HORIZONTAL DIRECTIONAL DRILLING (HDD)
Traditionally, installation of underground utilities involved open trenching. The contractor had to excavate around existing utilities to get to the depth required to install conduit. Costly sidewalks, pavement, brick paving, sod and other surfaces had to be cut open and replaced. There was always a risk of hitting existing underground utilities during excavation.
Additionally, the excavation usually causes interruption of traffic and inconvenience to nearby businesses.
Directional drills are relatively compact with a small footprint, allowing them to get into tight spaces and can be situated on the side of the road without impeding traffic.
A small crew is required: a drill operator and a tracking equipment operator, who electronically tracks the progress of the drill head beneath the surface using a hand held tracker.
The tracker gathers data from the sonde located in the drill head just behind the drill bit. The sonde gathers data such as location, depth, roll angle, pitch, and temperature to help the driller adjust the direction of the bit and control the bore path.
To prepare for the installation, the drill operator must first calculate the route, or bore path, of the pipe along a shallow, underground arc. The operator must also estimate the load applied to the pipe during pullback and select an appropriate pipe for the project.
As he bores the path, a bentonite polymer mix is injected into the hole to stabilise the hole, remove cuttings, reduce torque, lubricate the pipe, and cool the bit.
When the pilot hole has been bored and the bit emerges in the exit pit, the drill bit is removed. A reamer is placed on the end of the pipe string and pulled back to enlarge the borehole. Generally, the reamed hole is 120 to 150 % larger than the service pipe that will be inserted.
Lengths of polyethylene pipe are then fused together. The pipe is heated and the molecules are transformed into a crystalline state that enables a seamless joining of the pipe. The end result is a fusion joint that is as strong or stronger than the pipe itself.
BENEFITS OF HDD
HDD is a newer technology in pipe and utility installation that allows greater accuracy and flexibility in placement and ends the need for costly digging, large crews, road closures and other complications of traditional digging and pipe installation. The traditional system of digging down to install pipes and utilities is called “open-cut” and is far more disruptive than HDD and comes with many drawbacks. HDD is likely the best alternative for a repair, maintenance or installation project.