1 / 15

Edge effects in propagation tests

Study on snow propagation tests like ECT and PST, exploring stress concentration at edges and its impact on test results. Findings show significant far edge effects, influencing crack propagation and collapse patterns. Implications include test sensitivity to length and potential for increased accuracy with longer tests.

yanni
Télécharger la présentation

Edge effects in propagation tests

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Edge effects in propagation tests Edward (Ned) H. Bair1,2*, Ron Simenhois3, Alec van Herwijnen4, and Karl Birkeland5 1 US Army Corps of Engineers Cold Regions Research and Engineering Laboratory, Hanover, NH, USA 2 Earth Research Institute, University of California, Santa Barbara, CA, USA 3 Southeast Alaska Avalanche Center, Juneau, AK, USA 4 WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland 5 US Forest Service National Avalanche Center, Bozeman, MT, USA nbair@eri.ucsb.edu

  2. Introduction, propagation test length guidelines Extended Column Test (ECT), l = 90 cm Propagation Saw Test (PST), l = 100 cm or slab depth; whichever is greater Greene, E., et al., 2010: Snow, Weather, and Avalanches: Observational Guidelines for Avalanche Programs in the United States, 136.

  3. Introduction, stress concentration at edges

  4. G and G∞ • G – energy release rate of the slab • G∞ – asymptotic energy release rate (no far edge effect) • F(r/l) – correction factor • r is crack length • l is test length

  5. Overview • 163 PSTs and ECTs on beams with l = 1-10 m, including some centered ECTs and PSTs • Particle tracking on markers inserted into beams • Finite element modeling for 3 profiles from pits done at tests

  6. Major findings for ECTs and PSTs • Full crack propagation decreased with test length • Greater collapse occurred at the trigger and far end of the beam than in the center • Wavelengths were ~ 3 m, 2x what is predicted by the anticrack model • The far edge effect is significant for tests up to ~ 2 m

  7. Field test summary

  8. Particle tracking, collapse amplitude • Relative to the middle of the beam, the trigger edge collapsed 160% and the far edge collapsed 128%.

  9. Particle tracking, wavelength

  10. FE profiles

  11. Finite element (FE) results • 3 profiles (a,b,c) • fixed crack length (critical length) for each profile

  12. Correction factor from FE

  13. Centered tests • We experimented with centered PSTs (CPSTs) and found that the critical length doubled. • CPSTs require 2x as much digging for the same crack propagation length as a standard PST, so we find them less practical.

  14. Cool aside • We were able to track the collapse amplitude over time for some of the tests that failed on the same layer. • The average decrease was 0.65 mm/day.

  15. Implications • PST and ECT results are sensitive to test length • Longer tests could decrease false unstable results, *BUT* we need to test this hypothesis. • To test our hypothesis, we will examine the accuracy of 2 m tests vs. standard 1 m tests on slope stability.

More Related