Base friction test on unloading deformation mechanism of soft foundation waste dump under gravity

Problems of waste dumps induced by foundation weaken are quite common. A series of base friction tests were conducted in order to reveal the unloading deformation mechanism of soft foundation waste dumps. The displacement histories of waste dumps were measured by a speckle analysis and displacement measurement system and compared with hard foundation waste dumps. The test results showed that: (1) the stability of a soft foundation waste dump is obviously worse than that of a hard foundation waste dump. (2) The deformation and failure mode of a hard foundation waste dump shows a collapse-traction-push feature, and it starts from the low-grade slope and develops towards the high-grade slope. (3) The deformation and failure mode of a soft foundation waste dump is mainly controlled by the soft foundation. The non-uniform unloading settlement between front and rear parts of the waste dump results in the cyclic subsidence-crack-slip, until all the slopes above the soft foundation slide. (4) Cracks in a soft foundation waste dump first initiate at the slope bottom and propagate upwards until penetrate the whole slope, but the generation and extension pattern of cracks is opposite in a hard foundation waste dump. Cracks in a soft foundation waste dump are dislocation cracks; however, cracks in a hard foundation waste dump are tension cracks. (5) The reinforcement measures such as dynamic consolidation and borehole grouting are recommended for a soft foundation waste dump, and a drainage system could be constructed to discharge water from the dump site. These results can provide reference for further research of unloading deformation of soft foundation waste dumps under gravity. (C) 2020 Elsevier Ltd. All rights reserved.