Numerical simulation of rapid and highly mobile landslides during intense precipitation

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Cepeda, Jose
Holding Date 03 September 2008

Entrainment of runoff water in landslides during episodes of intense precipitation is normally not considered in numerical simulations, even though in some cases the reduction in sediment concentration may produce significant changes in the rheology of the flowing mass along the path. The procedure presented attempts to incorporate this effect of water entrainment. Initially, the failing mass is modelled as a frictional material using the program DAN3D. A hydrograph is calculated through a cross section at the toe of the release area. This hydrograph and a rainfall- intensity time history are fed into a FLO-2D simulation that incorporates a quadratic rheology characterised by a yield stress, a viscosity and a Manning’s n-value. The yield stress and the viscosity are obtained by testing samples of the landslide deposits in a ball rheometer. The samples are reconstituted to a range of water contents in order to account for the dilution due to water entrainment. The complete procedure is illustrated with two cases from El Salvador: a debris flow on the San Salvador volcano in September 1982, and a lahar on the Santa Ana volcano in October 2005 triggered by Hurricane Stan after an ash eruption.