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Geohazards: Risk Assessment, Mitigation and Prevention

Periodic Reporting for period 2 - GEO-RAMP (Geohazards: Risk Assessment, Mitigation and Prevention)

Reporting period: 2017-04-01 to 2019-03-31

The GEO-RAMP project aims to provide a step change in terms of our capacity to assess and predict risks due to geohazards (landslides and rock slides, earthquakes, floods). This will result in reduced loss of human life, reduced damaged to buildings and infrastructure and the associated disruption of economic activities, and will have far reaching consequences on the way insurers operate in calculating risk. Better understanding of the physico-mechanical causes of geohazards is pivotal to allow the establishment of cause – effect links between hazards and potential losses. This will lead to fairer insurance premiums and in turn hopefully a reduced use of exclusion clauses, sublimits, and coverage ceilings by insurers.
The project brings together the complementary expertise of world leading groups carrying out research on the engineering assessment, prevention and mitigation of geohazards, the main ones being floods, landslides, and earthquakes. In summary, the goals of the project are:
• To investigate the key physico-mechanical aspects of major geohazards with a multi-disciplinary approach in order to bridge the current gaps in knowledge and enable a step-change in the current capabilities of risk assessment, prevention, and mitigation.
• To generate new approaches to predicting geohazards by creating an international, interdisciplinary and intersectoral group which will combine existing knowledge to generate new research methodologies and applications by enabling knowledge exchange among researchers with expertise in complementary research fields.
• To train several Early Stage Researches (ESRs) during their stay at the host Institution who will form the next generation of researchers for academic and industrial applications.
• To improve the current normative standards and codes ruling geohazard prevention.
• To provide a competitive edge to European engineering software companies modelling geohazards.
The following is a brief description of highlights and results achieved so far from the scientific work packages following the structure of the project:

Landslide case histories and benchmarks [WP3, WP6]
A database of case histories for landslides occurring in European countries, America and China was completed during the first year of the project. As an example of this work, Table 1 show case histories of the most significant landslides occurred in the year 2015, while in Figure 1 the month-wise and country-wise distribution of the landslide events and number of casualties are presented. In the context of the validation of numerical methods in landslide modelling, benchmark cases and typical landslide scenarios were identified. Towards this goal, well performed laboratory tests were carried out in the centrifuge facility of the Institute of Geotechnical Engineering at the University of Natural Resources and Life Sciences in Vienna (Figure 2).

Earthquake case histories [WP4]
In order to improve the accuracy of the prediction models and to increase their capabilities against seismic hazard, ten major earthquake events were selected as case histories. They have been selected among the numerous available in the seismic database, based on the earthquake parameters and their environmental impact.

Stability of fissured slopes subject to seismic action [WP4]
A comprehensive parametric analysis was carried out to investigate the effect of seismic action on fissured slopes employing the upper bound theorem of limit analysis and the pseudo-static approach. The failure mechanisms assumed were 2D single wedge rigid rotational mechanisms with cracks of either known or unknown depth or location (Figure 4). Charts to be used by practioners to get an immediate estimate of the destabilizing influence of the presence of cracks on the slope of interest for any level of prescribed seismic action were produced (Figure 5).

3-D DEM analyses of rock fragmentation [WP5]
A series of numerical simulations by discrete element method (DEM) were performed for a simple rock block and slope geometry, where a particle agglomerate of prismatic shape is released along a sliding plane and subsequently collides onto a flat horizontal plane at a sharp kink point. A schematic view of the geometry of the model is shown in Figure 6 (Zhao et al., 2017). This work intended to reveal how dynamic fragmentation occurs at impact, together with the generated fragment size distributions and consequently their runout for different slope topographies.

Numerical simulation of triaxial tests in sand using discrete element method (DEM) [WP1, WP5]
The numerical results of triaxial test for sands were directly compared to the corresponding experimental results of several triaxial tests performed in the Grenoble INP laboratory. For the numerical modelling the software PFC 5.0 [1] developed by ITASCA Inc. was used, based on the DEM. Indicatively, Figure 7a shows the numerical specimen, isotropically compressed first and then tested in triaxial conditions at 100 kPa confining pressure, kept constant by a servo-controlled mechanism. The model parameters have been set trying to fit the experimental response. Figure 7b shows the comparison between the vertical stress evolution for the experimental and numerical materials: it is evident that the stress-strain responses are comparable at both the peak and critical state conditions.

MPM modelling of landslides [WP6]
The material point method (MPM) is a useful tool to model both the onset of ground failure and the subsequent debris flow. MPM is currently being applied by partners and beneficiaries of GEO-RAMP for studying the onset of slope failure as well as for the thermo-hydro-mechanical modelling of the Vajont landslide.

[1] Itasca Consulting Group, Inc. (2014) PFC — Particle Flow Code, Ver. 5.0. Minneapolis: Itasca.
The current project contributes to the knowledge on landslides and other catastrophic events, such as earthquakes, flooding etc, by creating a detailed database of case studies and investigating the causes and results, making use of state of the art techniques and theories. The outcome is an insight on the roots of each catastrophic event, together with the development of the necessary tools and push of the boundaries of the used methods. The investigation is supported by thorough experimental evidence and advanced numerical and analytical methods. Awareness of all responsible parts about the risk and hazard of these events plays a vital role in minimizing the catastrophic effects. Prevention and planning for future events can delimit the number of casualties and loss of properties. The results of this project are expected to show a twofold effect both by developing widely recognized procedures and also by allowing authorities and industry to take advantage of these for prevention planning.
Reported major landslides with highest number of casualties in the year 2015.
List of the major landslide case histories occurred in 2015.
Schematic presentation of the centrifuge testing facility at BOKU.
Failure mechanism [Utili & Abd, 2016].
(a) Geometry of physical model, (b) DEM representation of the sliding block.
Stability factor vs slope inclination for the most unfavourable crack scenario [Utili & Abd 2016].
(a)Numerical specimen representing Caicos sand, (b)comparison between experimental and DEM results