The Selborne cutting stability experiment

The paper describes a field experiment in which a 9 m deep cut slope in Gault Clay was brought to failure by pore pressure recharge. The geology of the site is described and the procedures used to form the slope are explained. A novel feature was the use of low-friction panels at each end of the study section to form isolation trenches and thus encourage primarily two-dimensional displacements. The site was extensively instrumented using piezometers, inclinometers and surface wire extensometer lines. The system used for the pore pressure recharge is described in detail. This paper also describes the laboratory testing programme performed as part of the project and discusses instrument performance, including key results and observations drawn from the experiment. It was found that the failure of the slope took place as a result of a progressive failure mechanism,,vith movements initiating at the toe of the slope at an early stage in the experiment. There is some evidence that a similar progressive failure mechanism also developed from the crest of the slope. An important feature of the experiment is the detailed information obtained on slope movements throughout the period up to and beyond failure. Some results from limit equilibrium analyses are presented, which indicate that significant displacements occur even when the factor of safety is well above unity.