PAPER TITLE :GEOTECHNICAL AND GEOPHYSICAL INVESTIGATION OF SUBSOIL FOR CONSTRUCTION OF A WASTE WATER TREATMENT PLANT IN COASTAL ENVIRONMENT, SOUTHWESTERN NIGERIA

JOURNAL OF EARTH AND ATMOSPHERIC RESEARCH | VOLUME 1 NUMBER 1 2018

Paper Details

  • Author(s) : 1 2 1 1 OLORUNTOLA, M. O., * FOLORUNSO, A. F., ODUKOYA A. M.; and OBASAJU, D. O.
  • Abstract:

A combined geophysical and geotechnical studies were conducted in a coastal environment in Lagos, Nigeria
in order to delineate subsurface lithologies and evaluate their suitability as foundation for a proposed waste
water treatment plant. The geophysical study carried out involved electrical resistivity tomography (ERT)
resulting in 2-D resistivity imaging along 3 profiles with spread length ranging from 145 – 190 m. The ERT
data obtained along the profiles were analyzed using DIPRO for window, a 2-D resistivity inversion program
to provide estimates of vertical and horizontal spatial distribution of resistivity beneath the survey line. A total
of eight cone penetration test and four standard penetration borehole logs in were conducted to determine the
strength and characteristic nature of the foundation soils. In addition, pH and sulphate concentration of a
water sample from one of the SPT boreholes were determined to predict if there is possible infiltration of
leachates into the groundwater. The results of the integrated investigation revealed the occurrence of thick
peat, and clay (≈ 22.00 m) which prevented the further infiltration of leachates plumes as revealed by the ERT
images and sandy units at depths greater than 23 m. The occurrence of thick peat/clay horizons makes the use
of shallow foundation infeasible to mobilize the proposed structure. The chemical analyses show pH to be
slightly acidic (6.88) and sulphate concentration of 31 mg/l which are both within World Health Organization
standard, confirms that there is no infiltration of pollutants/leachates into the groundwater, therefore the
water in the area will not be inimical to Portland cement concrete at deeper depths.
Both geophysical and geotechnical methods reveal that the subsoil contains clayey material which serves as
good containment and that pile foundation be used to mobilise the proposed structure to the deeper sand layer.

JOURNAL OF EARTH AND ATMOSPHERIC RESEARCH