Behavior Of Sand Research Articles

Rheological behavior of granular materials under different relative densities

Granular materials typically exhibit complex behaviour especially during shearing under different states. The material behaviour transitions from fluid-like to unfluid-like primarily due to various fundamental mechanisms involved during the shearing process such as momentum transport, compaction, and jamming. Describing this transition is particularly relevant in a variety of natural phenomena like landslides, debris flow, mudflow, and liquefaction. The mechanism involved in the transitional response is predominantly governed by the initial packing of granular medium, shear rate and boundary stresses. In this study, the influence of relative densities (20% to 74%) on the rheological behaviour of sand is studied using a vane-shear apparatus. The variation of critical shear strength (during jamming), yield strength, apparent viscosity, and the maximum shear rate with relative density is determined from this experimental program. Further, the characterization of the flow behaviour of sand revealed the existence of pre-jamming and post-jamming regimes. The post-jamming response is evaluated by using slope parameters (m and ξ) which predicted an increasing trend with increase in relative density and overburden pressure.

Advancing Understanding of the Influence of Drained Cyclic Loading on Sand Behavior Using DEM

Advancing Understanding of the Influence of Drained Cyclic Loading on Sand Behavior Using DEM

Preliminary findings on the experimental investigation of the small-strain behaviour of Pizzoli silty sand

The dynamic properties of soils play a crucial role in solving many geotechnical problems with special attention to earthquake engineering. In particular, the small-strain soil behavior should be accurately reproduced in geotechnical modelling to allow quantifying of the earthquake-induced site response. If the determination of the small-strain shear modulus can be easily inferred from in-situ measurements of shear wave velocity, the small-strain damping ratio of soils is rarely obtained from in-situ tests and it is commonly defined through cyclic or dynamic laboratory tests. This paper describes preliminary findings obtained from a laboratory investigation performed to measure the small-strain dynamic properties of the silty sand deposit of the Pizzoli site (L’Aquila, Italy). Due to the remarkable seismic hazard of the considered area, demonstrated by several seismic events, such as recently the 2009 L’Aquila and the 2016-2017 Central Italy earthquakes, and in the past, the 2 February 1703 earthquake, a specific investigation program including boreholes, geophysical and geotechnical in-situ tests was carried out. Resonant column tests have been also performed at the Geotechnical Laboratory of the University of L’Aquila in both forced and free vibration modes. The interpretation of the results has been used to identify the small-strain shear modulus and damping ratio. The shear modulus as obtained from the laboratory has been compared with that obtained via the existing in-situ shear wave velocity measurements. In contrast, the damping ratio has been compared with the value estimated with a literature relationship proposed for soil deposits of Central Italy.

Temperature-dependent elastic shear modulus of a saturated lateritic clay

The thermo-mechanical behaviour of saturated clays and sands has been studied by many researchers, considering that it is useful in many geotechnical problems, such as the analysis of energy foundations and the effects of climate change on earth structures. Despite the fact that temperature is known to affect the yielding and volume change behaviour of soils, the effects of temperature on the elastic shear modulus (G0) of soils are rarely studied. In this study, a temperaturecontrolled oedometer equipped with bender elements was developed. It was used to investigate the effects of temperature on G0 of a compacted lateritic clay at saturated conditions. The G0 was measured at 5 and 40°C during loading and unloading in the stress range of 30 to 400 kPa. Four tests were conducted in which two different initial densities (95% and 85% of maximum dry density (MDD) were considered. The results will be interpreted and discussed with reference to the elastoplastic modelling of thermo-mechanical soil behaviour.

Effect of fibre orientation on the mechanical response of reinforced sand, detected with x-ray tomography

The mechanical behaviour of fibre-reinforced sands (FRS) has been thoroughly explored with a laboratory study, firstly investigating the influence of relevant parameters such as grading index, soil density, amount, diameter, and length of fibres then focusing on their orientation with respect to the principal stress directions. This aspect has been deeply investigated performing parallel tests on samples of pure sand and on samples with randomly and uniformly oriented fibres compacted at a similarly high relative density (Dr≈1). Direct and triaxial shear tests have been performed, the former enforcing deformation on a predetermined shear plane. The results show that reinforcement with oriented fibres provides a higher strength and ductility to the sand. The grain scale investigation of the materials’ response to direct shearing has been carried out performing X-ray tomography post-mortem (i.e., after the test). The evolution of porosity in several samples prepared with the same procedure and sheared under the same conditions has been studied freezing the material fabric with nanosilica grout injected at different displacement levels. On the contrary, X-ray tomography performed along with miniature triaxial tests (operando method) enabled the analysis of the spatial distribution of deviatoric strain too. In both cases, maps show the relevant role of fibres orientation with reference to the shear band. If adequately activated, fibres tension modifies the strain field in the samples, preventing the fragile rupture along a shear plane and transferring the stresses to the outer soil portions, in this way providing a more dilatant and ductile overall response of the reinforced material.

