Set-up, Boring, and Fusing
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, mud mixer/vacuum
operator and a tracking equipment operator. The tracking operator electronically tracks the progress of the drill
head beneath the surface using a hand held tracker. 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 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 stabilize
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 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
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. The Henniker Directional Drilling crew is certified in pipe fusion.
Problems HDD Solves
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 open cut 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.
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.
Labor requirements are minimal, as it only takes a small crew to operate a small 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:
- HDD eliminates the need for removal, restoration and long-term costs associated with trench settlement
- In open areas, horizontal drilling provides an efficient method for crossing obstacles such as rivers, highways, rail tracks or an active runway
- Surface disruption is minimized
- Less negative impact on residents and businesses
History of HDD
Directional drilling has traditionally been applied in telecommunications, electric installations, oil, forced water,
sewer lines and gas distribution. More recently, HDD has been applied to horizontal environmental wells and geothermal
systems. Contractors are developing new HDD applications every day.
The directionally controlled horizontal drilling process was developed in the U.S. and is commonly used for crossing
under natural or manmade obstacles, especially river crossings. This method has revolutionized complicated river
crossings for pipelines, which were initially done by conventional dredging methods or were rerouted through long
distances and crossed over at a bridge location.
This method is an outgrowth of the oil well drilling technology, developed in the early seventies by Titan Construction,
Sacramento, California, U.S.A. The first installation was accomplished in 1971 for Pacific Gas and Electric Company, which
involved the installation of approximately 600 LF (180 m) of 4-inch (100 mm) diameter steel pipe under the Pajaro River
near Watsonville, California. Prior to 1979, the method was limited to the installation of short lengths. Since 1979,
the method has advanced tremendously, enabling long crossings with a wide variety of pipe sizes.