Instability caused by a seepage impediment in layered fill slopes

Abstract

The underlying cause of loose fill slope failures in Hong Kong has been attributed to static liquefaction during heavy rainfall. A series of centrifuge model tests and numerical analyses were conducted to illustrate that instability of a fill slope inclined at approximately the internal friction angle of the soil can be triggered by confined groundwater flow due to soil layering in the fill slope. The results also showed that slope failure could occur irrespective of the density of the fill material when seepage was sufficiently impeded leading to a localised buildup of pore-water pressure in the slope. A numerical parametric study was carried out to examine the effect of variations in hydraulic conductivity in the layered fill slopes. The results showed that the excess pore pressure distribution and hence the failure mode were strongly dependent on the location of the inhomogeneous soil layers and their hydraulic properties. It was also demonstrated that layered fill slopes with spatial variation in hydraulic conductivity of as small as one order of magnitude were vulnerable to global failure under confined groundwater flow.