MODELING FAILURE MECHANISMS TO EXPLAIN ROCK SLOPE CHANGE ALONG THE ISLE OF PURBECK COAST, UK

Results are presented of distinct element computer modelling used to e xamine rates and mechanisms of change in rock slopes and cliffs, where material intact properties determine process and form but the most si gnificant controls are the joint pattern and cross-joint properties. T he modelling approach does not appear to have been used before in a ge omorphological context and provides an alternative approach for examin ing cliff development. Field and laboratory data have been collected f or the Portland Limestone outcrop of the Isle of Purbeck, central sout hern England. The Portland Limestone is a hard, shelly, crystalline se diment of the Upper Jurassic. It has a regular discontinuity pattern t hroughout the outcrop in Purbeck. While joint orientation remains rela tively constant, bedding changes from horizontal to vertical, a conseq uence of the Purbeck Monocline. There are resulting implications for s patial variations in rock slope evolution. The modelling exercise enha nces previous knowledge on rock failure mechanisms and slope developme nt along the Purbeck coast and demonstrates its potential in research where landforms are developed in lithified, jointed rock masses. (C) 1 998 John Wiley & Sons, Ltd.