Sediment bulk density

Resuspension and scour of noncohesive sediments are well understood as functions of particle diameter, and reasonable estimates of resuspension rates can be determined for noncohesive sediments with information about the system hydraulics and physical properties of the sediment. However, widely applicable relationships predicting cohesive sediment erosion have not yet been developed. Quantifying resuspension of cohesive sediments usually requires development of site-specific data and experimentation. Cohesive sediment resuspension has been observed to depend on sediment bulk density (or porosity), particle size, surface and porewater chemistry, algal colonization, bioturbation and gas formation within the sediments, in addition to bottom shear velocity. 

In the United States, a number of physical tests are performed on siUcon carbide using standard AGA-approved methods, including particle size (sieve) analysis, bulk density, capillarity (wettabiUty), friabiUty, and sedimentation. Specifications for particle size depend on the use for example, coated abrasive requirements (134) are different from the requirements for general industrial abrasives. In Europe and Japan, requirements are again set by ISO and JSA, respectively. Standards for industrial grain are approximately the same as in the United States, but sizing standards are different for both coated abrasives and powders. 

Comparison with observations Soil and vegetation are only represented as single layer (topsoil) surfaces in the MPI-MCTM, hence their contamination is expressed as a mass per surface area. Soil burdens were converted into concentrations by dividing them by soil dry bulk density and a fixed soil depth of 10 cm. The average DDT concentration in soil between 40 °N and 60°N was compared to measured soil and sediment concentrations from Northern North America and Great Britain [Dimond and Owen (1996), Meijer et al (2001), and others compiled by Schenker et al (2008a)]. For intercomparison reasons only relative soil concentrations are compared to observational data. Each set of observations was normalised to its 1990 value. 

In submerged soils there tends to be a gradient of bulk density with depth as a result of the settling of disturbed sediment. As a result, the bulk density is... 

Before turning to the two procedures above to eliminate / from the sedimentation equation, one other consideration inherent in the use of Equation (4) should be discussed. As noted above, Equation (4) uses the bulk density of the pure components. If the continuous and bulk phases are totally noninteracting, this may be justified. However, for aggregates or solvated lyophilic particles, the density of the settling unit is intermediate between the densities of the two pure components. In these cases, choosing an appropriate density for the settling particle can be a real problem. 

The use of Kollidon CL-M as a suspension stabilizer has nothing whatever to do with the principle of increasing the viscosity. The addition of 5-9% has practically no effect in changing the viscosity, but strongly reduces the rate of sedimentation and facilitates the redis-persability, in particular, an effect that is consistent with the low viscosity. One of the reasons for this Kollidon CL-M effect is its low (bulk) density, which is only half of that of conventional crospovidone, e.g. Kollidon CL. It can clearly be seen from Fig. 5 that a relative volume of sediment of normal micronized crospovidone of high bulk density (= Crospovidone M) is less and more compact that of Kollidon CL-M, which undergoes hardly any sedimentation. 

Assuming a bulk density of 1.05 g/cm3 and a dry weight fraction of 0.1 for the interface sediment, 0.38 mm of sediment would supply the observed 160-m water-column burden of resuspended phases, approximately half the basinwide average annual linear sedimentation. The corresponding amount of sediment was consistent with the mass of allochthonous components in the water column during the March-May spring mixing period (200-300 mg/m3). The quantity of resuspended P was calculated as the product of mass of resuspended sediment (g/m2) and phosphorus concentration in surface sediment (mg of P/g). For a 160-m water column, the amount was 48 mg of P/m2 (25 mg of P/m2 for the mean water-column depth of 85 m). The resuspended P flux (25 mg of P/m2) was also obtained from the product of resuspended Al (mg/m2) and the P Al ratio in bottom sediment. 

R = retardation factor. The retardation factor is the ratio of the solution velocity to the radioelement velocity in a system of solution flow through a porous medium. The retardation factor R = 1 + Kd (p/) where p is bulk density of Hanford sediment (=1.65 g/cm3) and is the fraction of void volume in the sediment (=0.38). 

Fig. 55. Reduction in sedimentation of micronized crospovidone (low bulk density) with povidone K 90...

