Determining the Correct Construction Drill for Your Project

drill rig operatorDrills, from rigs to truck-mounted units to skid steer loader attachments, are used in a variety of applications. Construction drill rigs are high-performance, technologically advanced, and well suited for multiple applications.

Larger drill rigs are used to mining, exploration, geotechnical and construction applications. They are used to drill wells (water, oil wells, and natural gas), sample subsurface materials, and install sub-surface fabrications, such as underground utilities.

“The three most popular uses for our drills are blasting, putting in fences when you hit refusal—hard rock that can’t otherwise be excavated—and foundational drilling—anchors, soil nails, micropiles, stabilizing buildings—real geotechnical work,” says John Patterson, president, WORD Rock Drills.

Blasthole drilling is used in mining, quarrying, tunneling and construction applications. A drill pattern is developed in order to maximize the effects of the explosives. 

“In a shoring or caisson installation scenario, depth, diameter and the necessity for segmental casing to line the hole will dictate the size and type of the machine,” says Jeff Calow, technical sales representative, foundation and surface drilling, Selix Equipment, dealer representative for both Soilmec and Sandvik drills. “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.”

According to Callow, the majority of the projects in which you would find a Soilmec or Soilmec-style drill rig  would be any commercial condo development wherein a temporary shoring wall would be installed. They can also be used for the installation of structural caissons and for the use of ground improvement/stabilization such as turbo jetting.

“Smaller machines are often the preference due to decreased mobilization costs, better more efficient fuel consumption as well as a smaller labour force and support equipment,” says Calow. “Access is of course is 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.”

“We provide excavator and skid steer drilling attachments. The capital cost for an attachment is so much less than a whole machine, especially if you are only drilling part time,” says Patterson. “Our clients don’t get much forewarning. They get a job and they have to be on site three days later. That seems to be the way construction  is going these days. We have made it easy to get a drill attachment to a jobsite in a short time.”

ranger drillThe Diversity of Drills

Drills are engineered in one of two different configurations: rotary and percussion.

“You can choose either rotary/auger or percussion. You use percussion when you hit rock that is too hard to put an auger through,” says Patterson. “Auger pulls the earth out as you are drilling, which is great in soft soil, but once you hit material at 60 below count, you need a rock percussion drill.

Sandvik identifies several subcategories of drills and the applications for which they are intended. “Tophammer (TH) is designed for drilling smaller-diameter holes in more uniform rock formations, and is faster and cheaper cost per foot than down the hole (DTH) drills, which are designed for drilling larger-diameter holes in more severe rock conditions,” says Wes Vietmeier, business line manager underground drills, Sandvik Mining and Rock Technology. “Rotary (or pedestal) drills can be DTH as well and normally for bigger holes—between six and a half and 16 inches—and where high-production volume is needed. Boom drills can be either TH or DTH and they tend to be adaptable to challenging base/surface ground conditions.”

Drilling contractor, Construction Drilling, describes rotary drills in more detail. “Rotary drill systems use a lower rotary drive to advance casing through unconsolidated overburden and, where applicable, socket that casing into bedrock. The drill string is equipped with either a down-the-hole hammer or a rotary bit to remove material and bring it to the surface.”

Choosing the a Drill Head

There are numerous drilling head options. In order to choose a drill bit, consider the application and material being drilled. “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,” says Vietmeier. “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.”

sandvik drillFor foundation drilling, which is the most popular construction application for a drill, there are five categories of drill heads:

1. Earth/Soil Augers. Earth augers use a spade style tooth—similar to what an excavator bucket would use—in softer ground conditions, such as sands to clays and tills.

2. Rock Augers. Rock augers use a bullet style round shank carbide tooth for drilling in harder ground conditions, typically when conditions exceed the hardness of clay

“Among rock augers, there are three choices: Double Start Centreless, which is effective in medium to medium hard rock conditions and for larger diameter holes; the Single Start, which works excellently in smaller diameters and large diameter drilling applications in medium to hard rock; and the Double Start Progressive, which is the auger of choice for the hardest of drillable rock.”

3. Core Barrels. Core barrels typically use a bullet style round shank carbide tooth, but occasionally can be found using pin-on or weld on carbide bars/teeth, this drill is used when an obstruction encountered 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.

4. Drilling Buckets. Available in earth (spade teeth), rock (bullet teeth) and cleanout designs (flat edge), drilling buckets work either as 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 suspension slurries or polymers.

5. Continuous Flight Auger (CFA). 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. This allows you to pump concrete through the auger when the desired hole depth is achieved. This creates a stable shaft, as material is essentially only removed during the concreting phase, creating an in situ (cast in place). CFA does not work in hard rock or in earth that contains numerous obstructions.

Drills are diverse in form and application. By knowing the features of each kind of drill, as well as the work site drilling conditions, you can choose a drill that is best for your construction site.

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