Trenches are often required to be created for installing underground utilities, like water pipelines, sewers, cables and many other facilities that can be used to deliver the required services at any point. Trenches can cause a lot of disruption at the surface, especially when they are required to be installed next to roads, which is an alignment commonly chosen.
All this inconvenience can be avoided if use is made of trenchless installation. Pilot tube auger boring is one such method that allows for pipes and other utilities to be installed from shafts located along the alignment of the pipes. These shafts are located at a fair distance from each other, thus greatly reducing the disturbance to the surface. The equipment in this form of boring consists of a pilot tube assembly that has a segment of a pilot tube and a steering head that is mounted to this segment. The steering head will guide the pilot tube from the first shaft to the second one. There is an intermediate sleeve assembly that has a cutting head which is the auger. The diameter of the cutting head is greater than the pilot tube and its direction of cutting is guided by the pilot tube.
An enlarging cutting head that has a drive sleeve assembly has a diameter greater than the diameter of the intermediate sleeve assembly, is the next part of a pilot tube auger boring device. The drive assembly advances the pilot tube assembly, the assembly that has the intermediate assembly, the product pipe from the first shaft to the location of the second shaft. Once the product pipe has reached the second shaft, the monitoring equipment is shifted to the second shaft and a similar operation is conducted to reach the next shaft. In most cases, shafts are located at distances of about a 100 meters, though some equipment has been known to be used for double this distance. The shorter distances help to maintain accuracy, especially where grade and line are very important, as in the case of sewers that operate through gravity.
This form of boring using a pilot tube is best suited to cohesive soils that are above the water table. It may not be the right solution where the ground is rocky and has a lot of gravel or boulders. Microtunneling, which is another form of trenchless excavation, is more suitable for these types of soils.