CONSTRUCTION OF THE CONTINUOUS FLIGHT AUGER, CFA, PILES
CFAs is drilled by Continuous Flight Auger and has the advantage of giving higher capacity piles. The drilling method allows
to excavate in a wide variety of soil-dry or water-logged, loose or cohesive and soft rock. Another advantage of CFA piles is
that it is sound-proof; produces no noise or vibration during execution. That is why it is mostly used in built-up areas, even
at close proximity to existing structures, sometimes as close to 1-2metres. CFA Piles are environmentaly friendly since no
drilling mud is required. The diameter of CFA piles ranges from 40-80cm, and a depth of between 20-30metres.
Basically, there are two main types of sheet piles-Concrete or Steel
Steel Sheet Pile: This is mostly used for deep walls where deep depth of excavation is required. The steel sheet piles come in
different shapes depending on the manufacturer. However, they are driven into the soil by means of an hydraulic, diesel or
vibrator hammer, according to the geometry of the steel profile. Connected together with mechanical joints, they are a
suitable system to form barries, continuous sealed walls for excavating support, shore protection. They are mostly used in
marine structures, where depth greater than 17m are required. The disadvantage of steel sheet pile is the corrosive
impact of the sea water on the steel structure. Concrete sheet pile it has an advantage of being resistant to the
corrosiveness of sea water once the right thickness is adopted. They are precast concrete elements of various dimension,
usually a thickness of between 20-30cm are adopted, and length up to 16m. They are also driven into the soil by means of
hydraulic or electric vibrators. The elemental sheet piles are sealed with special joints successfully grouted and connected
together by capping beams, anchored with tie-backs if required by design. They are mostly used for shore protection.
Secant piles can be constructed either with conventional drilling methods or through the use of CFA techniques.
Secant piles are constructed so that there is an intersection of one pile with another. The usual practice is to construct
alternative piles along the line of the wall leaving a clear space of a little under the diameter of the required intermediate
piles. The exact spacing is determined by the construction tolerances which can be achieved. These initally placed piles do
not have to be constructed to the same depth as the intermediate piles which follow, depending on the way in which the
wall has been designed and reinforced.
Micropiles are used where the conventional piles, i.e driven or board piles, cannot be used to construction constraints
like headroom and space. As the name implies, sizes range between 200mm-350mm, and a depth of up to 30m. Light
equipment like small rotary machine or pilcon machine are used.
A through sub-soil investigation is vital to any civil engineering project. Understanding the soil through various
equipment such as Pilcon machine, Dutch cone penetrometer and the interpretation of the result therein will always
result in a cut effective project.
HENRY KAY is always in contract with other associates in the field of geotechnical engineering to carry out sub-soil
investigation, onshore or ofshore. Some of our associates are ITB foundation, Osmo Geotechnical engineering services, to
mention of few.
PILE INTEGRITY TEST (PIT)
The test basically involves inducing a stress wave in the pile by tapping the pile top with a small hammer and measuring the
resulting pile top motion with an accelerometer attached to the exposed pile top. The record of hammer impact is filtered
and exponentially amplified to enhance important record features. The equipment for the testing included a PIT collector
manufactured by Pile Dynamics Inc and a hand-held hammer ranging from 2N to 27N. The collector averages, analyses
and stores the records. It displays them such that an immediate assessment of data and pile quality was possible. The
stored data is further analysed with the aid of a Personal Computer (PC) running a provided program (PITW).