STRESS STRAIN EFFECTS IN STRUCTURED UNSATURATED SOILS ON COUPLED MECHANICAL AND HYDRAULIC PROCESSES

Abstract

The stress strain processes in structured unsaturated arable and forest soils very much depend on the internal soil strength and on the existing hydraulic and mechanical boundary conditions, which affect soil deformation by compaction and shearing to a great extent. As soon as the internal soil strength defined as the precompression stress value is exceeded by external forces, an intense virgin compression process and in combination with shearing forces at high pore water pressure values a complete homogenisation of the soil profile down to depth occur. In situ stresses and strain will be determined by the Stress State transducer System (SST) while the Displacement of soil particles will be described by the DTS (Displacement Transducer System). During the determination of the stress strain processes and the shear parameters also the changes in the pore water pressure and gas exchange must be determined by mini - tensiometers installed inside the undisturbed soils as the stress and time dependent changes in the compacted and sheared soil greatly affect the total strength system. Consequently both the hydraulic and the gas fluxes will be affected by such mechanical properties, which result in an intense alteration of ecological and mechanical properties of the site. The consequences of such compaction and shearing on strength and sustainable land use have to be considered with respect to the sustainability of the system.