Pilot Tube Microtunneling Proves Effective Under Busy Houston Street

By Jeff Griffin, Senior Editor | September 2008 Vol. 63 No. 9

Many underground utility projects are necessary when construction for a variety of improvements requires relocation of existing buried infrastructure. In such situations, work often is complicated by surface improvements and heavy traffic in and around the job site.

A good example is a recent project in Houston that required improvements to a portion of the city's sanitary sewer. The Westheimer to West Alabama Sewer Relocation Project was located on one of Houston's busiest thoroughfares and excavation would have caused major disruptions of traffic, making trenchless construction the best option for most segments of the project. Wet boring, pilot tube microtunneling and a limited amount of open cut construction were used to complete the project.

Magnum Tunneling, LLC, used the pilot tube microtunneling method to install 2,440 linear feet of Mission Clay No Dig pipe in diameters of 8, 10 and 12 inches. Magnum was a subcontractor for ACM Contractors, Houston.

"Pilot tube microtunneling enabled pipe to be installed while maintaining continual traffic flow during construction," said Patrick L. Mann, Magnum’s chief operating officer.

All about pilot tube

The pilot tube procedure provides many of the advantages of conventional microtunneling for installation of smaller diameter pipes at shorter distances and at significantly lower costs than microtunneling installations of larger size pipes.

Unlike conventional microtunneling, a pilot tube installation establishes line and grade with a small diameter pilot tube before pipe is jacked into place.

The hollow pilot tube provides the optical path for the theodolite to display head position and orientation for steering the path of the tube. Sections of tube are added as the drive continues, connected by hex connectors with threaded couplings. Spoil from the pilot tube installation is displaced for removal. As the drive progresses, pilot tube pipe joints are removed in the receiving pit. Pilot holes are enlarged by backreaming to accommodate the outside diameter of the pipe being installed, and spoil is removed by an auger system.

Pilot tube installations employ smaller, less expensive equipment, require smaller jacking pits, and topside footprints require less space than conventional microtunneling projects. Pilot tube projects generally are for pipe from 4 to 12 inches in diameter and for drives to distances of 250 feet.