Open Bored Piles
Use sectional flight auger sections at varying diameters 200mm to 600mm to form piles to the design founding levels through dry/self – supporting cohesive substrata
CFA Flight Auger (CFA Piling)
In this method the auger stays in the pile bore to the final depth, being withdrawn slowly with the pile spoil whilst concrete is pumped through the hollow auger stem into the pile. As well as in loose or granular soils, CFA may be the only viable solution for noise and vibration sensitive work, and on some restricted access sites.
CFA is the quietest form of piling and is suitable for forming piles in most types of soil, particularly inter- bedded sequences of clays and sands and water bearing cohesion-less strata.
Bored Temporary Cased Piling
Bored temporary Cased piles are used where the ground conditions are comprised of fluvial cohesion-less strata overlying clays where deep reinforcement cages are required. Typically casings are for contiguous bored pile walls and secant piled walls or where full depth cages are required for tension.
They are formed by drilling through a temporary casing to the designed depth, using an auger to cope with a variety of ground conditions. The casing gives support to the pile through unstable ground. Once the required depth is reached the auger is removed, the reinforcement is added and the concrete poured. When the concrete reaches the required level, the casing is removed allowing it to be reused in future. In cases where the ground is still unstable at depth, support fluids such as bentonite or polymers can be added.
We design bored temporary cased secant and contiguous piled retaining walls allowing for tighter vertical tolerances and therefore retained heights, compared to traditional CFA solutions.
Bottom Driven Piling
Bottom driven piles can be installed successfully into most ground conditions including peats, soft clay and loose sand where some other techniques are inappropriate. Bottom driven piles are self-testing when driven to set. Permanent casing prevents any risk of concrete loss, thus ensuring pile integrity.
1. Bottom driven drop hammer piling technique
Close ended thin walled steel tubes are driven using a cylindrical drop hammer operating within the casing striking a dry mix concrete plug. The steel tubes are typically 2 to 3 metres in length and are joined by full fillet welding as installation proceeds. The bottom driven piles are installed to a predetermined set or depth depending on design criteria. Single bar or cage reinforcement is introduced and the bottom driven pile casings are filled using workable high strength concrete.
Using bottom driven piling has a number of distinct advantages:
- low noise and vibration
- no spoil is generated
- Dry concreting conditions in a single operation to a controllable level
- Self-proving design
- Cost effective in difficult ground conditions
2. Pneumatic Driven Piles
Similar process as above using pneumatic hammers to drive 100mm to 150mm diameter piles.