Prior to the design of piles and pile caps, the working load of the pile is estimated. A pile is known to bear load by either skin friction or end bearing or both. These mechanisms of load bearing for the pile are considered when determining the pile working load. Other parameters required for this design such as the soil unit weight, the underlying soil across the stratum of installation and their depth, the depth to the water table, etc are all determined from soil tests carried out for the location.
Example
The figure below is the column application plan of an 8-storey office complex, showing the
loads at the serviceability limit state. It is required to find this building on a pile foundation.
Design the pile section illustrated below using the information provided in Table 6
below and using 25 – 460 concrete.
A soil test was carried out for the proposed location of the building. During the soil test,
three (3) layers of soil were encountered viz:
Medium to firm, red and yellow sandy clay up to a depth of 2 m;
Medium dense yellow fine sand up to a depth of 6 m, and
Medium dense to dense brown fine sand up to a depth of 15 m.
The proposed length of the pile is 15 m which cuts across the three layers of the soil. The Table
7 below shows the necessary information obtained from the soil tests to enable the design of
the pile via theoretical soil mechanics.
Determine the pile working load for the design of the piles and pile caps and design the piles and pile caps.
Solution
Table 12 shows the formulae for calculating skin friction and end resistance of different materials:
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