In the bored piles construction we had looked at the method how bored piles are generally drilled. Continuing on the subject of drilling, this post we will look at the type of drilling tools used.
There are a number of ways to drill or to form the required diameter and depth of the bored piles. In this post we will look at the rotary method. The rotary method is perhaps the most common method used. The circular action produced by the engine is used to remove or excavate away material from the ground to form the bored pile of the right diameter and depth.
In normal dry ground situation, the most common tool used with the rotary method is the auger.
There can be two types of auger, the short auger or the continuous flight auger.
Bored Pile Auger
Both tools will be rotated into the ground and by the rotary action , soil is excavated in the process. This is repeated until the required design depth is achieved.
The process of auguring can only be carry out when the drilled bore pile hole remains dry. That is the bored pile hole remains dry and stable ie without collapsing. Should the hole be unstable, it can be stabilized using casings.
Continuous Flight Auger
On the other hand, if the ground water table is high and the drilled whole is wet or filled with water, casing can still be used with the hope that it sealed of the hole thus allowing dry condition drilling.
If this is not possible than drilling had to be carried out in submerged condition ie under water. In this case the auger will need to be changed to a drilling or boring bucket.
Drilling or boring bucket
Again in drilling under water, the bored hole has to be stabilize from collapsing during and after drilling. Most commonly casing is used and if this failed, than there is the option of using bentonite slurry or polymer fluids to stabilized the hole. Drilling will still make use of drilling bucket.
Cleaning Bucket
When the founding depth is reached, the base of the bored pile will cleaned using a cleaning bucket before concreting. Thus far the drilling discussed in this blog is for soft to hard cohesive soil. However if boulder or drilling in rocks is required, than the drilling tools will be different.