Load effect upon soil stress and deformation state in structured and disturbed sandy loam for two tillage treatments

Abstract

Soil stress and deformation state under loads inform us about mechanical properties of soil. There are numerous factors influencing stresses and deformations generating in soil, where load and tillage treatments are two of them. Monolith samples (600×400×300 mm 3 , L×W×H ) of sandy loamy Luvisol derived from glacial till (Ap horizon) were investigated using stress state transducer (SST) with a displacement measuring system. The SST used in the experiment was a spherical body, 60×50×50 mm 3 (L×W×H ) with six pressure sensors. Pore water pressure in soil samples was set up to −60 hPa prior to the measurements. The soil used in the experiment was taken from two tillage treatments: conventional, with the loosening depth of 350 mm, and conservation, with the loosening depth of 80–100 mm. The same procedure was repeated in disturbed soil samples compacted to bulk density of monoliths. The experiment was conducted in respect to free gravity loading of soil surface by a circular plate. The complete stress state in soil, i.e. the three major stresses, mean normal stress and shearing stress were calculated from measured pressures. Vertical displacement of the SST and bulk density changes were also quantified. The effects of external load as well as tillage variants and soil state on stress and deformation state were discussed. The effect of load was significant for all the soil variants. The measured stress values increase for the greater load, although the intensity of stress increase was different for the soil variants. A superiority of the shearing over the compression in the soil failure process was observed based upon the analysis of shear to normal stresses ratio. Tillage variants influence soil stress and deformation significantly, but stress and strain determination as a function of the load applied does not show the same tendency for the ploughed and rototilled soil.