Accu bore directional drilling1/7/2024 The conical shape means there is some compromise on drilling speed. Chisel tooth drilling heads can accomplish fast drilling speeds and are more resistant to breakages in harder rocks.Ĭonical tooth profiles give the best protection for hard rock. The shape is similar to the milled tooth but much smaller. The gouging effect of milled teeth removes large pieces of rock or soil.Ī chisel tool profile is best for medium rock. This design has a larger tooth surface compared to other designs making it more efficient. Fly cutters are often used with jetting capabilities so that the pressure of drilling fluid accelerates the drilling progress as well as removing cuttings from the bore.Ī milled tooth drilling head is ideal for harder soil and soft rocks. In clay conditions, fly cutters should be designed to drill their way out of the hole. They have an open structure allowing soil particles to fall into the center. There are several types of drilling head designed for different conditions.įly cutters are suitable for most types of soil. Particles stick together and swell when hydrated.Ĭuttings can stick together and bridge. Minimal resistance to drilling although borehole stability can be an issue. Loose collection of particles that do not stick together. Very hard rock with compressive strength of 18,000 psi and above. Soft rock with compressive strength less than 7,000 psi.Ĭonsolidated crystalline structures formed under extreme heat and pressure. Rocks forming layers like shale, sandstone, and coal. Medium hardness with compressive strength of 7,000 psi to 18,000 psi. The table below summarizes the different types of rock and soil.įormed under high temperatures and pressures - includes granite and marble. Each type has its own characteristics that influence which trenchless method will be most effective. The earth’s crust consists of different types of rock and soil. Read: Geotechnical Engineering Factors to Consider in Underground Pipeline Design and Installation An Introduction to Soil and Rock Properties The more thorough the geotechnical survey, the more confident the drilling team can be that they have the right materials for the job. Once engineers gain an accurate assessment of ground conditions, they can evaluate the cutting head options. It is never a good idea to make too many assumptions about the conditions. In some extreme conditions, it may be advisable to change this path to avoid a section that will be difficult to drill through. Engineers can map the proposed routing and see how the conditions change along the drilling path.
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