Methods Compared
Conventional Round Pile |
|
 |
A conventional round pile works by transmitting the induced load back into the substrate by SKIN FRICTION or by END BEARING or by a combination of both. They are usually driven using large heavy machinery and the disruption is usually considerable. Conventional piles may be driven or augered. A copious amount of water is produced when driving a pile and augering leaves a mound of earth to be removed. The upper part of the pile is usually sleeved to cope with any potential heave in the soil. The pile is usually over specified due to the difficulty in assessing in situ performance and the lack of any on site testing. |
Finned Pile |
|
 |
Conventional piles are available but with the addition of fins on the lower end. Installation of the finned pile is achieved by a screwing action which will involve heavy duty plant to gain the desired effect. The induced loading is transmitted by skin friction, end bearing and the additional bearing produced by the fins. There is also an additional resistance to pull out provided by the fins. Performance is usually far better than the conventional pile, but the installation method employed is much more complicated. |
New Heli Pile |
|
 |
The new Heli Pile is installed using lightweight driving equipment and transmits the induced loads via the wedge-shaped fins at an angle into the surrounding substrate. The shape of the fins compresses the substrate and increases the effective diameter of the pile. The skin friction is greatly enhanced by compression and the mechanical effect of the fins. The end bearing load is greatly enhanced by the ‘cone’ effect of the compression.
The imposed loading, whether in tension or compression, is equally shared along the whole length of the pile. As the sections of Heli Piles are only 1 metre long they are easily installed internally through a solid floor without the need for major disruption. If a longer pile is required it is a simple matter to screw on additional lengths as each metre length is driven home. |
Uses
Although the Heli Pile was originally developed as a lightweight piling system for remedial works to housing, its versatility has allowed the applications to be much wider and more varied than first imagined.
Used in combination with the Target Beaming system the Heli Pile is used as a standard pile and beam repair method. The system is very quick and easy to install giving an efficient and cost-effective solution.
New foundations may also be cast on the previously driven Heli Piles. The lightweight equipment ensures that there is little disruption, even on the wettest sites.
Because of its unique design it is very effective in tension. This allows it to be used for retaining wall stabilisation and soil pinning operations for cuttings and embankments.
A series of Standard Details are available showing the various uses and giving a full method statement. Full specifications can be supplied.
Materials
Site testing
Site testing is achieved by means of a small hydraulic testing kit and, to suit all site conditions, may be performed either in tension, for soil stabilisation, or compression where it is utilised as a pile. Because of the ease of testing, it is also possible to use a correlation between a tensile test and a compressive load.
Instead of working to characteristic loadings which have been attained in laboratory conditions the capability of in-situ testing allows the Heli Pile to be tested in the actual site conditions in which it is installed. Proof testing gives the specifier confidence in the Heli Pile’s ability to cope with the imposed loads and allows a much lower factor of safety to be used.
