GEOMETRICAL SIMULATION STUDIES OF COASTAL CLIFF FAILURES IN LIASSIC-STRATA, SOUTH-WALES, UK

Three numerical models of cliff failure have been developed, based on analyses of rockfalls along the 22 km Liassic coastline of the Glamorg an Heritage Coast, U.K. Detailed field investigation of the bucklandi (limestone dominated) and angulata (mudstone dominated) Lias series at four locations confirm the veracity of the models. Translation failur e was correctly predicted at the mainly limestone buttressed cliff sit es in the bucklandi and at locations where the angulata series formed a high proportion of the cliff mass. Toppling was predicted for vertic al and overhanging cliffs with basal undercutting. The factor of safet y reduces as the ratio of undercutting depth (d) to tension fracture d istance (D) from the cliff face increases. Instability can be triggere d by thrust forces generated by wave/tide impact, freeze/thaw and expa nsion/contraction associated with clay infill. Thrust forces can be mo dest, ranging from 1.7 to 2.7 MN m(-2), but can exceed the cross-joint strength as weathering proceeds.