Both in-situ and precast piling systems can be used to provide fast and effective foundation solutions.
In-situ techniques available include:
- Bored piling with permanent or temporary casings
- Continuous Flight Augered Piles (CFA)
- Continuous Helical Displacement Piling (CHD)
These piling techniques are regarded as non-displacement meaning there is less risk of ground heave. The length of in-situ piles can be readily varied to suit ground conditions and they can be installed with very large diameters or long lengths. An additional advantage is the low level of noise and vibration produced during piling.
Precast concrete piles are used in the construction of foundations for a wide range of different structures in the civil engineering and building sectors. As precast piles are suitable for all applications and ground conditions, they provide a very cost-effective piling solution. They are quick to install without producing spoil or arising material in the process, providing a further saving on waste disposal costs.
Factory production techniques, using high performance precast concrete and rigid reinforcement cages, means that precast concrete piles can tolerate high loadings. Generally, design safety factors for piling are taken to be loadings in the range of 2.0 to 3.0. It is normal to use safety factors at the lower end of the range for precast concrete piles because of the:
- Enhanced quality control procedures operable in the factory manufacturing environment.
- Availability of a full product inspection to ensure that no defects are present prior to installation of the pile.
Precast piles are generally top driven into the ground using hydraulic drop hammers. Sound levels from modern drop hammers are comparable to other piling systems such as continuous flight auger (CFA). Noise during piling can be further reduced by shrouding the drop hammer. The variety of segment lengths available, along with specialist piling equipment, makes precast piles particularly suited to restricted access and low headroom sites.
Precast mini-piles and precast concrete beams can be used for underpinning existing wall foundations to repair and improve the stability of housing and other structures. Specialised installation techniques and equipment have been developed to enable underpinning to take place in areas of difficult and restricted access with minimal disruption to the building occupants, and to any neighbouring buildings.