Compression Of Sand Research Articles

Compressibility and crushing of coral sands under one-dimensional dynamic compaction

Compressibility and crushing of coral sands under one-dimensional dynamic compaction

Compressibility, stiffness and electrical resistivity characteristics of sand–diatom mixtures

The engineering characteristics of ocean sediments are significantly affected by fine particles such as diatoms. The objective of this study is to investigate experimentally the compressibility, small-strain stiffness and electrical resistivity of sand–diatom mixtures by way of oedometer tests. Sand–diatom mixtures are prepared at a fixed density with varying diatom contents ranging from 0 to 20% by weight. The vertical displacements are monitored during oedometer tests, and shear wave, compressional wave and electrical resistance are measured using bender elements, piezo-disc elements and an electrical resistance probe, respectively, at the end of each loading step. The test results show that the compression index increases, whereas the swelling index and shear and compressional wave velocities decrease with increasing diatom content because of the small and crushable diatom particles. The attenuation of shear and compressional waves increases continuously, while the shear and compressional wave velocities decrease with an increase in the diatom content due to weak inter-particle contact and a soft soil skeleton. In addition, the sand specimens with a lower compression index, Cc, a higher swelling index, Cs, a higher shear wave factor, α, and a lower shear wave exponent, β, gradually change to clay-like soils, which exhibit a higher Cc, a lower Cs, a lower α and a higher β as the diatom content increases. This study suggests that diatoms may affect the compressibility, small-strain stiffness and electrical resistivity of soil.

Undrained compressibility characteristics and pore pressure calculation model of foam-conditioned sand

Soil conditioning with foam is widely used to transform natural soil into the desired state suitable for mechanised tunnelling. Since the excavated soil is rapidly discharged out with little water drained during earth pressure balance (EPB) shield tunnelling, it is necessary to investigate the undrained compressibility characteristics of foam-conditioned soil under chamber pressure. In this study, a series of compression tests were carried out in a large-scale, self-designed compression device equipped with pore pressure and lateral earth pressure sensors. The results demonstrated that the foam considerably enhanced the compressibility, pore pressure and lateral pressure of the conditioned sand. The workability of foam-conditioned sand may be well conducted in slump tests under the atmospheric condition, but the compressibility of foam-conditioned probably cannot satisfy its requirement for EPB shield tunnelling due to compression of foam under high chamber pressure. In addition, the total and effective lateral pressure coefficients of the foam-conditioned sand increased and decreased, respectively with increasing foam injection ratio and total vertical pressure. Then, the mechanism of the compressibility of foam-conditioned sand is explained with an existing two-dimensional (2-D) model. Finally, according to Boyle’s law, an analytical model is proposed to predict the pore pressure of the foam-conditioned sand under compression pressure, and a satisfactory agreement between the calculated values and the test results was found.

Splash detachment of sand particles under varying contact stress field of wind‐driven raindrop impact

AbstractThe effects of wind‐driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two‐dimensional experimental set‐up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind‐free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s−1and rainfall intensities of 50, 60, 75 and 90‐mm h−1to assess the sand detachment rate (D, in g m−2 s−1). The effects of sand moisture state (dry and wet) on the detachment of different‐sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KExand KEy, respectively, in J m−2 s−1) along with their vector sum (KEr, in J m−2 s−1) explained the variation inD. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KEr, KExand KEywith the sand size and three‐way interaction of KEx, sand size and moisture were statistically significant. These results can be explained by size‐dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind‐driven oblique raindrops (KEx/KEy). Further analysis of the variation of the unit sand detachment rate (Du = D/KEr = g J−1) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity onDuthat further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non‐cohesive particle detachment rates, to some extent interacted with size‐dependent compressibility and interface shear strength of sand grains.

A new isotropic hardening constitutive model based on reference compression curve

In this paper we revisit the problem of simulating the compression and dilatancy behavior of sand by means of a new isotropic hardening constitutive model. First, the reference compression curve, which is constructed as a straight line in the log-power space, is used to establish the volumetric hardening parameter by considering the unified hardening parameter. In addition, a stress-ratio dependent compression curve is regarded as the state parameter reference curve, to describe the shearing behavior as well as the isotropic compressive behavior of sand. Finally, results of triaxial tests for Fujian standard sand and Toyoura sand are used to determine the parameters and verify the proposed model. Comparisons show that this constitutive model is able to describe the stress–strain relationship and dilatancy of sand in a convincing accuracy.

