Sand Shear Research Articles

Stress–Dilatancy Behavior of Alluvial Sands

Based on the Frictional State Concept (FSC), the stress–dilatancy behavior of alluvial sands in drained triaxial compression was investigated. The dilatant failure state is equivalent to the minimum plastic dilatancy state for sands. The dilatant failure state slightly precedes the failure state. The straight line approximating dilatant failure states in the stress ratio–plastic dilatancy plane defines the slope of the critical frictional state line in the q-p’ plane, i.e., the critical frictional state angle. The stress ratio–plastic dilatancy relationship, obtained from the FSC, defines the sand shear angle as a function of the critical frictional state angle and plastic dilatancy. The shear angle of the tested sand is a maximum of 2° greater than that obtained from Bolton’s formula. According to the authors, these differences are affected by the transverse anisotropy of sand in the tested samples and the difference between the dilatant failure state and the failure state.

3D DEM investigation of shear behavior and interaction mechanism of woven geotextile-sand interfaces

This paper presents a numerical study on the investigation of microscopic mechanism governing the interaction of woven geotextile and angular sand employing the 3D discrete element method (DEM). The surface texture and tensile properties of the geotextile were simulated using overlapping spherical particles, and the angular sand was simulated using rigid blocks. The DEM models were fully calibrated based on previous experimental data. The shear and dilation zones of sand near the interface were quantitatively determined based on particle displacement gradients. Analysis of contact forces was conducted to explain the microscopic mechanism behind the macroscopic strength evolution. The influence of geotextile surface roughness on the shear strength of the geotextile-sand interface is also discussed. The results show that the failure mode of the woven geotextile-sand interface is a combination of particle sliding failure along the geotextile surface and shear failure of the sand within the shear zone above the interface. There is a rapid redistribution of contact forces prior to reaching peak shear resistance, and the average normal contact force within the shear zone remains relatively constant after the peak shear stress is achieved. A completely developed shear zone stabilizes soil deformation, typically after achieving the peak shear resistance.

A unified thermo-mechanical bounding surface model for saturated clay and sand

To accurately predict soil thermal effects is of great importance for simulations of complex boundary value problems such as the energy foundations and nuclear waste disposal. Existing thermo-mechanical constitutive models only account for clay, and cannot simulate the sand’s behaviour under thermo-mechanical conditions. In this study, a unified thermo-mechanical bounding surface (UTMBS) model is proposed for saturated clay and sand. Based on the thermal effects on the isotropic compression line, the model proposes a new unified thermal softening relationship and a plastic modulus for clay and sand, with the thermal cyclic behaviour replicated by a memory surface. The unified model considers the thermal effects on the critical state line and the shape of the bounding surface, accounting for both drained and undrained shearing of clay and sand at different temperatures. In addition, the non-linear elasticity relationship represents the hysteresis loops of the stress–strain relationship in the mechanical cycles. The performance of the proposed model is evaluated against existing experimental results for clay and sand in terms of their thermal cyclic behaviour, drained/undrained triaxial compression, and mechanical cyclic behaviour at different temperatures. It is evident that the UTMBS model is able to simulate various thermo-mechanical behaviours of clay and sand.

Shear strength recovery of sand with self-healing polymeric capsules

Self-healing approaches are increasingly being explored in various fields as a potential method to recover damaged material properties. By self-recovering without external intervention, self-healing techniques emerge as a potential solution to arrest or prevent the development of large strains problems in soils (e.g., landslides) and other ground effects that influence the serviceability of structures (e.g., differential settlement). In this study, a microcapsule-based self-healing sand was developed, and its performance during mixing and compaction, shearing, and recovery of shear strength was demonstrated. The cargo used for sand improvement, a hardening oil, tung oil, was encapsulated in calcium alginate capsules by the ionic gelation method. The surface properties, internal structure, thermal stability and molecular structure of the capsules were evaluated by advanced material characterization techniques. The survivability of capsules during mixing and compaction was assessed by measuring the content of tung oil released into the sand, while their influence on sand shear strength and its recovery was assessed with shear box tests. The results showed that the capsules could rupture due to movement of the sand particles, releasing the tung oil cargo, leading to its hardening and minimizing its strain-softening response and enhancing up to 76% of the sand shear strength (at a normal stress of 10 kPa and capsules content of 4%). This study demonstrates the potential of a capsules-based self-healing system to provide ‘smart’ autonomous soil strength recovery and thus with potential to actively control the large strain behavior of soils.

