RECENT ADVANCES IN OVERBURDEN AND DOWN-THE-HOLE DRILLING TECHNIQUES-Paper

Paper

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The paper reviews recent advances in drilling through overburden and rock for specialty geotechnical construction, driven by demands for faster, more reliable, lower-cost, and easier-to-operate equipment.<br /><br />For overburden, it describes systems designed to work with standard casing sizes. The SuperJaws and Elemex systems improve casing advancement and hole cleaning; Elemex also limits compressed-air escape into surrounding ground. Center Rock’s Roto Loc system uses mechanically locked cutting wings that extend to cut clearance for casing and retract for removal. It leaves no sacrificial parts, helps prevent casing slippage in soft or voided ground, and improves stability and straightness in challenging formations such as karst.<br /><br />Air-powered down-the-hole (DTH) hammer improvements include more efficient air cycles, steel hybrid valves, better air passages, and external jet subs that bypass excess air without reducing hammer performance. Lighter, better-matched piston and bit designs enable higher-frequency, smoother operation, reducing vibration and wear. Accessories further improve air control and reliability.<br /><br />Water-powered DTH (WDTH) hammers use pressurized water to drive the impact mechanism and flush cuttings. Their low-pressure, moderate-flow discharge reduces ground disturbance and component wear, while hydrostatic pressure helps stabilize boreholes and supports straight drilling in soft ground. WDTH is used for grout holes and can work with Roto Loc casing systems. Its drawbacks include substantial water needs and higher initial equipment costs; a blocked hole could expose the formation to pump pressure, though the authors report no resulting dam-safety incidents.<br /><br />Overall, the paper finds that equipment innovation continues across both overburden and DTH drilling, supported by contractor needs, manufacturer competition, and advanced computer-aided design.

Keywords

overburden drilling

geotechnical construction

casing advancement

down-the-hole hammer

water-powered DTH

compressed air control

Roto Loc system

hole stability

karst formations

drilling equipment innovation