Development of a technique for assessing the behaviour of soil under load

The way in which soils behave during plate sinkage tests has a direct influence on the extent and severity of the resulting soil deformation. Photographic evidence of soil deformation behind a glass screen, obtained during this study, suggests that the mode of deformation, directly below the plate, is initially one of soil compaction owing to vertical soil displacement followed by a change to lateral compaction owing to lateral soil displacement. The transition from vertical to lateral deformation was found to be abrupt and occurred during the first few centimetres of sinkage. The point of change (compaction point), for a given situation, can be determined in terms of stress and sinkage by examining results from a confined compression test in conjunction with those from a plate sinkage test. Experiments were conducted in a soil bin on sandy loam soil and also in the field on sandy loam and clay soil, at a range of water contents anti bulk densities, to observe the compactive nature of soil. Stress-sinkage relationships obtained from plate sinkage and confined compression tests were al,proximated by hyperbolas. These data were used to validate procedures proposed for predicting the compactive behaviour of soil under load. The initial gradient of the stress-sinkage curve (m(ps)), and stress at the compaction point (sigma(cp)) are important parameters in determining the mode and extent of soil deformation under imposed loads. These were found to be related to, and could be predicted from, initial volumetric water content and initial dry bulk density. A strong relationship was found to exist between sigma(cp) and m(ps) for combined data from sandy loam and clay field soils. This relationship could allow predictions of sigma(cp) to be made from measures of m(ps). This would provide simplification of assessment procedures in the field as m(ps) can be determined from a simple plate sinkage test, whereas sigma(cp) requires data from a confined compression test in addition to that from a plate sinkage test. (C) 1997 Silsoe Research Institute.