Analysing the role of Fe (II) on flocculation of sand-clay mixtures under estuarine mixing

Estuaries are fragile environment that are most affected by climate change. One of the major consequences of climate change on estuarine processes is the enhancement in salt intrusion leading to higher salinity values. This has several implications on the estuarine sediment dynamics. Of the various factors that affect the flocculation of cohesive sediments, salinity and turbulence have been recognized as to have great significance. Many of the estuaries are contaminated with heavy metals, of which, the concentration of Iron (Fe (II)) are generally on the higher range. However, the influence of Fe (II) on the flocculation of cohesive sediments at various estuarine mixing conditions is not well known. The present study investigated the influence of Fe (II) on the flocculation of kaolin at various concentration of Fe (II), salinity and turbulence shear. The results indicated that Fe (II) and salinity have a positive influence on kaolin flocculation. The increase in turbulence shear caused an initial increase and then a decrease in floc size. In case of sand-clay mixtures, that are observed in mixed sediment estuarine environments, a reduction in the floc size was observed, which is attributed to the breakage of flocs induced by the shear of sand. Breakage coefficient, which is a measure of break-up of flocs, is generally adopted as 0.5 assuming binary breakage. The present study revealed that the breakage coefficient can take values from 0 to 1 and is a direct function of Fe (II) and salinity and an inverse function of turbulence and sand concentration. Thus, a new model for breakage coefficient with the influencing parameters has been proposed, which is an improvement of existing model that is expressed in terms of turbulence alone. Sensitivity analysis showed that the proposed model can very well predict the breakage coefficient of Fe (II) – kaolin flocs. Thus, the model can quantify the breakage coefficient of flocs in estuaries contaminated with Fe (II) that is a vital parameter for population balance models.

Not a Rolling Stone: On Dragging a Stone Weight-Anchor on the Seabed

The force required to drag a stone anchor over several types of surfaces was measured, recorded, and analyzed. It was found that the force involved in the movement of the anchor over the various surfaces cannot be described just by the sliding solids theory, but it involves several additional physical processes, such as increasing the sand shear strength by the pressure the anchor applies on the sand under it; the sinking of the anchor into the saturated sand; shearing the sand in front of the moving anchor and accelerating it to the velocity of the anchor; accumulating sand in front of the anchor, thus adding to the pulled mass; and moving some of the accumulated sand sideways. In many instances, the beginning of the anchor movement involves the liquefaction of the sand under it, thus enabling the relatively easier sliding of the anchor. In addition, movement over rocky surfaces, encountering the irregularities that abound on such surfaces, also differs from classic sliding friction theory. In several situations, the use of an effective coefficient of friction, combining all the processes, can serve to obtain approximate values of the required forces.

Effect of Rolling Resistance Model Parameters on 3D DEM Modeling of Coarse Sand Direct Shear Test

This paper deals with the micro and macro behaviors of coarse sand inside a direct shear box during a geotechnical test. A 3D discrete element method (DEM) model of the direct shear of sand was performed using sphere particles to explore the ability of the rolling resistance linear contact model to reproduce this commonly used test considering real-size particles. The focus was on the effect of the interaction of the main contact model parameters and particle size on maximum shear stress, residual shear stress, and sand volume change. The performed model was calibrated and validated with experimental data and followed by sensitive analyses. It is shown that the stress path can be reproduced appropriately. For a high coefficient of friction, the peak shear stress and volume change during the shearing process were mainly affected by increasing the rolling resistance coefficient. However, for a low coefficient of friction, shear stress and volume change were marginally affected by the rolling resistance coefficient. As expected, varying the friction and rolling resistance coefficients was found to have less influence on the residual shear stress.

