an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
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4<br />
1.4 Summary <strong>of</strong> case problems<br />
The Nairobi city has a current population <strong>of</strong> about 3 million people (Nairobi City Council, 1999). It<br />
is also characterised by a number <strong>of</strong> social - economic activities which involve construction <strong>of</strong><br />
residential housing <strong>an</strong>d industrial facilities. Other activities involve construction <strong>of</strong> roads, rail lines,<br />
bridges, airports <strong>an</strong>d sports facilities; power <strong>an</strong>d telephone lines; water <strong>an</strong>d oil pipelines; as well as<br />
sewerage lines. Tunnelling <strong>an</strong>d dam projects are also found. The population <strong>of</strong> the city is expected<br />
to grow in the coming years. It is also expected that the above - mentioned activities will exp<strong>an</strong>d<br />
<strong>an</strong>d/ or multiply, while totally new ones may also be introduced. It is therefore <strong>an</strong>ticipated that there<br />
will be increasing pressure on currently available space <strong>an</strong>d facilities in the city, prompting the need<br />
by the Nairobi City Council <strong>an</strong>d City pl<strong>an</strong>ners to consider exp<strong>an</strong>ding into adjacent areas.<br />
In the past, residential construction on the outskirts <strong>of</strong> Nairobi city, which include the present study<br />
area, were predominated by structures constructed out <strong>of</strong> timber <strong>an</strong>d iron sheets, with strip/ pad<br />
footings. However, the recent ten years have witnessed strict regulations put in place by the Nairobi<br />
City Council aimed at encouraging construction <strong>of</strong> more durable low-rise buildings <strong>an</strong>d bungalows<br />
(Plates 1.1 (a) & (b)) on slab foundations using dimension stones <strong>an</strong>d / or bricks to cater for the<br />
increasing urb<strong>an</strong> population. This shifting trend towards masonry construction justifies a close<br />
study, examination, <strong>engineering</strong> properties <strong>characterisation</strong> <strong>an</strong>d assessment <strong>of</strong> the potential<br />
capabilities <strong>an</strong>d/ or limitations <strong>of</strong> the soils found, especially the exp<strong>an</strong>sive black cotton soils.<br />
Plates 1.1 (a) & (b) New stone structures coming up in the study area.<br />
The current project area is therefore also a potential area <strong>of</strong> exp<strong>an</strong>sion <strong>of</strong> the Nairobi metropolit<strong>an</strong><br />
due to its proximity to the city. It is especially favoured by a number <strong>of</strong> major communication lines<br />
already traversing it <strong>an</strong>d include the north - south running Nairobi - Mombasa road <strong>an</strong>d the Kenya -<br />
Ug<strong>an</strong>da railway; while the Jomo Kenyatta International Airport <strong>an</strong>d Wilson Aiport are also found<br />
within. However, the ambitious pl<strong>an</strong>s by the Nairobi City Council to locate new <strong>an</strong>d light<br />
constructed facilities in the study area may be complicated by the fact that the area is covered by<br />
black cotton soils <strong>an</strong>d also receives heavy rainfall during the wet season. These soils are highly<br />
exp<strong>an</strong>sive <strong>an</strong>d reactive, <strong>an</strong>d would usually exhibit very strong shrink-swell capabilities during<br />
alternating dry <strong>an</strong>d wet months <strong>of</strong> the year, with accomp<strong>an</strong>ying general lowering or rise <strong>of</strong> the<br />
ground surface, respectively (Mitchell,1993; Nelson <strong>an</strong>d Miller, 1992).