Sand Bed Research Articles

Experimental Study on the Riverbed Coarsening Process and Changes in the Flow Structure and Resistance in the Gravel Riverbed Downstream of Dams

Following the construction of a reservoir, sediment is intercepted, which greatly reduces the sediment concentration in the discharged flow. This reduction causes riverbed scouring and flow structure adjustments downstream, thereby impacting the river habitat. This study used the generalized flume test with different bed sand compositions and discharge rates to simulate the scouring adjustment process of a sand pebble riverbed channel downstream of a reservoir. The results show that the bed sediment composition affects the water surface gradient, scour depth, turbulence intensity, and sand resistance directly after final scouring. Coarse-grained bed sediment demonstrated the greatest final turbulence intensity and sand resistance, while bed sediments with reduced coarseness exhibited a greater scouring degree; the resistance for sand grains of moderate coarseness showed the greatest change. Sand resistance was exponentially and positively correlated with the median grain size and the fractal dimension of bed sediment mass. The mass fractal dimension expression was suitable for the analysis of bed sand grain-size distribution; it contributed to the calculation of grain resistance with fewer hydraulic parameters. The relationship between the mass fractal dimension and the adjusted grain resistance was also established, which can aid the calculation of the resistance changes in sandy gravel-bed river reaches downstream of reservoirs, enabling the prediction of their effects on aquatic habitats.

Comparative Study of Aragvadha Phalamajja (Cassia fistula Linn.) w.s.r. to its Sangrahana Vidhi

Ayurved advocates that drug should be collected with proper classical methods. In Ayurvedic texts, specific time, season and procedures or methods have been highlighted for getting better potency, efficacy and therapeutic properties of drug by describing the standard methods of drug collection and preservation in details. Now a day, due to lack of proper traditional knowledge and time very few people bother to follow all these methods of collection given by Acharya. Hence, the potency of medicines is of question. Aragvadha (Cassia fistula Linn.) has been popular as a common drug of choice treatment since ancient time. Classic text like Charaka Samhita has quoted the classical and particular method for the collection and preservation of Aragvadha Phalamajja (Cassia fistula Linn.). Acharya Charaka has quoted this collection method of Aragvadha Phalamajja(Cassia fistula Linn.)as follows- The good qualities of collected pods should be kept covered in river bed sand for seven days. After seven days these pods should be removed and kept in sunlight for some time. And thereafter, fruit pulp (phalamajja) should be extracted and stored in a clean vessel. Therefore, study of classically collected Aragvadha Phalamajja (Cassia fistula Linn.) and Market sample of Aragvadha Phalamajja (Cassia fistula Linn.) was carried out.

An Idealized 3D Model of Interfacial Instability of Aeolian Bedform

An idealized morphodynamic model is constructed for formation of the aeolian sand ripples from small bottom perturbations of a two-dimensional sand bed. The main goal of the analysis is to evaluate the influence of the gravity flow (including “impact-induced gravity flow” in the reptation flux and “topography-induced gravity flow” in the creep flux) on the formation of the aeolian sand ripples and to clarify the relative contribution of various factors to the bed instability. A 3D linear stability analysis reveals that gravity flow appreciably affects the dynamics behaviors of aeolian sand ripples, which decreases the growth rate of sand ripples, tends to stabilize the sand bed, and leads to longer wavelength. We found that the competition between the destabilizing effect of reptation flow and the stabilizing effects of gravity flow leads to pattern selection. The along-crest diffusion of topography driven by impact and gravity is beneficial to the transverse stability of sand ripples, producing sand ripples with straighter and more continuous crests. For moderate values of D, the most unstable mode has zero value of the transverse wavenumber (ky = 0), thus corresponding to aeolian ripples with crests perpendicular to the wind. Moreover, when the impact angle is 9–16°, it has little effect on the characteristics of sand ripples for the initial stage of ripple development. For every increase of the impact angle by 1°, the initial wavelength only increases by about 1.5%. In conclusion, the influence of the gravity flow on the dynamics of sand ripples formation stage cannot be neglected.