Study on the Safety Analysis of Dredger Fill Sea Sand Reused in Embankment Slope near the Yangtze River

In view of the shortage of sand and gravel aggregates, the sea sand in coastal areas is used as roadbed filler in road restoration of tunnel project by the Yangtze river. The basic mechanical performance tests were carried out to demonstrate the particle gradation and consistency limit of dredger fill sea sand. Triaxial test and direct shear test were performed to analyze the stress-strain relationship of sea sand shear strength in riverside environment and the law of shear displacement under vertical pressure. The road performance was analyzed by testing the compaction characteristics and deformation resistance of dredger fill sea sand. The riverside slope is always damaged by water flow, therefore, the stability of the dredger fill sea sand road slope under the measures of wrapping soil was analyzed. Based on the analysis of existing measures to improve the safety of sea sand used in road, the technology of sea sand solidified by alkaline coupling agent is proposed.

Experimental Studies for Shear and Multi-Impact Resistance Performance of Sand–Geofoam Material

In the case of earthquake and rockfall disasters, it is proposed to replace part of sand with geofoam material to form sand–EPS and sand–EPE composite cushions to improve the ability of structures to resist disasters. The shear performance of the sand–EPS beads mixture material with different moisture contents, the impact resistance of sand–EPS beads and sand–flocculent-EPE layered composite materials with different cushion thicknesses and different mass ratios were studied by direct shear tests and multi-impact tests. The results showed that with the increase in the moisture content, the shear strength of the sand–EPS beads decreased, the internal friction angle of sand–EPS decreased first and then increased, and the cohesion of sand–EPS increased first and then decreased. The sand–geofoam layered cushion had better buffering performance. Sand–EPE has better durability than Sand–EPS.

Neural network model to predict strength parameters of dune sand at Jodhpur City

The shear strength of the soil is a significant factor in determining bearing value and determining stability. This study investigates a neural network model for determining the strength parameters (cohesion & friction angle) of locally accessible dune sand in Jodhpur city in India. Model has been developed considering grain sizes ,dry density ,relative density , void ratio, liquid limit, plastic limit etc as independent variables and strength of dune sand as dependent variable. The findings show that the model is capable of forecasting dune sand shear strength parameters . R programming is used to generate an ANN model, which is then compared to MS-Excel. A response analysis was used to establish the best algorithm and neuronal numbers for improving the model design. The use of a neural network to forecast dune sand strength variables was shown to be very accurate. For the experimental results and model outputs, the relative mean squared error, coefficient of decision (R2), and mean absolute relative error are determined. For performance analysis, Levenberg Marquardt algorithm is used. In the ANN model, the quantity and least value of R2 for training data sets are 98.2 percent and 96.2 percent, respectively. The suggested ANN models for dune sand strength are accurate and highly close to the experimental values, according to statistical results. As a result, the ANN model appears to be a useful tool for predicting dune sand strength parameters.

Ultimate pullout capacity of single vertical plate anchors in sand

This paper presents a limit equilibrium solution for calculating the ultimate pullout resistance of shallow vertical plate anchors in sand, considering the combined effects of anchor embedment ratio, sand shear strength, sand-anchor interface strength and anchor aspect ratio. The geometry of the failure mechanism in the solution reflects observations from model tests. The ultimate failure load of a strip plate anchor was then determined by global equilibrium analysis of the passive and active failure soil wedge. The two-dimensional limit equilibrium solution is extended for rectangular plate anchors by introducing the shape factors of Ovesen and Strømann. The solution is compared with a database of 102 pullout model tests of vertical plate anchors in sand assembled from the literature and some limit analysis results. The comparison results suggest that the proposed solution can provide a reliable analytical tool for the ultimate pullout capacity prediction of shallow vertical plate anchors buried in sand.