The effect of low-density micronized crospovidone (e.g. Kollidon CL-M) in stabilizing suspensions can also be partly explained in terms of Stokes law Its particle size is very fine (see Section 3.2.2), its bulk density low and its density in water also low as a result of swelling. The product differs in these properties from the coarser products and other micronized types which have a higher bulk density with a similar swelling volume, and make it useful as an auxiliary for oral and topical suspensions for reducing sedimentation and improving redispersibility [98]. The same applies, whether the commercial product is a suspension or a dry syrup, or instant granules from which the patient prepares an oral suspension. 

When micronized crospovidone of low bulk density is used in such suspensions, it is found beneficial in practice to combine it with other auxiliaries such as sodium citrate as an electrolyte, sugar, poloxamer or povidone, to increase the sediment volume. In the example given in Section 2.4.6.2 (Fig. 55), this is done by adding povidone K 90. A suspension of 7.5% of low-density micronized crospovidone with 5% povidone K 90 showed no further sedimentation after a 24-hour test. 

Fig. 86. Effect of the concentration of micronized crospovidone of low bulk density on the sediment volume of an amoxicillin suspension (Table 143)...

Ra, produced by detrital materials, A2io the decay constant of Pb, t0 the age of the top layer, m the cumulative dry mass per unit area and r the mean accumulation rate (Bollhofer et al., 1994). For A(z) the weighted average of (1.25 0.03) dpm/g was inserted. The plot of the ratio on the left hand side of the equation versus m is shown in Fig. 3C. From an exponential fit to the data points, a mean accumulation rate of (3.57 0.27) g/cm2/a and an age of the top layer of to = (21 1) a is determined. Using the average dry bulk density of 0.93 g/cm3, a mean sedimentation rate of (3.8 0.3) cm/a is calculated. Since compaction effects are almost negligible for this core, accumulation and sedimentation rate yield identical ages within limits of error. 

The interstices of the plant matter contain inorganic sediment and are generally saturated with saline water. The mass content of a given volume of material may be conveniently described in terms of bulk densities of its component phases. Mean-bulk densities for a core may be calculated from the weight and volume data averaged over all slices. 

Table 1. Bulk Density of Salt-Marsh Sediments"...

It is possible to calculate the trace-metal flux to the salt-marsh surface using the sediment chronology based on Pb, the excess concentrations of metals within each slice C, ( jLgm/gm ash), and the bulk density p (gm ash/cm ), from the equation... 

Physical properties provide a lithological and geotechnical description of the sediment. Questions concerning the composition of a depositional regime, slope stability or nature of seismic reflectors are of particular interest within this context. Parameters like P- and S-wave velocity and attenuation, elastic moduli, wet bulk density and porosity contribute to their solution. 

Measurements of physical properties usually encompass the whole, undisturbed sediment. Two types of parameters can be distinguished (1) bulk parameters and (2) acoustic and elastic parameters. Bulk parameters only depend on the relative amount of solid and fluid components within a defined sample volume. They can be approximated by a simple volume-oriented model (Fig. 2.2a). Examples are the wet bulk density and porosity. In contrast, acoustic and elastic parameters depend on the relative amount of solid and fluid components and on the sediment frame including arrangement, shape and grain size distribution of the solid particles. Viscoelastic wave propagation models simulate these complicated structures, take the elasticity of the frame into account and consider interactions between solid and fluid constituents. (Fig. 2.2b). Examples are the velocity and attenuation of P-and S-waves. Closely related parameters which mainly depend on the distribution and capillarity of the pore space are the permeability and electrical resistivity. 

In what follows the theoretical background of the most common physical properties and their measuring tools are described. Examples for the wet bulk density and porosity can be found in Section 2.2. For the acoustic and elastic parameters first the main aspects of Biot-Stoll s viscoelastic model which computes P- and S-wave velocities and attenuations for given sediment parameters (Biot 1956a, b, Stoll 1974, 1977, 1989) are summarized. Subsequently, analysis methods are described to derive these parameters from transmission seismograms recorded on sediment cores, to compute additional properties like elastic moduli and to derive the permeability as a related parameter by an inversion scheme (Sect. 2.4). 

Porosity and wet bulk density are typical bulk parameters which are directly associated with the relative amount of solid and fluid components in marine sediments. After definition of both parameters this section first describes their traditional analysis method and then focuses on recently developed techniques which determine porosities... 

Porosity and wet bulk density are closely related, and often porosity values are derived from wet bulk density measurements and vice versa. Basic assumption for this approach is a two-component model for the sediment with uniform grain and pore fluid densities (p ) and (p, ). The wet bulk density can then be calculated using the porosity as a weighing factor... 

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