Environmental Engineering Reference
In-Depth Information
are characteristic of compacted clay soils and also of silts. In the latter case drying and
crusting after early spring rain gives platy aggregates which can cause serious problems
with the emergence of young seedlings (Plate 18.2).
WATER
The total volume of pore space in soil is its porosity or air capacity . It is calculated from
the bulk density , the weight of soil per unit volume. Assuming that the mineral density
of soil particles is 2·65 g cm −3 , then:
where BD = bulk density and PD = particle density. Bulk density values range between
about 0·8 g cm −3 and 2·4 g cm −3 , which is equivalent to a range of soil porosity from 70
per cent to 10 per cent respectively. After a very wet period most of the porosity will
become filled with water,
Plate 18.2 Vertical view down on to a cylinder measuring the
infiltration rate of the soil. The added water has destroyed the
coarse, blocky structure shown in the surrounding dry soil.
Photo: Ken Atkinson.
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