Experimental Study of the Premonitory Factors for Internal Erosion and Piping Failure of Landslide Dams

Abstract

A good knowledge of sediment transport processes, including the hydraulics and hydrodynamics is prerequisite for a better understanding of the complex mechanisms of internal erosion and piping failure of landslide dams. To this end, a series of large-scale (outdoor) physical experiments were conducted to evaluate the premonitory factors and the critical conditions for piping failure of landslide dams. The experimental facility comprises a horseshoe-shaped trapezoidal barrier of length 8 m and height 2 m, with an open end for the construction of the dam models. Internal deformations associated with the onset of internal erosion were monitored with four strain gauges inserted into a PVC pipe and laid ~0.5 m above a 0.2 m-wide artificial drainage channel comprised of uniformly-sized pebbles and gravel. The rate of internal erosion and piping was measured with a turbidity sensor installed near the potential exit point of the seepage water to record the changes in turbidity of the fluidized sediments. Transient variations in the upstream reservoir were monitored with a 50 kPa capacity pore-pressure transducer while the hydrodynamic changes that occurred during the onset of internal erosion and piping were monitored with three pore-pressure transducers. The deformation behaviour of the dam models was monitored with two multi-function analog laser displacement sensors while self-potential measurements were made to track the development of the piping hole under steady-state flow conditions. The experimental results indicated that the emergence of an effluent seepage of high turbidity at the downstream face of the dam models coincided with high negative self-potential anomalies. This was also found to correlate with the development of high pore-water pressures (4–8 kPa) which subsequently led to a gradual decrease in the dam height (settlement). These large-scale (outdoor) physical experiments provide important information which may be useful in estimating the breaching process of landslide dams as triggered by piping.