GENERAL NEWS
Michael Hughes explains the process behind the
implementation of raft foundations.
Raft
foundations
In our Setlhoa Office Park development we have used a raft
foundation system which is being supplied by Litedek (Botswana).
Raft foundations make use of a large concrete slab which can support
a number of columns and walls. The slab is spread out under the
entire building or at least a large part of it which lowers the contact
pressure compared to the traditionally used strip or trench footings.
Why did we decide to use this type of foundation?
Initially, the site was surveyed and we conducted tests on the soil –
this is called a geotechnical survey. This survey is the first step in the
construction or consolidation of a site. It includes information about soil
consistency and structure, groundwater level and recommendations for
the technical project. Following the excavation of trial pits, the samples
collected from the ground are taken to the lab for analysis. Based on
these results and field observations, the geotechnical report is produced.
The report determines the bearing capacity of the soil. This is the
capacity of soil to support the loads applied to the ground by the
building. The reports indicated that the use of a raft foundation would be
the best type of foundation solution to use based on the conditions that
we have on the site (poor bearing capacity).
The construction of the raft foundation
The surface of the site is first levelled and prepared to form a base
called a platform. This may be above or below the ground level. After
the necessary compaction tests and inspections, the engineer gives the
instructions to proceed with the raft installation. The area is sprayed with
insecticide and the waterproof layer is placed on top of the ground.
WASTE PIPES FROM THE TOILETS ALREADY INSTALLED UNDER THE RAFT.
ISSUE 36 - DECEMBER 2018
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