Investigation of a landslip in the Fuller's Earth Clay,

Rubbish dumping into an abandoned quarry in the Great Oolite on a south facing slope of Lansdown, Bath, has provoked a series of slides which now sterilises 12 acres of grazing land. The first major slide in October 1969 was followed by two further movements by January 1971. They account for a total downhill movement of 210 m. Where access to the site made investigation possible, a distinctive shear zone was exposed, sandwiched between the base of the fill and top of the weathered Fuller's Earth clays. Adjacent o the slip, the natural ground succession showed a mixed stony soft brown reworked clay (solifluction) layer, overlying interbedded clay mudstone bands of the Fuller's Earth series. Drained triaxial tests on the brown clay gave shear parameters of,k ' = 17"4 ~ c ' = 0; and an estimate of residual strength of, ~ = 12 ~ The former value would accord with a high (perched) water table on the adjacent slopes at 12.7 ~ ~ Whilst accurate back analysis is not presently possible, due to absence of specific measurements of the surface ground water levels, it is concluded that a limiting stability exists on the slope generally, irrespective of the fill dumping. 1