Investigation of Subgrade Properties of Nairobi Red Coffee Soils.

Abstract
The performance of a pavement depends on the quality of its subgrade layer. As the
foundation for the pavement’s upper layers, the subgrade layer plays a key role in mitigating
the detrimental effects of static and dynamic stresses generated by traffic. Therefore, building
a stable subgrade is vital for constructing an effective and long lasting pavement system.
This study proceeds from the basis that, construction of foundations of most engineering
structures, requires that adequate information about the engineering properties of the soil and
sub-soil condition of the area are established prior to the conception of works. This is
necessary for the engineering planning, design and construction of such foundations to be
based on sound geotechnical parameters.
This is more important especially in the design and construction of highways, where there is
need for a good and sound knowledge of the geotechnical and engineering properties of the

sub grade and, more importantly, the construction materials’ properties for sound engineering
decisions to be taken. Such geotechnical parameters include the strength, the maximum dry
density (MDD), the amount of fines (clay and silts) as well as the compaction performance of
the proposed highway construction materials.
This study entailed carrying out geotechnical investigations with a view of establishing
geotechnical properties of soils in the project area. These properties would warrant the
suitability of such soils for design and construction of pavements, as sub grade material. The
investigations were carried out by field observations and sampling. This was followed by
laboratory tests of the samples obtained.
To achieve the objectives of the study, analysis of the test results was carried out in relation
to the project and site conditions. The geotechnical properties obtained from a basis of
discussion of the design and construction limitations that could arise, in relation to the site
and its geotechnical nature.

Conclusions on the suitability of Nairobi Red Coffee soils are then drawn and
countermeasures recommended for reversal or elimination of design and construction
problems, concerning the soil conditions attained.

 

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