WorldWide Drilling Resource

Determining the Correct Drill for Your Project Adapted from Information by the Association of Equipment Manufacturers Drill rigs are used in a wide variety of applications. Among them, construc- tion dri l l rigs are high-performance, technologically advanced, and well-suit- ed for multiple applications. Larger drill rigs are used for mining, exploration, geotechnical, and construc- tion projects. They can also be used to drill wells (water, oil, and natural gas), sample subsurface materials, and install subsurface fabrications, such as under- ground utilities. According to Jeff Calow, technical sales representative, foundation and surface drilling for Selix Equipment, a dealer for both Soilmec and Sandvik drills, “In a shoring or caisson installa- tion scenario, depth, diameter, and the necessity for segmental casing to line the hole will dictate the size and type of the machine. Larger diameter and deeper holes will require larger machines with greater torque and larger winch capacities, allowing a greater amount of material to be extracted from the shaft.” Smaller machines are often chosen for limited-access projects and offer decreased mobilization costs, better more efficient fuel consumption, and a smaller labor force. “Access is of course always a consideration as a machine physically fitting on a jobsite is only half the battle - you often need a greater lay down area available on-site for the assembly and disassembly of the machine,” stated Calow. Drills are engineered in one of two different configurations: rotary and percussion. Percussion is used to hit rock which is too hard to put an auger through. Augers pull the earth out as you are drilling, which is great in soft soil, but once you hit harder materials, you will need a percussion drill. Rotary drill systems use a lower rotary drive to advance casing through unconsolidated overburden and, where applicable, socket the casing into bedrock. The drill string is equipped with either a down-the-hole (DTH) hammer or a rotary bit to remove material and bring it to the surface. There are also several drilling head options to consider. The application and material being drilled will determine which is best for your project. “If it is hard rock or soft rock, does it have clay in it? This will determine the flushing characteristics and the type of carbide used,” said Wes Vietmeier, business line manager underground drills, Sandvik Mining and Rock Technology. “Also, the type of drilling equipment the customer has will be a factor: percussion drilling, DTH, top hammer, rotary, or auger drilling. The drilling depth and hole size will also affect the choice of bits.” For foundation drilling, the most popular construction application for a drill, there are five categories of drill heads: Earth/Soil Augers - Used in softer ground conditions, such as clay, sand, or till, earth augers have a spade-style tooth, similar to what an excavator bucket uses. Rock Augers - This style of auger uses a bullet-style round shank carbide tooth for drilling in harder ground conditions, typically when conditions exceed the hardness of clay. Core Barrels - Core barrels also use a bullet-style round shank carbide tooth, but occasionally they can be found using pin-on or weld-on carbide bars/teeth. This is used when an obstruction cannot be passed up the flights of a standard auger, or the obstruction is simply too large and must be cored through. Core barrels pickup where rock augers leave off. Drilling Buckets - Available in earth (spade teeth), rock (bullet teeth), and cleanout designs (flat edge), drilling buckets work either as a centrifugal bucket with a swinging door plate on the bottom or as a double-action centrifugal with a plunger actuated fall away door plate on the bottom. Drilling buckets are used to excavate material when the shaft is saturated in water, or when drilling with sus- pension slurries or polymers. Continuous Flight Auger (CFA) - This auger is actually designed to drill the entire length of the hole in one shot. The stem of the auger is hollow with a port on the bottom of the auger, which allows concrete to be pumped through the auger when the desired depth is achieved. This creates a stable shaft, as material is only removed during the concreting phase. CFA does not work in hard rock or in earth containing numerous obstructions. By knowing the features of each kind of drill, as well as work site drilling conditions, you can choose a drill which is best for your specific construction site. 28 NOVEMBER 2019 WorldWide Drilling Resource ® C&G