The Selborne cutting stability experiment

Abstract

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, with 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. L'article décrit une expérience sur le terrain qui a consisté à induire la rupture ďun talus remanié de 9 mètres dans de &caronlargile Gault sous ľeffet de la recharge de la pression ďean interstitielle. Les auteurs décrivent la géologie du terrain et expliquent les méthodes utilisées pour former le talus. Une innovation a consisté à utiliser des panneaux à faible coefficient de frottement à chaque extrémité la section à ľétude pour former des tranchées ´isolement et, donc, favoriser des déplacements surtout bidimensionnels. Un grand nombre &acutelinstruments ont été utilisés: piézomètres, inclinomètres et extensomètres à câblage saillant. Le système utilisé pour la recharge de la pression ďeau interstitielle est décrit en détail. ľarticle décrit également le programme ďessais en laboratoire exéé dans le cadre de cc projet et examine la performance des instruments, y compris les principaux résultats et les observations faites à partir de cette expérience. On a constaté que la rupture du talus a éé progressive, commençant au pied du talus pen après le début de ľexpérience. Certaines indications font penser qˇun m&acutelcanisme semblable de rupture progressive a également eu lieu au sommet du talus. Un aspect important de cette expérience est ľinformation détaillée obtenue sur les mouvements du talus pendant toute la période qui a préé la rupture, ainsi qˇaprès la rupture. ľarticle présente certains résultats des analyses ďéquilibre limite qui indiquent que ďimportants déplacements se produisent, même quand le coefficient de sécuré est bien supérieur à ĺunité.

An acoustic emission landslide early warning system for communities in low-income and middle-income countries

“…d A view of a sensor located on the waveguide inside a cover progressive failure occurs and post peak strengths are mobilised (e.g. Leroueil 2001;Cooper et al 1998).…”

Modeling Slope Instability as Shear Rupture Propagation in a Saturated Porous Medium

“…In the experiment of Cooper et al (1998), decreases in measured pore pressure during early-stage slope movement indicate a stabilizing dilative suction preceding total slope failure. Subaerial flume studies of densely or loosely packed sandy sediment also show a tendency for dilatant stabilization in the case of dense sediments and transition to debris flow when loosely packed (Iverson et al 2000).…”

“…However, a failure location and time can be constrained by artificially creating failure conditions. For example, Cooper et al (1998) induced slump failure in a naturally deposited clay slope by artificially elevating pore pressures. Excavation revealed an O(mm) thick intense shear zone within an O(cm) thick disturbed region.…”

Frictional heating lubrication for submarine landslide

“…As shown in the observations of many subaerial landslides, the thickness of this "basal shear zone" is often very small ranging between mm-scale and decimeter-scale. For example, (1) an excavation of a failed clay slope in England artificially triggered by a fluid injection discovered that the basal shear zone was nested within a very thin disturbed zone (Cooper et al 1998); (2) an investigation of a landslide in Hong Kong naturally triggered by a heavy rainfall found out that the basal shear zone of this landslide might be a few millimeters thick appearing at 2 -5 m depth below the slope surface Aydin 2003, 2004); (3) a four-year monitoring of a landslide in Italy, during which inclinometers were inserted into the landslide to measure the slide-soil displacement vs. the slope-normal depth, released that the landslide moved as a stiff body over a narrow zone (≈ decimeters thick) with most shear deformation localized to this thin zone (Picarelli et al 2005); (4) a landslide experiment carried out on a natural slope, in which soil-strain probes were inserted into the sliding soil to measure the shear deformation, showed that the basal shear zone was only about 10 cm thick (Ochiai et al 2004); (5) a field investigation of a sensitive clay landslide with a volume of 2.5 × 10 6 m 3 which occurred near British Columbia, Canada found out that the thickness of shear zone in this landslide could be narrowed down to a very thin "slip surface" (cf. Figs.…”