MICROTUNNELING BETWEEN PILES FOR PIPELINE REPLACEMENT

The presence of piles supporting primary clarifier basins, along with the risk of settlementinduced damage, led to the use of microtunneling techniques to replace primary sludge drain pipelines at the Jones Island Wastewater Treatment Plant in Milwaukee, Wisconsin. To avoid the clarifier support piles a Soltau RVS 80 microtunnel boring machine was used to replace the 6-inch-diameter pipelines, which were installed 30 feet below the surface. The Soltau boring machine utilized an innovative laser-guided, steerable pilot tube to establish a pilot alignment between the support piles. When obstructions causing refusal conditions were encountered, the steerable pilot tube was retracted and the pilot alignment was adjusted. The pipeline was then jacked in place behind an auger that followed the pilot tube alignment. This installation method minimized the risk of damaging the support piles and significantly contributed to the success of the pipeline replacements.