Experiences using a leader system for long CFA(ACIP) piles in Hawaii-Paper

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The paper describes the use of a crane-mounted leader system to install long CFA/ACIP piles in a single pass. In this method, a hollow-stem continuous flight auger is rotated to the required depth, then concrete is pumped through it as the auger is withdrawn. A reinforcing cage is inserted into the fresh concrete afterward.<br /><br />Compared with Kelly drilling, CFA/ACIP can substantially increase installation speed because drilling and concreting proceed continuously. Conventional extensions can reach beyond a rig’s mast height but interrupt the process and may compromise borehole stability. A crane and leader system avoids these interruptions, enabling single-pass installation at greater depths. Electronic drilling and concreting assistance systems monitor and regulate penetration, extraction, concrete flow, and pressure. These controls help prevent over-flighting, excessive soil removal, concrete overconsumption, and instability.<br /><br />The method is best suited to cohesive soils or granular soils with sufficient cohesion and without boulders or obstructions. It also requires workable concrete and a reinforcement cage designed to be placed in fresh concrete. Typical CFA pile diameters are up to about 3 ft and depths up to 100 ft, although larger and deeper piles are possible with suitable equipment.<br /><br />The paper’s case study is Ko’ula Tower in Honolulu, a 40-story building founded on soft lagoonal deposits, loose sands, and coral shelves. A Bauer MC-128 duty-cycle crane with a Berminghammer leader installed more than 300 piles, each 24 inches in diameter and 55–105 feet deep. The system drilled through hard coral shelves and completed drilling and grouting in one pass, avoiding extension-related delays.<br /><br />The authors conclude that crane-and-leader systems combine production capacity, stability, integrated hydraulic power, and computerized control, making them an effective option for long CFA/ACIP piles.

Keywords

CFA piles

ACIP piles

crane-mounted leader

continuous flight auger

single-pass installation

Kelly drilling

reinforcing cage

concrete pumping

borehole stability

Ko’ula Tower