towed at various speeds on a saturated sand bed. Results reveal that increasing the towing speed reduces the mean penetration depth and the steady-state towing resistance of the gears. Smaller scale physical model tests incorporating tickler chains in sand, demonstrate that the towing resistance is significantly influenced by the soil compaction and particle sizes. Moreover, our study offers a simple and efficient method to estimate the penetration depth and towing resistance of prototype beam trawl gears in sand. This approach, along with the associated research, may be valuable for marine scientists assessing trawling impacts and demersal fishing gear designers seeking to optimize efficiency while minimizing seabed disturbance. [ABSTRACT FROM AUTHOR]

To address the issue of seepage and soil plugging during the sinking of mono-column composite bucket foundations (MCCBFs), experiments were conducted on the installation of foundations under a variety of complex geological conditions. The effect of negative pressure sinking mode on the foundation's seepage field was analyzed, the formation mechanism of soil plugging in sand was explained, and an efficient method for calculating the height of soil plugging was proposed in conjunction with these investigations. The findings demonstrate that the finite element method simulation of the soil's seepage field is the most accurate, that the pumping volume of the foundation during sinking through is high, that the formation of the soil plug height is high, and that clear depressions can be seen on the foundation manifold's exterior. The equation presented in this study makes it easier to forecast the height of a foundation plug and can offer direction for engineering design. [ABSTRACT FROM AUTHOR]

Expansive clayey soils often pose challenges for construction projects due to their low bearing capacity, swelling, and shrinkage properties. While previous research has explored additives to enhance these soils' properties, the potential of sand remains underexplored. This study investigates the impact of varying sand percentages on expansive clayey soils' consistency, compaction, and permeability. This study examines how adding different percentages of sand influences the physical properties of expansive clayey soils. Laboratory tests involved systematic testing of texture, compaction, and permeability. Findings reveal a notable improvement in the physical properties of the soil with the addition of sand. Results from the laboratory tests provided data for empirical equations that facilitate the prediction of soil properties based on the sand content. The enhancement in soil properties underscores the potential of sand as an additive for expansive clayey soils. The empirical equations presented here provide practical benefits to geotechnical engineers and practitioners engaged in construction projects involving these soils, offering them valuable insights into the benefits of sand additives to improve physical characteristics. The insights gained from this research hold promising prospects for improving construction practices and addressing the challenges associated with these soils. [ABSTRACT FROM AUTHOR]

The current simplified liquefaction assessment method based on the shear‐wave velocity, Vs has uncertainties about how the fine contents change the Vs‐based liquefaction resistance. According to the simplified method, for a given Vs, the cyclic resistance ratio (CRR) increases with an increase in fine contents. However, field investigations recently revealed that for various silty sands, the correlation between CRR and Vs is soil‐type index dependent and not specific for all sand‐silt mixtures with the same fine contents. Therefore, a detailed experimental research program is performed in this study to clarify the effect of the soil‐type index on the shear wave velocity and CRR correlation. In the first part of the present study, the cyclic resistance of sand mixed with non‐plastic (NP) fines (dry weight of 0%, 5%, 15%, and 35%) was investigated using cyclic direct simple shear (CDSS) tests. Seismic cone penetration (SCPT) tests were performed inside the large‐scale box to facilitate normalized cone penetration resistance (qc1N) and shear wave velocity measurements on the soils used in the CDSS tests. A new correlation was proposed between the qc1N and normalized shear wave velocity (Vs1) using the soil‐type index Ic representing the behavior of soil. Then, CRR‐Vs1 correlation was obtained experimentally for four distinct ranges of soil‐type index. Finally, the results of this study and the proposed CRR‐Vs1 trends in other investigations were used to discuss the soil‐type dependent Vs‐based liquefaction susceptibility zones. [ABSTRACT FROM AUTHOR]

Land use changes modify soil properties, including aggregate structure, and thus, profoundly affect soil quality and health. However, the effects of land use changes originating from alpine grassland on soil aggregates and aggregate-associated organic carbon have received little attention. Soil aggregate fraction, aggregate-associated organic carbon and relevant influencing factors were determined at 0–20, 20–40 cm soil layers for alpine grassland, cropland and abandoned land in the eastern Qinghai–Tibet Plateau (QTP), and their relationships were analyzed by partial least square regression (PLSR). Results showed the following: (1) conversion from alpine grassland to cropland resulted in a significant decline macroaggregate fraction (R0.25), mean weight diameter (MWD), mean weight diameter (GMD), soil organic carbon (SOC), and microaggregate-associated SOC; (2) almost all aggregate stability indexes, SOC, and aggregate-associated SOCs were significantly positively correlated with silt and glomalin, suggesting that the binding of fine particles (silt) with the organic cementing agent (glomalin) was probably a key mechanism of SOC formation and aggregate stability in the studied region; (3) compared with biotic factors such as SOC, glomalin and root biomass, abiotic factors including silt and sand can better predict aggregate stability and SOC fraction using the PLSR model. The above results indicated that the conversion of alpine grassland to other land use types in high altitude areas would destroy soil structure and decrease soil organic carbon content, and then reduce soil quality. [ABSTRACT FROM AUTHOR]

