Drilling Method

Directional drills are relatively compact with a small footprint, allowing them to get into tight spaces and situate on the side of the road without impeding traffic. A small crew is required: a drill operator, and locating equipment operator. The locator operator electronically tracks the progress of the drill head beneath the surface using a hand held locater. He then 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 head 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 stabilize the hole, remove cuttings, reduce torque, lubricate the pipe, and cool the drill head. When the pilot hole has been bored and the head emerges in the exit pit, the drill head 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 about 50% larger than the pipe. 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 as or stronger than the pipe itself. Strong fusions are essential, as service pipe is subject to soil loads without side support from the surrounding hole. This load requirement is a major difference between HDD pipe and pipe installed in a trench.

Problems HDD Solve

Traditionally, installation of underground utilities involved open trenching. The contractor had to excavate around existing utilities to get to the depth required to install the service. Costly footpaths, carriage ways, block paving, maintained greens and other surfaces had to be open cut and replaced. There was always a risk of hitting existing underground utilities during excavation. Additionally, the excavation caused interruption to traffic and the environment also inconvenience to public.

Advantages to HDD Over Other Methods

HDD equipment requires a relatively short set-up time; a mini rig can be set up and start boring within an hour of arriving on site. Labour requirements are minimal, as it only takes a small crew to operate a drilling rig. The need for traditional excavation during horizontal directional drilling is minimal or non-existent. In crowded urban areas, horizontal directional drilling is increasingly viewed as "the preferred technology" because: