WorldWide Drilling Resource

7 MARCH 2021 WorldWide Drilling Resource® No Doubt Hammer and Grout Adapted from Information by LKAB Wassara Using water to power a down-the-hole (DTH) hammer is an ideal choice for many drilling applications. Add a jet-grouting feature, and this makes a unique single-pass drilling and grouting system. Challenges with anchor drilling, immersed tunnels, cut-off walls, ground reinforcement, and survey, grout, and drainage holes are no match for such a system. It can handle many formations, including hard rock, boulders, concrete, limestone, granite, wood, till, and dense clay. In multiple drilling applications, jet-grouting plays a vital role in sealing and securing the boreholes. Whether grouting tunnel anchors or jet-grouting columns to stabilize walls, the single-pass system performs efficiently. Even when using a traditional drill and blast or tunnel boring machine, there is a need to drill long, straight holes to minimize production stops for surveying and grouting purposes, and the water-powered hammer and jetgrouting system maintains speed and accuracy throughout the entire hole length. The parts of this water-powered DTH hammer and jet-grouting system complement each other, while operating independently. The DTH hammer is connected directly to the drill bit and usually uses up to 79 gallons per minute of clean water with a pressure of up to 2611 psi. No power is lost through the drill string during operation, which enables the hammer to sustain high efficiency for any borehole length, even thousands of feet long. Water exits with sufficient velocity to move cuttings and debris to the surface and clean the borehole with minimum impact on the formation. It delivers cement grout through a channel during jetting, and a small amount of water runs to keep the cement grout from entering the hammer. There are four nozzle sockets for multiple configurations and preventing fluid backup on the jet-grouting hammer with an integrated check valve in the backhead. LKAB Wassara, headquartered in Huddinge, Sweden, is the developer of this world-patented water-powered DTH hammer and jet-grouting system. In the demanding McCook Reservoir, part of the gigantic Chicago Underflow Plan, a grout curtain had to be installed for the overburden cut-off wall to minimize the flow of water in and out of the reservoir. Wassara’s water-powered DTH hammer was selected for the deep holes required. Quality control indicated an average hole deviation of just over 1%. In another application, ground stabilization was needed for a huge storage building in Hässleholm, Sweden, because of sand and friction soil in different layers above the bedrock. Using the Wassara system, 288 columns were created, each 18 feet in length and 32 inches in diameter average size, with an average production of 15-20 grout columns per day. The sequence of drilling down to the bedrock took 7-8 minutes with an average penetration rate of 3.3 feet per minute while the grouting sequence took 14-15 minutes. Tried and tested, it is a most environmentally-friendly percussion-drilling method. C&G Stockholm, Sweden - Wassara’s largest water-powered 12-inch hammer W280 in a pile-drilling application. Mills Machine Company, Inc. manufactures stabilizersto keep drill rods centered in the borehole. Their heavy-walled steel pipe stabilizers are made with heat-treated steel tool joints, plus all wear surfaces are coated with carbide hard-facing. Mills Machine’s stabilizer collection includes: 0Smooth Stabilizer - Are normally a couple of inches smaller than the borehole inside diameter and can have an inner and outer barrel. 0Flow Through- Its variation for larger diameters allows the cuttings to flow between the inner and outer barrel. 0Straight Ribbed- They can have three or more ribs, which are welded to the steel tubing and are hard-faced the entire length. 0Spiral Ribbed - Hard-faced ribs are spiraled around the steel body to give 360-degree wall contact and assist in cutting removal. 0Spiral-Straight Ribbed - Has the wall contact of the spiral stabilizer, while reducing the cost of the spiraling process. 0Overhammer - They are built with standard rugged construction, with the ability to take the punishment of the downhole hammer and designed for the specific hammer it is coupled with. Mills Machine Company, Inc. is a Valued WWDRAdvertiser.