Pre-augering is a commonly used technique associated with sheet piling which is carried out in advance of sheet pile installation to disturb difficult ground the piles will be installed into. The effect of locally reducing the driving resistance encountered is achieved.
ABI TM14/17 leader rig fitted with an ABI MDBA 4500-2 auger drive motor and 400mm diameter flight, the flight is drilled into the soil and then reversed as it is withdrawn.
Zaxis 250LC Excavator fitted with a BA2200 ‘Dangle Drill’, and 400mm diameter flights.
Some arisings are produced but they are kept to the minimum by back-spinning the flights as the aim is not to empty the bore. The holes are spaced to coincide with the pile clutches, which would generally be a 600mm centres. By using a flight that is narrower than the width of the pile wall all the disturbance is kept within the wall profile and thus does not have an effect on the pile wall design and wall integrity. The process of installing the pile will have the effect of reconstituting the ground.
Generally the ground is pre-augered to the full depth of the pile but the technique can be used solely to penetrate a dense band of soil. When used as an advanced operation to silent piling using our WP150 or JZ100 Silent piler, dense granular strata, which tend to overlay clays, can be driven through, and a reduction in water usage will also result. In this instance we would advise only to pre-auger to the clay interface.
There are multiple benefits to be derived from pre-augering:-
- Piles can be installed with greater speed and accuracy
- Lighter pile sections can be used particularly where a heavier section may have been needed for installation, but not required for the final design case
- A reduction in ground borne vibration is possible
- Sheet piles can be used as an option when they may have been previously discounted due to difficult soils
We have found that our leader rig and auger is ideal for use in probing the ground in advance of concrete pile installation particularly on city centre site where previous construction has taken place and the risk of encountering underground obstructions is high. By augering through the ground down to virgin soil in advance of the concrete piling, obstructions can be located and removed thus eliminating expensive standing time.
Our rigs will swiftly and economically move between pile locations and will operate on the same piling mat required by the main piling rig. We can also offer a larger diameter auger for piles over 400mm.