Pure Sand Research Articles

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.

Influence of Adding Tire Chips on the Mechanical Behavior of Calcareous Sands

Scrap Tire disposal has been a critical environmental problem in many urban cities due to the enormous boost in the number of vehicles. This problem can be somehow mitigated by finding applications for these unusable materials in engineering. For instance, Scrap Tire can be executed as lightweight materials for backfill in geotechnical engineering projects. The Scrap Tire reuse in Sand-Tire Mixtures can effectively address growing environmental concerns and, at the same time, provide solutions for geotechnical problems associated with the low shear strength of the soil which fundamentally is determined as the main characteristics of Calcareous (or Carbonate) soils. In order to deeply understand the mechanical behavior of Sand-Tire Mixtures, a series of Consolidated Drained Triaxial Test were conducted in this study employing specimens with two different relative densities (i.e. 30% and 60%) under the specific confining pressures (i.e.100, 350, and 600 kN/m2). The results revealed that by adding 10% Scrap Tire into the Sand-Tire Mixtures, the loose specimen’s shear strength increases from 6 to 14% in comparison to pure sand. Furthermore, the particle breakage factor of the mixtures is considerably less than that of pure specimens.

Sand–tyre chips mixtures in undrained and drained cyclic triaxial tests

This paper deals with the stress-controlled cyclic triaxial response of saturated sand rubber chips (RC) mixtures at different gravimetric contents. Three types of sand were utilised, namely, uniform medium and coarse sands, as well as a combination of the two at two relative densities. A series of consolidated undrained and drained single-stage cyclic triaxial tests was performed using standard equipment to evaluate the development of the accumulated excess pore-water pressures, permanent axial and volumetric strains. Samples were anisotropically consolidated prior to cyclic loading. The results showed that for all sands adding 10% RC increases the liquefaction potential. Compared to pure sand, increasing the chips content beyond 20–30% generally yields an improvement as long as the sand is not too coarse. Expressions have been derived for the evolution of accumulated pore-water pressure and the relation between excess pore-water pressure from the undrained test and cumulative volumetric strain from drained tests. Although the findings were derived for a single set of loads, they reveal the basic characteristics of the cyclic composite material behaviour.

Impacts of range-dependent bottom type on mid-frequency propagation

The Target and Reverberation Experiment in 2013 (TREX13) focused on mid-frequency propagation and reverberation in shallow water off the coast of Panama City Beach, FL. The seafloor at the site primarily consisted of long-wavelength (150–200 m), small-amplitude (∼1 m) sand ridges with narrow (20–30 m wide) regions of mud in the swales. Backscatter measurements using a multibeam sonar indicated that roughly 10%–20% of the seafloor was covered in mud. During the experiment, a source transmitting tones from 1.5 to 4.0 kHz was towed past two stationary vertical line arrays to measure the transmission loss (TL) along the track. The measured TL was found to be midway between the predictions for pure sand and puremud sediments, despite the limited amount of mud at the site. Range-dependent propagation models which incorporate this variation in sediment type, indicate that the mud regions act as sinks of acoustic energy producing a significant increase in loss. Also, the spatial distribution is such that the mud regions cannot be discerned in the TL range-dependence. The implications of this range-dependence on both inversion and reverberation will be discussed. [Work supported by the U.S. Office of Naval Research.]

Laboratory assessing of the liquefaction potential and strength properties of Sand soil treated with mixture of nanoclay and glass fiber under dynamic and static loading

