In Situ Subsoil Stress-Strain Behavior in Relation to Soil Precompression Stress

Soil compaction negatively influences many important soil functions, including crop growth. Compaction occurs when the applied stress, sigma, overcomes the soil strength. Soil strength in relation to compaction is typically expressed by the soil precompression stress, sigma(pc). Deformation is assumed to be elastic and reversible as long as sigma <= sigma(pc). This work examined soil stress-strain behavior as measured in situ during wheeling experiments and related it to the stress-strain behavior and sigma(pc) measured on soil cores in uniaxial compression tests in the laboratory. The data analyzed were from a large number of wheeling experiments carried out in Sweden and Denmark on soils with a wide range of texture. Contradicting the concept of precompression stress, we observed residual strain, epsilon(res), at sigma <= sigma(pc). These observations were supported by stress-strain data measured in uniaxial compression tests, which likewise showed epsilon(res) > 0 at sigma <= sigma(pc). Residual strain was observed in the field when sigma exceeded approximately 40 kPa, and when the ratio sigma/sigma(pc) exceeded roughly 0.1, although epsilon(res) was very small at sigma/sigma(pc) < 0.5. These values were similar to those obtained on confined uniaxial compression curves. On the basis of our findings, we question the use of sigma(pc) as a measure of soil strength and call for a reevaluation of the precompression stress concept.