Investigating the effect of Lignocellulose Mulch on Sand Shear Strength

Investigating the effect of Lignocellulose Mulch on Sand Shear Strength

DEM study on effect of particle roundness on biaxial shearing of sand

In this study, discrete element method (DEM) simulations of a biaxial test were used to examine the effect of particle roundness on the mechanical behavior of sands at both the macro and micro scales. First, a stack of microcomputed tomography images were binarized, segmented, and labeled using advanced image processing and analysis techniques. Second, a spherical harmonic (SH) analysis, which involves a complete set of orthogonal functions, was implemented to rebuild the natural particle shape. Then, five templates of virtual particles were built in a DEM simulation, four of which were obtained from SH degrees of 3, 8, 12, and 15, and one template was an elementary sphere. A flexible membrane was numerically generated to allow the material to deform freely under a prescribed confining stress. Finally, the effect of particle roundness on the mechanical properties of granular materials was investigated and discussed. Two shear bands were found to intersect, forming an X shape in both the rotation and displacement fields. Moreover, a lower particle roundness results in higher deviatoric stress and stronger dilation in the volumetric change. A decrease in particle roundness leads to less rotation of particles despite a higher displacement value. In addition, a larger SH degree leads to smaller normalized contact forces of the particles. This implies that decreasing the roundness results in higher anisotropy of the contact forces.

Numerical Investigation of Particle Shape Effect on Sand Shear Strength

The particle shape contributes significantly to sand mechanical properties but is difficult to study in laboratory experiments. In this study, microscopy experiments were used to classify sand particle morphologies as spherical, non-spherical and ball-shaped. Particles with these three morphologies were modeled using the discrete element method to analyze the effect of the particle shape on the shear strength in a direct shear test simulation. The simulation results showed that the non-spherical particles and balls exhibited the highest and lowest peak shear strengths, respectively, under a low vertical stress. The highest and lowest contact force numbers were observed for the non-spherical particles and balls, respectively. The sand particles exhibited a higher resistance to motion with increasing contact force numbers, resulting in a higher shear strength. For particles with low sphericity (S) and roundness (R) values, a high number of contacts and interlocking structures can form, increasing resistance to external forces. As the S decreased, the anisotropy in the contact force increased during the test, and the contact number distribution of the spherical particles tended to remain isotropic during the entire process.

3D DEM simulations of basic geotechnical tests with early detection of shear localization

Abstract This paper deals with elementary geotechnical tests: triaxial and direct shear of cohesionless sand using the discrete element method (DEM). The capabilities of the numerical DEM code are shown, with a special focus on the early phenomena appearance in localization zones. The numerical tests were performed in 3D conditions with spherical grains. Contact moments law was introduced due to simulate not perfectly round sand grains. The influence of different physical parameters was studied, e.g. initial density or confining pressure. The sieve curve corresponded to the Karlsruhe sand [1]; however, in some tests, it was linearly scaled. Special attention was laid on the behaviour of the sand grains inside localization, e.g. rotation, porosity, fluctuations, etc. and forces redistribution. Emphasis was given on the pre-failure regime and early localization predictors.

Effects of Relative Roughness and Particle Size on the Interface Behavior of Concrete Suction Caisson Foundation for Offshore Wind Turbines

The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the interface shear behavior between sand and concrete. Sand samples with three particle size ranges (0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm) and concrete plates with different relative roughness were used to explore the influence of the relative roughness parameter (Rn) and mean particle size (D50) on shear behavior. The responses from the pure sand shear test are also discussed for comparison. Test results show that the higher the relative roughness (Rn), the greater the maximum shear stress (τmax) appeared. The interface shear stress was weaker than that of the pure sand test. Furthermore, the interface friction angle (φ) of sand–concrete was closely related to the relative roughness of the concrete surface. Under the same conditions, the interface friction angle (φ) increased with relative roughness due to the effect of sand particles breakage and redistribution. By contrast, the effect of the mean particle size (D50) on the interface friction angle (φ) was less significant. However, for the pure sand shear test, the friction angle (φ′) obtained from the traditional shear test apparently increased with D50, indicating that the friction angle was more affected by D50 in the pure sand test than in the interface shear test.