Dynamic Analysis of Machine Foundation with and without Geosynthetic Reinforced Soil Beds

Most of the machine foundations are located in the regions with poorly graded soil including loose sand. Hence, the experimental studies are undertaken to evaluate the dynamic parameters of geosynthetics using cyclic PLT. This paper presents the results of the 10 m2 area of the model cyclic plate load test conducted on geosynthetics reinforced soil beds with similar density, supporting square footing, the results of cyclic PLT from the laboratory-model tests on square footings resting on a sand bed. The various intensity of cyclic load (loading-unloading) applying on the footing and then the elastic recovery of the footing alike to each intensity of loading obtains during the tests to determine the coefficient of elastic uniform compression (Cu) of sand. Results showes that the provision of geosynthetics like geogrid and jute the value of Cu decreases due to elastic recovery increases as compared to unreinforced soil bed, by 06% to 94% and natural frequency 03% to 76% . Introduction of planer geogrid at the base of the geosynthetic matress not only enhance the load carrying capacity but also increasing the elastic recovery to making them more elastic and prevents footing to failure due to vibration. In addition to the experiments also analyses various dynamic parameters of the machine foundation using cyclic PLT on the geosynthetics

DEM modeling of one-dimensional compression of sands incorporating statistical particle fragmentation scheme

This paper presents a novel framework of modeling crushable granular materials under mechanical loadings based on the discrete element method (DEM). The framework is featured with the construction of the one-to-one model in which every particle in a physical experiment has its own numerical twin and allows the modeling of irregular shaped fragments during the continuous breakage process. First, image processing techniques and spherical harmonic (SH) analysis were adopted, respectively, to segment and label particles and to construct a one-to-one model mathematically in DEM. Then, a particle crushing criterion based on the maximum interparticle contact force was used to predict the crushing events, showing fitting results that agreed very well with a large number of single particle crushing tests. Next, a statistical approach for the generation of particle fragmentation modes of a given type of sand particles based on the principal component analysis (PCA) was proposed. The aim of the PCA was to analyze the statistical trends of the coefficient matrix, which was composed of the SH coefficients of all the particles involved in the analysis. Finally, a successful modeling of a particle crushing event was achieved by replacing the particle, which was judged by the crushing criterion to undergo crushing, with a few subparticles chosen randomly from a specific fragment template constructed using the microcomputed tomography (micro-CT) data.

Experimental Investigation on Seismic Compression of Sand Subjected to Multidirectional Cyclic Loads

The ground is simultaneously subjected to both horizontal and vertical motions during earthquakes; however, the majority of existing studies on seismic compression are still limited to the horizontal earthquake motions only. In this work, the objective is therefore to experimentally investigate the effects of multidirectional nature of load application on seismic compression of sand. Multiple series of hollow cylindrical torsional shear tests were conducted on dry sand specimens with different relative densities, where different scenarios of stress conditions induced by earthquakes were simulated by applying various combinations of vertical and horizontal cyclic loads. Test results revealed that coupling with horizontal motions, the vertical component of seismic loads would significantly contribute to the development of both shear and vertical strains in the sand specimen. The increment in vertical strain under coupled motions could be up to over 70% compared to its counterpart for the sand specimen under horizontal cyclic stress alone. Nevertheless, it is also interestingly found that the contribution of superimposed vertical motion alone to the growth of vertical strain is limited. Besides, the effect of relative density on the change of vertical strain is nonlinear, and the decreasing rate of vertical strain diminishes with the increase of relative density.

Applicability of Waste Rubber Particles as Buried Pipe Backfill Material

The primary purpose of this work is to evaluate the viability of using waste rubber particles as buried pipe backfill. By applying confined compression test and model test, this research studied the compressibility of sand and rubber-sand mixtures (RSM) and also, investigated the behavior of pipe surrounded by sand and RSM subjected to impact loading. The findings are as follows: 1) The vertical elastic strain and plastic strain of compression test samples increase with rubber content, and the elastic strain and plastic strain of saturated samples are greater than those of dry samples. 2) The settlement of RSM model soil is greater than that of pure sand model soil subjected to impact loading. The addition of rubber particles to pure sand reduces the earth pressure increment. The cumulative strain of pipe surrounded by dry RSM is less than that surrounded by dry pure sand. However, the cumulative strain of pipe surrounded by saturated RSM is greater than that surrounded by saturated pure sand. This investigation provides an environmentally friendly approach for recycling waste tire particles in geotechnical engineering.

