The puddling of clay soils.

Effects of mechanical treatments on micro-structure at increasing moisture contents & on the swelling process are described. Increasing moisture causes a rapid decrease in cohesion within aggregates & an increase in friction between aggregates. Due to the weak intra-aggregate cohesion near the moisture equivalent, an infinite number of shear planes may develop & the movement of primary particles in relation to each other results in an equilibrium between swelling pressure & suction, so that moisture is taken up; at a moisture content near saturation, friction decreases again, with a consequent decrease in the degree of puddling caused per unit of mechanical action. In puddled soils, the air-filled pore volume is greatly reduced, permeability & resistance to raindrops decreased, & suction & deformability increased; their regeneration requires drying either through evapotranspi-ration or by freezing. (Abstract retrieved from CAB Abstracts by CABI’s permission)