SAMPLE-SIZE FOR DETERMINATION OF COARSE FRAGMENT CONTENT IN A STONY SOIL

Particle size analysis of soils containing coarse fragments requires sufficient amounts of soil material. We tried to quantify the sample volume for coarse fragment measurements in a Rendzina soil with more than 50% coarse fragment content. A monolith of 50 cm x 80 cm was excavated to a depth of 160 cm, hardened with an epoxy resin and cut into six sections. The coarse fragment contents were determined on the cross sections by counting the aerial fractions belonging to the fine earth, fine gravel and gravel classes. Additionally, 24 samples with a volume of 3.2 to 4.5 l were sieved to determine the coarse fragment content. The contents estimated from the cross sections equalled the contents measured with particle size analysis. The data were evaluated in terms of the representative elementary area and volume. The coarse fragment content as a function of the sampling size exhibited the features of the representative elementary volume graph. The side length of the representative elementary area ranged from 11 to 19 cm. The estimated representative elementary volume ranged from 400 to 2100 cm3.