Horizontal directional drilling (HDD) is a trenchless method for installing pipes, ducts and cables below the surface. Instead of digging a continuous trench, a drilling rig creates a steerable underground bore between an entry point and an exit point.
A typical crossing has three stages. First, a small pilot hole is drilled along the designed path, with the drill head tracked and steered as it advances. Next, the hole is enlarged with reamers to the diameter required. Finally, the product pipe or duct bundle is pulled back through the bore.
Drilling fluid — usually a bentonite-based mixture — cools the tooling, carries cuttings to the surface and supports the bore wall. Managing and recycling this fluid properly is an important part of a clean, safe operation.
HDD is often the preferred choice for crossing roads, railways, rivers and built-up or environmentally sensitive areas. It avoids closing traffic lanes or disturbing watercourses, and it greatly reduces the reinstatement work that follows open-cut trenching.
Good results start with good information. Before a crossing is designed, it helps to have details of existing underground utilities, the ground conditions along the route, the pipe material and diameter, and any permit requirements from the relevant authorities.
