Experiments on the Pickup Flux of Sand at High Flow Velocities

Soil and Sediment Contamination, 2006

In the laboratory, this study investigated hydraulic conductivities of such mixtures at different hydraulic pressure (hydraulic gradient), dry unit weights, and bentonite contents. The bentonite content and the dry unit weight of the samples were both important factors, significantly affecting the hydraulic conductivity of the liner material. A bentonite content of 5% was found to be sufficient in reaching a hydraulic conductivity under 10 −9 m/s, when the liner material was compacted under near optimum moisture content. Nevertheless, hydraulic conductivity was found to increase with hydraulic pressures, especially for the 5% bentonite mixtures subjected to pressure above 40 kPa, suggesting some degree of internal erosion (washing out of particles).

Proceedings of Advances in …, 2010

Recent research studies revealed that most bridge piers and other hydraulic structures such as levees and embankments adopted in flood protection schemes in maritime environment have collapsed due to the failures attributed to scour associated with a soil-hydrodynamic interaction phenomenon (e.g. Shirole and Holt, 1991). Though erosion characteristics of coarse sands and gravels are relatively well known, soil-hydrodynamics interaction for finer sands such as silts and clays is not fully investigated. A series of small-scale laboratory experiments were conducted in a moveable sediment tank to investigate scour characteristics under various flow and soil conditions. The present paper discusses preliminary experimental observations and the analysis of hydrodynamic erosion of soils in line with the extensive research project "Mathematical and Physical Modelling of Hydrodynamic Erosion of Soils (HES)" carried out under the "UEL Promising Researcher Fellowship 2009-2010" funded by the University of East London (UEL).

Physics and Chemistry of the Earth, Parts A/B/C, 2011

Scour and Erosion, 2010

Internal erosion has long been a major problem associated with earth structures. Laboratory experiments provide a potential insight into the processes involved. The design of dam embankments is usually based on hydraulic criteria. Some of the hydraulic criteria are based on sediment transport theory where the critical velocities are derived from the different approaches comparing the drag force of the particles and the hydraulic load. Many hydraulic criteria for suffusion are based on tests with consistent soil samples or on analytical descriptions of the particle and pore geometry derived from characteristic parameters. An experimental study of soil suffusion is performed on a laboratory column subjected to different flow conditions and soil parameters. The permeability variation along the soil column is controlled. The initiation and the kinetics of soil suffusion are investigated using a laboratory fine grained so il (mixed sand and clay) and a natural soil. Attempts are also made to assess the influence of the clay content and the type of fine particles. The results demonstrate that low hydraulic gradients can cause suffusion. The critical shear stresses for various soil tested differ slightly when the nature of grains and fines are varied. The hydraulic gradient affects the cumulative eroded mass upon a certain threshold value.

Journal of Hydrology, 2011

The processes and mechanisms of entrainment and transportation of soil particles by surface runoff was investigated in the laboratory by a 0.05×0.2×3 m flume for two contrasting soil samples. The results show that there are at least two different mechanisms affecting particle transport by flow, with their relative importance relating to hydraulic condition, especially flow streampower. Different particle size classes are transported mainly by one mechanism. Suspension/saltation was observed to be the only mechanism at low streampowers (< 0.1 W m-2). Bed load transport, probably involving rolling was shown to be activated at the streampowers greater than a specific threshold of about 0.1-0.15 W m-2 , becoming the dominant transport mechanism at these modest streampowers. The relative importance of the two transport mechanisms was also related to soil types. Particle density seemed to have a main role in this context. Comparison with theoretical prediction of sediment concentration provided some support for the increasing dominance of bedload transport mechanisms with increasing streampower in these experiments.

Journal of Geophysical Research, 2008

1] Field studies suggest that bedrock incision by granular flows may be the primary process cutting valleys in steep, unglaciated landscapes. An expression has been proposed for debris flow incision into bedrock which posits that erosion rate depends on stresses due to granular interactions at the snout of debris flows. Here, we explore this idea by conducting laboratory experiments to test the hypothesis that bedrock erosion is related to grain collisional stresses which scale with shear rate and particle size. We placed granular material in a 56-cm-diameter rotating drum to explore the relationship between erosion of a synthetic bedrock sample and variables such as grain size, shear rate, water content, and bed strength. Grain collisional stresses are estimated as the inertial stress using the product of the squares of particle size and vertical shear rate. Our uniform granular material consisted of 1-mm sand and quartzite river gravel with means of 4, 6, or 10 mm. In 67 experimental runs, the eroded depth of the bed sample varied with inertial stresses in the granular flow to a power less than 1.0 and inversely with the bed strength. The flows tended to slip on smooth boundaries, resulting in higher erosion rates than no-slip cases. We found that lateral wall resistance generated shear across the channel, producing two cells whose widths depended on wall roughness. While the hypothesized inertial stress dependency is supported with these data, wear mechanics needs to account for grain dynamics specifically at the snout and possibly to include lateral shear effects.

