By R Moore, E M Lee and A R Clark, Rendel Geotechnics.
This paper was first published in GE’s March 1992 issue.
During the extremely wet winter of 1960/61 parts of Ventnor, on the south coast of the Isle of Wight, were affected by ground movement. A number of properties were damaged beyond repair, some of which had to be temporarily evacuated. The Ministry of Housing & Local Government offered financial assistance to those affected and around 278 000 of insurance claims were made. This was not, however, the first time Ventnor had experienced trouble from ground movement. Indeed, it has long been recognised that the town was built upon a massive ancient landslide complex known as the Undercliff. Over the last 100 years at least 50 buildings have had to be demolished because of ground movement and Chandler and Hutchinson (1984) estimated that between 1960 and 1980 landslide damage costing over R1.5M occurred in the town.
In 1988 the Department of the Environment commissioned a study of the landslide problems in Ventnor as part of its planning research programme. One of the aims of this study was to identify ways in which ground movement information and an understanding of landslide processes could be used to assist local planners in making decisions on the most effective use of land. It was recognised that once there was a detailed understanding of the nature and extent of the landslide problems, management strategies could then be formulated to reduce the consequences of future movement.
The assessment of landslide hazard at Ventnor, Isle of Wight has necessitated the development of a new method for assessing the ground behaviour of an existing landslide complex. The scale and complexity of the landslides dictate that conventional engineering solutions to contemporary instability problems are unlikely to be cost-effective; localised engineering treatments aimed at reducing the magnitude and frequency of movements and their impact on the community are considered more realistic. The results of the study have been published in a Technical and Summary report (Lee & Moore 1991; Lee et al 1991a) and have led to a wider public and professional awareness programme and the development of the Undercliff Landslide Management Strategy.