This method
loosens the soil by means of boring a hole of sufficient diameter through
the difficult soil layer into which receive the pile must be installed.
Pre-drilling is usually carried out by auger drilling. Pre-drilling may
also be required on sites where it is important to avoid noise and vibration.
Mechanical augers have been used to bore uncased holes to receive piles
which are installed in the hole and then driven a short distance to their
required bearing level. This method would only be used where cast-in-situ
piles are unsuitable because of ground or structural conditions.
A limitation
of pre-drilling is that the bearing capacity of the pile may be reduced
due to decompression. This aspect must be taken into consideration when
the load carrying capacity of the pile is estimated.