Effect of flooring system on maintenance behaviours of cows

To evaluate the effect of floor on maintenance behaviours of cow in loose housing system, four groups, viz. T0 (concrete in covered and brick-paved in open area), T1 (concrete in covered and sand bed in open), T2 (rubber mat in covered and sand bed in open) and T3 (rubber mat in covered and brick-paved in open) were studied. Feeding was the major activity (39–44%) of day, with significant difference between groups. In covered area, lying and standing rumination, while in open area idling, were significantly different between groups during day. During night lying-rumination was major activity (62–69%). Night idling, standing-rumination, lying and lying-rumination behaviour, were significantly different between groups. Overall most of the time in each group was devoted to lying-rumination (45–53%) and feeding (18–21%). Area wise, open area was more occupied and posture wise sitting posture dominated in all the groups. Overall feeding, idling and standing-rumination in open, lying-rumination (in open or covered area), sleeping, total standing time and total sitting time were significantly different between groups. Feeding time showed positive trend in rubber matted floor (T2, T3). More lying-rumination and sleeping time was seen in rubber matted covered area. Sand bedding in open area reduced the standing and standingrumination activity, while promoting the sitting/lying time. Rubber matting in covered area and sand bedding in open area, was found favourable for maintenance behaviour of dairy cows.

Propeller jet flow scour around pile group supported piers

In this study, scouring formation around pile groups with different configurations and exposed to a ship's main propeller jet flow was investigated experimentally. The experiments were conducted in a flume by installing cylindrical piles on a horizontal sand bed. The selected pile configuration was a 3 × 3 square arrangement. Different tests were performed by changing the space between the piles. The effect of the distance between the piles with respect to the densimetric Froude number (Frd) on scour formation was investigated by considering three different propeller rotation speeds (590, 670 and 745 rpm) with 5 and 7 cm pile diameters (d0), using propellers with diameters (Dp) of 6.5 and 10 cm located 10 cm above the sand bed (G) and 10 cm away from the front piles (X). In addition, the 3D global scour-hole geometry was obtained using photogrammetric data collection and analysis techniques. The equilibrium scour hole morphology was described in detail, and the characteristic dimensions of the resulting scour hole were thoroughly analyzed. The equilibrium scour depth of the pile groups was found to depend on the space between piles (Xt), densimetric Froude number and also position of the propeller. The equilibrium (maximum) scour depths around piles with respect to their configuration were larger than the scour depth around a single pile under same flow conditions.

Real-scale DEM simulations on the fault evolution process observed in sandbox experiments

The study of fault structures and stress states in accretionary prisms is important to elucidate the building and releasing of seismic energy as they control the generation of great earthquakes and tsunami. In this paper, we present the evolution process of three-dimensional fault structures performed in sandbox simulations using a discrete element method (DEM). To realize a real-scale sandbox simulation, we developed state-of-the-art techniques in high performance parallel computing for the DEM and performed the world’s largest DEM simulation using up to 1.9 billion particles with a similar grain size as real sand to identify the three-dimensional fault structure. The DEM simulations reproduced the undulation of fault structures, similar to those commonly found in nature. In addition, the characteristic grain motion was observed near the frontal fault before the commencement of the uplift event of the sand bed, which could be a precursor of tectonic events behind accretionary prism formation.

Effects of pile-cap elevation on scour and turbulence around a complex bridge pier

ABSTRACT In this study, the local scour and the associated flow hydrodynamics around a complex pier with rectangular pile-cap at three different pile-cap elevations are investigated. The pile-cap elevations were selected with respect to the initial sand bed, such that the pile-cap was unexposed (case I), partially exposed (case II), and fully exposed (case III) to the flow. The experiments were performed in a recirculating flume under clear-water scour conditions, and the instantaneous flow velocity was obtained at different vertical planes using the particle image velocimetry (PIV) technique. The partially exposed pile-cap case showed the maximum obtained scour-depth (MSD). The reason behind the MSD occurrence in case II was enunciated through the analysis of turbulent flow field which showed that as the pile-cap got exposed to the flow, it dominantly affected the generation of vortices from the pile-cap corners responsible for the higher scour depth. The effect of the pile-cap on the flow field was prominently seen in case III through the mean velocities, vorticity, Reynolds shear stresses and turbulent kinetic energy contours, but since the pile-cap was away from the bed, the pile-cap corners did not show any direct effect on the scour.

