 |
| Titel |
Effects of different vegetation types on the shear strength of
root-permeated soils |
| VerfasserIn |
Anil Yildiz, Frank Graf, Christian Rickli, Sarah M. Springman |
| Konferenz |
EGU General Assembly 2016
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250136769
|
| Publikation (Nr.) |
 EGU/EGU2016-17879.pdf |
|
|
|
|
|
| Zusammenfassung |
| The effects of vegetation and, in particular, of forests on the stability of slopes are well
recognized and have been widely studied in recent decades. However, there is still a lack of
understanding of the underlying processes that occur prior to triggering superficial failures in
root-permeated soil. Thus, appropriate quantification of the vegetation effects on the shear
strength of soil is crucial in order to be able to evaluate the stability of a vegetated slope.
Direct shear testing is widely employed to determine the shearing response of root-permeated
soil. However, mechanical aspects of direct shear apparatuses may affect the shear
strength parameters derived, which often remains unnoticed and hampers direct
comparison between different studies. A robust Inclinable Large-scale Direct Shear
Apparatus (ILDSA), with dimensions of 500x500x400 mm, was built in order to shear
root-permeated soil specimens and to analyse the influence of the machine setup
on the results, too. Two different sets of planted specimens were prepared using
moraine (SP-SM) from a recent landslide area in Central Switzerland: a first set
consisting of Alnus incana, Trifolium pratense, Poa pratensis and a second set,
consisting of these three species complemented with Salix appendiculata, Achillea
millefolium, Anthyllis vulneraria. Direct shear tests were conducted on specimens planted
with the different vegetation types, at a constant rate of horizontal displacement
of 1 mm/min up to a maximum horizontal displacement of 190 mm, and under
three different applied normal stresses: 6 kPa, 11 kPa and 16 kPa. Artificial rainfall
was applied at a constant intensity (100 mm/h) prior to shearing. Tensiometers
had been installed close to the shear surface and were monitored continuously to
obtain the matric suction during the saturation process. Suctions were reduced as
close to 0 kPa as possible, in order to simulate the loss of strength after a heavy
period of rainfall. The analyses of the above ground biomass and roots yielded a
positive correlation (R2 = 0.80) with their dry weights. On the one hand, the peak
stress ratio, the ratio of peak shear stress and the normal stress, was calculated with
the value of the applied normal load (WUpper) and, on the other hand, with the
value of the normal load transferred to the shear surface (WLower). There was no
obvious relationship between the peak stress ratio calculated with WLower and the dry
weight of the roots, as WLower is related to the dilatancy. However, different linear
relationships were found between the peak stress ratio calculated with WUpper and the dry
weight of the roots for specimens with low level (R2 = 0.75) and high level plant
factor (R2 = 0.51). Hence, it can be concluded that such variations indicate two
different mechanisms of contribution of roots to the shear strength of the soil, which is
due to the dominant growth angle and the amount of roots within the shear box. |
|
|
|
|
|
|