Seismic Compression of Unsaturated Silty Sands: A Strain-Based Approach

The vast majority of surface structures are located on or surrounded by unsaturated soil deposits and may suffer excessive settlements during earthquakes. However, the fundamental understanding of the mechanisms by which the degree of saturation impacts the volumetric deformation of soils during seismic loading is still not mature. Consequently, it is critical to develop and calibrate seismic compression models while considering these mechanisms. The objective of this paper is to experimentally investigate the impacts of the degree of saturation, fines content, and desaturation technique on the seismic compression of sand and silty sands. The experimental program involved undrained cyclic direct simple shear tests on specimens prepared using suction control and wet-compaction techniques with similar relative densities but different levels of saturation. A strain-based predictive model was adapted and modified to capture the observed trends in the seismic compression of soils with different degrees of saturation. The suitability and applicability of the model were verified by comparing the measured and estimated compression values in this study with ones reported in the literature for other soils and desaturation approaches.

Lightly Stabilized Loose Sands with Alkali-Activated Fly Ash in Deep Mixing Applications

Abstract Deep mixing using cementitious compounds are an in-situ ground improvement method for improving the strength and compressibility of loose sands. Low-calcium class F fly ash (FA) is a susta...

Undrained Seismic Compression of Unsaturated Sand

Unsaturated soils in engineered geostructures like embankments or retaining walls may experience seismic compression during earthquakes due to particle rearrangement associated with large-strain cyclic shearing. Although previous studies have investigated volume changes during drained cyclic shearing of unsaturated soils, undrained cyclic shearing presents a more complex situation. During undrained cyclic shearing, changes in total volume, matric suction, degree of saturation, effective stress, shear modulus, and damping ratio may occur that have complex coupling effects that affect seismic compression. To better understand these coupling effects, this study performed a series of undrained cyclic simple shear tests on unsaturated sand specimens. Contractile volumetric strain after 200 cycles in these tests was found to vary nonlinearly with degree of saturation. The largest volumetric contraction occurred at a degree of saturation of 0.4 and coincided with the largest decrease in mean effective stress. The sand specimens followed a wetting-path scanning curve during shearing, with small changes in matric suction. The decrease in mean effective stress during cyclic shearing for all specimens followed the same linear relation with the accumulation of volumetric strain.

Investigation of 1D sand compression response using enhanced compressibility model

1D sand compression response to ko-loading experiences volume contraction from low to high effective stress regimes. Previous study suggested compressibility model with physically correct asymptotic void ratios at low and high stress levels and examined only for both remolded clays and natural clays. This study extends the validity of Enhanced Terzaghi model for different sand types complied from 1D compression data. The model involved with four parameters can adequately fit 1D sand compression data for a wide stress range. The low stress obtained from fitting parameters helps to identify the initial fabric conditions. In addition, strong correlation between compressibility and the void ratio at low stress facilitates determination of self-consistent fitting parameters. The computed tangent constrained modulus can capture monotonic stiffening effect induced by an increase in effective stress. The magnitude of tangent stiffness during large strain test should not be associated with small strain stiffness values. The use of a single continuous function to capture 1D stress-strain sand response to ko-loading can improve numerical efficiency and systematically quantify the yield stress instead of ad hoc methods.

Linking shape and rotation of grains during triaxial compression of sand

Particle shape has a strong effect on the mechanical response of coarse soils. This has been usually observed examining specimen-scale or engineering-scale responses, which are the sum of many microscale interactions. In this work we observe the effects of particle shape directly at the microscale level. X-ray tomography (μ-CT) of two sand specimens is exploited to measure three-dimensional particle shape descriptors but also to track individual particle motions during triaxial compression. A discrete digital volume correlation algorithm is employed to track the motion of individual grains (around 50,000 for each sand specimen) during the test and measure, with good precision, their cumulated displacements and rotations. The specimens examined failed in a clearly localised shear mode. Advantage is taken of this to obtain data relevant for very different kinematical regimes: one uniform and more constrained and the other close to critical state. A direct comparison between the shape and kinematic databases shows to what degree particle shape descriptors are related to observed kinematics. It appears that true sphericity is a good predictor of upper bound rotational restraint.

Numerical Simulation of the Effect of High Confining Pressure on Drainage Behavior of Liquefiable Clean Sand

