IMPROVEMENT OF PLANOSOL SOLUM - PART 7, MECHANICAL-PROPERTIES OF SOILS

The planosol solum in China is a binary mixture of soil particles wher e silt forms the frame structure and clay fills the pore spaces. It is extremely hard and impermeable and has particular mechanical properti es. This paper deals with the mechanical properties of the three horiz ons (Ap, Aw and B) of the planosol solum as an aid to understanding th e draught requirement of a three-stage subsoil mixing plough for impro vement of the planosol solum. Pseudogley soil which is a typical heavy clay soil in Japan was also tested for comparison. Tensile strength, compressive strength, shearing strength, soil-metal friction as static properties and soil brittleness as a dynamic property were determined . The results show that the cohesive strengths of all soils, except th e B horizon, had maximums at particular soil water contents. These val ues were nearly the same as the plastic limits. The B horizon did not have a maximum value in the range of soil water content studied. The c ohesion of the pseudogley soil was the smallest and that of the Aw hor izon was the largest. The Ap and Aw horizons had the same trend in bri ttleness; the impact energy required to fracture both soils increased with decreasing soil water content. The required impact energy of the B horizon showed a quite different trend from that of the other soils and was a maximum at 30% d.b. soil water content. When the B horizon w as dry, the required impact energy decreased and it became brittle. Th e commonly occurring soil water content in the actual planosol fields was more than 20% d.b. In this range, the tensile strength of the Aw h orizon was the largest, followed by the B horizon, Ap horizon and pseu dogley soil. Comparing the cohesion at soil water contents in excess o f 20% d.b., the tensile strength of the pseudogley soil was about one- seventh of its cohesion but the tensile strengths of all planosols was about one-half of their cohesive values. (C) 1998 Silsoe Research Ins titute.