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 Problems may also occur where a pile is driven to a
set on a corestone, overlying medium dense saprolite,
or where depth of soil is thin so pile is driven to set on
rock at shallow depth.

 The Hiley Formula has generally resulted in
satisfactory foundations as adequate depth is usually
achieved in fairly uniform soil profiles (Davies &
Chan, 1981).

 However, this is not the case for piles driven through
thick layers of soft marine clays to the underlying
decomposed rocks, and there are a number of cases
of large building settlement and tilting occurring as a
direct result of inadequate penetration of the piles
into the bearing stratum (Lumb, 1972; Lumb, 1979).

 Extreme caution should be exercised in placing
total reliance on the use of pile driving formulae
without due regard to the ground conditions.

 It is recommended that the design of a driven pile
should be supplemented by a 'static' capacity
calculation, using either soil mechanics principles
or established correlations with insitu tests.

 The design pile length should be taken as the
greater of those calculated from a pile driving
formula and that from at least one 'static' method.

 Thus, if the Hiley set cannot be achieved when the
pile is driven to the minimum design length
calculated from 'static' method, the pile will be
required to be driven further until the Hiley set is
achieved.

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