Cast insitu reinforced concrete piles, diaphragm walls and barrettes have many inherent virtues and offer the most economic solution to many civil and structural engineering challenges. There is one inherent drawback with the technique, however. As construction proceeds, the excess concrete has to be trimmed away to bring the pile or wall to the final level.
This is usually undertaken by operatives armed with power tools, an expensive, time consuming and messy business. Elliot Europe has come up with an ingenious alternative, which the judges considered to be a major breakthrough, offering significant cost, time and environmental benefits to the contractor.
As with most good ideas, the basic principles are simple. Reinforcement above the final cut off level is prevented from bonding with the concrete by isolating sleeves, fixed before the cages are lowered into position. When the pile or wall is finally exposed a horizontal 51mm diameter hole is drilled into the concrete at cut off level reaching to a little past half the diameter of the structure. A standard hydraulic splitter is inserted and activated. After 30 seconds the concrete cracks across at the desired level, and the excavator used to expose the concrete lifts off the surplus in a single piece via a lifting eye cast into the top surface.
Elliot claims the secret is the application of the physics of crack propagation. The line of least resistance is the junction between the bonded and unbonded reinforcement, so the pile will split cleanly and horizontally. The remaining concrete has an undamaged upper surface with clean, straight steel bars protruding from it.
'Experience has shown that piles up to 1,200mm in diameter only need one hole drilling,' says Elliot managing director Bob Merritt. 'The whole operation takes about 10 minutes on average.'
Merritt points to another benefit. 'Hand-arm vibration is cut by more than 90% when the hole is drilled and virtually eliminated by the use of cast-in tubes.'