When drilling through rocks, conventional rock augers and buckets (and even core barrels) quickly lose their effectiveness as the strength of the rock begins to exceed 25 MPa. HEMCO Multi-Hammer drills are a modern solution for drilling in hard rock formations and we have developed a highly effective Multi-Hammer for drilling 610mm to 1200mm boreholes in medium rocks as well as the hardest formations.

Multi-Hammer Drill for 600mm to 1200mm Borehole

• HEX connections for ease in assembly and disassembly.
• Robust construction, yet lightweight.
• All HEMCO Multi-Hammer drills can undertake (a) drilling with standard kelly bar (b) drilling with CFA (c) “reverse” drilling with RCD drill string.
• All Multi-Hammer drills utilize our standard 200mm DTH hammer.
• Can work without shock absorber as vibrations are low.

Working Principle

The drill employs 200mm diameter multiple DTH hammers with drill bits of 300mm diameter mounted on the lower end of the DTH hammer. The hammers work inside a steel barrel and each drill bit extends about 25mm beyond the barrel. The DTH hammers are arranged in a geometry such that the complete pile diameter is covered by the DTH hammer bits as the barrel is rotated or oscillated by the drilling rig.

“Straight” Drilling:

“Straight” drilling is very conveniently possible using any normal piling rig working with a standard telescoping kelly bar.

A kelly box of the required size is bolted onto the top of the hammer barrel and air is supplied through an inlet below the kelly box form where it is distributed to each individual DTH hammer through a distribution chamber at the top of the barrel. As drilling proceeds utilizing 180 degree oscillatory motion of the kelly bar, the cutting are lifted upwards through the annulus between the borehole wall and the steel barrel and these cuttings settle into a collection barrel mounted on top of the drilling barrel. Once the collection barrel becomes full, the drill is lifted out of the borehole and the collection barrel is pulled upwards by the auxiliary winch of the drilling rig to empty the cuttings.

Alternatively, CFA drill string instead of kelly bar can be attached to top of the Multi-Hammer barrel through standard HEX joints. In this case, continuous drilling can be undertaken as the cuttings settle on the flights of the CFA. Once drilling to the required depth is completed, the CFA is withdrawn and the cuttings cleared from the flights of the CFA.

Reverse Circulation Drilling (RCD):

RCD drilling when done in conjunction with the HEMCO Multi-Hammer is a very efficient method of boring through all types of formations. This method is equally effective for both shallow drilling depths as well as depths exceeding 100m.

For RCD drilling with the Mutli-Hammer, a special coupling is bolted to the top of the steel barrel which connects the barrel with the RCD drill string through a HEX connection. The drill string comprises of a series of standard (but robust) RCD drill rods coupled together with HEX box and pin joints. The top of the drill string connects to the lower side of the drilling rig gearbox through a drive adapter while an air swivel sits on top of the gear box. Air is supplied to the inlet of the swivel through an air hose which connects on the other side to air compressors of adequate capacity and pressure. 

Multi-Hammer   

Drill Rod