28. The recent history and geotechnics of landslides at Gore Cliff, Isle of Wight

The landslide of 1978 which led to the destruction of four properties at Gore Cliff was the latest in a series of movements which have affected the stretch of the Isle of Wight coastline between Blackgang Chine and Rocken End over at least the last two centuries. Investigations into the landslide showed that it was the reactivation of earlier slides with a basal slip surface controlled by bedding, and occurring at approximately 18 m above the base of the Gault. Most of the slide debris comprised materials derived from the Upper Greensand, with the uppermost part of the Gault removed by previous slide movements.

The paper describes the investigations into the geomorphology, history, engineering geology and geotechnics of the slide complex. Geotechnical investigations have included boreholes and piezometers, together with a laboratory test programme. Results of back analyses of the slide are compared with laboratory measured ring shear test results, and on the basis of this and other data, the cause of the landslide is inferred. The implications of the findings at Gore Cliff to the Undercliff generally are explored in the paper.

• GEOGRAPHICAL PERSPECTIVE

• BACKGROUND TO THE PROJECT

• GEOLOGICAL SUCCESSION & STRUCTURE

• SLOPE INSTABILITY

• INVESTIGATIONS CARRIED OUT IN THE 1978 SLIDE

• INFERENCES FOR THE UNDERCLIFF GENERALLY

• ACKNOWLEDGEMENTS

• REFERENCES