The effect of temperature on the drained shear behavior of calcareous sand

In answer to the growing demands for temperature-related engineering applications in marine geotechnical engineering, this article explores the effect of temperature on the drained shear behavior of calcareous sand. Sixteen drained triaxial shear tests were therefore performed on calcareous sand under various temperatures, and in addition, a further eight were carried out on Fujian standard quartz sand by way of comparison. The results showed that an increase in temperature aggravated the particle breakage of calcareous sand in shear. Increasing the temperature improved the strength and dilatancy of quartz sand but weakened them in calcareous sand. This aggravation of particle breakage at high temperature seems to be one of the main reasons behind the decrease in the strength and dilatancy of calcareous sand. Increasing the temperature led to a decrease in the peak-state friction angle φps, the maximum dilatancy angle ψps, the critical-state friction angle φcs and the critical-state void ratio of calcareous sand. A stress-dilatancy equation for the impairment of the stress-dilatancy behavior caused by increasing the temperature was proposed for calcareous sand, and an empirical model for estimating φcs was then put forward. An increase in the temperature caused the increase in relative particle breakage Br of calcareous sand. φps and ψmax decreased with Br as a negative correlation power function. Additionally, the effect of particle breakage on φcs had a correlation with the stress state. This study may be helpful in reducing the deterioration of structural stability in projects with an inadequate design due to the lack of a full understanding of the effect of temperature on calcareous sand.

A Constitutive Model for Saturated Gravelly Sand Based on Higher‐Order Dilatancy Equation

A standard stress path triaxial test system was applied to carry out conventional triaxial shearing tests for gravelly sands under confining pressures ranging from 50 kPa to 400 kPa at the initial relative densities of 0.15, 0.35, 0.55, and 0.75, respectively. The test results show that all the samples of gravelly sand present strain hardening and shear contraction during the process of shearing test. Additionally, gravelly sands are significantly affected by the initial relative density. The hardening degree of gravelly sand samples rises in line with increasing initial relative densities during shearing tests. When initial relative densities Dr are at 0.15 and 0.35, the volume shrinkage of samples decreases with the increasing confining pressures. Instead, when initial relative densities Dr are at 0.55 and 0.75, the volume shrinkage of samples increases with the growth of confining pressures. To describe these triaxial shearing mechanical properties of gravelly sands, a higher‐order dilatancy equation was proposed based on the concept of a super yield surface. A constitutive model which can describe the mechanical properties of gravelly sand was established when the associated flow laws were applied to compare with the results of the triaxial shearing test under the consolidated drained condition. The comparison results showed that the proposed model can reflect the strain hardening and shear contraction characteristics of gravelly sands from low to high confining pressures under different initial relative densities.

Study the grain size and infiltration method effects for sand soil improvement using the microbial method

Today, with regard to land shortage and ever-increasing growth of the world’s population, construction on loose soil has been inevitable. Therefore, to deal with this issue, it is necessary to improve project site materials. The conventional soil improvement techniques are limited due to high costs and environment unfriendliness. In this regard, microbial-induced calcite precipitation (MICP) is a relatively environment-friendly method that is efficient for soil improvement. In this method, hydrolysis of urea by bacteria containing urease enzyme and in the presence of soluble calcium ions leads to the precipitation and attachment of CaCO3 among the soil grains. In this study, the effects of grain size, a method of infiltration, infiltrated bacteria suspension (BS) volume and infiltrated fixation solution (FS), and cement solution (CS) on Quartz sand shear strength are investigated. The results of the conducted tests showed that among four different infiltration methods, continuous infiltration of BS and CS, have the strongest effect on shear strength. Studying shear strength two different sand sizes based on direct shear test showed that sand with larger effective size and higher permeability has a shear strength 6.2 times compared to non-treated sand. The results showed that soils with less volume of infiltrated bacteria have a higher shear strength. Adding a FS to three different BS volumes showed the one with the lowest amount has the highest shear strength. According to the X-ray diffraction and scanning electron microscopy analyses, the efficient CaCO3 precipitation between the soil particles is confirmed.

Analytical Description of Fibre Reinforced Sand Shear Strength

Analytical Description of Fibre Reinforced Sand Shear Strength