Soil Grain Size Research Articles

Modelling raindrop impact and splash erosion processes within a spatial cell: a stochastic approach

AbstractA new approach is proposed to simulate splash erosion on local soil surfaces. Without the effect of wind and other raindrops, the impact of free‐falling raindrops was considered as an independent event from the stochastic viewpoint. The erosivity of a single raindrop depending on its kinetic energy was computed by an empirical relationship in which the kinetic energy was expressed as a power function of the equivalent diameter of the raindrop. An empirical linear function combining the kinetic energy and soil shear strength was used to estimate the impacted amount of soil particles by a single raindrop. Considering an ideal local soil surface with size of 1 m × 1 m, the expected number of received free‐falling raindrops with different diameters per unit time was described by the combination of the raindrop size distribution function and the terminal velocity of raindrops. The total splash amount was seen as the sum of the impact amount by all raindrops in the rainfall event. The total splash amount per unit time was subdivided into three different components, including net splash amount, single impact amount and re‐detachment amount. The re‐detachment amount was obtained by a spatial geometric probability derived using the Poisson function in which overlapped impacted areas were considered. The net splash amount was defined as the mass of soil particles collected outside the splash dish. It was estimated by another spatial geometric probability in which the average splashed distance related to the median grain size of soil and effects of other impacted soil particles and other free‐falling raindrops were considered. Splash experiments in artificial rainfall were carried out to validate the availability and accuracy of the model. Our simulated results suggested that the net splash amount and re‐detachment amount were small parts of the total splash amount. Their proportions were 0·15% and 2·6%, respectively. The comparison of simulated data with measured data showed that this model could be applied to simulate the soil‐splash process successfully and needed information of the rainfall intensity and original soil properties including initial bulk intensity, water content, median grain size and some empirical constants related to the soil surface shear strength, the raindrop size distribution function and the average splashed distance. Copyright © 2007 John Wiley & Sons, Ltd.

Comparative study on the geographical, physical and engineering properties of soils of West Bengal. Part-1

Studies on the geographical aspects of West Bengal like land elevation, slope, water courses, river sands, soil colours etc. were made. Three important physical and engineering properties of soils like grain size, free-swell index and permeability of soils from different parts of West Bengal were determined. Usual conclusions were derived from these results.

The role of mineralogy, geochemistry and grain size in badland development in Pisticci (Basilicata, southern Italy)

AbstractMineralogical, geochemical and grain‐size composition of soil and pore‐water chemistry parameters were characterized on both eroded (south‐facing) and non‐eroded (north‐facing) clayey‐silt slopes in the Basilicata region (southern Italy).Only a few grain‐size parameters and clay mineralogy discriminate eroded from non‐eroded substrates. Compared with the latter, the former have fractions of over 63 µm and 1–4 µm lower and fractions 4–63 µm higher. Grain‐size characters of crusts did not discriminate with respect to substrate.Bulk rock mineralogy was not distinctive, but the clay mineral assemblage shows that the eroded slope is enriched in kaolinite, mixed layers (illite–smectite) and chlorite, whereas illite decreases, although overlaps are common.Chemical data enable discrimination between eroded and non‐eroded slopes. pH, SAR (sodium adsorption ratio), TDS (total dissolved salts) and PS (percentage of sodium) are distinctive parameters for both eroded and non‐eroded slopes. TDS increases in depth in the non‐eroded slope, whereas the maximum TDS is just below the crust in the eroded one. On average, eroded substrates are higher in pH, SAR and PS than non‐eroded ones. The ESP (exchangeable sodium percentage) of the eroded slope has a higher value than the non‐eroded one. Crusts are less dispersive than eroded substrates, and non‐eroded substrates behave as crusts. This suggests that the portion of the slope most severely exposed to weathering tends to stabilize, due to strong decreases in SAR, PS and ESP. Several diagrams reported in the literature show similarly anomalous crust samples on eroded slopes, compared with other samples coming from greater depths on eroded slopes. In the present case study, the exchangeable form of Na characterizes crusts more than the soluble form.This study describes the erosional mechanism, which involves morphological and geographic exposure and climatic elements, as well as grain size, mineralogy, chemistry and exchangeable processes of soils. Copyright © 2006 John Wiley & Sons, Ltd.

