59 WorldWide Drilling Resource ® DECEMBER 2020 Microtunneling for Water and Sewer Pipelines Compiled by Bonnie Love, Editor, WorldWide Drilling Resource ing Resource ® One method of pipe installation for water and sewer pipelines is microtunneling. This process uses a remote-controlled microtunnel boring machine (MTBM) combined with hydraulic jacks to install pipes in a single pass. MTBMs have a rotating cutting head to drill through the ground, while a crushing cone is used to pulverize larger particles into pieces small enough to go through the slurry lines. It is ideal for running pipelines under highways, railroads, runways, harbors, rivers, and environmentally sensitive areas where a maze of underground utility lines may already exist. Microtunneling involves the following steps: jExcavating the launch and reception shafts at opposite ends of the tunneling drive. jHydraulic jacks are used in the launch shaft to push the microtunnel boring machine (MTBM) into the earth. jPipes containing slurry water transport excavated spoils to the surface. jThe jacks are then retracted and the slurry lines and control cables are disconnected. j Pipe or casing is lowered into the shaft and inserted between the jacking frame and the MTBM. j The slurry lines and control cables are then reconnected and the pipe and MTBM are advanced another drive stroke. This process is repeated until the MTBM reaches the reception shaft. jOnce the drive is completed, the MTBM and trailing equipment are retrieved, plus all equipment is removed from the pipeline. Known for safety, microtunneling features the following benefits: , Remote controlled - Since the MTBM is operated from a control panel normally located on the surface, operators do not have to enter the shaft. The system installs pipe while drill cuttings are being removed. , Guided - The guidance system typically uses a laser beam projected onto a target in the MTBM; it is capable of installing gravity sewers or other types of pipelines to the required tolerance for line and grade. , Pipe jacking - The process of constructing a pipeline by consecutively pushing pipes and MTBM through the ground using a jacking system for thrust. , Continuously supported - Continuous pressure is provided to the face of the excavation to balance groundwater and earth pressures. Microtunneling is a good option for small-diameter, unmanned tunnel boring projects. WTR Photo courtesy of the City of Portland, Oregon.
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