This study evaluated an improvement method based on static and dynamic tests for dune sand soil on the coast of Bandar Anzali city. This soil has very poor and insufficient mechanical performance for many construction projects as well as the potential for liquefaction. Short glass fibers have been used in this improvement method to reinforce the soil modified with nanoclay. The effects of simultaneously adding glass fibers and modified nanoclay at optimal weight percentages on the sand specimen were evaluated through static triaxial tests at consolidated drained conditions. The results showed that the simultaneous addition of glass fibers and nanoclay at lower confining pressures had more significant effects and was more useful for soil modification. The results indicated increases of more than 31% and about 23% in the peak deviatoric stress of the modified sand specimen at the confining stresses of 50 and 100 kPa, respectively, compared to the pure sand specimen. Furthermore, the modified sand specimen had a 20% reduction and a 50% increase in failure axial strain, compared to the pure sand specimen, under the static triaxial test at the confining pressures of 50 and 200 kPa, respectively; however, its failure axial strain did not change at the confining pressure of 100 kPa compared to the pure sand specimen. The results of static triaxial tests showed that the simultaneous addition of glass fibers and nanoclay at the optimal weight percentages increased the cohesion of the sand specimen and did not change its internal friction angle. To investigate the effect of this improvement method on dune sand under dynamic loading, the cyclic liquefaction potential of pure and modified sand specimens was evaluated through cyclic triaxial tests under consolidated undrained conditions. The results showed a significant effect of sandy soil improvement on reducing its liquefaction potential. The number of loading cycles causing liquefaction was increased, by more than 5.5 times at the cyclic stress ratio of 0.27, by about 3 times at the cyclic stress ratio of 0.3, and finally, by more than 2 times at the cyclic stress ratio of 0.34 for the modified sand specimen compared to the pure sand specimen. By defining the cyclic stress ratio corresponding to liquefaction in the twentieth loading cycle as the specimen cyclic strength, the cyclic strength of the modified sand specimen was increased by more than 13% compared to the pure sand specimen. Based on the results of a series of different experiments conducted in this study, it was concluded that the simultaneous addition of glass fibers and modified nanoclay at their optimal weight percentages (0.5% and 1% by total dry weight of specimen, respectively) significantly improved many different resistance characteristics of dune sand soil from the Bandar Anzali coast, and using this composition can be considered as an effective and efficient way to improve this very special type of soil.

Dynamic Shear Modulus and Damping Ratio of Sand-Rubber Mixtures under Large Strain Range.

Adding rubber into sands has been found to improve the mechanical behavior of sands, including their dynamic properties. However, ambiguous and even contradictory results have been reported regarding the dynamic behavior of sand–rubber mixtures, particularly in terms of the damping ratio. A series of cyclic triaxial tests were, therefore, performed under a large range of shear strains on sand–rubber mixtures with varying rubber volume contents, rubber particle sizes, and confining pressures. The results indicate the dynamic shear modulus decreases with increasing rubber volume content and with decreasing particle size and confining pressure. The relationship of the damping ratio to the evaluated parameters is complicated and strain-dependent; at shear strains less than a critical value, the damping ratio increases with increasing rubber volume content, whereas the opposite trend is observed at greater shear strains. Furthermore, sand–rubber mixtures with different rubber particle sizes exceed the damping ratio of pure sand at different rubber volume contents. A new empirical model to predict the maximum shear moduli of mixtures with various rubber volume contents, rubber particle sizes, and confining pressures is accordingly proposed. This study provides a reference for the design of sand–rubber mixtures in engineering applications.

Characterization of Sand From Jebel Ad-Darin Sened (Gafsa-Tunisia)

In order to widen the industrial uses of Jebel Ad-Darin sand from Orbata formation of the region of Sened, different investigations have been made to determine the characteristics of the natural raw material using several techniques. The analyses were carried out by atomic adsorption, X-ray diffraction (XRD) as well as by microscopic observations under a scanning electronic microscope (SEM). Grain size analysis indicates the dominance of medium to coarse sands (> 250 µm) in our studied quarry, with good ranking and strong asymmetry towards small sizes. The mineralogical analysis by X-ray diffraction and scanning electronic microscope SEM showed that the sand of studied career consists essentially of quartz, whose percentage varied from 98–100%.The chemical analyses of these samples confirmed these results. Mineralogical and physico-chemical characterizations indicated that the pure sand of Jebel Ad-Darin in Sened could be of great interest in the industrial sector.

