Laboratory test for sand boil formation near a flood protection dike

Abstract

The sand boil is the first stage of a piping failure of river dikes which may form in either free granular soil surface or in areas covered with a less permeable layer that is not thick enough to maintain a balance with water pressure if the water's exit speed exceeds a given value. The aim of the research is to see whether a laboratory model is capable to the examination of this phenomenon. The reason for it is the sand boil is starting at a hydraulic gradient much less than the critical value and it may be assumed that the equilibrium condition of individual grains forces may explain this. The model test is made using a simplified Hungarian river dike section where a fine sand layer is placed between the impermeable cover layer and the permeable subsoil. It can be clearly observed that while the flood occurs upstream, the stability of the fine sand grains at the downstream side is not ensured after the cover layer is cracking. The sand boil phenomena also appeared. This proved that a laboratory sandbox model is applicable to modeling and examining sand boiling with controlled circumstances.