Connoisseur's Choice: Sand Calcite, Rattlesnake Butte, South Dakota

When minerals such as calcite (CaCO3), gypsum (CaSO4·2H2O), and baryte (BaSO4) form in sand beds, grains of sand are generally incorporated into the crystals. The resulting sand-included crystals a...

Using nanomaterial to minimize the local scour downstream of sluice gate

Prediction of scour depths is an important aspect related to the overall stability of hydraulic structures. In this research, small-scale laboratory experiments were carried out to explore the effectiveness of mixing different percentages of Nanomaterial (Silica fume) to non-cohesive (alluvial) movable bed soil to develop mixture of bed material with significant characteristics to minimize the local scour caused by high-velocity jets downstream of a sluice gate. The experiments were executed employing 9 jet Froude numbers ranged from 1.88 to 2.81 associated with 3 heights for gate opening, and 3 tailwater depths. The bed material has 5 different percentages of Silica fume mixed by weight and 2 types of mixing with and without water were used. Ninety-nine experiments were conducted, out of which 9 experiments were done using fine sand as a bed material for the referenced cases. Graphical relationships were presented for maximum scouring and silting depths for different hydraulic conditions and bed materials. This research demonstrated that the type of mix (dry-mix or wet-mix) had a significant influence on the geometry of scouring and silting for the same flow conditions and the mixed percentage ratio of Silica fume. For dry-mix, the scouring and silting depths increased as the percentage ratio of Silica fume increased. While for wet-mix, the scouring and silting depths decreased as the percentage ratio of Silica fume increased. Also, the wet-mix effectively reduced the local scour volumes by 34.65% and 83.05% and decreased the silting volumes by 33.35% and 89.42% according to the percentage of Silica fume. Using a bed mixture of 8% Silica fume wet-mix showed 83.05% and 89.42% decrease in scouring and silting volumes, respectively, compared to pure fine sand bed material. From practical and financial aspects, the presented composition of bed material can effectively replace the smooth apron or at least decrease its length to reduce the construction cost. The obtained results present an untraditional technique for local scour protection downstream hydraulic structures.

Hydrodynamics and sediment transport under a dam-break-driven swash: An experimental study

An experimental study is presented consisting of swash zone hydrodynamics, sediment transport flux estimates, and bed changes under a single dam-break-driven swash event over a steep (1:7), movable sand bed. The study provides resolved measurements of instantaneous water depths, cross-shore flow velocities, sheet flow and suspended sediment concentrations, and morphological response. An ensemble-averaging over 24 repetitions of the swash event allows convergence in the time-averaged measured swash quantities. The sand bed profile was re-constructed after each run with a re-smoothing procedure that allowed for minimum variations that are within the profiler system accuracy (<0.006 m). High-resolution measurements are employed to reconstruct the spatial-temporal evolution of the flow velocity field. Temporal extrapolation and spatial logarithmic/exponential fits are employed to fill velocity gaps in the measured data for the estimation of instantaneous and depth-integrated sediment flux. The spatial gradients of instantaneous sediment flux indicate that the sheet flow sediment dominates over the suspended load during the most relevant phases for sediment transport. Upon bore arrival and initial uprush, the relative contribution of the sheet flow load is larger than during the backwash phase and is decreasingly dominant onshore. Depth-integrated instantaneous sediment flux and total sediment transport estimates, based on two different approaches, are compared with equivalent total sediment transport estimates obtained from the observed morphological changes and the sediment continuity equation. The close agreement between the various approaches indicates that existing models and empirical estimates for the sheet load concentration profile can be used as first order estimates for sediment transport in the swash zone.