Study of the recent sediment movement features in the vicinity of Deepwater Navigation Channel, Yangtze estuary

Intensive anthropogenic impacts have been implemented in the Yangtze estuary during the last several decades, which significantly modified the global and local hydro- and morpho-dynamics. Subsequently, sediment movement characteristics in the vicinity of the Deepwater Navigation Channel (DNC) change in accordance with such human interactions. The present study is focusing on the recent sediment moving features around the DNC in between 2017 and 2019, after the elevation of the partition dike in 2016. Five successive in-situ regular campaigns for flood and dry seasons, together with field surveys pre- and post-typhoon in 2018, were conducted to collect bottom surface sediment samples. Sand and silt samples with different physical properties were identified. Under the normal weather condition, sand samples are generally found in the South Channel (SC) and the middle reach of the North Passage (NP), whereas silt samples are prevailed elsewhere. Considering the different features in the grain size distribution curve of sand samples, more attentions were paid to the spatiotemporal variations of sand samples. Grain size parameters of sand samples indicate that under the normal weather condition, relatively pure sands with almost no silt constituent exist in the SC, whereas relatively mixed sands with certain silt compositions are located in the middle reach of NP. Nevertheless, only relatively mixed sands could be found in the SC and there are no sand samples in the NP after typhoon events. Subsequently, the recent sediment movement characteristics in the vicinity of DNC were figured out. Under the normal weather condition, relatively mild siltation owing to the back-filings from the dike fields and seaward of DNC occurs in the middle and lower reaches of DNC, which is consistent with the temporal variations of the magnetism analysis of sand samples. In contrast, intensive siltation occurs inside the DNC after the extreme weather events, which comes from three possible provenances, i.e., overtopping from the south dike, back-fillings from dike fields and seaward of DNC. These findings provide some helpful information for the efficient management and reasonable regulation in the Yangtze estuary.

The micro-mechanical behaviour of sand–rubber mixtures under shear: An experimental study based on X-ray micro-tomography

The micromechanical behaviour of two sand–rubber mixture samples (i.e., a glass bead–rubber mixture sample (GB–R) and a Leighton Buzzard sand–rubber mixture sample (LBS–R)) under triaxial compression is investigated using X-ray micro-CT (μCT). Both samples contain sand and rubber grains with similar size and have a rubber content of 30% by mass. The results are compared to those of two pure sand samples (i.e., GB and LBS). Both sand–rubber mixture samples are found to exhibit a significantly lower strain localisation than the pure sand samples. The average coordinate number (CN) of sand–sand contacts of the sand–rubber mixtures experiences a significant decrease at the late shear stage, although volumetric compression of the samples occurs. Meanwhile, sand–sand contact fabrics of the sand–rubber mixtures are found to remain almost unchanged throughout the test, with an anisotropy degree of around 0.04 for GB-R and −0.15 for LBS-R, respectively. In contrast, increasing contact areas and bias towards the major principal direction of sand–rubber contacts are observed in the sand–rubber mixtures as shear progresses, with the maximum anisotropy degree of about 0.27 for GB-R and 0.15 for LBS-R, respectively. Moreover, large-sized and small-sized sand–rubber contacts are found to concentrate towards the major and minor principal directions, respectively, throughout the test. The experimental observations highlight the important role of sand-rubber contacts in the stress-transmission behaviour of sand-rubber mixtures.

Strength and deformation behaviour of sand-rubber mixture

ABSTRACT Loose specimens with a void ratio of 0.86, corresponding to a relative density of 30% for the pure sand, and normal stresses of 50, 100 and 150 kPa were used in this work to study strength and deformation behaviour of sand rubber mixtures. Three types of rubber particles with D-rubber/D-sand = 0.25, 1, and 4, and different rubber to sand ratio of 5, 10, 15, 20, 25, 30, 40 and 50% were investigated by performing more than 300 direct shear tests. The shear strength and deformation characteristics of sand-rubber mixtures were dependent on rubber proportions of the mixtures and size ratio. Angle of friction and cohesion intercept increased and reduced when up to 20% rubber fraction was used, but reduced and increased afterwards. Dimensional analysis of the data suggested that shear strength is a weak function of the rubber fraction for the types of rubber particles used in this study.

