Imiriland
Impact of Large Landslides in the Mountain
 
 

project structure

The multidisciplinary programme of activities is built on a four-stage structure:

  • Phase 1: Data collection and organisation.
  • Phase 2: Development of risk assessment methodologies.
  • Phase 3: Application to management.
  • Phase 4: Dissemination of risk management methodologies.

It is subdivided into 9 workpackages (WPs, see figure 1).

PHASE 1: DATA-COLLECTION AND ORGANISATION

The eight selected cases imply a complex risk situation, for which no reasonable stabilisation works can be achieved. The partners involved in the project have already some knowledge about the sites (some of them are very well known, while some others are in an initial stage of study), the data of which are already available but very dispersed (data banks, reports, publications…). In this way it will be relatively easy to collect a large amount of information without dispersion of energies.

 

A general scheme for data description has been created and compiled for each site (WP1). Each partner is then able to access to data, which can be managed in a homogeneous manner. The objective is also to check the reliability of the available data, to individuate which ones are to be considered.

 

Selected sites are summarised in table 1 and their location is shown in figure 2.

 

Figure 1. Graphical presentation of the project's components

 

 

PHASE 2: DEVELOPMENT OF RISK ASSESSMENT METHODOLOGIES

The purpose of Phase 2 is to provide the overall framework for risk assessment methodologies. Hazard analysis is the first step, and consists in the following activities:

  • models to calculate the probability of preparatory or triggering events,
  • models of progressive development of failure,
  • interpretation of monitoring data,
  • effect of tectonic or weathering action on the rock mass,
  • models of propagation of the moving mass, in order to determine a certain affected zone for a certain probability of occurrence.

 

As a result hazard analysis methods give the scenarios needed for the risk assessment. Several methodologies have been proposed in the past for the establishment of the hazard. Scenarios for the evolution of large landslides obtained through such methodologies provide different results, so it is difficult to express hazard in a unique way. It is therefore fundamental to compare and organise the different approaches so as to give to the EU all the elements necessary to practise an effective co-ordination role.

 

Within the project the following methodologies will be considered:

 

  • field analysis: the ability of geology, geomorphology and tectonics will be shown in order to obtain qualitative scenarios of evolution of large landslides (WP2);
  • mechanical modelling for the landslide triggering: application of numerical methods. Partners have specific experience in Boundary Element, Finite Element and Finite Difference methods. Existing computer codes will be improved and applied to the study of the selected large landslides in 3D. The results obtained through the different methods will be at the end compared on some cases (WP3);
  • mechanical run out modelling: application of numerical methods. When the possibility of instability has been established through the methods of WP2 and WP3, the landslide run-out is studied through two different specific numerical methods, taking into account the dynamic character of the phenomena. Scenarios of evolution of the slide will be the result of this WP, and in some cases the scenarios obtained through the different methods will be compared (WP4);
  • black box models: application of neural network and statistical methods. This application will complement the numerical analyses of landslides, for which it may be difficult to get the input parameters with a sufficient degree of accuracy. The statistical and heuristical methods are applied by using a large amount of previously gathered environmental data, which may influence the behaviour of landslides, in an undetermined way (WP5).

 

Figure 2. Location of the study sites

Table 1. Investigated landslide sites

 

 

Site
PDF
Country
VOLUME of main landslide [m3] /globally affected area [km2]

Elements at risk

Italy
50·106 m3/ 5.5 km2 Rosone village and main road SS 460 Hydroelectric power plant Downstream valley
Italy
15·106 m3/ 0.9 km2 Highway A32 (Frejus)
International railway Torino-Modane
Downstream valley
Italy
5·106 m3/ 0.5 km National Road N. 549, only connection to the Macugnaga tourist resort
Prequartera and Campioli hamlet
Spain

Several tens·106 m3/ 1 km2

Important ski resort
El Tarter small village
Main road Andorra - France Downstream communities

