- Percussion drilling:
Percussion drilling is a useful method for dealing with the soils of UK as it provides wide suitability to a wider range of soil variety. It is known as cable tool drilling. The borehole is being lined with the casing to prevent caving in of the soil. Using a drooping weight the casing is installed. Bailer or chopping bit is used to advance the hole. By the use of manual power or the motive power the rig is operated. For the soils free from boulders or gravels light percussion rigs are more suitable for drilling. Heavy duly percussion rigs with chisel are required for the gravely or rocky formations. This method is suitable for a wide range of soil samples. It can also be used both above GWT and below GWT while it is faster in clayey soils. It is also preferred for the boulders and gravels formation.
- Rotatory drilling:
With the hydraulic downward pressure to the drilling rods in conjunction with the use of churning action of high speed rotating bit, this method of drilling can be advanced. The use of drilling mud bentonite slurry with density of about 1.1 to 1.2 g/ cm3 is effective during boring for:
- Stabilizing the borehole against the caving.
- During churning action keeping the rotating bit cool.
- By sealing the sides of the borehole it permeability is reduced.
- In case of wash boring bringing the soil cuttings to the ground surface.
This method is quite expensive and its progress is quite slow in gravely stratum. It is the most advanced drilling technique and is suitable for a large variety of rocks types. By the use of drilling mud this method casing can be avoided. Due to the presence of cavities difficulties may be caused in progress of this process.