Soil slips on weathering-limited slopes underlain by coarse-grained granite or fine-grained gneiss near Seoul, Republic of Korea

The chemical, mineral, physical, and mechanical properties of two soil layers on soil-slip scars in slopes underlain by coarse-grained granite and fine-grained granitic gneiss near Seoul, Republic of Korea, were examined. Our aim is to study the effect of the mineral grain size of the bedrock on the soil layer structure and the return period of shallow soil slips. Because of the coarser slope materials in granite resulting from weathering, the permeability is larger and the weathering front has a copious water supply; also, because of the smaller specific surface area of the minerals, restricted leaching produces grus from the bedrock, so that the rate of formation of soil (and in particular the slip plane) due to chemical weathering is faster. Since, on granite slopes, the leaching proceeds toward the surface, the sliding plane is deeper with coarser soft grus, resulting in the existence of a minimum c value in the soil layer. On gneiss slopes, by contrast, leaching cannot proceed with decreasing soil depth, and the sliding plane is deeper with finer soft grus just above hard grus and has similar c and ϕ values as the upper soft grus because the grain size of both soils is the same. In the granite soil layers, the sliding plane corresponds to the minimum shearing resistance, whereas in the gneiss soil layers, the shearing resistance increases gradually with soil depth, and the sliding plane is formed when the weathering front is located deeper. Because of the faster soil formation rate and the shallower slip depth in granite slopes, the return period of occurrence of soil slips should be shorter in granite slopes than in gneiss slopes.

Estimating the groutability of granular soils: a new approach

This paper evaluates different parameters that affect the grouting of soil, and presents a new approach to predict the groutability of granular soil. An accurate prediction of the groutability of granular soils has always been complicated due to the effects of different soil parameters. We know that these parameters are the grain-size of soil and cement-based grouts, the relative density and fine contents of soil, the water/cement ratio of grout mixture and grouting pressure, which directly affect the groutability of soil media. However, the relative density, fine contents of soil, the water/cement ratio, and grouting pressure are seldom considered as the prediction of groutability. In order to study the effects of the parameters on groutability, an alternative empirical formula to estimate the groutability of granular soils is presented in this paper and supported by experimental results obtained from the grouted sand samples prepared with various relative densities. The newly developed approach will help for the more accurate prediction of the groutability in granular soils and may also be used to provide first-hand information about the groutability of soils.

Empirical Correlation between SPT N-Value and Relative Density for Sandy Soils

ABSTRACT It has been known that the penetration resistance depends on the grain size of soils, and that fines-containing sands have smaller SPT N-values than clean sands. Previous investigations on the link between the penetration resistance and relative density have indicated that the ratio between the normalized N-value and the square of the relative density, N1/D2r, is dependent on the grain size of sands. While this dependence has not been properly quantified, it has been customary to utilize the well-known expression of Meyerhof with N1/D2r being fixed at 41. In this paper, an attempt was made to correlate the penetration resistance and relative density by accounting for the grain size properties of soils. The void ratio range (emax – emin) was used as a measure indicative of the grain size and grain size composition. It was found that M is highly dependent on the value of (emax – emin) and that this ratio gradually decreases with increasing void ratio range from a value of about 100 for gravels to a value of about 10 for silty sands. This dependence is mathematically formulated and used to establish an empirical correlation between the SPT TV-value and Dr that is applicable to various kinds of soils ranging from silty sands to gravels. The correlation is developed by using data of high-quality undisturbed samples and results of SPT measurements on natural deposits of sandy soils and gravels.

Comparison of laser grain size analysis with pipette and sieve analysis: a solution for the underestimation of the clay fraction

ABSTRACTClassically, the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method, based on the ‘Stokes’ sedimentation rates, for the fine fractions. Results from the two methods are compared with results from laser diffraction size analysis, which is based on the forward scattering of monochromatic coherent light. From a point of view of laboratory efficiency, the laser sizing technique is far superior. Accuracy and reproducibility are shown by measurements on certified materials. It appears that laser grain size measurements of certified materials correspond very well with the certificated measurements. Tests were also done on a set of randomly selected sediments of fluvial, aeolian and lacustrine origin. Except for the (<2 μm) clay fraction, there is a coarsening of the mean diameter of one to two size classes (0.25 ɛ), caused by the non‐sphericity of the particles. The platy form of the clay particles induces considerable differences (eight size classes) between pipette and laser measurements: the <2 μm grain size, defined by the pipette method corresponds with a grain size of 8 μm defined by the Laser Particle Sizer for the studied sediments. Using a higher grain size level for the clay fraction, when laser analysis is applied, enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique.

