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| Titel |
Effects of Dilatancy on the Shearing Behaviour of Root-Permeated Soil |
| VerfasserIn |
Anil Yildiz, Frank Graf, Christian Rickli, Sarah M. Springman |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109094
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| Publikation (Nr.) |
 EGU/EGU2015-8972.pdf |
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| Zusammenfassung |
| The effects of vegetation and, in particular, of forests on the stability of slopes are well
recognized and have been widely investigated. However, there is still a considerable lack of
understanding on the underlying processes that contribute to triggering superficial soil failure
in root-permeated soil. Therefore, it comes as no surprise that a period of heavy rainfall in
August 2005, affecting an extensive area in Praettigau region in canton Grisons, resulted in
numerous shallow landslides of which about half, 26 out of 50 events, occurred in the forest
area. Thus, quantification of the vegetation effects on the shear strength of soil is important in
order to be able to evaluate the contribution of root reinforcement to slope stability.
Root reinforcement has been investigated through different approaches, including
laboratory or in-situ shear tests of root-permeated soil, and analytical models of
soil-root interaction. Traditional methods, generally, consider roots passing through
the shear surface with full development of the roots’ tensile strength. However,
it has been shown that lateral roots contribute to strength as well, and that roots
and soil do not necessarily fail simultaneously, and hence the strengths of both
components of root-permeated soil are displacement dependent. A robust inclinable
large-scale direct shear apparatus (ILDSA) was constructed in order to evaluate
the combined effects of the root system on the shearing behaviour of soil. Two
different sets of planted samples, a first set consisting of Alnus incana, Trifolium
pratense, Poa pratensis and a latter set, consisting of these three species complemented
with Salix appendiculata, Achillea millefolium, Anthyllis vulneraria, have been
prepared in moraine (SP-SM) from a recent landslide area in Central Switzerland.
Planted samples are maintained in shear boxes (500x500x400 mm) inclined at 30º,
simulating a slope, and the corresponding natural growth of roots on it. Direct shear tests
have been conducted on unplanted and planted soil samples at a constant rate of
horizontal displacement of 1 mm/min to a maximum horizontal displacement of 200
mm. Three different applied normal stress levels, namely 6 kPa, 11 kPa and 16
kPa, were chosen to be comparable to the average depth of shallow landslides. An
artificial rainfall at a constant intensity (100 mm/h) was applied prior to shearing in
order to simulate the loss of strength after a heavy rainfall period under continuous
monitoring of the matric suction with tensiometers, which was brought as close as
possible to 0 kPa around the shear surface to ensure saturation. Dependence of
contribution of root reinforcement to the additional shear strength of soil due to
dilatancy was investigated in this study, and a comparison between the two levels
of number of plant species, in terms of shear strength parameters, was presented. |
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