Piling equipment and methods 129to the walls of the borehole or to the lining tubes should be cleaned off. The reinforcing cage
can then be placed and concreting commenced. The time interval between the final
cleaning-up and placing concrete should not exceed 6 hours. If there is any appreciable
delay the depth of the pile bottom should be checked against the measured drilled depth before
placing the concrete to ensure that no soil has fallen into the hole. If the reinforcing cage
extends only part-way down the hole it should be suspended from the top of the pile shaft
before commencing to place the concrete.
The concrete used in the pile base and shaft should be easily workable with a slump of
100 to 180 mm as recommended in BS1536. Such a mix is self-compacting and does not
Figure 3.40Defective shaft of bored pile caused by collapse of clay after lifting casing.