DOI: 10.17603/ds2-59px-fm97
title: Centrifuge Test Data from Fly Ash Deposits Subjected to a Loss of Confinement
title: in Centrifuge Modeling of the Slope Stability, Run-out Behavior and Static Liquefaction of Fly Ash Deposits subjected to a loss of Confinement

description: Numerous industries are concerned by the humanitarian, environmental, and economic consequences
of debris flows, landslides and material run-outs. However, the run-out behavior following a loss of
confinement e.g., dam failure, is not well understood. The material’s complex constitutive behavior
means multiple mechanisms contribute to the deformation e.g., slope instability, seepage forces, erosion
or static liquefaction. In this study, centrifuge models of fly ash deposits, with varying initial deposit
density and water table height, were subjected to a rapid loss of lateral confinement. Deformation,
pore pressure and water content measurements were used to investigate and separate the mechanisms
governing the run-out. Static liquefaction was observed in deposits initially looser than the critical state
and led to a rapid material outflow. Slope instability was the initial failure mechanism for denser deposits
or those with reduced water tables, with transient stability due to dilation-induced negative excess pore
pressures followed by progressive failures caused by seepage pressures from drainage and pore pressure
dissipation. Cone penetration tests, performed before loss of confinement and with different penetration
rates, characterized the material run-out and volume change tendencies and may be a practical tool for
assessing the run-out risk of deposits in the field.
description: Four centrifuge models of fly ash deposits, with varying initial deposit density and water table height, were subjected to a rapid loss of lateral confinement. FR02 and FR03 feature dense deposits with the water table either just below or above the fly ash surface; FR05 is an initially loose deposit with the water table just below the fly ash surface whilst FR06 had an intermediate density and a water table lowered in-flight to near the deposit mid-height.

Instrumentation included tensiometers to measure the development of positive and negative excess pore pressures, water content sensors, conventional and depth sensing video cameras, bender elements and miniature cone penetration tests conducted at two different rates to elicit undrained and drained tip resistances.

The different instruments were used to investigate and separate the mechanisms governing the run-out. Static liquefaction was observed in deposits initially looser than the critical state and led to a rapid material outflow. Slope instability was the initial failure mechanism for denser deposits or those with reduced water tables, with transient stability due to dilation-induced negative excess pore pressures followed by progressive failures caused by seepage pressures from drainage and pore pressure dissipation. 

The run-out data can be used to validate experiments conducted at various scales and numerical models of run-out problems. This data could be of particular use to validate newer numerical methodologies, e.g., the MPM method, as the material's initial state and boundary conditions, in addition to its progressive behavior in terms of deformations and pore pressures, are clearly defined by the experiments. 

Cone penetration tests, performed before loss of confinement and with different penetration rates, characterized the material run-out and volume change tendencies. Combining these datasets demonstrates a practical tool for assessing the run-out risk of deposits in the field.