an engineering geological characterisation of tropical clays - GBV

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Chapter 2
Previous works
2.1 Summary
A German professor, Suess (1892) summarised the geology and structure of the Eastern Rift
Valley, to the west of Nairobi city and the present study area. The Eastern Rift Valley runs
across Kenya from Malawi in the south to the Dead Sea in the north.
Gregory traversed the country of Kenya in the period of 1896 to 1919. He made important
early contributions by studying and establishing the geology of some selected areas. He also
studied and described the major volcanic series underlying Nairobi and the study area; and
which include the Kapiti phonolites, trachytes, agglomerates, the Nairobi building stone and
the basic lavas of the Ngong volcanic centre. He named and designated the Kapiti phonolite
as the oldest unit of the series. He published his works and findings two years later (Gregory,
1921) as well as a number of papers dealing with various aspects of the Rift Valley and its
environs.
Prior, of the Mineral Department of the British Museum, later examined a large number of the
rock specimens collected by Gregory from around the country and which included Kapiti
phonolite and phonolitic quartz trachytes from Nairobi and the current study area. In his
published works (Prior, 1903), he recognised various subdivisions of the phonolitic series.
Kunzli (1901) gave an account of the volcanic rocks of the Eastern Rift Valley that included a
description of the riebeckite trachytes and phonolitic trachytes of the Kikuyu highlands and
north – western parts of the present study area.
In 1905, Maufe, then of the Geological Survey of Great Britain, conducted a geological
survey along the railway from Mombasa (in the south) to Kisumu (in the west), through
Nairobi. He later published his works and findings (Maufe, 1908) in which he gave a brief
summary of the geology between Nairobi and Kijabe (to the north of the study area) by
describing the principal rock types found. He also commented on the nature of faulting on the
east flank of the Rift Valley.
Earlier works and brief comments on the geology of Nairobi and its surroundings were also
done by Walker (1903), Collie, (1912) and Krenkel (1925). Krenkel described the volcanic
succession found by making reference to specific rock types, based on the earlier works of
Maufe (1908) and Gregory (1921).
Sikes, then Director of Public Works Department, Kenya, conducted underground water
surveys in the Nairobi area in the period of 1920 to 1925. He also described the grid – fault
structures caused by late faulting in the areas to the west of Nairobi city and in the Rift region.
The results of his observations and findings were published in subsequent reports (Sikes 1926,
1934 and 1939). Additional hydrological investigations were undertaken in the years that
followed by staff of the Ministry of Public Works, Nairobi, who examined in detail boreholes
drilled at the time in the rapidly – growing Nairobi metropolitan area. The results of this work
were incorporated in a technical report by Gevaerts (1964).
Wayland, formerly Director of Geological Survey Uganda, made a survey of materials in
Kenya, including Nairobi and the present study area. He investigated the materials for their