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Electronic journal of the International Association
for Environmental Hydrology
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JEH Volume 7 (1999), Paper 6, May 1999
Posted May 31, 1999
GEOLOGICAL AND GEOTECHNICAL ASSESSMENT OF SELECTED GULLY SITES, YOLA
AREA, NORTHEAST NIGERIA
G. I. Obiefuna, A. Nur, A. U. Baba and N. E. Bassey
Department of Geology, Federal University of Technology, Yola,
Nigeria,
ABSTRACT
A geological and geotechnical assessment of selected gully sites in
the Yola area, northeast Nigeria, is presented. The geotechnical results
indicate a mean plasticity index of 6.0 percent and a mean silt/clay content
of 4.0 percent. Maximum dry density ranges from 1.48 mg/m3 to
1.56 mg/m3. An optimum moisture content ranging from 9.80 percent
to 11.40 percent was recorded. The shear strength test indicated values
of cohesion ranging from 1.60 mg/m2 to 2.40 mg/m2
in an angle of internal friction ranging from 26o to 29o.
The soil is thus not compact but loose because it is highly weathered.
The fractive force due to runoff and seepage flux are resisted mainly by
the angle of internal friction, since the value of cohesion is low. The
hydraulic properties of the upper aquifer were analyzed and used to infer
the surface and subsurface processes that contribute to the formation and
continued expansion of existing gullies in the area. A specific discharge
value of 79.81 m/yr and an average linear groundwater velocity of 207 m/yr
were recorded, indicating high pore pressures and seepage fluxes. From
the geotechnical analysis recommendations for erosion control were suggested.
Reference: Obiefuna,G. I., A. Nur, A. U. Baba and N. E. Bassey
; Geological and Geotechnical Assessment of Selected Gully Sites, Yola
Area, Northeast Nigeria, Journal of Environmental Hydrology, Vol. 7,
Paper 6, May 1999.
G.I. Obiefuna
Department of Geology
Federal University of Technology
P.M.B. 2076
Yola
Nigeria