Instability of loose dry granular slopes observed in centrifuge tilting table tests

Abstract

Landslides in loose saturated granular materials can experience significant deviatoric strain softening leading to static liquefaction and flow failure. This research study aimed at understanding the instability conditions leading to softening has been conducted under triaxial or plane strain conditions on loose granular soils brought to failure under undrained or drained stress paths. In this paper, it is hypothesised that the onset of granular instability should also be reproducible in tilt-table tests of loose dry granular soils. A centrifuge tilt-table apparatus was developed to test this hypothesis in which the stress path imposed on the soil layer could be inferred from an infinite slope analysis and the shear and volumetric strain be measured through the transparent side walls. Experiments performed at 1g, 20g, 40g and 60g illustrate that this approach can capture the constitutive behaviour of the soil layer. Critically, as the tilt-table test is a load-control test, instability was observed as a rapid acceleration in shear strain rate accompanied by a rapid volumetric collapse of the pore space. The tilt-table test therefore not only enables a measurement of the angle of repose, but provides a method to characterise the instability behaviour of granular materials at low stress levels found in shallow landslides.