Evaluation of geolological suitability of Kiserian damsite, Kajiado

Abstract

This thesis presents the results of geological investigations carried out at the Kiserian damsite, Kajiado district. The study was undertaken with the aim of obtaining information that could help in the design and construction of the proposed dam. The ma in parameters to be determi ned were, the structure, lithostratigraphical sequence, hydrogeological conditions and the depth to the bedrock. Field investigations were conducted by approach. The methods used included geological mapping, seismic refraction, electrical profiling and core-logging. way of an integrated photo-interpretation, electrical sounding, The dam site is underlain by the Ngong Basalts. Seismic refraction results suggest a highly irregular bedrock surface. There "is a substantial variation in velocity within the overburden as well as in the sound rock. These variations are explained in terms of fracturing and weathering of the rocks. Geoelectrical sections revealed a low resistive zone below the foundation bed. This is attributed to a weathered zone. Corelogs show that the overburden materials are underlain by fresh basalts,weathered basalts, agglomeratic zone and residual soils resulting from weathering. The seismic and resistivity results allowed interpolation of the bedrock surface between drill holes with much more confidence than would otherwise have been possible. On the bas is of the resu 1ts obtained, it is recommended that the overburden be excavated to depths of 1.5 m to 2 m. Grout cap should be used to seal off the fractures. This will strengthen the fractured foundation. A deep cut-off or grout curtain is recommended at the heel of the dam to provide a better anchorage which will increase resistance to sliding