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| Titel |
Analysing the influence of preferential flow on pressure transmission and landslide triggering |
| VerfasserIn |
Wei Shao, Thom Bogaard, Mark Bakker, Ye Su, Matteo Berti |
| 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 |
250107853
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| Publikation (Nr.) |
 EGU/EGU2015-7571.pdf |
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| Zusammenfassung |
| Rainfall-induced shallow landslides are the most frequent natural hazards in mountainous
areas. As a result of rainfall, an increase in pore water pressure reduces the effective stress
and shear strength of a slope, which could further trigger the occurrence of slope failure.
Recognizably, such landslides are characterized by thresholds of rainfall magnitude and
intensity, which are commonly evaluated in hydro-mechanical models via integration of a
hydrological and a soil mechanics model. Mechanisms of slope instability and water pressure
transmission in a natural subsurface hydrological system are very complex, because
the soil hydraulic behaviours in the saturated and the unsaturated zones are rather
different. Regarding the pressure transmission mechanism, in the saturated zone the
pressure wave propagation is nearly instant, while, in the unsaturated zone the pressure
fluctuates due to the variability of soil moisture content and the existence of preferential
flow. However, the diffusion wave model has been derived to quantify the celerity
of pressure waves in a near-saturated soil and also been applied in the landslide
triggering analysis. Yet, the functionality of the preferential flow in landslide-triggering
mechanisms under the high-intensity rainstorm is rarely quantified, and its role in pressure
wave propagation is not well studied. The pore water pressure is still calculated
based on a single-permeability assumption in most hydro-mechanical models. The
dual-permeability approach, however, couples the matrix flow and preferential flow with
two Richards equations, which has a great potential to investigate the influence of
preferential flow on pressure transmission and slope stability in a heterogeneous
hillslope.
In this study, a hydro-mechanical model was developed that couples a 1D dual-permeability
model with an infinite slope stability analysis. A series of synthetic experiments simulates
and quantifies the rainfall amount, intensity, and duration for the occurrence of shallow
landslides in a predefined heterogeneous hillslope, which is parameterized with typical soil
hydraulic and mechanics properties. The results highlight the soil hydrological
condition which controls water and pressure wave propagation in case of a dual
permeability subsurface, and will further detail on the importance of preferential flow in
pressure wave propagation and thus slope stability assessment. The theoretical
results will also be confronted with published case study data of the Rocca Pitigliana
landslide consisting of 2-4m weathered clay overlying a clay-shale bedrock and
located roughly 50 km south of Bologna. Three-year field data of pore pressure
provide a reliable understanding of the dynamic hydrological response to the transient
rainfall intensity. The Rocca Pitigliana landslide has been successfully modelled
using a diffusion wave approach. Our study shows that fast pressure response due to
preferential flow is important for landslide triggering and highlights the difference
between a single domain diffusive wave approach and a dual-permeability approach. |
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