**Landslide runout**

Landslide travel distance is of importance in a number of applications relating to slope design and maintenance. This is a complex area of research requiring detailed rheology and material parameterisation that is rarely if ever available. Nonetheless it is highly relevant to include some estimation methodology within CHASM to provide some indication of likely landslide impact a s far as runout distance and depth is concerned.

Finlay et al. (1999) used data from the Geotechnical Engineering Office in Hong Kong to carry out an empirical analysis of the landslides recorded. 1100 landslides were included, out of a possible 3000, which had occurred between 1984 and 1993 in man-modified slopes of weathered granite and other volcanics. Most of these landslides had volumes of less than 1000m3 and debris ran out onto a near horizontal surface below the slope.

Multiple regression models based on slope geometry were developed for the prediction of landslide travel across horizontal surfaces at the base of slopes using the geometry of a failure in a cut slope:

and it is this empirical model that is used in CHASM. The required independent variables are tan A (slope angle), D (depth to slip surface) and H (height of landslide). The dependent variables are log L and H4 (depth of debris at base of slope) for cut slopes. Three equations are given for each dependent variable – lower confidence interval (95%), mean predicted value, and upper confidence limit (95%).

CHASM returns the landslide runout distance, R, for each hour of the simulation runtime

**Reference:**

Finley, P.J., Mostyn, G.R. and Fell, R. 1999. Landslide Risk Assessment: prediction of travel distance. Canadian Geotechnical Journal, 36: 556-562.