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Geotechnical characteristics of soils susceptible to severe gullying in eastern Nigeria

  • Okagbue C. O. 
  • Ezechi J. I. 
Article

Abstract

The geotechnical characteristics of soils that are susceptible to severe gullying in the rain forest zone of Nigeria were studied. The soils are predominantly sands whose fines (silt/clay) contents are very negligible.

The sands are loose (dry density 1.42–1.73 g/cm3) and highly permeable (permeability 9.43×103−3.4×102cm/s) with permeability increasing with depth. Porosities and void ratios are also high (41.6–50.3% and 0.71–1.01 respectively), while cohesion is small to zero (0–85 kN/m2). It is thought that although these conditions favour less runoff and high infiltration, they lead to high internal flow velocities and seepage pressures, and ultimately high internal erosion.

It is concluded that once a gully is initiated, the soil properties become responsible for rapid propagation. Non response of the gullies studied to afforestation control measures is thought to result from these soil properties.

Keywords

Nigeria Void Ratio Direct Shear Test Optimum Moisture Content Lateritic Soil 

Caractéristiques géotechniques de sols sujets à des ravinements importants dans l'est du Nigéria

Résumé

Les caractéristiques géotechniques des sols qui sont susceptibles d'être sérieusement ravinés dans les régions forestières du Nigéria ont été étudiées. Ces sols sont essentiellement des sables dont la fraction fine (limon et argile) est négligeable.

Ces sables sont meubles (densité à sec 1,42–1,73 g/cm3) et présentent une perméabilité très importante qui augmente avec la profondeur (perméabilité 9,43×10−3−3,4×10−2cm/s). Les porosités et les indices de vides sont également élevés (respectivement 41,6–50,3% et 0,71–1,01), tandis que la cohésion est très faible à nulle (0–85 kN/m2). Bien que ces conditions soient peu favorables au ruissellement et permettent une infiltration importante, elles entrainent des vitesses d'écoulement interne et des pressions d'infiltration élevées qui conduisent à une forte érosion interne.

Une fois qu'un ravinement est initié, les propriétés du sol sont responsables de sa rapide propagation. Nous pensons que les difficultés de reboisement sur ces sols résultent de leur propriétés particulières.

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Copyright information

© International Assocaition of Engineering Geology 1988

Authors and Affiliations

  • Okagbue C. O. 
    • 1
  • Ezechi J. I. 
    • 2
  1. 1.Department of GeologyUniversity of NigeriaNsukkaNigeria
  2. 2.Geological SurveyP.M.B.MakurdiNigeria

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