Crossing Challenges Where HDD is the Best Solution

Horizontal Directional Drilling (HDD) started as an alternative to traditional open-cut or excavation methods for laying cables and pipes, first pioneered in the 1960s.

Today, HDD is the preferred drilling method in various crossing projects and environments. Learn about examples where HDD is the best solution for installing pipelines, ductwork, or cables.

How HDD Works

Horizontal Directional Drilling is a drilling method that allows operators to drill horizontal holes beneath the surface of a job site without digging trenches or excavating. This characteristic makes HDD a steerable, trenchless drilling method.

A typical HDD project consists of three phases: Pilot drilling, reaming, and pipe pulling.

Pilot drilling

During the pilot drilling phase, the construction team uses a drill bit to cut a small-diameter hole through the substrate between the desired start and endpoints. The drill is equipped with a positioning system to steer it in the right direction.


After completing the pilot hole, the crew switches to a bigger drill bit called a reamer. The reamer’s purpose is to expand the pilot hole until it reaches the desired diameter for the project. Multiple reamer sizes are available for different jobs, minimizing the void (dead space) around the pipe.

Pipe pulling

Once the crew has reamed the space needed for laying the pipes, they may begin pipe pulling. The crew pulls the pipe into the reamed passage using a special reamer fitted with a pull-head. After laying the pipe, the team tests it for stability, then welds it to the piping segments at the start and endpoints.

The Evolution of HDD

After witnessing other construction companies using guided drills to install gas lines, Martin Cherrington imagined the concept that eventually became HDD in the early 1960s.

However, in 1971, Cherrington, then working for the Pacific Gas & Electric Company, applied the concept in a river crossing for the first time. His new methods allowed his crew to cross the 500 ft. wide Pajaro River near Watsonville, CA, installing a 4” gas line under the 500 ft. river bed.

Cherrington later completed jobs of a similar nature in Louisiana and Texas, eventually founding the Cherrington Corporation in 1984. The corporation specializes in this drilling technique and helping HDD become an industry standard.

When to Consider HDD

HDD is typically employed for installing cables, pipes, and gas lines under roads, railways, and rivers. HDD is the best drilling solution around urban areas, residential communities, parks and golf courses, and many other project settings.

You should consider this drilling method if your project meets at least two of the following characteristics:

  • The job site is already congested with other utilities
  • The job site is in an urban or residential area
  • The job site takes place under a roadway, a railway, a waterway, a shore approach, or an environmentally sensitive area (e.g., parks, wetlands, lakes, bays)
  • The total installation length exceeds 180 ft.
  • The pipe is 5 ft. deep or more
  • The pipe is located beneath unstable soil or below the water table

Benefits of HDD

Horizontal Directional Drilling may be the best solution if traditional trenching or excavation methods are impractical. HDD offers many benefits over these methods:

Faster deployment

Unlike trenching or excavation, HDD requires less equipment and allows workers to set up more quickly. Because there is no need to dig an open trench along the entire project length (only at the start and end), HDD removes less material, allowing the drill to progress faster.

Not only does this make HDD projects naturally immune to weather like rain, hail, and snow, but there is also no need to rebuild the surface over the piping system. This eliminates a significant source of delays.

Increased flexibility

HDD is steerable and employs drill locator systems, allowing crews to adjust the drill’s direction as needed even if the pilot drilling process is underway. This flexibility makes it possible to drill around obstacles and create non-straight reamed passages.

This is in contrast to open excavation methods, where changes in direction and alignment are much more challenging and where the straightest path possible is needed to reduce costs.

Environmental impact

Because HDD removes less material and minimizes the amount of open digging required, this drilling method produces less noise, less waste and disrupts the environment above it the least.

The crew needs less machinery to move the waste out of the job site and fewer construction materials to repair the excavations. These characteristics make it highly practical around shores, lakes, rivers, wetlands, and other environmentally-sensitive zones.

Impact on traffic

Open excavations under roadways and intersections can significantly disrupt traffic flow, causing road closures, traffic congestion, and noise pollution.

HDD eliminates as many of these disruptions as possible. HDD drilling does not require road closures, resulting in fewer traffic cones. Pedestrians and vehicles can traverse the road, as usual, even when an HDD drill is working underneath.

The same principles apply to projects under railways. There is no need to close the railroad down and disrupt trains and other rail traffic to drill.

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