Landslide triggering

Unstable soil, rock or combination of both materials, manifests in a land sliding mass when the driving forces are higher than the resisting forces. In essence a landslide forms when the shear strength providing the resisting force becomes smaller than the driving force which may be a combination of weight, external load etc. The usual conditions that trigger a landslide are the increase in water pressure which lead in a reduction of effective stress and shear strength.

The water or pore pressures increase when heavy or prolonged rainfall occurs or when snowmelt takes place. Unfortunately these conditions cannot be controlled and a long term prediction is not possible (rainfall prediction is of a couple of days at most and the magnitude (mm/day) not easily evaluated beforehand).

130228 Landslide triggeringWater seeps in the soil/rock mass and can increase the external pressure on the backside of an unstable mass (especially in rock slopes), can increase the pore pressures in the sliding surface, and can increase the weight of the soil mass.

It is very interesting to note that although the best way to stabilize a landslide  may be by controlling the water pressures, engineers tend to ignore that and try to use more complex methods such as pile walls, ground anchors etc with questionable results. It would be great to have comments on this issue…

About Chrys Steiakakis

Chrys Steiakakis is a practicing geotechnical engineer with more than fifteen years of experience in the field of geotechnical engineering. He earned his bachelor and master in mining engineering from the Technical University of Crete, Greece and a second master’s degree in Civil Engineering from Virginia Polytechnic Institute and State University, USA. He has been the technical director of engineering department of General Consulting ISTRIA for four years and now he is a partner and also provides his own consultancy services via Geosysta ltd. He has been involved in numerous highway, railway and mining projects. Chrys with his long term collaboration with the Technical University of Crete has participated in numerous research projects in the field of geotechnical engineering and rock mechanics and has provided self sustained seminars of geotechnical engineering in related areas for the Industry. His main field of experience covers all aspects of tunnel design, earthworks design and monitoring (slope stability, embankment in difficult ground, reinforced embankments and retaining walls), landslide investigation and mitigation, foundations for bridges and structures, risk assessment in geotechnical projects and value engineering in large projects.