Swissboring uses various techniques to install foundation piles, depending upon the soil condition, site condition and the specifications. Commonly adopted methods in constructing bored cast in situ piles are as follows.
A) Rotary Method
Pile driving using a crane mounted rotary tricone rig, probably the fastest piling method available, given the soil conditions prevalent in the U.A.E. Using a slurry support it is possible to eliminate the secondary tasks of advancing a casing for hole support and subsequently removing the casing during concrete placement. Harnessing the lifting capability of the thixotropic mud, the hole can be advanced in a continuous, smooth operation without the need to continuously withdraw, clean and replace an auger, bucket or bailer. Lastly, on reaching the hard strata, the rotary tricone is the fastest and most efficient means of advancing the hole to the desired depth.
B) Bucket and Auger Method
Bore holes are drilled using a Drilling Bucket, and Auger under Bentonite Slurry Support. In this method Bentonite is filled from the top of the borehole as the borehole advances. The slurry support system relies on the presence of a thixotropic mud-water mix to maintain the stability of the sidewall in a drilled borehole. This is achieved by a positive hydrostatic pressure developed by the slurry. Bucket and Auger drilling is normally used in construction of large diameter piles.
C) Contiguous Flight Auger Method
In Contiguous Flight Auger system the spiral of the continuous flight auger is supported by a 100 mm diameter hollow stem. The Auger is rotated into the soil in a continuous operation until the design depth of the pile is reached. Concrete mortar is then pumped through the hollow stem under pressure which, with the assistance of a mechanical override, extrudes the auger and soil column from the boring. The concrete is therefore placed under high pressure, creating an excellent concrete-soil interface without any disturbance of the surrounding soil, and assures stability of the sidewalls, even in very loose soil conditions.