How difficult is to evaluate superficial landslides – mudflows?

Reading on the news about the dramatic landslide-mudflows (picture) that occurred (again) in Petropolis near Rio de Janeiro, with significant fatalities, one thinks could this have been predicted and more so avert it?Brazil mudflow

Even in an area prone to superficial mudflows and thin landslides, it is very difficult to accurately predict the occurrence of such a landslide. This is for the following principal reasons:

  1. It is difficult to assess the geotechnical parameters of a superficial material that undergoes continuous drying and wetting cycles.
  2. The tests are usually performed in saturated samples and in higher effective stresses that are usually present in superficial slides.
  3. A linear Mohr – Coulomb failure criterion is used when it may be more appropriate to use a power function that defines a curved strength envelope with minimum or even zero effective cohesion in very low to zero confinement (especially for uncemented soils).
  4. The soil is usually unsaturated with some (or even large) suction which is modified during rainfall infiltration. The pore pressure regime is very difficult to assess without continuous specific monitoring.
  5. Numerical techniques that can accommodate such complex problems are not widely available and not everybody knows how to use efficiently such models.
  6. The usual triggering mechanism is intense rainfall which increases the pore pressures in the superficial soil.  Since the way water infiltrates in the unsaturated soil, depends mostly on permeability, water content at the time of rainfall, the vegetation cover and the angle of the slope, the problem of evaluating such pore pressures becomes even more difficult.

This problem of predicting mudflows is usually assessed based on prior experience and some statistical evaluation of past mudflows and amount and intensity of rainfall. Can we do better?

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.

4 thoughts on “How difficult is to evaluate superficial landslides – mudflows?

  1. Hi Chrys,

    Based on the attached photo (and many other ones from different similar failures), I don’t think that we can do better than what you mentioned. Mudflow slides are triggered by the various processes that you rightly described, but also with other minor details related to topographic (drainage patterns, hydraulic excavation induced by cumulative runoff paths, natural obstructions, etc.)and material characteristics (cemented / sensitive / collapsible soils).

    By the way, better to evacuate the houses in the photo asap before next rainfall.


Comments are closed.