Non-invasive characterization of particle morphology of calcareous sands from São Tomé & Príncipe

Calcareous sands of biogenic origin are widely spread throughout the world’s seabed. They are the foundation soils for many offshore geotechnical structures, and, in addition, onshore uses of this material are becoming more significant with the growing demand of backfill material for transport infrastructure. These sands comprise the remains of marine organisms such as shells and tests, and the grains can vary from platy to hollow thin-walled forms with highly angular features. Geotechnical design on calcareous sands is challenging owing to the many uncertainties related to their microscale properties. This study uses non-invasive X-ray micro-computed tomography (μCT) and advanced three-dimensional (3D) image analysis techniques to quantify the morphology of bioclastic calcareous sands from São Tomé & Príncipe. The statistics of particle shape parameters of the São Tomé sand are compared to that of the previously studied Ledge Point sand. In spite of an order of magnitude difference in particle size, São Tomé and Ledge Point sands are markedly similar and, as seen in other calcareous sand, São Tomé shows a strong correlation in 3D sphericity and convexity. The results presented here help to better understand the mechanisms of grain interlocking, and the role of intra-granular void ratio on the mechanical behaviour of calcareous sands from different parts of the world.

Pore-scale precipitation pattern and grain-scale cementation strength by microbially induced calcium carbonate precipitation (MICP)

Microbial induced calcium carbonate precipitation (MICP) is widely investigated as a sustainable method of soil improvement. The pore-scale precipitation habit of calcium carbonate (CaCO3) and the grain-scale mechanical strength of the cementing bonds play a significant role in determining the mechanical response of MICP-treated soils. This study presents the pore-scale precipitation patterns in MICP-treated sands and the grain-scale cementation strength of two beads cemented by MICP. X-ray computed microtomography imaging of MICP-treated sands with different grain sizes reveal that the surface area, number of contacts, and flow-induced shear detachment as well as bacterial cell loci have a profound effect on the pore-scale precipitation. With different grain size, the precipitation can show either a contact-cementing pattern or a surface-coating habit. Particularly, evolution of the precipitation pattern is observed for large-sized grains from the surface-coating mode to the contact-cementing mode with an increase in CaCO3 content. The grain-scale mechanical strength tests on MICP-bonded bead pairs demonstrate that the failure with MICP bonding occurs in three modes: debonding, internal, and mixed failure modes. Amongst, the debonding failure mode has the greatest strength and the internal failure mode shows the lowest strength. The tensile strength is greater than the shear strength in all modes; particularly in debonding failure mode, the tensile strength of ~35 kPa and shear strength of ~13 kPa. The presented results advance our insight into pore-scale and grain-scale behavior of MICP-treated sands, which can be further extended to develop DEM models and transport models.

Normalized Behavior and Residual Shear Strength of Sand

Normalized Behavior and Residual Shear Strength of Sand

The cyclic behavior of sand polluted by leachate

The cyclic behavior of sand polluted by leachate

Laboratory Investigation of the Unsaturated Shear Strength Characteristics of Sand–Clay Mixtures

Sandy‐clay mixtures are commonly used in civil engineering projects, such as transportation and water resources, due to their unique construction properties. While the macromechanical characteristics of these mixtures under saturated conditions are well understood, their behavior in unsaturated states is still not fully elucidated. This study aims to investigate the mechanical behavior of sand–clay mixtures under unsaturated conditions by examining the influence of varying sand content and matric suction on their shear strength. The research includes unsaturated shear strength tests and nuclear magnetic resonance (NMR) experiments to analyze the pore characteristics within the mixtures at different sand content levels. The correlation between changes in pore structure and shear strength is systematically analyzed. The unsaturated shear strength of the mixtures is predicted using the Fredlund shear strength formula and compared with the measured values. The results indicate that the unsaturated shear strength of the mixture decreases as the sand content increases but stabilizes once the sand content reaches 20%. Below 20% sand content, the changes in micropore distribution are not significant with increasing sand content. However, beyond 20% sand content, there is a noticeable increase in the ratio of large pores and a decrease in the proportion of small pores. The sand content of 20% represents a critical threshold for the strength and porosity variations in the mixture. Under constant matric suction, the unsaturated shear strength of the mixture improves with the increase in sand content. However, the predictive accuracy of the Fredlund shear strength formula gradually diminishes as the sand content increases.

