Mumbai University > Civil Engineering > Sem 8 > Construction Engineering

Marks: 10Marks

Drilling equipments can be grouped as:

Percussion drilling: Percussion drilling is a manual drilling technique in which a heavy cutting or hammering bit attached to a rope or cable is lowered in the open hole or inside a temporary casing. The technique is often also referred to as 'Cable tool'. Usually a tripod is used to support the tools. By moving the rope or cable up and down, the cutting or hammering bit loosens the soil or consolidated rock in the borehole, which is then extracted later by using a bailer. Just as with hand augering, a temporary casing of steel or plastic may be used to prevent the hole from collapsing. When the permanent well screen and casing are installed, this temporary casing has to be removed.

Percussion drilling is suitable for unconsolidated and consolidated formations: Sand, silt, stiff clays, and sandstone, laterite and gravel layers. Manual percussion drilling is generally used up to depths of 25 meters. Before drilling starts, it is good to analyze where the water might be.

Rotary drills

In rotary drills the movement of the bit is due to the rotation of the drill bit

• Pressure drilling:

In this system, drilling action is provided by applying the down pressure on the bit. The pull down pressure and the drill rotation is created by the hydraulic or electric variable speed motors. These drills are powered either by diesel engine or electric motor. Air compressors remove the cuttings, from the hole as drilling progresses. The bit pressure and quantity of air are controlled as per requirement.

• Abrasion drilling

Diamond core drills and shot core drills are common drills of this category.Diamond core drills are more common.Shot core drills are used for large dia drilling and are slow in drilling. Shot core drills are suitable for dia upto 1.8 m and depths upto 300 m.