Gasification Kinetics of Victorian Brown Coal-Derived Char in Fluidized Bed Reactor

Abstract In a chemical looping combustion (CLC) system, gasification kinetics of char holds immense importance being the rate-limiting reaction in the fuel reactor. This paper studied the gasification kinetics of char derived from Victorian brown coal (VBC) in a fluidized bed reactor which mimics the fuel reactor conditions of a chemical looping combustion process. Mass of char, char particle size, and gas flow conditions were optimized to ensure the gasification reaction free from mass transfer limitations. Effect of oxygen carrier (OC), hematite, being the bed material was also studied. The experiments were conducted in the temperature range of 800 °C–950 °C, which is a typical range for fuel reactor. The experimental results were modeled with the help of grain model (GM) and random pore model (RPM) to analyze the kinetic parameters. Activation energy was found to be around 177 kJ/mol in sand bed and 175.5 kJ/mol in the hematite bed. Reaction in hematite bed was found to be 42% faster on average compared with the reaction in a sand bed. Fastest total conversion of char took as low as 4.1 min in hematite bed at 950 °C. While catalytic effect of hematite was ruled out due to insignificant change in activation energy, it was concluded that increase in CO2 partial pressure at the vicinity of char particle enhanced the reaction rate in the case of hematite bed. This study has generated relevant information for the CLC of Victorian brown coal with hematite as the oxygen carrier.

An Experimental Study of Nailed Soil Slope Models: Effects of Building Foundation and Soil Characteristics

A soil nailing system is a proven effective and economic method used to stabilize earth slopes from the external (factors increasing the shear stress) and internal (factors decreasing material strength) failure causes. The laboratory models with scales of 1:10 are used to study the behavior of nailed soil slope with different soil and building foundation parameters. The models consist of Perspex strips as facing and steel bars as a nailing system to increase the stability of the soil slope. The models of sand beds are formed using an automatic sand raining system. Devices and instruments are installed to monitor the behavior of soil-nailed slope during and after construction. The effect of the soil type, soil slope angle, foundation width and position on the force mobilized in the nail, lateral displacement of the slope, settlement of the foundation and the earth pressure at the slope face, under and behind the soil mass at various foundation pressures, has been observed. It is found that the increase of soil density reduces both slopes facing displacement and building foundation settlements. The slope face displacement and footing settlement will increase with an increase in the width of the foundation and foundation position near the crest of the slope.

Survival of Streptococcus uberis on bedding substrates

Streptococcus uberis (S. uberis) is a mastitis pathogen with an environmental reservoir. Management factors related to housing design and bedding are associated with the risk of S. uberis mastitis. This study aimed to investigate the ability of five distinct strains of S. uberis to survive and replicate on three common bedding materials (sand, wheat straw and kiln dried pine sawdust). Sterilized bedding substrates were inoculated with S. uberis and incubated at room temperature. Bacterial recovery from these media over time indicated that S. uberis numbers increased on used bedding materials, suggesting the addition of faeces and urine promoted replication. The bacterium was recovered for at least 35 days on straw and sand bedding, but could not be recovered beyond 7 days on clean or used sawdust. This study demonstrates the importance of bedding type and management on the environmental survival of S. uberis.

Relative role of sediment entrainments on log-law parameters of longitudinal velocity distributions in mobile bed flows

Abstract In alluvial channel, the non-cohesive bed particles are frequently accelerated by the flows and there has been an inconclusive debate on the deviations of logarithmic law parameters that demonstrate the velocity distributions in flows. Present study aims to elucidate the current knowledge of overwhelming theoretical and experimental evidences in this regard within the scope of near-bed turbulent flow characteristics. The study was conducted in two folds collecting instantaneous velocity of flow over a rigid sand bed under clear water flow conditions and compared to those over mobile sand beds under equilibrium bed-load. Results corroborated additional support to confirm the upward shifting of zero-velocity level in mobile bed flows. Most importantly, the conventional value of von Kármán coefficient significantly deviates in mobile bed flows compared to those in rigid sand bed. Also, the frictional velocity obtained from the bed slope consistently differs to those obtained from the Reynolds shear stress (RSS) distributions owing to transfer of stress aliquot to the bed particles. The mechanism is well demonstrated with the energy-momentum transfer within the framework of energy budget concept which shows near-bed negative pressure energy diffusion rates with increasing turbulence production in mobile bed flows.