Evidence for better microphytobenthos dynamics in mixed sand/mud zones than in pure sand or mud intertidal flats (Seine estuary, Normandy, France).

Understanding the dynamics of microphytobenthos biomass and photosynthetic performances in intertidal ecosystems will help advance our understanding of how trophic networks function in order to optimize ecological management and restoration projects. The main objective of this study was to investigate microphytobenthic biomass and photosynthetic performances as a function of the sedimentary and environmental variabilities in the range of intertidal habitats in the downstream Seine estuary (Normandy, France). Our results highlight higher biomass associated with more stratified biofilms and better photosynthetic performances in areas characterized by a sand/mud mixture (40–60% of mud) compared to pure sand or pure mud environments. This type of sediment probably offers an efficient trade-off between the favorable characteristics of the two types of sediments (sand and mud) with respect to light penetration and nutrient accessibility. Moreover, the large quantities of exopolysaccharides produced in sand/mud mixtures emphasizes the functional role played by microphytobenthos in promoting sediment stability against erosion. This allows us to show that despite the strong increase in sand content of the downstream Seine estuary, intertidal flats are still productive since microphytobenthic biomass, photosynthetic performances and exopolysaccharides secretion are highest in sand-mud mixtures. This study also underlines the impact of ecosystem modifications due to human disturbance and climate change on the dynamics of key primary producers in estuaries.

A method for 3D printing bio-cemented spatial structures using sand and urease active calcium carbonate powder

The substitution of Portland cement with microbially based bio-cement for the production of construction materials is an emerging sustainable technology. Bio-cemented building components such as bricks have been fabricated in molds, where bacteria-containing aggregates solidify when treated with a cementation solution. This restricts component size due to the limited fluid penetration depth and narrows options for component customization. The use of additive manufacturing technologies has the potential to overcome those limitations and to expand the range of bio-cement applications. In the present work an automated process for the production of spatial structures has been developed, in which sand and urease active calcium carbonate powder were selectively deposited within a print volume and treated with a cementation solution. This method provided conditions for calcite precipitation in the powder-containing areas, whereas areas of pure sand served as removable support structure allowing improved fluid exchange. The 3D printed structure was geometrically stable and had sharply defined boundaries. Compressive strength tests on cylindrical specimens showed that the used powder-sand mix was suitable for the production of high-strength bio-cemented material. The present work demonstrates an application of bio-cement in an additive manufacturing process, that can potentially be used to produce resource efficient sustainable building components.

Experimental study on the permeability of methane hydrate-bearing sediments during triaxial loading

The permeability of methane hydrate (MH)-bearing sediments is closely related to the exploitation efficiency of MH deposits. During the exploitation of MHs, the stress state of hydrate-bearing reservoirs is complex, and stratum deformation may occur simultaneously. Both the change in the stress state and stratum deformation may influence the permeability of hydrate-bearing sediments. In this paper, a series of permeability measurement tests was conducted to study the influence of the effective confining pressure and triaxial compression process on the permeability of MH-bearing samples. The test results indicated that the permeability of hydrate-bearing samples was influenced by the effective confining pressure. With increasing effective confining pressure, the permeability of the pure sand sample gradually decreased. For the hydrate-bearing samples, the permeability was also influenced by the effective confining pressure. When the effective confining pressure reached a specific value, a sharp drop in the permeability of the hydrate-bearing samples occurred. The change in permeability might be caused by the increase in fine hydrate particles in the pore space. Based on the test results, the permeability of the hydrate-bearing samples was influenced by the triaxial compression process. During the shearing process, the permeability greatly increased when the axial strain reached a specific value. This phenomenon might be caused by the formation of a shear band. During the production of hydrates, controlling the change in stress applied to the hydrate particles could possibly promote production. Furthermore, the appearance of shear bands or fissures might also increase production by certain methods, such as the hydraulic fracturing process.