The object of study is the vertical wave propagation in a sand deposit. This paper is aimed at analyzing the vertical wave propagation in a sand deposit through micromechanical modeling that inherently takes account of intergranular slips during deformation. Such a problem, which is part of the general framework of wave propagation in the soil, has long been analyzed using continuum models based on approximate behavior laws. For this purpose, a 2D Discrete Element Method (DEM) model is developed. The DEM model is based on molecular dynamics with the use of circular shaped elements. The intergranular normal forces at contacts are calculated through a linear viscoelastic law while the tangential forces are calculated through a perfectly plastic viscoelastic model. A model of rolling friction is incorporated in order to account for the damping of the grains rolling motion. Different boundary conditions of the profile have been implemented; a bedrock at the base, a free surface at the top and periodic boundaries in the horizontal direction. The sand deposit is subjected to a harmonic excitation at the base. Using this model, the fundamental and resonance frequencies of the deposit are first determined. The former is determined from the low-amplitude free vibration and the latter by performing a variable-frequency excitation test. It is noted that there is a significant gap between the two frequencies, this gap could be attributed to the degradation of the soil shear modulus in the vicinity of the resonance. Such degradation is well proven in classical soil dynamics. The effects of deposit height and confinement on resonance frequency and free-surface dynamic amplification factor are then investigated. The obtained results highlighted that the resonance frequency is inversely proportional to the deposit’s thickness whereas the dynamic amplification factor Rd increases with the deposit’s thickness. In the other hand, when the confinement increases the deposit becomes stiffer, which results in reducing the amplification. Such result is in accordance with theoretical knowledge which states that the most rigid profiles such as rocks do not amplify seismic movement. [ABSTRACT FROM AUTHOR]

The paper presents a rigorous analytical approach to predicting the load–settlement behavior of axially loaded piles embedded in sandy soils, adopting the advanced SANISAND model. The problem of the soil state around the pile during loading is formulated as a system of first-order ordinary differential equations, which can be solved as an initial value problem. The derived load–settlement (t–z) curve is then implemented into the load-transfer method to determine the pile's load–settlement behavior in sands and the deformation mechanism of the soil around the pile during axial loading. To verify the proposed analytical approach, a FEM simulation is performed with a user-defined subroutine, demonstrating its capacity to capture the dilatancy behavior of sands as the pile moves downwards. Additionally, a parametric analysis is conducted to assess the influence of the initial void ratio on the stress–strain relationship of the sandy soil around the pile during the loading process. The proposed analytical approach is also compared with a well-established finite-element model and a centrifuge test. The results indicate that the present approach can well predict the elastoplastic load–settlement response of the pile and reflect important phenomena observed from pile tests. [ABSTRACT FROM AUTHOR]

The principal stress rotation is often studied by considering the uniaxial rotation of principal stress. In this paper, the stress path on biaxial rotation of principal stresses is considered. The hollow cylindrical apparatus was used to achieve the principal stress rotation around the second stress principal axis. A novel specimen preparation device was developed, which was used to achieve the principal stress rotation around the third principal stress axis. The influence of principal stress biaxial rotation on the dense sand behavior was investigated under undrained conditions. The results revealed that the deformation properties of dense sand were closely associated with the stress direction dependence of the soil. An increase in the inherent anisotropy changed the slope of the effective stress path and the phase transition pore pressure, influenced the shear dilatancy and shear shrinkage characteristic of sand. Likewise, an increase in the stress-induced anisotropy changed the shape of the effective stress path, the development of pore pressure, the shear dilatancy and shear shrinkage characteristic of sand. More importantly, deformation properties of sand were affected by the coupling of the two factors, which was predominantly controlled by stress-induced anisotropy. [ABSTRACT FROM AUTHOR]

• A hybrid-driven fabric evolution law is proposed to describe the induced anisotropy. • The fabric tensor is properly integrated into the constitutive relations. • A novel anisotropic model for clay and sand is proposed. • The performance of the model is validated under different loading paths. • The model can reasonably describe the anisotropic characteristics of both clay and sand. This paper presents a novel critical state model for both clay and sand considering the inherent and induced anisotropy, named as CASM-h. The CASM-h model is developed based on the well-calibrated CASM model and incorporates the concepts of subloading surface and fabric anisotropy. To describe the induced anisotropy, a hybrid-driven fabric evolution law is proposed, defining fabric evolution as driven jointly by stress and strain rates. Subsequently, the fabric tensor together with its evolution law is appropriately incorporated into constitutive relation by employing the anisotropic transformed stress approach, without introducing additional mechanical mechanisms. The CASM-h model is validated under a series of stress paths, including triaxial tests, simple shear tests, shear tests with fixed principal stress direction as well as principal stress rotation (PSR) tests. The simulation results show that CASM-h model can satisfactorily capture the anisotropic behaviours of both clay and sand, such as the loading direction dependency of strength, non-coaxial behaviour, PSR effects and so on. [ABSTRACT FROM AUTHOR]