Bore holes in soil or rock may be drilled using augers, percussion rig, wash boring rig, and rotary drilling rig.
1. Auger boring:
Auger is a device which is used for boring manually. For advancing the bore holes for ground water to a depth of about 10 m hand augers or manual augers are commonly used. For deeper depths of about 50 mm to 300 mm other auger such as helical auger or post auger etc. are commonly used. We can also obtain disturbed soil sample from the cutting of the auger when brought to the surface and the recovery of the undisturbed soil particles form the bottom layer of the hole which is forcing the thin wall tube sampler. In USA for the purpose of deep investigations hollow stem augers are frequently used it is best suited for the soils which are susceptible to caving in problems. For the diameter range of about 30 m to 1 m the type of auger used is power auger. and are Stable only above GWT.
2. Wash boring:
In this method a pipe is passed down the hole and by passing high pressure water jet through it soil is loosen and the hole is advanced. With the help of the water which passes back up the outside of the jet pipe the soil cutting are brought to the surface. This method is followed on a large scale in USA but it is very rarely used in UK. This method is effective for cohesion soil and does not require a large budget to be performed. Another aspect of this method is that it offers minimum disturbance of the soil while working with cohesion less soil. We can also advance this technique but using sampler at the bottom dry sampling can be done. This method is not restricted to the GWT it can be used both above GWT and below GWT. This method is not suitable for collapsible soil.
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