Statistical analysis of experimentally determined critical hydraulic gradients for heave

Abstract

Heave is a type of deformation that occurs due to seepage, which may evolve into backward erosion piping and eventually lead to the total collapse of a hydraulic structure. It may occur downstream of the hydraulic structure when uniform non-cohesive soil is subjected to upward seepage. In this study, the limit state condition for heave was formulated based on the equilibrium of acting forces and with the use of corresponding partial factors. During extensive laboratory research, glass beads of 0·2, 0·5 and 1·0 mm in diameter, three natural and three artificially prepared sands with grain diameters ranging from 0 to 4 mm and a uniformity coefficient CU ranging from 1·4 to 5 were subjected to upward seepage in cylindrical permeameter. The hydraulic gradient was gradually raised until heave of the material occurred. The porosity of specimens varied from 0·31 to 0·54 according to the method of placement and compaction degree. In total, 425 experiments were carried out. The results were statistically processed for nine sets of materials and partial factors were derived for a selected structure reliability. The values obtained for the factors may be used by practitioners during the safety assessment of the hydraulic structures exposed to potential heave.