Preservation and distribution of detrital clay coats in a modern estuarine heterolithic point bar in the Gironde estuary (Bordeaux, France)

ABSTRACT Estuaries provide an excellent depositional environment to study the interaction between minerals (clays, quartz sands…) and biofilms. The estuary bottom is largely covered by biofilms that impact sediment stability, the mud and clay-coat content in sands, and sedimentary-structure stability, thus influencing sandstone properties during burial. Although numerous oil, gas, and geothermal reservoirs are exploited in estuarine heterolithic point bars, many questions remain about the origin of reservoir properties and heterogeneities in these sedimentary bodies. In order to better understand the sedimentary and microbiologic processes in estuarine systems and to better predict the reservoir quality of estuarine sandstones, this study characterizes a modern heterolithic point bar located in the Garonne estuarine channel at various scales, ranging from the microscopic (thin section) to the macroscopic (core) scale. Three piston cores 4.5 to 6.8 m long were drilled in the Bordeaux North Point Bar. Three main facies were identified in these cores: 1) sandy gravel, 2) heterolithic, medium-grained sand dunes, and 3) thin heterolithic, fine-grained sand beds with mud drapes. The sands are classified as lithic arkoses to feldspathic litharenites. Detrital clay grain coats, which at deep burial depths are transformed to permeability preserving authigenic chlorite coatings, are observed from the base to the top of the point bar. These detrital clay grain coats are mainly composed of smectite, illite, kaolinite, and chlorite, intermixed with other components, such as diatoms or pyrite. Biofilms of exopolymeric substances (EPSs), mostly produced by diatoms, are believed to control the adhesion of the clay coats to the surface of sand grains. Quantification by thin section shows that on average about 30% of the sands are coated in the point bar. The proportion of clay-coated grains appears to be independent of facies. Radiocarbon age dating measured on organic matter points to significant vertical mixing, highlighting the significance of erosion and redeposition. The activities of 137Cs and 210Pb indicate a vertical sedimentation rate of ca. 0.02 m.yr–1 in the muddy chute channel. These ages, coupled to historical maps, suggest that the present-day point bar has developed over the last 300 years with a vertical sedimentation rate ranging from 0.015 to 0.036 m.y–1 and a lateral migration rate of about 1 m.y–1. The combination of sedimentary geology, thin-section petrography, and mineralogy at high spatial and temporal resolutions highlights the potential of this study area as a modern analogue for ancient tidally influenced point-bar deposits associated with clay coatings.

Applicability of hiding-exposure effect to suspension simulation of fine sand bed

Applicability of hiding-exposure effect to suspension simulation of fine sand bed

Impacts of vertical salt welding on pore pressure, stresses, and deformation near the weld

We use a forward finite-element model to explore pore pressure, stresses, and deformation near a vertical weld. Dipping layers of mudrocks interbedded with a mixture of basin-center and basin-wide sand layers are deposited sequentially over a salt layer. After a salt wall rises at the downdip end of the model and emerges at the basin surface, shortening is imposed on the system until the salt wall almost welds where the wall feeder is narrowest (waist). Welding causes a significant increase in horizontal stress, which results in increased pore pressure near the weld. The pore-pressure increase adversely affects hydrocarbon accumulation and drilling near the weld because it: 1) causes remigration of pore water downdip along sand beds cresting near the weld, 2) decreases the hydrocarbon-column capacity of these beds, and 3) narrows the mud-weight window for drilling wellbores near the weld. The least principal stress near the weld is almost vertical and equal to the overburden stress in mudrocks, but horizontal and significantly lower in sand beds. Welding of the salt wall causes steepening of flanking strata and shortening of the weld wall rocks. The impacts of welding begin at a waist width of 1.35 km, long before the salt wall welds.

