An investigation of the re-expansion of unsaturated, structured soils during cyclic static loading

A procedure is presented that quantifies soil resilience to compressive stress, through elastic deformation or re-expansion after stress removal, with a single numerical index. This was achieved by comparing the three parameter coefficients of static-loaded and rebound compression lines (normal stress range = 0–1.0 MPa) which had been fitted to a non-linear density-stress model equation. The difference between the static-loaded and rebound values of one of these coefficients was significantly correlated to the clay and organic matter contents, the gravimetric moisture content and the initial dry bulk density of the 33 soils sampled as intact cores at field moisture content (coefficients of determination=0.533–0.973, P<0.05). The magnitude of the sample rebound observed varied between 0.018 and 0.075 Mg m^?3 at the maximum applied stress of 1.0 MPa. This is likely to be a significant component of the error in prediction inherent in compaction models based on static-loaded compression data. The data further support the segregation of soils into groupings of comparable mechanical behaviour for soil compaction modelling purposes. The implications of these findings for improving soil resilience to compressive stress through soil and crop management are discussed.