Ground deformations and stress redistribution due to a reduction in volumeof zones of soil at depth

The ground deformations and stress redistribution resulting from collapse c ompression in discrete zones of highly collapsible fill located at differen t depths within fill with little or no collapse lapse potential has been in vestigated in the 4-m-deep BRE large test pit facility. The moisture conten ts and densities of the colliery spoil fill which was used in the test were selected to ensure that, as well as high collapse potential, the zones of dry fill had lower compressibility than the surrounding wetter fill. During fill placement, significant stress transfer occurred, resulting in the mea sured vertical stresses in the zones being much higher than the stresses in the bulk of the fill. As the fill was inundated by a rising water level, c ollapse compression occurred in the dry zones and the stress transfer was r eversed, with stresses in the zones reducing to very low values. The collap se compression in all the zones was of similar magnitude but the measured s urface settlements were dependent on the depth of the zone. The test was mo delled using the Sage-Crisp finite element package together with a simple p rocedure for simulating collapse compression. The observed behaviour was re plicated with sufficient accuracy for the numerical procedure to form a mea ns of estimating behaviour with zones of fill of different geometries and l ocated at different depths.