23 November 2009

The ten greatest landslide papers?

Posted by Dave Petley

Whilst pushing my five year old daughter on the swing the other day (a task that leaves plenty of time to think!), I was pondering upon the greatest landslide papers of all time. I thought that it would be interesting to compile a list and invite suggestions of alternatives. So, here is my list, in no particular order:

1. Terzaghi on the principle of effective stress
In 1936 Karl von Terzaghi laid the foundation for modern soil mechanics, and the basis of our understanding of how landslides move, by stating the principle of effective stress. The recognition that pore water pressures control the frictional resistance of slopes remains the most important concept in understanding landslide behaviour.
Reference: Terzaghi, K., 1936. “The Shear Resistance of Saturated Soils”. Proceedings of the first International Conference on Soil Mechanics and Foundation Engineering, Cambridge, U. S. A., 1, 54-56.

2. Keefer on earthquakes caused by landslides
Dave Keefer’s 1984 paper on landslides triggered by earthquakes was a remarkable analysis. Taking a huge dataset of earthquake-triggered landslide inventories, Keefer demonstrated both the simplicity and the complexity of the relationship between numbers and areas of landslides and the earthquake parameters. The approach taken in this paper has been much reproduced since; remarkably it the core conclusions are essentially unaltered.
Reference: Keefer, D.K., 1984, Landslides caused by earthquakes. Geological Society of America Bulletin, 95, 406-421.

3. Hutchinson and Bhandari on undrained loading
Undrained loading is one of those concepts that makes you go “of sourse” when it is explained to you. The idea is that the sudden application of a load (such as for example a rockfall from a cliff onto an mudslide below) drives a dramatic increase in pore pressures, which can’t dissipate quickly. This reduces the effective normal stress, allowing the slope to move. It explains landslides in many settings – a crucial step forward.
Reference: Hutchinson, J. N. & Bhandari, R. K. 1972. Undrained loading, a fundamental mechanism of mudflows and other mass movements. Geotechnique 21, 353-358

4. Caine on thresholds associated with landslide initiation

Almost all of the working large area landslide warning systems are based on this paper. Caine set out to understand the rainfall thresholds at which landslides occur, recognising that it is a combination of medium term low intensity rainfall (to get the ground wet) and short duration rainfall (to get initiate movement) that is the key. This is literally the paper that launched a thousand studies – and more appear every year. There is even a website dedicated to this type of work: http://rainfallthresholds.irpi.cnr.it/threshold_info.htm
Reference: Caine, N., 1980. The rainfall intensity-duration control of shallow landslides and debris flows. Geografiska Annaler, 62A, 23-27.

5. Skempton on the principle of residual strength
Residual strength is a key idea within landslide science. Skempton’s work was prompted by the difficulties of explaining why low gradient slopes were failing. The idea that materials have a residual strength that is less than the peak strength is key – slopes that have in previous times been reduced to this lower strength will fail much more easily when disturbed. This concept really made Skempton’s career, and he was ultimately knighted for his scientific contributions.
Reference: Skempton, A.W. 1964. Long term stability of clay slopes. Geotechnique, 14, 77-101 (the fourth Rankine lecture).

6. Carson and Petley on the existence of threshold slopes
In case you are wondering, this Petley is not me, but shall we say that when I was a child I spent a great deal of time with him (and continue to do so, but more rarely now). In many ways the dataset in this paper is not comprehensive, but the ideas that it introduced are fundamental. The paper suggested that in any environment a slope will relax to a constant gradient that reflects its stength and the conditions to which it is exposed. The idea was spot on, and is just being rediscovered by geophysicists!
Reference: Carson, M.A., and Petley, D.J., 1970, Existence of threshold hillslopes in denudation of
landscape. Transactions of the Institute of British Geographers, 49, 71–95.

7. Carrara on the evaluation of landslide hazardLandslide hazard assessment is big business these days. Carrara’s paper was not the very first to do this, but it was a pioneering study in terms of using the rapidly evolving technologies that were becoming available. The myriad of factor and suchlike based studies that have followed over the last 26 years all owe a great deal to this study.
Reference: Carrara, A. 1983. Multivariate models for landslide hazard evaluation. Journal of the International Association for Mathematical Geology, 15, 403-426.

8. Hoek and Bray on rock slope engineering
This is the only item on my top ten that is a book rather than a paper. The stability of rockslopes is primarily controlled by the properties, orientations and interactions of discontinuities rather than by the intact material strength. This book brought together for the first time the principles of rockslope stability and design. It has been revised and reprinted on numerous occasions, and remains the bible of rock slope engineers.
Reference: Hoek, E. and Bray, J. 1974. Rock slope engineering. Institution of Mining and Metallurgy, 309 pp.

9. Bjerrum on progressive failure
The principles and processes of progressive failure remain poorly understood, but Bjerrum’s 1967 examination of this key topic remains the salient work in this area. Bjerrum proposed a model for the weakening of slopes with time as a crack grows through the base. The concepts remain fresh and valid today – there is surely a great opportunity for someone to take this issue and produce the definitive follow-up on how this process actually operates.
Reference: Bjerrum L. 1967. Progressive failure in slopes of overconsolidated plastic clay and clay shales. Journal of the Soil Mechanics and Foundations Division, ASCE, 93, 1-49.

10. Bishop and Wesley on soil testing
Without laboratory testing of laboratory materials slope engineering would still be in the dark ages. The key research machine in every geotechnical laboratory is the triaxial cell, and research purposes t
he stress path cell is the most important tool. This paper described just such a machine, opening the way to our fundamental understanding of soil behaviour.
Reference: Bishop, A.W. and Wesley, L.D. 1975. A hydraulic triaxial apparatus for controlled stress path testing. Geotechnique 25, 657-670.
I’m sure that you don’t agree with me, so please tell me why I am wrong, and suggest alternatives. I am worried that there is nothing since 1984 – surely there must have been great papers in the intervening 25 years. What have I missed?