Austria
0.5-2·106 m3/ 2.9 km2 Downstream villages of Tröpolach and Watschig
Main road “Naßfeld – Bundesstraße”, important connection to the valley “Gailtal“

SÉCHILIENNE

France
25·106 m3/ 0.9 km2 National road RN 91
Downstream valley
Switzerland
25 km2 over a total length exceeding 10 km New A28 national road
Lanquart town
Downstream valley
Switzerland
100·106 m3/ 1.5 km2 Regional railway line
National road
Sedrun touristic resort

 

Next step is the risk analysis, which includes:

 

  • the consideration of endangered population and objects, their value and their vulnerability, i.e. the degree of loss from a particular danger;
  • the risk analysis itself, through the evaluation of costs due to direct and indirect impact as well as the assessment of variable warning time which is a general characteristic of a well monitored pre-failure phase

Workpackage WP6 is dedicated to the state of the art in the evaluation of vulnerability and risk analysis. In order to quantify risk levels, three components will be analysed, related to the exposed objects, which may be influenced by landslides:

  • the nature, structure and spatial distribution of exposed objects on the landslides mass or within the exposed zones, with due consideration of their long-tem behaviour;
  • the sensitivity of these objects to movements, in order to assess how they are directly or indirectly affected by movements;
  • the value of these objects, in a wide sense, as well as the indirect economical impact of the changes they may suffer.

Finally, the results of phase 2 will be exemplified on the selected sites in the workpackage WP7, which will summarise the scenarios and give the risk evaluation for each site. Limits and applicability of the proposed risk assessment methodologies will be illustrated.

 

PHASE 3: APPLICATION TO THE MANAGEMENT

Phase 3 is related to the application of the developed methodologies to the management of endangered landslide zones (WP8). Mitigation strategies will be formulated in order to:

 

  • allow the local or regional authorities responsible for the affected areas to control the evolution of the studied dangerous phenomena;
  • predict the potential development of a critical event that might induce serious damage to infrastructures or cause victims;
  • take the necessary safety or preparedness measures so as to limit the direct and indirect consequences of the foreseen disaster.

Corresponding types of actions are proposed in relation to the degree of urgency of the problem. For example, if a real crisis is expected within some weeks or even days, an evacuation plan must be prepared including large buffer zones and alarm systems must be placed to stop the traffic in case of a sudden failure. On the contrary, if the expected event is uncertain and might occur within months or years, alert systems must be installed and threshold values have to be determined for different types of possible landslide behaviours; it is also wise to determine alternative routes and to check if they present limitations or hindrances.

 

All the suggested actions related to safety criteria depend of course on the legal framework and on the powers that local or regional authorities have to solve critical situations or to manage minor or residual risks (i.e. limited risks that are induced by the later or final degradation of a failed slope, which can affect the exposed objects after years). This legal framework depends on the national or regional legislation, so that management policies have to be duly adapted. A catalogue of typical mitigation actions to face several hazard situations is also established.

 

Possible actions will be also proposed on the basis of the relevant economical conditions. Direct or indirect consequences are considered. For example a road leading to a major industrial site or tourist resort endangered by rockfalls will justify major protection investments to ensure a permanent transit even though the exposed infrastructures themselves are hardly affected by the stones falling on the road. The cost of works and labour force will also be a significant criterion for the selection of mitigation solutions.

 

The assessment of acceptable risks will also be based on the type and extent of hazard that might occur. A large sudden landslide causing the death of one hundred persons has not the same psychological impact as one hundred small rockfalls inducing each one victim; this effect, called the aversion factor, has to be included in the determination of mitigation strategies.

 

PHASE 4: DIFFUSION

The diffusion of risk management methodologies is the natural conclusion of the project (WP9). As regards this topic:

  • information dissemination will be promoted, which improves public awareness of landslide hazard, through hazard and risk maps, information on typical damage and risk to life and goods, using not obscure and univocal terminology (relevance of metadata);
  • understanding of public response establishing better knowledge will be improved, as an instrument to take the proper decisions about landslide mitigation actions.