Wasserspannungsabhängiger Eindringwiderstand von Modellböden

The resistance to penetration of model soils depending on water tension The device used for measuring resistance to penetration (Becher 1978b) allows to measure varying resistances corresponding to differences in texture, bulk density and moisture. Model soils consisting of varying layers of sand (0,2–0,5 mm) and silt (～ 10–60μm) were equilibrated with water tensions ranging from 20 to 600 cmH₂O. The resistances to penetration measured after equilibrium were significantly influenced by water tension corresponding to second power regressions. The extrema of these regressions being found between 250 and 350 cmH₂O water tension were always maxima for silt and in most of the cases minima for sand regardless of thickness and arrangement of the textural layers. Moreover, silt showed an overall higher resistance to penetration (30 kp/cm²) than sand (15 kp/cm²). The interaction between unwieldiness of soil particles, cohesive and adhesive forces, and rate of change of negative pore water pressure (= water tension) probably causes at the same tension the differences of friction and resistance to penetration as stated for sand and silt.