Pumice sand behavior on undrained cyclic loading

Pumice sand behavior on undrained cyclic loading

Influence of geosynthetics reinforcement on liquefaction and post-liquefaction behaviors of calcareous sand

To provide new insights into the liquefaction and post-liquefaction behaviors of calcareous sand with and without geosynthetics reinforcement, a series of multi-stage cyclic triaxial tests were conducted. The geosynthetics employed in this study include geogrid, geotextile, and geotextile-geogrid composite. The multi-stage tests consist of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading without excess pore pressure dissipation. The effect of different arrangements of reinforcement layer on the behaviors of calcareous sand is examined and discussed in this study. The test results indicate that a unique relationship can be observed between the double amplitude axial strain and the pore pressure ratio of calcareous sand, irrespective of the influence of reinforcement layer arrangement, providing an effective means of predicting the strain at a given pore pressure level. The liquefaction resistance of calcareous sand increases with the increase in the number of reinforcement layer and decreases with the increase in the distance from the first layer of reinforcement to the sample’s top surface. Compared to geogrid and geotextile, the proposed geotextile-geogrid composite exhibits better efficiency in enhancing the liquefaction resistance of calcareous sand. The reinforcement also accelerates the recovery of strength for liquefied calcareous sand and increases the maximum shear strength of sand at large axial strain during the post-liquefaction stage.

Stress-strain response and deformation behavior of hydrate-bearing sands under different grain sizes: A particle-scale study using DEM

Natural gas hydrates are crystalline solids found in sediments beneath the seabed and permafrost, which significantly affect the mechanical behavior of sediments. The effect of hydrates often varies for different sediments, which has been captured in some laboratory studies. But the particle-scale information involved is obscure and the underlying mechanisms often rely on assumptions. In this study, discrete element method (DEM) was used to improve understanding of the hydrate effect on the mechanical behavior of different sands. Triaxial compression tests were carried out using DEM on the digital hydrate-bearing sands (HBS) with different grain sizes. Simulation results shows that the large-grain samples often yield earlier and tend to strain-hardening behavior, while hydrate occurrence induces strain-softening behavior. In terms of stress-strain response and porosity changes, the hydrate strengthening on the small-grain samples is much greater than the large-grain samples. Particle-scale observations indicate that particle rotation usually occurs in regions with small particle displacement and is more intense on shear slip surfaces. Hydrate bonds are mainly subjected to tensile failure, and large grain size may hinder bond shear failure. Hydrates restrict the development of radial fabrics and enhance the stress-induced anisotropy, rendering a more stable framework for sediments.

Experimental study on monotonic to high-cyclic behaviour of sand-silt mixtures

The naturally deposited soil usually does not consist of pure coarse or fine-grained soil but of a mixture of both. The mechanical behaviour of a saturated fine sand mixed with varying amounts of low-plastic fines was evaluated by monotonic as well as high-cyclic triaxial tests. The test results were used to conclude on the effect of fines content on the critical state, phase transformation line, secant Young’s modulus, the residual strain accumulation as well as strain amplitude during drained cycles of the mixtures in relation to the global void ratio as well as to the equivalent void ratio. It was found that while the choice of void ratio definition is important for the uniqueness of the critical void ratio, both approaches can be used as state variables for the phase transformation line. However, some seemingly contradictive results are found from the drained high-cyclic tests. Eventhough, an increase of the residual strain accumulation with decreasing fines content compared at the same initial equivalent void ratio is rendered by the laboratory data, a unique and on fines content independent relationship between εacc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varepsilon ^{\\rm{acc}}$$\\end{document} could be established only with respect to the initial global void ratio.

Investigation of particle-scale mechanical behavior of hydrate-bearing sands using DEM: Focus on hydrate habits

Natural gas hydrates are commonly found in onshore permafrost and seabed regions. Hydrates often exhibit different pore habits in different regions, which may affect the mechanical behavior of hydrate-bearing sands (HBSs). In this study, pore-filling, load-bearing and cementing HBSs were prepared using discrete element method (DEM). The numerical biaxial compression tests show that the digital cementing HBS specimen well capture the stress-strain response of the gas-saturated HBS specimen in experiments under σc = 3 MPa, which justify the DEM model in this study. The pore-filling hydrates contribute little to the stress-strain response of sediments, while the load-bearing and cementing hydrates significantly enhance the failure strength and stiffness, and also induce strain-softening behavior and higher volume dilation. Hydrate cementation hinders the lateral fabric development in HBS, and renders orderly particle displacement and abundant strong force chains. The yielding of HBS is dominated by the buckling of strong force chains. Particle sliding, dislocation and rotation are responsible for the formation and development of shear bands, which governs the volume dilation and non-uniform deformation of HBS. Comprehending the geomechanical behavior of HBS under different hydrate habits facilitates the optimization of engineering solutions for hydrate exploitation.

