Analogue modelling of pre-failure strain accumulation for landslide failure prediction

Lead Research Organisation: Durham University
Department Name: Geography

Abstract

Landslides are one of the most destructive geological hazards, resulting in excess of 100,000 fatalities between 1990 and 2006. There is now considerable evidence that landslide impact is increasing. These effects are focussed upon mountainous areas in developing countries, where losses can be 2 / 3% of GDP per year. To undertake a full assessment of landslide hazard, an understanding of the likely location, style, size, speed and timing of the failure is needed, but the last of these remains poorly understood; a problem well illustrated by the 17th February '06 landslide at Leyte, Philippines. This event killed more than 1,100 people and occurred on slopes previously identified as potentially unstable. Prior to the landslide ten days of intense rainfall occurred, a period during which cracks on the slopes above the village were noted. After five days of rainfall the town was evacuated, but after the cessation of rain five days later, the town was re-occupied. Disastrously, the landslide occurred shortly after. The potential for a large landslide was known, precursory signs observed, but a poor understanding of landslide timing, resulted in catastrophe. One approach to understand failure timing has been developed after observations of movements, or strains, on unstable embankments by Japanese engineer, Saito. He observed that when the inverse of velocity of deformation prior to failure was plotted against time, a straight line was observed (Saito, 1965), termed 'Saito linearity'. The implication was that the linear trend could be extrapolated to a point at which velocity reached infinity, predicting of failure. More recently, others noted characteristic movement patterns in landslides, termed 'three phase creep' Varnes (1978), in which a failing slope exhibits three distinct periods of movement. Recently attempts to understand the failure mechanisms which control this pattern have used monitoring of failing slopes and novel geotechnical testing. Questions remain surrounding the application of this model to real slopes particularly with respect to the influence of slope geometry on the evolution of failure, and the complexity of interpreting strain state from real-world monitoring data. Research is proposed to observe the influence of variations in slope geometry and strength on the mechanisms of pre-failure deformation, using a newly developed technique named a vertical 'gravity accelerator' table. In this model a slope, formed from a material with elasto-brittle-plastic properties, that at scale behaves comparably to natural slope materials, is subject to cyclic-loading by dropping onto a hydraulic ram imposing a rapid acceleration in the same direction as gravity. Hence, a 2,000 m slope is simulated using a 0.4 m scale analogue. In a series of model configurations the influence of slope angle, slope length, curvature and strength will be tested. Deformation will be monitored using a high-precision 3D structured light scanner, which measures the surface deformation. In a final set of experiments the processes acting within three well-instrumented real-world landslides will be replicated. These will be the Selbourne cutting stability experiment, UK, the Ota-Mura Landslide, Japan, and the Pos Selim Landslide, Malaysia. Using 3D printing each slope will be recreated, failure simulated and deformation results compared to monitoring data, to establish the controls on the mechanisms and evolution of failure. These data will then be compared to a new database of landslide movement collated from the literature to exmaine landslide mechanisms and movement in a large number of failures. Determining the controls of slope form and material strength on landslide mechanisms and resulting pre-failure surface deformation will give enhanced understanding of deformation trends observed in landslides, mechanisms for landslide triggering and ovement, and will have implications for the use of Saito methods for slope failure prediction.

Publications

10 25 50
 
Description This grant focussed upon using simplified analogue models to assess geometrical controls on the rate of landslide failure evolution. Numerical models use a synthetic constraint on failure time, which means that translating findings to real world applications where time is important, such as early warning systems, is problematic. By using an analogue material that has a time-dependent failure behaviour equivalent to real landslides, i has able to illustrate how steeper, higher and more convex slopes accelerate to a point of failure in differing manners.
Exploitation Route The outcomes from this research are useful for validating numerical models which otherwise have no real-world basis for failure timing. As such this approach is useful for developing slope failure warning systems, and are vital for interpreting real-time monitoring data. This might include those concerned with slope management, landsliding, engineering geologists and mining engineers.
Sectors Environment,Manufacturing, including Industrial Biotechology

 
Description Findings from this project were used to underpin a new KTP project with UK SME 3D Laser Mapping Ltd on slope failure and early warning. This includes using strain-based filaure prediction models for intepreting real-time slope monitoring in large open pits.
First Year Of Impact 2010
Sector Digital/Communication/Information Technologies (including Software),Environment
Impact Types Societal,Economic

 
Description Industry funding - Cleveland Potash Ltd
Amount £790,000 (GBP)
Organisation Israel Chemicals Limited UK 
Sector Private
Country United Kingdom
Start 02/2012 
End 02/2014
 
Description Industry funding - Cleveland Potash Ltd
Amount £3,000,000 (GBP)
Organisation Israel Chemicals Limited UK 
Sector Private
Country United Kingdom
Start 02/2014 
End 02/2019
 
Description Knowledge Transfer Partnership
Amount £201,458 (GBP)
Funding ID KTP#8878 
Organisation Innovate UK 
Sector Public
Country United Kingdom
Start 10/2012 
End 10/2012
 
Description NERC Small Grant - Debris Flows
Amount £27,604 (GBP)
Funding ID NE/G009104/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 04/2009 
End 06/2011