Undrained cyclic responses of granulated rubber-sand mixtures

Undrained cyclic responses of rubber-sand mixtures are essential for its applications in earthquake-prone areas. Hence, the present study is intended to examine the liquefaction behaviour and modeling the undrained cyclic responses of granulated rubber-sand mixtures with size of sand and granulated rubber less than 2 mm. The stress controlled undrained cyclic triaxial tests followed by undrained monotonic tests were carried out on mixtures with rubber content 0% (pure sand), 10%, 20%, 30%, 50%, 75%, and 100% (pure rubber) to examine liquefaction and post-liquefaction behaviour of the mixtures. The test results show that the mixture possesses higher liquefaction resistance when rubber content is between 30% and 50%. The post-liquefaction behaviour of the mixtures identified as pseudo-elastic-hardening and its corresponding modulus is found to vary marginally with its static modulus. In addition, the post-liquefaction strength of the mixtures is observed to be more than that of sand at the lower axial strain. Further, the undrained responses such as hysteretic behaviour and excess pore water pressure are modeled using Masing’s rule and the relation between degradation index (δ) and excess pore water pressure ratio (ru), respectively. The proposed model effectively predicts the cyclic behaviour of mixtures with rubber content between 10% and 75%.

Controlling the Permeability of Sandy Soil Using Different Local Waste Materials

Advanced developed technologies associated with people demands have caused production and expansion of different local wastes where the process of managing such waste becomes a real need for controlling the pollution risk. One of the procedures for recycling can be made through using local wastes in permeability control for sandy soil since the soil permeability plays a crucial function on the water drainage, pore water pressure buildup and dissipation, and ground movement for saturated sand during and after earthquake occurrences. In addition, any economical mixture should maintain hydraulic constraints for practice use. In this study, a laboratory experiment was prepared to perform tests for estimating the water movements and permeability in a pure sand column and treated sandy soil with different locally waste materials including plastic, glass, rubber, and aluminum. In addition, a numerical investigation including finite element method has been adopted to verify the experimental procedure. It was shown that the permeability could be controlled to different rates using these local wastes.

Experimental Analysis of the Effects of a Polyurethane Foam on Geotechnical Seismic Isolation

ABSTRACT A new experimental apparatus for performing impact tests is presented, to analyse the wave propagation phenomenon in pure sand and in composite sand-polyurethane specimens, with the final aim to explore the seismic mitigation given by a polyurethane inserted into a real soil under existing structures. Polyurethane layers at three different thicknesses are considered. Experimental results show that composite specimens provide acceleration reductions increasing with the increase of polyurethane thickness. Result interpretation in the light of the elastic wave propagation theory is presented, pointing out the experimental set-up limitations, mainly due to the lack of sufficient specimen confinement.

Morphological Characteristics of Low-angle Dunes on a Tidal Ridge, the Jiangsu Macrotidal Coast, China

Wang, L.; Yu, Q.; Zhang, Y., and Gao, S., 2020. Morphological characteristics of low-angle dunes on a tidal ridge, the Jiangsu macrotidal coast, China. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 717-721. Coconut Creek (Florida), ISSN 0749-0208.Subaqueous dunes are typical flow-transverse rhythmic bedforms in fluvial, intertidal and marine environments. The low-angle dunes (LADs), commonly associated with a leeside angle of less than 15°, differ in terms of the formation mechanism from the high-angle dunes (HADs). Here, multibeam echosounder exploration and seafloor surficial sediment sampling were carried out on a tidal sand ridge off the Jiangsu coast, China, a macrotidal area with the spring tidal range exceeding 6 m. The spatial distribution of the dune morphological parameters, including wave height, wavelength, asymmetry, and lee-side angle, are analyzed in association with the water depth and seafloor sediment. The following results are obtained. (1) Two-dimensional linear dunes are superimposed on the tidal ridge, and a total of 3599 dunes detected are all LADs with an average maximum leeside angle of 5.46°. (2) The spatial distribution of the dune parameters is closely related to the topography of the ridge-swath system. The asymmetries and migration directions of the dunes on the northern and southern slopes of the tidal ridge are opposite, indicating a clockwise residual sand circulation, while the ridge represents the transition zone with relatively symmetrical dunes. (3) Water depth is the controlling factor for the dune geometry in shallow water places. In areas where water depth is below 7.5 m and the seafloor sediments are composed of pure sand, the scales of LADs are proportional to the water depth. (4) Bed sediment composition becomes important for the deeper water areas. For water depth more than 7.5 m, the ratio of cohesive particles (< 8 µm) of bed sediment, which increases with the water depth, inhibits the growth of the LADs. These observations reveal the behavior of LADs in association with sediment particle size and water depth.

