THE FIRST MAJOR PILOT TUBE MICROTUNNELING PROJECT IN THE ST. LOUIS METROPOLITAN AREA

The pilot tube method of microtunneling (PTMT) was selected to construct the Black Creek Sanitary Relief Sewer project for the Metropolitan St. Louis Sewer District. The project is located in the parking lot of a major metropolitan retail mall. This project consists of the installation of approximately 580 m (1,900 ft) of 450 mm (18 in) gravity sanitary sewer installed at depths up to 7 m (23 ft). Minimizing impact and maintaining traffic flow was critical to the mall and adjacent major arterial streets. PTMT was selected as the installation method due to its smaller surface lay-down requirements and smaller jacking and receiving shafts. The contractor selected 2.4 m (8 ft) round shafts and a 3-step installation process utilizing a powered cutter head due to challenging soil conditions which included high blow-count soils, creek gravel, and shale. Even with handling these soil conditions, the final product pipe has been successfully installed to within a 10 mm (⅜ in) tolerance or better for line and grade accuracy at distances up to 85 m (280 ft). This paper will discuss the process of PTMT, the reasons that it was chosen as the installation method, design considerations, construction process, and the social-impact that it had on the mall and surrounding area.