TABLE OF CONTENTS A basic horizontal-directional drill-rig is illustrated in Figure 3-1. Horizontal directional drilling is accomplished using a drill rig. It services a bottom-hole assembly (BHA) that is responsible for creating a curved bore hole. The BHA consists of a drilling tool that is capable of creating a curved bore hole and a guidance system that locates the bore hole and directs changes in the trajectory. There is a variety of HDD rigs currently in use. Table 1-3 lists the three general categories of drill rigs typically used in the HDD industry. Directional drill rigs currently used in HDD typically consist of a carriage that slides on a frame and holds the drill rods at an angle of 0 to 25 degrees. In most cases, hydraulic power is used to energize a motor on the carriage that rotates the drill rods. A chain drive or rack-and-pinion drive is used to push or pull the carriage to advance or retract the drill string.
Drill rigs are available in a range of sizes and are distinguished chiefly by the torque and push/pull force they provide. Despite the range in sizes and details offered by particular manufacturers, the rigs share some common features. The drill rig provides thrust to the drilling tool and pullback to the drill string. When drilling a vertical bore hole, the downward force on the drill bit is provided by the weight of the drill motor and the drill string. While...