Experimental study to evaluate the effect of particle size on the small strain shear modulus of coarse-grained soils

Abstract Coarse-grained soils are found commonly in nature and are extensively used for a wide range of engineering applications, such as slopes, earth dams, and railway foundations. This study presents an experimental investigation on the effect of mean particle size D50 on the small strain shear modulus Gmax of coarse-grained poorly-graded and well-graded soils. Combined with particle morphology analysis, a series of shear wave velocity tests were performed on pure sand, pure gravel and sand-gravel mixture specimens by taking advantage of a torsional vibration measurement device in a large scale triaxial apparatus. The results demonstrate that Gmax is insensitive to D50 for uniform sand and gravel specimens. On the other hand, Gmax increases gradually with D50 for well-graded sand-gravel mixture specimens. The discrepancy in the relationship between Gmax and D50 for poorly- and well-graded soils is related to the degree of size polydispersity in the specimens.

Sedimentation and Transport of Different Soil Colloids: Effects of Goethite and Humic Acid

Soil colloids significantly facilitate the transport of contaminants; however, little is known about the effects of highly reactive iron oxide and the most representative organic matter on the transport of soil colloids with different physicochemical properties. This study investigated the effects of goethite (GT) and humic acid (HA) on the sedimentation and transport of soil colloids using settling and column experiments. The stability of soil colloids was found to be related to their properties and decreased in the following order: black soil colloids (BSc) &gt; yellow soil colloids (YSc) &gt; fluvo-aquic soil colloids (FSc). Organic matter increased the stability of BSc, and ionic strength (Ca2+) promoted the deposition of FSc. Colloids in individual and GT colloids (GTc) coexistence systems tended to stabilize at high pH and showed a pH-dependence whereby the stability decreased with decreasing pH. The interaction of GTc and kaolinite led to a dramatic sedimentation of YSc at pH 4.0. HA enhanced the stability of soil colloids, especially at pH 4.0, and obscured the pH-dependent sedimentation of soil colloids. The transport ability of soil colloids was the same as their stability. The addition of GT retarded the transport of soil colloids, which was quite obvious at pH 7.0. This retardation effect was attributed to the transformation of the surface charge of sand from negative to positive, which increased the electrical double-layer attraction. Although sand coated with GT–HA provided more favorable conditions for the transport of soil colloids in comparison to pure sand, the corresponding transport was relatively slow. This suggests that the filtration effect, heterogeneity, and increased surface roughness may still influence the transport of soil colloids.

Experimental and numerical investigation of sands and Geldart A biomass co‐fluidization

AbstractThis article investigated the fluidization of sands and small Geldart A biomass mixtures. The mixture fluidized like Geldart A type particles with a uniform bed expansion regime before bubbling. The video recorded color distance between pure sands and sands–biomass mixtures was used to estimate the sands–biomass mixing. The coarse‐grained computational fluid dynamics–discrete element method with a hybrid drag model which couples the Syamlal–O'Brien drag and a filtered drag can capture the mixing while the simulation with Gidaspow drag predicted a segregated bed. The simulations were further validated with experimental measured pressure drops. The time averaged pressure drop equals the weight of the bed material, however, its fluctuation is about three times of the bed material fluctuation.