Horizontal Directional Drilling (HDD)
HDD is a steerable, trenchless method of installing underground pipes, conduits and cables by using a surface launched drilling rig. It is suitable for a variety of soil conditions including crossing underneath roads, lakes and rivers. It is used for installing infrastructure such as telecommunications cable, water, sewer, and natural gas lines, to name a few. This method of utility installation provides less traffic disruption, deeper and/or longer installation, shorter completion times and it is environmentally sensitive. Pipes are made of materials such as PVC, polyethylene, iron, and steel.
Video courtesy SpectraEnergy1
Equipment
The equipment used in a directional drill operation depends on the size of the pipe, length of the run, and surrounding locations. A power drill is used with a reclaimer, excavator, and multiple pumps and hoses to move the fluid inside the drilling path. Drill heads are available with many features, depending on the rock or soil being penetrated.
Process
The process starts with receiving hole and entrance pits. These pits will allow the drilling fluid to be collected and reclaimed to reduce costs and prevent waste. In the first stage, a pilot hole is drilled on the designed path, and the second stage enlarges the hole by passing a larger cutting tool known as the back reamer. The reamer's diameter depends on the size of the pipe. The driller increases the diameter according to the material being cut and creates for optimal production. The third stage places the product or casing pipe in the enlarged hole by way of the drill steel and is pulled behind the reamer to allow centering of the pipe in the newly reamed path.
HDD is done with the help of a fluid known as drilling fluid or bore gel. It is a mixture of water and polymer continuously pumped to the drill bit to facilitate the removal of cuttings, stabilize the bore hole, cool the bit and lubricate the passage of the product pipe. The bore gel is sent into a machine called a reclaimer, which removes the drill cuttings and maintains the proper viscosity of the fluid.
Locating
Accurate location and guidance of the drill head is a critical part of the operation. Locating the drill head is done with a sonde, or transmitter, behind the drill head that registers angle, rotation, direction and temperature data. This information is transmitted through the cable fitted within the drill string and sent to the operator of the machine. Guiding the drill bit takes experience and skill to avoid any existing undetected underground infrastructure.