This article presents numerical simulations investigating pore pressure buildup of a sand layer with a free drainage boundary at the top under both low and high overburden pressures and subjected to earthquake base excitation. The numerical runs simulate two centrifuge experiments previously conducted and reported. In these tests, a 5-m layer of clean Ottawa sand with relative density Dr=45% was tested under overburden pressures of ∼100 and ∼600 kPa (1 and 6 atm). The simulations were performed using Dmod2000, a nonlinear effective stress numerical one-dimensional (1D) site response analysis code. The tests revealed that the response was partially drained rather than undrained, with much more partial drainage at ∼600 kPa (6 atm) compared to ∼100 kPa (1 atm). The simulations correctly modeled this behavior, with very good agreement between simulated and measured centrifuge excess pore pressures. A key aspect of this good accord in the simulations was the correct selection in the simulations of the 1D drained volumetric stiffness of the sand, M′=1/mv, because the coefficient of consolidation, cv, is proportional to M′. Both cv and M′ were 2.5–3 times greater at ∼600 kPa (6 atm) than at ∼100 kPa (1 atm) in both centrifuge tests and simulations. Any future simulation of pore pressure response of sand under field drainage conditions needs to consider this large increase in volumetric stiffness at high overburden pressure. Good agreement was found between values of M′ back-calculated from the centrifuge tests and from a consolidometer test on a different sand reported in the literature. The value of M′ seems to increase approximately with the root square of the overburden pressure, and future simulations for high overburden and realistic field drainage conditions should account for this increase. The proper high-pressure correction factor, Kσ, to be used in conjunction with liquefaction charts may be higher than 1 for some realistic field drainage conditions due to this substantial decrease of sand compressibility under high overburden pressure.

Dilatancy and liquefaction behaviour of clean sand at wide range of confining stresses

The state of clean sand was mainly dependent on its void ratio (density) and confining stress that greatly influenced the mechanical behavior (compression, dilatancy and liquefaction) of clean sand. Confirming whether the confining stress was a state variable of sand required precise element tests at different confining stress, especially the tests under very low confining stress whose test data were very limited. In this study, static-dynamic characteristics of clean sand was comprehensively investigated by a unified test program under low and normal confining stress ranging from 5 to 98 kPa, under monotonic/cyclic and drained/undrained conditions, together with the literature available data under confining stress of 1.0 to 3.0 MPa. For monotonic loading tests, the contraction/dilation phase transition was observed for loose sand at low confining stress, and dilatancy angles were stress-dependent. In addition, the liquefaction resistance was observed to increase with reducing of confining stress, and the axial strain varied from compressive to dilative when confining stress increased. Special attention was also paid to the enhancement effect of membrane, and it was observed that its influence on the test results was limited. In addition, the experimental results were proved reliable by reproducibility.

Evolution of particle morphology and mode of fracture during the oedometric compression of sand

This work uses synchrotron X-ray tomography to quantify the role of the particle shape on the interaction between collective comminution and individual grain fracture. Two sands (subrounded Ottawa and subangular Q-ROK#2) were compressed beyond their comminution pressure and imaged at the microscale. An algorithm was developed to track the sequence of breakage events stemming from compression, as well as the evolving morphology of the resulting fragments. The results show that the degree of grain shape evolution depends on the initial morphology of the particles, with subrounded particles exhibiting the most severe shape alterations. However, it was found that at high compressive stress all morphological indices approach similar values. Such a tendency is achieved when crushing involves primarily the finer grain fractions – that is, when cushioning hinders the rupture of larger particles. A quantitative assessment of the mode of particle failure also revealed that in both sands comminution (i.e. the pervasive fragmentation of individual particles) was not achieved abruptly, but was rather attained by way of successive stages of splitting and chipping. These findings suggest that in crushable granular solids the initial grain shape plays a key role during the first stages of compression leading to yielding, but its influence tends to vanish at higher pressures, when cushioning mitigates the impact of initial morphological differences and hinders further major breakage.

Drained Seismic Compression of Unsaturated Sand

AbstractUnsaturated soils in engineered geostructures like embankments or retaining walls may experience seismic compression during earthquakes due to particle rearrangement associated with large-s...

On the Yielding and Plastic Compression of Sand

On the Yielding and Plastic Compression of Sand

Experimental Study on Compressibility and Rebound Characteristics of Sand Reinforced with Polymer and Fiber

ABSTRACT The compressibility and rebound properties of sand reinforced with polymer and fibers were studied with respect to polymer content, dry density, and types and content of fibers using laboratory standard consolidation experiments. The following conclusions are drawn: (1) with the increase in polymer, the compressive coefficient of reinforced sand decreases gradually. Up to 4%, the compressive coefficient decreases slowly and the resilient rate keeps increasing; (2) with the increase in dry density, the compression coefficient decreases rapidly at first and then changes slowly. Up to 1.55 g/cm3, the compression coefficient changes slowly, while the resilient rate keeps increasing; (3) with the increase in fiber content, the compressive coefficient increases and the compressive characteristics of the sand after adding polypropylene fibers become stronger than those of the sand with addition of sisal fibers. The resilient rate of the reinforced sand keeps increasing and the sand reinforced with sisal fiber has a higher resilient rate; (4) the polymer forms a parallel connection model between sand particles, and the curing film can fill the pore between particles. A spatial stereo structure is formed within the sand mixed with fibers reducing the compression characteristics and increasing the resilience under larger vertical loads.