Spe Journal, 2020

An experimental study was conducted to investigate the transport of sand particles over the sand bed deposited in a horizontal conduit by using turbulent flow of water. The main objectives were to determine the near-wall turbulence characteristics at the onset of bed erosion (i.e., near-wall velocity profile, Reynolds shear stresses, and axial-turbulent intensity); to determine critical velocity required for particle removal from the bed deposits; and more specifically, to determine how the sand-particle size and surface characteristics would influence the critical velocity required for the onset of bed erosion and the near-wall turbulence characteristics. A large-scale horizontal flow loop equipped with a nonintrusive laser-based particle-image velocimetry (PIV) system has been used for the experiments. The effect of sand-particle surface characteristics (i.e., wettability) on the critical velocity and the near-wall turbulence characteristics were investigated by using treated and untreated industrial sands of four different mesh sizes (i.e., 20/40, 30/50, 40/70, 100). The PIV technique was used to determine instantaneous local velocity distribution near the stationary sandbed fluid interface under subcritical and critical flow conditions. The near-wall velocity distribution measured directly at the sand bed/fluid interface together with the measured frictional pressure-loss values were then used for the evaluation of the Reynolds shear stresses and axial turbulent intensities acting at the bed/fluid interface. The results indicated that critical velocity for the onset of particle removal from sand beds increased with the increasing particle size. When sands with special surface treatment were used, it was observed that the critical velocity required for the onset of the bed erosion was significantly lower than that of required for the untreated sands. The degree of reduction in critical velocity varied between 14 and 40% depending on the particle size. In this study, by conducting experiments under controlled conditions, we provided much-needed fundamental data that can be used for the development of improved solid-transport design criteria and suitable mitigation technologies. In particular, we have shown the proof of concept that the surface-treated sand particles might have great potential for improving the transport efficiency of proppants used for hydraulic-fracturing operations.

Earth Surface Processes and Landforms, 2007

Rock fragments can act as a controlling factor for erosional rates and patterns in the landscape. Thus, the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion. Laboratory flume experiments were conducted with soil material that was mixed with rock fragments. Rock fragment content ranged from 0 to 40 per cent by volume. Other treatments were slope (7 and 14%) and flow discharge (5·7 and 11·4 l min − − − − − 1 ). An increase in rock fragment content resulted in lower sediment yield, and broader width of flow. Rock fragment cover at the soil surface, i.e. surface armour, increased with time in experiments with rock fragments. Flow energy was largely dissipated by rock fragment cover. For more turbulent flow conditions, when roughness elements were submerged in the flow, hydraulic roughness was similar for different rock fragment contents. In experiments with few or no rock fragments a narrow rill incised. Flow energy was dissipated by headcuts. Total sediment yield was much larger than for experiments with rock fragments in the soil. Adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield. Figure 5. Change of the soil surface cross section 167 cm down slope from the inflow. The laser scanner profiles show surfaces with 40 per cent rock fragments by mass (above), and 0 per cent rock fragments by mass (below) at three different experimental stages.

Continental Shelf Research, 2004

The erosion behaviour of sand-mud mixtures is not well understood. As a first step, a conceptual framework for the erosion behaviour of sand-mud mixtures is proposed and validated with data from field and laboratory experiments based on appropriate parameters for cohesion and network structure. Six bed types with different characteristics are distinguished in relational diagrams. Validation with experimental data shows that observed transitions in erosion behaviour are clearly delimited in these diagrams. Mud content (%o0.063 mm) as a descriptor for the transition between non-cohesive and cohesive erosion behaviour turns out to be less generic than the clay content (%o0.004 mm). Furthermore, an estimation of the relevance of these compositional bed types in natural systems shows that the frequently observed constant ratio between clay and silt in the bed sediments of some depositional system strongly limits the number of relevant bed types in that system.

Coastal Engineering, 1994

The relationship between swash force, sand grain size, dune density and dune erosion was investigated in a series of laboratory experiments. The sands selected for the experiments were a coarse grain sand from North Carolina and a fine grain sand from Oregon. Small scale dunes were built and characterized as either high or low density. The swash was modeled as a bore which was generated using a head tank. The data consisted of bore height, bore velocity, specific volume eroded and dune density for ninety-seven individual tests. These data were analyzed using Maximum Likelihood Estimation (MLE) and Likelihood Ratio (LR) test methods. The conclusions are (1) swash force and dune erosion are related linearly, (2) decreasing the sand grain size of the dune decreases the amount of dune erosion for the same swash force, and (3) increasing dune density decreases the amount of dune erosion for the same swash force. In addition, for these test data, the difference in sand grain size influences the amount of dune erosion for a given swash force more than that due to the increase in dune density.