[01] Fabrice Mario Rahajanaharimamonjy, Laboratory of Mineral Chemistry, Faculty of Science, University of Antananarivo, Antananarivo, Madagascar. [02] Bruno Razanamparany, Laboratory of Mineral Chemistry, Faculty of Science, University of Antananarivo, Antananarivo, Madagascar. [03] Andrianirina Randriantsimbazafy, Department of Building and Public Works, Antananarivo Polytechnic School, University of Antananarivo, Antananarivo, Madagascar. [04] Koto-Te-Nyiwa Ngbolua, Department of Biology, Faculty of Science, University of Kinshasa, Kinshasa, Democratic Republic of the Congo. [05] Robijaona Rahelivololoniaina Baholy, Process Engineering and Industrial, Agricultural and Food Systems, University of Antananarivo, Antananarivo, Madagascar.

The objective of this study is to reduce the risk of flooding in the capital of Madagascar from the study of the left bank of IKOPA which is often broken during the periods of floods of this river. In order to carry out this work, two hand auger drillings at 8.00 m depth with a pressure test every meter were carried out. In both drillings, a permeability test of the Lefranc type (NF P 94-132) was carried out. At point RGT1, the site consists of a micaceous yellowish clayey silt with a limiting pressure varying from 0.11 to 0.18MPa, blackish peaty clay with a limiting pressure varying from 0.23 to 0.24 MPa, fine slightly grey clayey sand with a limiting pressure varying from 0.52 to 1.24 MPa, the permeability coefficient (KL) is 8.20 10^-5m/s. At RGT2, the site consists of brown, reddish to yellowish micaceous clayey silt with limiting pressure ranging from 0.06 to 0.10MPa, yellowish micaceous silty clay to blackish peaty clay with limiting pressure ranging from 0.17 to 0.24 MPa, gray fine sand with limiting pressure ranging from 0.11 to 0.70 MPa. The coefficient of permeability (KL) is 5.30 10^-5m/s. The results are not consistent with the overall stability of the bank. Thus, it does not resist during the flood, by this fact, the principle of embankment construction should be controlled to avoid the breach of this bank.

Flooding, Permeability Coefficient, Survey, Soil, Madagascar, Indian Ocean

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