Objectives and relevance of the joint exchange programme
The objective of the HYDRODRIL exchange programme is to create a strong multidisciplinary network of researchers based both in the European Research Area (Austria and United Kingdom) and in the economical growing countries of China, India and Mexico. This newly created intercultural network will benefit from its highly qualified and experienced staff in order to undertake a research project aiming to deeply contribute to the understanding of the hydrological issues involved in slope stability problems. The landslide hazard map of Europe (ESPON 2005) and of the World (World Bank 2005) shows that landslide hazard is rather widespread over the entire European territory and the whole World. Many places in the World suffered landslides and debris flows as a result of storms or torrential rains, causing high casualties and huge property losses, e.g. May 5, 1998: torrential rainfalls induced numerous landslides and debris flows destroying about 150 houses and killed more than 160 people in the District Salerno near Naples, Italy; December 14, 1999: heavy rainfall triggered a large number of landslides in Vargas, Venezuela, resulting in an ensuing debris flows with an estimated 30,000 deaths; March 31, 2003: massive landslides wiped out much of the mining town of Chima in Bolivia, leaving more 100 people dead and some 150 houses destroyed; August 8, 2010: massive rain-triggered landslides and debris flows hit Zhouqu county in north-western China, killing at least 1,467 people. As rural areas turn into urban one and the demand for new buildings and infrastructure grows rapidly, it is sometimes mandatory to utilize areas deeply subjected to the landslide danger. In order to protect buildings and human beings from this danger, it is highly recommended to have a clear understanding of the natural phenomenon. Methods based on limit equilibriums have been most popular for slope stability analysis (Duncan 1996, Yu et al. 1998). However, the limit equilibrium approach cannot capture the initiation of hydrologically driven slope failure, which is characterized mainly by transient processes (Johnson 1984, Fredlund and Rahardjo 1993). The modelling of infiltration, evaporation, propagation of the wetting front and reduction of matric suction involves different time scales governing the short-term and long-term behaviour (Iverson 2000, Griffiths and Lu 2005). Moreover, the initiation and propagation of the failure surface cannot be accounted for by the limit equilibrium approach (Mühlhaus and Vardoulakis 1987, Nicot and Darve 2007, Rabczuk et al. 2007). A consistent analysis of slope stability requires fully coupled analysis of the hydrological and mechanical processes in multiphase media, which takes into account of the spatial and temporal multiscale properties (Ehlers et al. 2004, Schrefler et al. 1996, 2006, Borja et al. 2010). The constitutive models for unsaturated soils play an important role in the numerical modelling of hydrologically driven slope failures. Recently, large progress has been achieved in the research on constitutive models for unsaturated soils (Alonso et al. 1990, Laloui et al. 2003, Santagiuliana and Schrefler 2006, Borja and Koliji 2009, Scholtès et al. 2009), which will be further developed and incorporated in the tasks of HYDRODRIL. The understanding of these processes, in terms of infiltration patterns, reduction of soil strength and reduced factor of safety of the slope as well as the countermeasures to avoid danger to people and nearby constructions will be the scientific focus of HYDRODRIL. The research communities have responded enthusiastically to the challenges of these geohazards. In most countries affected by landslides, research groups and institutions have been set up and intensive research is being carried out (Jacob and Hungr 2005, Takahashi 2007, Proc. 3rd Conf in 2003 and Proc. 4th Conf. in 2007). Despite the enormous research effort, however, a consistent physical model for reliable predictions of initiation, run-out, deposition and impact is not yet available. The reasons for this knowledge fragmentation, which addresses the scientific background of HYDRODRIL, are the complex system of landslides with a chain of events, including initiation, run out, entrainment, transport, sedimentation, deposition and impact force, and the intricate interaction among these events. Until now, mainly individual research projects and initiatives have been funded, which deal with one or two aspects of the problem. A systematic approach in a well coordinated research network which is able to cover extensive field investigation, laboratory tests (small-scale model tests in a centrifuge) and advanced numerical approaches is to be preferred. The IRSES Programme is an ideal vehicle for such an undertaking by enhancing the mobility of researchers. The following questions are to be answered by the research project to fulfill the previously sketched objectives:
- In which way does water influence the stability of slopes? To what extent is the safety factor reduced?
- What is the influence of hydrological parameters on the origin and development of the failure surface?
- How can an imminent landslide be predicted by field measurements?
- How can the danger be minimized? What safety measure can be undertaken?
- How can hazardous zones be detected reliably to minimize the risk potential?
As previously described, slope stability evaluation is strongly interdisciplinary: although the physical understanding of the problem is a merely geomechanical problem, the analysis has to be provided by several geological assessments and, moreover, topological skills are needed to properly describe the area involved in the land movement. All of the required skills are provided by the team joint together for this project as all the people involved have different scientific points of views ranging from geomechanics and geotechnics to geology, geophysics and geography. The team has a strong balance between theoretical and empirical skills and it thus fully capable of both analyzing slope stability by means of field measurements and laboratory experiments and to produce and develop numerical models for a better understanding of the physical process. The main topics to be developed will be:
- Water infiltration in soil
- Propagation of water and raising of water table in a slope
- Water influence on the reduction of strength parameters of soil
- Water influence on the factor of safety of a slope
- Assessing the risk for people and surrounding buildings
- Measuring soil changes in strength by means of geophysical investigations
- Protecting measures: drainage of slopes
- Understanding of water flow during drainage.