SOIL MECHANICAL PROPERTIES AND PROCESSES IN STRUCTURED UNSATURATED SOILS UNDER VARIOUS LAND USE AND MANAGEMENT SYSTEMS

摘要

The effect of structure formation on changes in mechanical parameters and in strengthening soils as three phase systems can be detected and quantified by precompression stress, the shear parameters: angle of internal friction and soil cohesion and the effect of stress and soil management on flux properties like air permeability or hydraulic conductivity. Changes in soil strength as a function of landuse, soil management and time are the more pronounced, the smaller the intensity of soil disturbance and the more negative the pore water pressure and the higher the number of wetting and drying cycles. Possible reasons for changes in site properties can be defined as soil deformation by divergent (i.e. compactive) processes and by shearing which however can either result in a complete homogenisation at constant soil volume and in a loss of total soil strength due to the combination of drainage off excess soil water and the continuous increase in accessible particle surfaces for further swelling. On the other hand it can result in a continuous decrease in pore volume and functioning. The extent to which these processes affect site properties under varioius landuse and management systems will be described in detail in the text.