Liquefaction susceptibility of clayey sands under saturated and partially saturated conditions

Experiences from previous earthquake events have indicated that sands containing non-plastic (silt) or plastic (clay) fines are susceptible to liquefaction. These experiences underline the need for improving the fundamental understanding of the seismic behaviour of silty and clayey sands and for developing appropriate methods to evaluate their liquefaction potential. This paper presents an attempt to elucidate the integrated effects of fines (non-plastic silt and plastic clay) inclusion and degree of saturation on the cyclic behaviour and liquefaction resistance of sands based on systematic experiments. One of the notable findings of the study is that, apart from the familiar mode of cyclic mobility, clayey sand can also undergo flow-type failure under either fully or partially saturated conditions. The unified correlation between the cyclic resistance ratio and the state parameter (ψ), established earlier for clean and silty sand in the framework of critical state soil mechanics, is found to work for clayey sand as well. Furthermore, it is shown that the impact of saturation on the cyclic strength of clean and clayey sands can be reasonably characterised using the compression wave velocity normalised by the shear wave velocity.

Enhancing Soil Resilience: Bacterial Alginate Hydrogel vs. Algal Alginate in Mitigating Agricultural Challenges.

Erosion and tillage changes negatively the soil physical structure, which directly impacts agricultural systems and consequently food security. To mitigate these adverse modifications, different polymeric materials from synthetic and natural sources, have been used as soil conditioners to improve the hydro-mechanical behavior of affected soils. One of the most interesting and used natural polymers is the alginate hydrogel. Although commercially available alginate hydrogels are primarily sourced from algal, they can also be sourced from bacteria. The gelation capacity of these hydrogels is determined by their molecular properties, which, in turn, are influenced by the production conditions. Bacterial alginate hydrogel production offers the advantage of precise control over environmental conditions during cultivation and extraction, thereby maintaining and enhancing their molecular properties. This, in turn, results in higher molecular weight and improved gelation capacity. In this study, we compared the effects of bacterial alginate (BH) and algal alginate (AH) hydrogels over the mechanical, hydraulic, and structural behavior of coarse quartz sand as a model soil. Mechanically, it was observed that the treatment with the lowest concentration of bacteria alginate hydrogel (BH1) reached higher values of yield strength, Young's modulus (E), shear modulus (G) and strain energy (U) than those treatments with algal alginate hydrogel (AH). Furthermore, the increase in the aggregate stability could be associated with the improvement of mechanical parameters. On the other hand, a greater water retention capacity was observed in the BH treatments, as well as a greater decrease in hydraulic conductivity with respect to the AH and control treatments. All these changes could be explained by the formation of bridge-like structures between the sand particles and the hydrogel, and this alteration may result in a shift in the mechanical and wettability characteristics of the treated soils. Finally, our findings emphasize the superior impact of bacterial alginate hydrogel on enhancing the mechanical and hydraulic properties of coarse quartz sand compared to traditional algal alginate. Besides, the use of bacterial alginate hydrogel could be useful to counteract erosion and water scarcity scenarios in agricultural systems.

Experimental study on cyclic behavior of aeolian sand stabilized with geopolymer and fines

Experimental study on cyclic behavior of aeolian sand stabilized with geopolymer and fines

The role of breakage-dependent critical state lines in constitutive modelling of sand under axisymmetric drained and undrained loads: A comparative study

Particle breakage usually takes place within sand when subjected to external loading, which changes the critical state line (CSL) and stress-strain behavior of sand. To consider such effect, different expressions for the CSL with consideration of particle breakage have been proposed, which can be sorted in two categories: (i) CSL through explicit incorporation of particle breakage ratio into the e – ln p′ relation, (ii) CSL through implicitly empirical correlation, e.g., e – p′ 0.7 and e – exp(p′ζ ) relations. However, limited studies were made on comparing the performances of these expressions. This study inspects the efficiency of three representative CSLs from categories i and ii, for SANISAND modelling of sand. It was found that all the CSLs can capture the constitutive responses of sands under axisymmetric drained and undrained loads, to some extent. However, e – p′ 0.7 and e – exp(p′ζ ) relations are comparatively simple and share an equivalently accurate performance at low to medium high pressures, whereas e – exp(p′ζ ) relation works the best among others at high pressures. To more highlight the physical role of particle breakage, the CSL in category i can be suggested. Otherwise, the CSLs in category ii are recommended in modelling practices, because of the comparatively succinct expressions and less model parameters.

Strength and wear behaviors of methane hydrate-bearing silty sand: insights from multi-reversal direct shear tests

Strength and wear behaviors of methane hydrate-bearing silty sand: insights from multi-reversal direct shear tests