E-19 Sequin Road to Nacogdoches Road, Segment 1

Completed in 2020 by Southland Contracting, the E-19 Sequin Road to Nacogdoches Road, Segment 1 Project consisted of the replacement and upsizing of 3.1 miles of 48-inch gravity wastewater mains with larger 78-inch mains, as well as the elimination of one siphon and the abandonment of the existing 48-inch main. The project included 6,340 linear feet of 96-inch microtunnel with nine individual drives. Three of the drives were over 1,000 feet with the longest being 1,325 feet. Each tunnel consisted of jacking 96-inch steel casing with a Herrenknecht microtunnel boring machine (MTBM), followed by the installation of 78-inch Hobas fiberglass reinforced (FRP) sewer pipe. The bore depths for each drive were in the 25 to 30-foot range. The project was unique in that a portion of the tunneling was below the Fort Sam Houston military installation. The project team worked closely with military officials to achieve construction goals while helping to maintain security and traffic circulation for the base. In addition, approximately 100 linear feet of tunnel was constructed under the Union Pacific railroad. The open cut portion of the pipe was installed at depths in excess of 35 feet in a narrow street right-of-way. Portions of the open cut and tunnel were installed in solid rock. The ground conditions varied, but in general, it was a sandy gravel mix on top, a clay mix in the middle, and a hard dense clay shale at the bottom that required hammering or other mechanical excavation methods. The northernmost 10,000 feet of the job was installed approximately 50 feet off of a major waterway, which resulted in wet and challenging ground conditions needing extensive dewatering. The scope of work also included multiple manholes, an 8-inch water line, a 16-inch water line, an 8-inch sewer line, a 10-inch sewer line, bypass pumping, pavement restoration, and road construction. The bypass required four 18-inch pumps to handle the 35 million gallon per day flow of the existing sewer line.