D.G. Milledge
Limits on the validity of infinite length assumptions for modelling shallow landslides
Milledge, D.G.; Griffiths, D.; Lane, S.N.; Warburton, J.
Authors
D. Griffiths
S.N. Lane
J. Warburton
Abstract
The infinite slope method is widely used as the geotechnical component of geomorphic and landscape evolution models. Its assumption that shallow landslides are infinitely long (in a downslope direction) is usually considered valid for natural landslides on the basis that they are generally long relative to their depth. However, this is rarely justified, because the critical length/depth (L/H) ratio below which edge effects become important is unknown. We establish this critical L/H ratio by benchmarking infinite slope stability predictions against finite element predictions for a set of synthetic two-dimensional slopes, assuming that the difference between the predictions is due to error in the infinite slope method. We test the infinite slope method for six different L/H ratios to find the critical ratio at which its predictions fall within 5% of those from the finite element method. We repeat these tests for 5000 synthetic slopes with a range of failure plane depths, pore water pressures, friction angles, soil cohesions, soil unit weights and slope angles characteristic of natural slopes. We find that: (1) infinite slope stability predictions are consistently too conservative for small L/H ratios; (2) the predictions always converge to within 5% of the finite element benchmarks by a L/H ratio of 25 (i.e. the infinite slope assumption is reasonable for landslides 25 times longer than they are deep); but (3) they can converge at much lower ratios depending on slope properties, particularly for low cohesion soils. The implication for catchment scale stability models is that the infinite length assumption is reasonable if their grid resolution is coarse (e.g. >25 m). However, it may also be valid even at much finer grid resolutions (e.g. 1 m), because spatial organization in the predicted pore water pressure field reduces the probability of short landslides and minimizes the risk that predicted landslides will have L/H ratios less than 25.
Citation
Milledge, D., Griffiths, D., Lane, S., & Warburton, J. (2012). Limits on the validity of infinite length assumptions for modelling shallow landslides. Earth Surface Processes and Landforms, 37(11), 1158-1166. https://doi.org/10.1002/esp.3235
Journal Article Type | Article |
---|---|
Publication Date | Sep 15, 2012 |
Deposit Date | Mar 8, 2012 |
Publicly Available Date | Dec 2, 2014 |
Journal | Earth Surface Processes and Landforms |
Print ISSN | 0197-9337 |
Electronic ISSN | 1096-9837 |
Publisher | British Society for Geomorphology |
Peer Reviewed | Peer Reviewed |
Volume | 37 |
Issue | 11 |
Pages | 1158-1166 |
DOI | https://doi.org/10.1002/esp.3235 |
Keywords | Infinite slope length, Stability model, Shallow landslide, Finite element method, Benchmark. |
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Copyright Statement
This is the accepted version of the following article: Milledge, D. G., Griffiths, D. V., Lane, S. N. and Warburton, J. (2012), Limits on the validity of infinite length assumptions for modelling shallow landslides. Earth Surface Processes and Landforms, 37 (11): 1158–1166, which has been published in final form at http://dx.doi.org/10.1002/esp.3235. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.
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