ADVANCED MICROTUNNELING TECHNOLOGY OFFERS NEW APPROACHES TO SEWER DESIGN AND CONSTRUCTION

Increasing emphasis on eliminating combined sewer overflow (CSO) and sanitary sewer overflow (SSO) will expand the need to construct new sanitary sewers in congested urban areas. Recent advances in the pilot tube system of microtunneling (PTSM), offer several advantages over other available systems for constructing 6-inch to 18-inch inside diameter sewers in areas where there is congestion, where the sewers are deep or where it is desired to minimize disruption at the ground surface. PTSM uses 8-foot diameter or smaller construction shafts, allowing a small surface footprint. Theodolite guidance produces better than plus or minus 0.1 foot line and grade accuracy anywhere along the finished sewer. Less sophisticated equipment and specialized construction techniques make the system cost effective. The City of Cape Girardeau, Missouri saved about 15 percent over open cut construction by allowing PTSM installation of about 40,000 feet of sewer.Features of the method may make it possible to modify some of the standard approaches to sewer project location and construction. Sewer separation becomes a more feasible alternative for addressing CSO. The small diameter construction shafts limit impacts on traffic, perhaps making it feasible to construct more sewers in public right-of-way. Construction on public property can minimize or eliminate the need for permanent and temporary easements, a time consuming and sometimes costly sewer project activity. Significant design and construction dollars can be saved by allowing the construction contractor to determine the final location of manholes and the final elevation of sewer inverts. PTSM is a new tool in the sewer construction toolbox.