Evolution of the grain size of clay-sandy soils subjected to dynamic and static compactions (in French) : Esteoule, J; Istvan, C Int Assoc Engng Geol BullN43, April 1991, P41–46

Evolution of the grain size of clay-sandy soils subjected to dynamic and static compactions (in French) : Esteoule, J; Istvan, C Int Assoc Engng Geol BullN43, April 1991, P41–46

Scale Effect in Anchor Pullout Test by Centrifugal Technique

Centrifugal technique can be applied to the model tests of bearing capacity, earth pressure, anchor pullout, etc. in sand. In this method, the soil mechanics law of similarity is satisfied by performing the model tests in the centrifugal field. However, the problems on the grain size of soil and the magnitude of acceleration of the test field have not been clarified. In this paper, the scale effect will be discussed based on the model tests of the anchor pullout resistance in dry sand by the centrifugal technique and the conventional model test in 1 g field. Important findings are: (1) no scale effect can be observed in the centrifugal model test for the 0.1 ~ 1. 0 mm grain size of sand and for the approximately 10 mm width or diameter of model anchor, and (2) since the scale effect is observed even by the centrifugal technique, the acceleration level must be set considering the scale effect.

Grain-size determination at the surface of Mars

Optical polarimetric and photometric analysis of the Martian surface with the instrument VPM on board the Orbiter MARS-5 produced information about the grain size of the Martian soil. The results were compared with the thermal inertia coefficients obtained at Mars' surface with the same spacecraft and with the Viking orbiters. Photopolarimetry is sensing the grain-size dp of the top surface soil. Radiometry characterizes larger fragments below the surface, or the presence of stones, rocks, or slabs imbedded into the dust layer or coated with the dust. At the resolution of 20 km, the top surface appears to be everywhere covered with small grains within the size range 20 to 45 μm, except on some very localized areas, usually related to tectonics. Below this coating, local densifications, or coarser structures, stones, or rocks are observed.

Experimental study on thermal properties of frozen soils

A series of measurements of the effective thermal conductivity, specific heat and unfrozen-water content of various soils exposed to a cold environment have been carried out by a transient probe method and a calorimetric technique. The present experiments were performed at a very slow rate of cooling of the moist-soil and using four kinds of soil samples from fine to coarse grain-size. It was established that the amount of unfrozen-water in the frozen soil was dependent on the initial moisture content, the grain-size of the soil and the temperature (below 0°C). Measured values of the effective thermal conductivity and specific heat show a strong dependence on temperature, initial moisture content and grain-size of soil in the temperature range T = 0°C to −10°C. The anomalous behavior of a decrease in the effective thermal conductivity of frozen soil for the finest grain-size with decreasing temperature (below 0°C) was observed for a large initial moisture content w = 30–40%.

Investigation of the drainage porosity of silty-clayey soils as a function of their physical and mechanical properties

In the present study it was thought desirable to investigate the relationship between the drainable porosity and the physical properties of the silty-clayey soils in an attempt to ascertain an accurate procedure for the determination of free water in soils. An equation was derived correlating the drainable porosity as a function of the voids ratio, porosity, effective grain size and depth of silty-clayey soils. A suggested soil coefficient, C, was found to vary according to the type of soil, being proportional to the coefficient of permeability K. Empirical formulae were computed correlating C and K.

Hydraulic and Particle Size Characteristics of Some Diatomite Filter Aids

This study presents data pertaining to the hydraulic and particle size characteristics of commercial grades of diatomite used as filter aids. To achieve this, the specific study objectives were to: evaluate the reproducibility and relative simplicity of two ASTM methods for determining the grain size of soils when those methods are used to determine the particle size distribution of diatomite filter aids; determine the particle size distribution of different lots of commercial grades of diatomite filter aids; determine K3 values of different grades and of different lots of the same grade of diatomite (K3 is a constant for a given grade of diatomite at 20°C and is inversely proportional to its coefficient of permeability); and, determine whether a relationship exists between the K3 value and particle size distribution. The determination of the permeability of diatomite filter aids in this study was confined to the evaluation of K3 coefficients in the recently developed diatomite filtration equation. The ASTM Method for Grain Size Analysis of Soils‐Designation D422‐39 (Method 1) and ASTM Tentative Method for Grain Size Analysis of Soils ‐Designation D422‐61T (Method 2) were used in this study for determining particle size distribution.

Radioactivity and grain size of soil

By measurements on separated grain size fractions 0–2 μ, 2–16 μ, 16–2000 μ of several sedimentary soils, evidence was found for a preference of the radioactive elements for the grain sizes 2–16 μ. From the variation of the activity with the amount of the material, spread each time on the same surface, as well as from the comparison of the of the radiation depends on the fineness of the material. The ratio's of the concentrations of the various radioactive elements, therefore, must vary with the grain size. It is suggested that this variation is not only related to the mineral composition of the original material, but also influenced by the combined processes of solution and adsorbtion during the process of sedimentation.