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IHG: AN INTEGRATED HYDROLOGICAL-GEOTECHNICAL MODEL FOR LARGE LANDSLIDES’ SUSCEPTIBILITY ASSESSMENTS
R. Passalacqua and R. Bovolenta ([email protected]; bovolenta @dicat.unige.it) Dept. Civil, Environmental and Architectural Eng.rg - University of Genoa (Italy)
Susceptibility Safety factor ColorInstable Fs < 1High susceptibility
1 < Fs < 1.2
Low susceptibility
1.2 < Fs < 1.3
Stable Fs > 1.3
Widespread and differential
movements at ground level cause damagements to
many buildings and structures.
Since the pore pressures build-up is the main trigger factor, a recent development consists in the simulation of the evolutions of the phreatic level by modeling the whole sediments' body as a charging-discharging subsurface reservoir, fed from selected rainfall histories.
PSInSAR rendering Map (1/10’000) Geotechnical characterizations and
soundings Geophisycal data (70 noise measurement points and 1 array for the evaluation of
the loose soil thickness) Hidrological data (the superficial water flow and the water flow inside the glacial
till investigated for the determination of the steady groundwater table ).
Curve Numbers' map (resolution: 5m)
Example of susceptibility map and observed damages
The kinematic phenomenon is heavily influenced by the subsoil features (complex lithology).
The main trigger actions are represented by the seasonal rain/snow falls on the watershed.
CNThe Curve Numbers' map [Soil Conservation Service- U.S. Dept. of Agriculture, 1972- 1975] has been realised by the observation of the site's georeferenced aerial images on the GIS interface.
A good fit with the ground level's movements is obtained.
(for a total of 7785713
operations). The overall
computational
time is about 1 minute.
REFERENCES•PASSALACQUA R., BOVOLENTA R.: “Integration of spatially
distributed data for the 3D modelling of a kinematic phenomenon in Italy”, Proc. of the IAMG (International Association for Mathematical Geosciences) 2011 Conference, 5-9 september 2011, pp. 111-119, University of Salzburg, Austria.•PASSALACQUA R., BOVOLENTA R.: “Characterization and study of a
complex landslide site in Northern Italy”, Proc. of The Second World Landslide Forum, held at F.A.O. (United Nations) Headquarters, Rome, 3-9 october 2011, to be published by Springer-Werlag Ed.s (in press).•BOVOLENTA R., PASSALACQUA R.: “A 3D model in GIS for the
analysis of a kinematic phenomenon in Liguria (Italy)”, Convegno GEOITALIA 2011, VIII° FIST Forum, 19-23 Settembre, Torino. •FEDERICI B., PASSALACQUA R., BOVOLENTA R.: “Realizzazione di
una piattaforma GIS per l’analisi di un esteso fenomeno cinematico in Liguria”, Proc. 15th Conferenza Nazionale ASITA, Reggia di Colorno (PR), 15-18 november 2011, Federazione Italiana delle Associazioni Scientifiche per le Informazioni Territoriali ed Ambientali - Milano, pp. 1003-1014.
Ground level
Steady groundwater
table Bedrock
b. IHG model developed in GRASS (free open-source GIS)
•Element base (variable in the loose soil stratum)
•Groundwater table (influenced by the rain history)
The research, here presented, consists into the on-GIS implementation of an Integrated Hydrological-Geotechnical method of analysis (IHG), which allows to obtain (1) the groundwater level’s variations, due to selected rain histories, and (2) the spatially distributed susceptibility of the loose-soils’ deposit to slide. The IHG model’s behavior shows a good conceptual fit with the ground level's movements, also rendered by a Permanent Scatterers' Interferometry analysis on SAR images (PSInSAR), yet carried out on this very site by Others.
c. 3D assessment of instability phenomena due
to meteorological events Classical but widespread slope stability
analyses by a Global Limit Equilibrium method (A.W. Skempton – F.A. De Lory, 1957):
sincos
'cos' 2
z
tgmzcF WS
•Ground level W
z mz
q
a. Case study: a large kinematic phenomenon in
Liguria (Italy)
Map of Liguria and View of the site
Santo Stefano d’Aveto
Pliocenic Glacial Till (Covered Area 5 km2 ;
Lenght 4,5 km)
Contour Level Technical Maps (1/5’000)
Geological Regional Map (1/25’000)
Land Use Map (1/25’000) Digital Terrain Model (original
Resolution 20x20 m, ad hoc interpolated to 5x5 m)
Reckoned and Assessed Slope Instabiities’ Map (1/10’000) IHG model (resolution: 5m)
Typical slice
For any rain history, the
calculation is done on a total of 29875 pixels
and two iterative
processes are performed for
each pixel
European Geosciences UnionGeneral Assembly 2012Wien (A), 22 – 27 April 2012Session NH3.6-Poster 11233
