ABSTRACT
Trenchless excavation techniques have been developed to allow installation of underground pipes, conduits, and tunnels with minimum or no surface disruptions. Compared to open-cut trenching, going trenchless results in minimal surface disruptions, and, reduced inconvenience to the general public, including safety hazards, loss of access, and damage to the surface environment. There are several trenchless techniques, including horizontal directional drilling, microtunneling, pipe bursting, and sliplining. Due to their cost and lack of versatility, however, the use of trenchless equipment is usually limited to situations where it is important to reduce environmental impact of trench excavation or to avoid existing obstacles, such as rivers, roads, existing facilities, or rails. The drilling is performed by a mobile, steerable tracked piece of equipment with an inclined carriage, which is often called the drill rig unit. As the pilot hole is being drilled, bentonite drilling mud is pumped down the center of the drill rods.
