Benefits of Directional Drilling:

Minimal disruption to road users, pedestrians and surrounding areas
Less disruption to the environment
Less use of newly quarried materials
Less waste to Landfill
Normal Surface operations can continue un-interrupted
Speed often quicker than open cut, especially over deeper and longer installations
More cost effective when all other related costs are added to open cut techniques

The typical technique for installing pipe by directional drilling uses a surface mounted drill rig that launches drill rods creating a string of rods (called the drill string) below the ground guided by a drill head that is directionally controlled by the drill operator.

The direction of the drill is along a pre-determined path (called the drill path) based upon the above ground and below ground, pre-construction investigations of the site. A locating device is used during the drill to track the location of the drill head so that the operator may make adjustments as necessary. A small diameter pilot hole is drilled from the entrance point (typically in a sending pit) to the desired exit point (receiving pit). It is necessary to use a drilling fluid during drilling to lubricate and protect the pipe, and to maintain the size of the hole being opened. Following the exit of the pilot drill bit, the hole is then enlarged by the use of a backreamer attached to the end of the drill string which is pulled back through the pilot hole. As the backreaming takes place, the pipe being installed is also pulled into the hole. 

Below you can find the typical process of Directional Drilling

A.) Pilot Hole
The pilot hole is the beginning of the Directional Drill crossing. The Pilot hole is achieved either by excavation by jetting or by a down hole motor. Depending on the condition of the soil the pilot is drilled along a pre-determined alignment in which the path is selected by traditional methods. The typical pilot hole on most rigs is 120mm but can vary depending on the soil conditions and rig size. Drilling fluid is pumped through the drill pipe to the drill head at which time it is jetted through or pumped through a drill motor. The end of the Drill Pipe is to core the pilot hole. The drill fluid lubricates the drill stem and carries out the cutting to the surface. The drill fluid is then recycled and re-injected into the drill stem. The pilot process can take several days, depending on the condition of the soil and may require changing of the drill stem or drill head.

 B.) Reaming Process
Once the pilot hole has been completed the 2nd step takes place with a reamer, or hole opener. The hole openers come in different shapes and sizes and vary depending on the soil conditions and density of the soil; typically a fly cutter is used in good ground conditions. The reaming pass is done in several steps depending on the size of the hole, (example: 600mm finish hole would be 3 different ream passes 250mm, 350mm, 500mm). The reamer is attached to the drill string and is rotated and pushed or pulled while rotating and drill fluid is pumped to the reamer through the drill pipe. The excavated soil is suspended in the drill fluid and then brought to the surface and recycled or disposed of in the appropriate environmental manner. When the reamer is attached to the Drill string there will always be a drill pipe on both sides of the reamer allowing for the drill string to be in the hole at all times. The reaming process can take a significant amount of time depending on the condition of the soil.