Cam-Clay Models Using Castem 2000^© and Plaxis^© for the Study of the Slope Stability of the “Corniche Ouest” of the Dakar Peninsula (Senegal, West Africa)

Meissa Fall, Serigne Sam Samb, Mapathé Ndiaye, Oustasse A. Sall, Fatou Samb

.

DOI: 10.4236/gm.2011.12009                

Abstract

The stability of the natural slopes of the “Corniche Ouest” of Dakar Capital was intensively researched by previous [1] in [2] and recent studies [3]. Soils near the surface consist of weathered lateritic cuirass, silt and marl that have been intensively altered and fractured. Below these altered layers are limestones that are interbedded with other thin volcanic layers. Prior to the 1950s the area had been less urbanized. In the 1950s demand for habitations and administrative offices led to the development of the area but, no drainage system was available. In 1984 the area began moving down slope toward the ocean. Rates of movement were the fastest several months after the end of the rainy season and the slowest during the dry season. In the next years the earthflow moved as much as some meters, but in the processes the expensive homes and administrative buildings built became uninhabitable. Movement was caused by a combination of wave erosion along the coast removing some the mass resisting flow, added water due to the disposal of wastes, watering of lawns, and rainfall causing the clays to expand and weaken, and by the added weight of development on top of the flow. The first investigations, due to a lack of geotechnical information describe a stable area even though it was observed cracks and failure in habitations. The main results obtained were specially obtained by analytical techniques of slices. It is well known that the mechanical response of a solid mass of soil depends primarily on the laws of behavior which were affected to him. The Cam-Clay model is used with two comparative numerical codes such as Castem 2000^©, a non commercial code and Plaxis 7.2^© so as to compare the mechanical response of the slopes. The models of Cambridge are founded as simple theory and use only some soil mechanical parameters easy to determine. The results are founded highly different from a code to another, but they attest all that the system described is non stable. Otherwise, this study has shown that Castem 2000© gives no realistic outputs as well as the soil behavior laws varies from a simple MohrCoulomb law to the softening or hardening complex laws.

Keywords

Corniche Ouest, Stability, Numerical Codes, Cam Clay, Movements, Natural Slopes

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	F. Tessier, “Contributions à la stratigraphie et à la paléontologie de la partie quest du Sénégal (Crétacé et Teritaite,” Dakar, Grande Impr.Africaine, 1952. 265 pp. 63.
[2]	R. Sarr, R. Khatib, P. Saint-Marc and Y. Bellion, “Nouvelles données stratigraphiques et sédimentologiques sur les formation des Madeleines et de l’Hopital de Dakar,” (Sénégal), 8th I.A.S. Regional Meeting of Sedimentology, Tunis 1-3 April 1987.
[3]	M. Fall, “Etude de la stabilité du versant naturel des Madeleines,” Mémoire IST n° 41/1993.
[4]	Chatelet et K’Vadec, Carte géotechnique de Dakar au 1/25000. Carte n° 1 carte de documentation. – Esquisse géologique et géotechnique, 1975.
[5]	S. Bongnard et P. Elouard (1968). – Nature pétrographique des formations de l’h?pital de Dakar. Ann. Fac. Sc. N° 22.
[6]	Chatelet et K’Vadec (1975). – Carte géotechnique de Dakar au 1/25000. Carte n° 1 carte de documentation. – Esquisse géologique et géotechnique.
[7]	Gladima S. (1988). – Etude de la stabilité de la corniche Est de Dakar. Mémoire IST n° 0012/1988.
[8]	CEA/DMT/LAMS (1992). – CASTEM 2000 Recueil d’exemples commentés. Edition Universitaire.
[9]	Elouard P. (1965). – Excursion géologique à Dakar. Notes africaines (Dakar).
[10]	Le Fichoux E. (1998). – Présentation et utilisation de CASTEM 2000. ENSTA-LME, avril 1998. Edition Universitaires.
[11]	Mestat P., Humbert P., Dubouchet A. (2000). – Recommandation pour la vérification de modèle d’élément fini en géotechnique. Bulletin des Laboratoires des Ponts et Chaussées.
[12]	Roscoe K. H., Schofield A., Thurairajah A. (1963). – Yielding of clays in states wetter than critical. Géotechnique, Vol. XIII n° 3 – p. 211-240.