El Portalet, Pyrenees, ES

El Portalet ESThe study area is located in upper part of Valle de Tena, the headwaters of the Gállego River in the central Spanish Pyrenees Pyrenees (Huesca), where climate is characterized by a marked seasonality, classified as of the mediterranean mountain type with Atlantic and Continental influences. The average annual precipitation is around 1500 mm with rainfall concentrated mainly in spring and autumn, followed by winter and with punctual intense convective storms during the summer. From the geological point of view, the study area is located in the Axial Zone of the Pyrenees, an extensive outcrop of the Variscan basement affected by complex contractional structures resulting from the superposition of the Variscan and Alpine orogenies.Three main stratigraphic suites bounded by major unconformities may be differentiated: (1) A Devonian succession approximately 500-m thick dominated by slates that grade to reef limestones at the top. (2) Carboniferous limestones and slates with a total thickness of about 1000 m. (3) A Late Carboniferous and Permian sequence including coal-bearing slates and red continental clastic sediments with basalt flows and andesitic sills and laccoliths. Overlying these materials, glacial, periglacial, colluvial, lacustrine and alluvial quaternary deposits are found in the slopes and in depressed topographic areas. The area is seismically active. Due to the geological and climatic settings, landslides are abundant in the area, and contribute to shape the landscape. The landslides cover 22.6% of the area. Large, deep seated flow-dominated and complex movements in very altered and tectonized Palezoic slates constitute 80% of landslides in the area. These large mass movements account for 86% of the area affected by landslides. The toe and flanks of the flows are often affected by secondary failures induced by fluvial erosion caused by the Gállego River and lateral streams and the buildup and oversteepening of the slide mass due to flow propagation. The action of old glaciers on the rock massifs shaped steep slopes and reliefs favouring the occurrence of falls, topples and rock avalanches in the upper part of the slopes. Part of the study area is covered by forests. However, forests have been replaced by cultivated fields that were abandoned at least from the middle of the 20th century. This glaciated area, includes the Formigal Ski resort, which constitutes the main source of income for the local economy. Land sliding has caused damage with a total cost in excess of 10 million euros on the infrastructure of the ski resort and the A-136 road that connects the valley with France through the El Portalet pass.The research will focus mainly in the Portalet lanslide area.

The Portalet landslide area is located in the north-western sector of the upper part of river Gállego basin, in the frontier with France. In this test site two landslides developed from 1850 and 1600 m a.s.l. along the southwest-facing hillside of Petrasos Peak, slightly alter the route of the Gállego River channel to the south. Geomorphological, geotechnical and topographical investigations have revealed that the both landslides affect the weathered bedrock composed mainly by shales of Carboniferous and Devonian age, characterised by an intense weathering and a high plasticity. Rock fall and rock avalanche deposits come from the limestone cliff found at the upper part of the slope are transported downhill by the slow flow of landslide deposit. The kinematics of this landslides, largely controlled by the hydrological processes (i.e., snow melting, rainfall) that influence pore water pressure, was dramatically accelerated due to anthropogenic alterations, mainly excavation at the toe and enhanced water infiltration.The slope excavation at the foot of the slope, carried out to build a parking area in summer 2004, reactivated both landslides generating new sliding surfaces with a faster movement affecting the connection road to France and the ski parking area. Measurement of the displacements performed with differential GPS, Ground-based SAR (GB-SAR) revealed that the moving mass was still active after the constructive solutions were undertaken.

Tested LAMPRE products

1 LIM-Product icon OFF2 ELIM-Product icon OFF3 LSMM-Product icon OFF4 LStats-Product icon OFF5 3DSDM-Product icon6 LRIM-Product icon OFF

Physiographic settings

Glacial valley where the original U-shaped morphology of the main and tributary glacial troughs was largely modified by the development of large deep-seated landslides on slates. The turf-covered landscape is characterized by rounded divides and landslide-related hummocky slopes.

Relevant phenomena

Deep-seated slow moving landslides whit man made reactivations, in rural mountain areas with sky stations.

Equipment

  1. One thermometer, three piezometers, one wire extensometer and one inclinometric automatic system (AIS) installed in four boreholes and one surface cable-extensometer installed in the head scarp with continuous recording data delivered via GPRS.
  2. A continuous recording rain intensity pluviometer
  3. A network of D-GPS points and 11 corners reflectors for InSAR TerraSAR-X data installed on the slopes slipped

Activities

  1. A 50 meters geotechnical borehole drilling, and installation of the AIS that performs a daily rate measured from 07/11/2013
  2. Taking data for D-GPS monitoring network, 14-17 October 2013
  3. Taking extensometric and piezometric data from 24/09/2013
  4. Installing reflectors corners, 4-6 November 2013

LAMPRE products testing

5 3DSDM-Product iconLAMPRE has prepared 3DSDMs for the El Portalet (Huesca, Spain) and for the Ivancich (Assisi, Umbria, Italy) landslides. In both areas, the slow-moving, deep-seated active landslides affect structures and infrastructures, producing significant damage.

To prepare the 3DSDMs, LAMPRE exploited Finite Element Modelling (FEM) to integrate in-situ monitoring data, surface and sub-surface geological, geotechnical and groundwater information, and surface deformation measurements obtained through advanced Differential SAR Interferometry (DInSAR).

3DSDM FigA 3DSDM FigB 3DSDM FigC

The El Portalet (Huesca, Spain) active landslide extends for 0.35 km2 with an estimated volume of about three million cubic meters. LAMPRE has measured the long-term movement of the landslide through space-borne DInSAR using ERS and ENVISAT SAR data acquired between 1992 and 2010 (Figure A). For the same landslide, continuous measurements of the surface and sub-surface displacements were obtained using GPS and inclinometer systems, including an Automated Inclinometer System (AIS, Figure B). LAMPRE determined the 3D kinematical evolution of the landslide using a 3D FEM constrained exploiting the available geological, geotechnical and groundwater information. A numerical procedure developed in COMSOL© Multiphysics software optimized the physical parameters needed to construct the FEM. The procedure determined the best-fitting kinematical behaviour of the landslide, compared to the available remote sensing and ground-based monitoring measurements (Figure C).

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Contact us

Fausto Guzzetti 
Consiglio Nazionale delle Ricerche - Istituto di Ricerca per la Protezione Idrogeologica

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FACTS & FIUGRES

GA n°: 312384
Project type: Small collaborative project
Start date: 01/03/2013
Duration: 24 months
Total budget: 2,488 mln. €
EC funding: 1,964 mln. €
Total effort in person-month: 284
Other info: Visit CORDIS

 

EU FP7

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement nº 312384. LAMPRE is managed by the Research Executive Agency (REA)

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