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Effect of precipitation on the stability of slope

Contact Bertrand François
Keywords Apparent cohesion, infiltration, rainfall, unsaturated soil, suction
Collaborations Prof C. Prépetit (Université d'état d'Haïti)

Prof. J.F. Thimus (UCL)

C. Van Rooten (CRR)

Description
Roads are normally equipped with drainage systems sized and implemented in accordance with the rules of art to evacuate as quickly as possible water precipitation. However, there are often water flows at the slope side. A succession of rain causes a certain amount of water infiltration, which varies according to climatic conditions and depending on the soil texture and structure. Such infiltrations have resulted in reduced safety factor of slopes.

Impacts resulting from infiltration of successive rains on the behavior of surface layers of unsaturated soils are usually not taken into account. Models for calculating the slope stability of unsaturated soils require many parameters that can be, in certain circumstances, difficult to assess and refer generally to cases of instability caused by a rise in groundwater level.

Based on laboratory tests (Figure 1), a suitable methodology for assessing the spatial and temporal variation of soil water content induced by a set of rains has been developed (Figure 2). This methodology facilitates the inclusion of the cumulative effects of the infiltration rates associated with rain events and infers from them the profile of suction and that of the apparent cohesion to be used to calculate, for a slope angle β, the range of variation of the safety factor. This methodology is particularly relevant in the case of limited budgets and infrastructures.

Finally, when the hydraulic profile in the ground has been established, the slope stability can be evaluated through classical slice-methods assuming potential rotational failure of the talus. So doing, the obtained method integrates the hydraulic and mechanical behaviour of the slope through a unified approach. The input data are the histogram of water precipitation, the strength parameter of the ground, the soil permeability and the geometry of the slope. The obtained results is the safety factor with respect to slope failure and the geometry of the most probable failure circle.

 

figure 5

Figure 1: Experimental device to simulate rainfall on a soil sample and to measure the propagation of the wetting front in the soi (developed at the "Université d'état d'Haïti).

 

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Figure 2: Development of a suitable model describing the progression of the wetting front as a function of rain intensity and soil permeability.

   
Selected publications H.G. Rameau (2010). Influences de la pluviométrie sur la stabilité de talus routiers: Méthodologie adaptée pour l'évaluation du profil hydrique temporel du sol et sa prise en compte dans les calculs de stabilité en Haïti. PhD Thesis, ULB.

H.G. Rameau, C. Prépetit, J.C. Verbrugge (2011). Pluviométrie et calculs de stabilité de talus routiers en Haïti. 19th Caribean Geological Conference. Le Gosier, Guadeloupe.