Abstract:
Geophysical methods were used in structural foundation investigation at Olkaria (V) field in
Kenyan rift valley prior to the construction works. Geophysical techniques were of preference
because they are faster, cost effective and non-destructive compared to conventional way such as
boring and drilling which are expensive, invasive and provide information in discrete area.
Geophysical investigations provide a wider picture of the subsurface that aid in evaluation of
ground fitness for construction purposes. The objective of this investigation was to determine the
depth to bedrock that forms a firm foundation for development purposes. Electrical resistivity
and seismic methods were used in ground assessment for its suitability in structural development. Data was collected using electrical resistivity imaging system, geographical positioning system
(GPS), receiver and seismograph. The RES2DINV and Geometrics SeisImager Software
respectively were used to process results obtained from these investigations. The methods used
gave results that are significant in the preliminary stages of site assessment for foundation works.
The techniques probe the depth to the bedrock and reveal weak soils zones. The analysis and
interpretation of geophysical data provide a better understanding into the subsurface geology for
foundation works.
Compact rock materials were observed from a depth of 14m below ground level extending down
to greater depths. Further, the area was characterized by weak Silty material, which has low
bearing and consolidation ability. Such materials are prone to frequent washout under conditions
of percolating waters hence require utmost care during the placement of engineering structures.
Utilization of piles is necessary and should be anchored to a depth greater than 14m below
ground level such that they rest directly on the competent bed. In-situ compaction should go
before utilization of reinforced concrete amid the development of shallow foundation to achieve
the maximum compaction limits due to the anticipated load of the proposed infrastructure.
Equally, excavation of the top soil is necessary and thereafter refilling with competent material
such as gravel and laterite in order to have a strong basement
