Down The Hole Drilling (DTH)

The DTH drilling method is growing in popularity, with increases in all application segments, including blasthole, water well, foundation, oil & gas, cooling systems and drilling for heat exchange pumps.

DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated from the fact that the percussion mechanism followed the bit down into the hole. Applications were later found for the DTH method underground, where the direction of drilling is generally upwards instead of downwards.

In DTH drilling, the percussion mechanism – commonly called the hammer – is located directly behind the drill bit. The drill pipes transmit the necessary feed force and rotation to hammer and bit plus compressed air for the hammer and flushing of cuttings. The drill pipes are added to the drill string successively behind the hammer as the hole gets deeper. The piston strikes the impact surface of the bit directly, while the hammer casing gives straight and stable guidance of the drill bit. This means that the impact energy does not have to pass through any joints at all. The impact energy therefore remains constant, regardless of the hole depth.

DTH Drilling features

In the hole range 100-254 mm (4”-10”), DTH drilling is the dominant drilling method today (especially when the hole depth is greater than 20 metres). The main features of DTH drilling in this hole range are:

• Excellent hole straightness within 1.5% deviation without guiding equipment
• Good hole cleaning with plenty of air for the hole cleaning from the hammer
• Good hole quality with smooth and even hole walls for easy charging of explosives
• Deep hole drilling capacity with constant penetration and no energy losses in joints
• Efficient energy transmission.

Drilled casings are one of most popular methods for foundations, reinforcement work and well drilling today. They especially lend themselves to metropolitan work such as bridge, utility line, and building construction. In fact, with the development of DTH drilling and the introduction of special drilling systems like Symmetrix, casing advancement in overburden has become more refined. Symmetrix is a truly revolutionary product. Not only is it an all-around multipurpose concentric drilling system, it has opened the way for engineering consultants to utilize new construction methods that save contractors time and money.