Storage density

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The term storage density is used both in engineering geology and in soil science . Both of these are parameters of the soil , but in engineering geology the degree of compaction of the soil is meant, while in soil science it simply means the density of the soil. In the latter case, it does not matter whether, for example, a high density is due to a substrate with a high density or a high compression of the soil matrix .

Engineering geology

The density of cohesive and non-cohesive soils indicates how densely compacted a soil is and how large its pore content is. The specific gravity (wet or dry) depends on the storage density. The storage density D is determined here in standardized tests.

definition

It is defined as:

in which:

  • n = percentage of pores in the soil sample
  • max n = proportion of pores in the case of loosest storage
  • min n = proportion of pores in the case of densest storage
  • ρ d = dry density
  • max ρ d = density with densest storage
  • min ρ d = density with loosest storage

The percentage of pores can be determined from the porosity of the material.

Determination of the storage density of non-cohesive soils

DIN 18126 specifies test procedures to determine the limits

  • "Loosest" storage ( n max )
  • "Tightest" storage ( n min )

non-cohesive soils. These come close to the natural conditions. When stored loosely, the pore proportion reaches its maximum value.

Determination of the storage density of cohesive soils

The density of cohesive soils is increased by the compaction under load. The success of compaction depends on:

Examples

  • dry, firm, lumpy clay → no compaction possible
  • almost water-saturated pulpy clay → no compaction possible

The determination of the water content and the particle size distribution are standardized in DIN 18121, DIN 18123-T4 and DIN 18123-T5.

Proctor attempt

The compression work in the Proctor test is also standardized in DIN 18127 so that comparable results can be achieved.

  • the Proctor test consists of 5 individual tests, each with an increased water content
  • the bulk density and the dry density are measured for each individual experiment
  • then dry densities are applied depending on the associated water content
  • the apex of the curve gives the Proctor density
  • this results in the optimal water content for compaction.

Soil science

In soil science, the storage density is the density of the dry soil. Since a higher porosity can be compensated for by a higher density of the solid fraction, it is only indirectly dependent on the porosity, in contrast to the storage density in engineering geology. It is determined on the oven-dry soil sample, that is, after the soil sample has been dried at 105 ° C. (according to DIN 19683, sheet 4).

definition

With

  • m f = mass of the dried soil,
  • V g = total volume

additional

If, on the other hand, you want to specify the density of the moist soil, for example to determine the gravimetric soil water content by differential weighing, the term gross density is common. The density of solids ( ) is usually close to 2.65 g · cm −3 , the density of quartz , which is the most abundant mineral in soils. Only basic igneous rocks and their minerals can have densities above 2.7 g · cm −3 . Organic matter has a density of 1.2 - 1.4 g · cm −3 . Usual values ​​for the storage density in [g · cm −3 ] are:

Sandy soils 1.67-1.19
Clay soils 1.96-1.19
Silt soils 1.53-1.19
Clay soils 1.32-0.92
organ. Floors 0.48-0.12

Knowing the storage density and the density of the solid substance, the porosity (ε) and the number of pores of the soil can be calculated.

See also

References and comments

  1. ↑ http://www.soil.tu-bs.de/lehre/Skripte/2013.Skript.Bodenphysik.pdf
  2. ↑ a b c F. Scheffer, P. Schachtschabel, revised and expanded by H.-P. Blume, GW Brümmer, U. Schwertmann, R. Horn, I. Kögel-Knabner, K. Stahr, K. Auerswald, L. Beyer, A. Hartmann, N. Litz, A. Scheinost, H. Stanjek, G. Welp , B.-M. Wilke, Textbook of Soil Science, 15th edition, Spektrum Akademischer Verlag, 2002, ISBN 3-8274-1324-9 , p. 163f
  3. ↑ The soil water content is actually determined almost exclusively as a gravimetric soil water content using differential weighing
  4. ^ H. Schumann, Introduction to the Rock World, 5th edition, Vandenhoeck & Ruprecht, Göttingen 1975, ISBN 978-3525425039
  5. ↑ R. Heinonen, The volume weight as a characteristic of the "normal" soil structure, Maataloustieteellinen Aikakauskirja (Z. Landwirtsch.-wiss. Ges. Finland) 32, 81–87 (1960)
  6. ↑ KH Hartge and R. Horn, Introduction to Soil Physics, 2nd edition, Enke, Stuttgart, 1991, ISBN 3-432-89682-4