Horizontal Directional Drilling (HDD) involves the installation of underground utilities by using a specialized machine to drill in a horizontal fashion creating a hole of sufficient size to then pull the product through. The product could be pipe for a water system, sewer connections, communication cables such as fibreoptic, television, or telephone, or even an underground electrical connection. The benefits of HDD is evident because the process avoids open cuts in the earth or trenches making HDD a superior choice for crossing transportation corridors (highways, city streets, railways, and even airport runways). HDD is also an attractive and efficient means to traverse environmentally sensitive areas like rivers or streams.
Typical application options for the use of HDD are rivers and canals, landfills and outfalls, roads, and railways, and airport runways.
The basic elements of an HDD installation are:
- A drill rig which provides the physical means – thrust and torque – to open the hole and pull the product.
- A transmitter/receiver system for tracking the location of the bore.
- The down-hole equipment – drill pipe, drill bits, and a reamer which converts the physical properties of the drill rig to open the hole and pull the product.
- The drilling fluid which does three jobs at once – stabilizes the hole being drilled, helps to cool down the down-hole equipment, and removes the spoil from the hole.
- The drilling fluid recovery system madeup of tanks, mixing systems, and pumps. When the system is recycling fluids, there is a system of screens, filters, and shakers to remove spoils in the fluids that have been brought to the surface.
More on HDD…
The world of Horizontal Directional Drilling (HDD) is creating exciting new opportunities in Canada! The possibilities are almost endless for the installation of underground utilities (water, gas, sewer, electrical, telecom, etc.). The ability to work safely around sites like environmentally sensitive areas (lakes, rivers, shorelines), high traffic sites (land roadway, rail systems, and even marine applications), and even archaeological sensitive areas. By avoiding open surface cuts, the reality is HDD can be very competitively priced with open cut methods, specially when considered the reduced restoration costs, not to mention the minimal interruption to residents and businesses.
The Horizontal Directional Drilling (HDD) process is really quite simple consisting of a machine that has the capacity to pull, push, and rotate the drill rod. The drill rod is a threaded steel pipe that has been specially constructed to withstand the flexing and the rotational torque that is part of the process. A mixing tank holding the drilling fluid (consisting of Bentonite and water) is attached to the back for the drill rig with a high pressure hose. The operator uses the mixture as required to create a slurry that displaces the material underground to help in making room for the eventual installation of the services. The drillhead is attached to the front of the rod and has a hollow cavity that will carry a transmitter. The transmitter emits a signal that when read by the HDD crew’s tracker, the signal provides the depth, pitch, and the rotational position of the drill head. This information is sent to an electronic unit located on the drill, as well as a handheld unit carried over the bore path. To help steer the drill, a tapered cutting bit is attached to the front of the drillhead and the allows the operator to position the tapered bit in the required direction, all without any rotation of the drillhead. Once the correct amount of steer is achieved, the operator resumes rotation and thrust of the drill rod again. As long as the drill rod is rotated, the drillhead will continue to maintain the course set with minimal deviation. Drill rods can vary in length depending on the size of the full of the HDD machine being used. During the drilling process, once the gearbox has reached full stroke or the length of the rod is used, it is quickly detached from the rods installed underground and an additional section is added to continue the bore. The process is followed until the drillhead reaches its destination point.
Once the destination point is reached the drillhead is removed from the front of the drill stem and a back reamer is installed. The back reamer cuts a larger hole to allow enough room for the product to be installed. The product is attached to a swivel behind the reamer and is pulled into the ground while the reamer is being rotated and pulled backwards towards the machine. The drill rods are now removed as they reach the drilling unit and this process continues until the product reaches the drilling unit.