HDD drilling is a trenchless method for installing underground utilities such as pipe, cable, and conduit. This method offers minimal impact on the surrounding landscape. This method is preferred over the traditional open-cut excavation due to its minimal inconveniences and impact on the environment.
Brief History Of Hdd Drilling
- First started in the 1960s by Martin Cherrington in Los Angeles, California.
- Cherrington built his own drill rig to perform road boring for various utility companies in the Sacramento area.
- In 1997, John English (Horizontal Technology Inc.) modernized hdd drilling. He addressed the environmental benefits of HDD, and developed methods for surface tracking (magnetic steering tools).
When To Consider Hdd Drilling
HDD drilling is recommended for the following conditions:
- pipe is 5 feet deep or more
- pipe is below the water table
- soil is unstable
- underground is congested with other utilities
- installation will be done in an urban area, under a roadway, river, or railroad
- installation is in a residential area
The HDD Process
Horizontal directional drilling has three (3) main stages namely:
- Drilling A Pilot Hole
Drilling a pilot hole is the initial step. Drilling fluid is pushed through the drill pipe to the drill bit, which grinds the soils ahead of the drill stem with high-pressure jets and the drill bit. The drilling fluid will also transport the cuttings back to the drill rig’s entrance pit.
Depending on the size and complexity of the shot, there are numerous options for tracking the pilot hole. A walkover guidance system is used for smaller shots, while a wire line magnetics system is used for larger, more intricate shots.
For both methods, a transmitter or steering tool is placed near the drill head and sends a signal to the location engineer with the exact drill stem coordinates. Readings of the drill head’s depth, alignment, and percent slope are taken on a regular basis.
Pre-Reaming
The following stage involves using a reamer, or hole opener, once the pilot hole has been completed. Reamers are available in different shapes and sizes, depending on the conditions and density of the soil. In favorable ground conditions, a fly cutter is often used.
To enlarge the hole, a reamer is pushed back and turned as drilling fluid is pumped. The number of cuttings extracted from the hole will determine the pre-reaming pace.
To ensure a clean and stable hole, bentonite and other additives will be utilized. During pre-reaming, bentonite is used to build a “cake layer” around the outside of the hole. This will aid with bore hole stability as well as fluid loss or infiltration. Polymers and other additives are used to help break up clay soils.
Any clogs inside the bore hole will be avoided by using a well-mixed drilling fluid.
Pipe Pullback
In this stage, the pipe is now pulled into the reamed hole. The pipe is fitted with a weld cap, while the swivel is attached to the drill string to prevent the pipeline from rotating. An artificial buoyancy measure may be used, depending on the pipe’s size. This is done in order to keep the pipeline as close to neutral buoyancy as possible.
Several issues may arise if no steps are taken. For example: coating damage from pipe floating in drill fluid. Pumping water into the pipeline using P.V.C. pipe and measuring the gallons pumped is the most common way to manage buoyancy.
HDD Drilling Vs. Directional Boring
HDD drilling is often used interchangeably with directional boring. However, they are distinct in terms of scale. Directional boring is reserved for small sized drilling rigs and small diameter bores, while directional drilling is used to describe larger sized drilling rigs, and is intended for crossing lengths in terms of thousands of feet.
At the same time, directional boring and HDD are similar in terms of purpose, particularly when conducting oil extractions and other related functions. This method can be used with different pipe materials, such as steel, iron, and PVC, as long as the pipe’s properties allow it to be installed under specific stress limits.
Locating The Drill Head
Locating the drill head is important in hdd drilling. The drilling head is not visible from the surface of the ground, and it can be at risk of unguided drilling and may result in substantial underground destruction.
The drill head can be located using any of the three ways:
- Walk-over locating system – a transmitter placed behind the bore head that registers rotation, angle, direction, and temperature data.
- Wire-line locating system – a magnetic guidance system that reads inclination and azimuth.
- Gyro-based locating system – can easily access locations above the drill path, and is not susceptible to magnetic distractions.
Takeaway
Traditional open-cut trenching, or excavations, take up a lot of space on the site and can harm environmentally-sensitive areas. These methods are frequently associated with costly weir, dam, and pier building when working near rivers and wetlands.
Trenching can result in the destruction of existing above- and below-ground infrastructure, as well as traffic problems in urban areas. Furthermore, excavation projects are frequently accompanied by substantial and costly repair and infrastructure rehabilitation.
Horizontal directional drilling, on the other hand, is a low-impact in situ construction approach that addresses the severe environmental shortcomings of traditional excavation and trenching. Since it does not involve the construction of above-ground trenches, it is the preferable construction approach in locations where minimal environmental disruption is needed.
