The engineering geology of the landslides on the north coast of the Isle of Wight their analysis and stabilisation

Abstract

The geological history of the north coast of the Isle of Wight is outlined and the published stratigraphy corrected. The engineering properties of the beds are summarised.

The state of stress within the ground is discussed together with the effect that may have on the formation of shear zones and slip planes. Pore water pressure profiles in the slopes are described and the time scales involved in changing pore water profiles are discussed in terms of their effects on slope stability.

Alternative methods of analysis are described and the results of several methods are compared for a slope typical of those on the north coast of the Isle of Wight. Long term movements on slides are considered and both progressive and episodic failure examined.

Methods of stabilising landslides are discussed. The use of piles as stabilising elements is considered in some detail and a new method of calculating the moments and deflections on a passive pile is derived. Methods of extending the results of calculations on a single pile to rows of piles, i.e. group effects, are also summarised.

The results of all the known boreholes in the Cowes, Gurnard area that penetrate the full depth of the land slipped material are plotted and a 3D model of the area presented. This is then used to draw sections which can be used to delineate the depth to the in situ geology. Finally, a number of case histories are described in both the Cowes Gurnard and Seagrove Bay areas which illustrate the problems encountered and the wide variety of methods used to overcome them.

Many of the concepts discussed are illustrated by way of computer programs, written for the purpose.

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