Shear strength characteristics of interlocked EPS-block geofoam-sand interface

Translation of entire geofoam embankment at the bottom of geofoam block assemblage and bedding sand is a possible internal failure mode due to unbalanced hydrostatic forces. In addition, available shearing resistance along the bottom of geofoam block assemblage and bedding sand is an important design issue for internal seismic stability analysis. This study has focused on the methods to increase the interface shear resistance along the traditional flat surface geofoam block and bedding sand interface. In addition to traditional flat surface geofoam-sand interface, the effect of four different interlock configurations composed of geofoam blocks with one- and four-triangular and one- and four-square ledges were quantified by using direct shear tests. Two different densities (EPS19 and EPS29) and two different types of sand (Ottawa sand and Adapazari sand) were used. Therefore, the effects of geofoam stiffness, interface geometry, grain size and particle shape of the bedding sand on the interface stress-strain behavior was quantified. Manufacturing ledges along the traditional geofoam surface significantly improved the geofoam block-sand interface shear resistance. In addition, interrupting the failure plane with ledges changed the interface shear mechanism of the traditional flat surface geofoam block-bedding sand interface from purely frictional to frictional-cohesive behavior.

Stratigraphic evidence of two historical tsunamis on the semi-arid coast of north-central Chile

On September 16, 2015, a Mw 8.3 earthquake struck the north-central Chile coast, triggering a tsunami observed along 500 km of coastline, between Huasco (28.5°S) and San Antonio (33.5°S). This tsunami provided a unique opportunity to examine the nature of tsunami deposits in a semi-arid, siliciclastic environment where stratigraphic and sedimentological records of past tsunamis are difficult to distinguish. To improve our ability to identify such evidence, we targeted one of the few low-energy, organic-rich depositional environments in north-central Chile: Pachingo marsh in Tongoy Bay (30.3°S).We found sedimentary evidence of the 2015 and one previous tsunami as tabular sand sheets. Both deposits are composed of poorly to moderately sorted, gray-brown, fine-to medium-grained sand and are distinct from underlying and overlying organic-rich silt. Both sand beds thin (from ∼20 cm to <1 cm) and fine landward, and show normal grading. The older sand bed is thicker and extends over 125 m further inland than the 2015 tsunami deposit. To model the relative size of the tsunamis that deposited each sand bed, we employed tsunami flow inversion. Our results show that the older sand bed was produced by higher flow speeds and depths than those in 2015. Anthropogenic evidence along with 137Cs and 210Pb dating constrains the age of the older tsunami to the last ∼110 years. We suggest that the older sand bed was deposited by the large tsunami in 1922 CE sourced to the north of our study site. This deposit represents the first geologic evidence of a pre-2015 tsunami along the semi-arid north-central Chile coast and highlights the current and continuing tsunami hazard in the region.

Interparticle effects in the cotransport of viruses and engineered nanoparticles in saturated porous media

The effects of P25 TiO2 nanoparticles on the transport in saturated porous media of the bacteriophage PP7 was investigated. Two levels of ionic strength were considered, given by monovalent and divalent cations, Na+ and Ca2+. The viruses and the P25 particles were characterized with respect to size and surface charge, by dynamic light scattering and electron microscopy. The breakthrough curves were obtained for suspensions of each particle and both combined, using UV absorbance to quantify P25 and RT-qPCR for PP7. In the single transport experiments, P25 was retained, while the viruses mostly eluted the sand bed. However, in the cotransport experiments, retention increased for the virus and decreased for the TiO2 nanoparticles under high viral content, due to heteroaggregation among the colloids in the incoming suspension, electrostatic interactions, and ripening. The interparticle interactions were modeled by DLVO theory, resulting in agreement with the experimental observations, which highlights the electrostatic nature.