microtunneling

Microtunneling is a trenchless construction method used to install pipelines and conduits beneath obstacles such as roads, railways, and buildings with minimal surface disruption. It employs a remotely controlled tunnel boring machine (MTBM) that is advanced from a launch shaft toward a receiving shaft. The bore is aligned and steered during advance, typically using laser guidance and reference targets, and the pipe string is installed behind the MTBM as the machine progresses.

Construction begins with the excavation of launch and receiving shafts and the setup of jacking equipment. The MTBM is typically guided remotely by operators from the surface, while hydraulic jacks in the launch shaft push the machine forward. Ground support and stability are provided by grout injected around the leading face and along the annulus. Spoils are removed from the tunnel by a slurry system or pumped muck, and pipe segments—usually steel or reinforced concrete—are installed behind the machine and connected to form the bore liner.

Advantages include limited surface settlement, suitability under existing infrastructure, and the ability to cross obstacles without excavating along the route. Limitations include high capital costs, dependence on favorable soil conditions, the need for access shafts, and restrictions on curvature and alignment changes. Typical diameters range from a few hundred millimeters to several meters, with project lengths ranging from tens to hundreds of meters.

Common applications are potable water, wastewater, and stormwater pipelines, as well as conduit installations for electrical and communication cables beneath roads, railways, or rivers in urban areas.

Microtunneling was developed in the late 20th century as a precision trenchless technology and has since been adopted worldwide for urban underground installations, often as part of comprehensive utilities upgrades and new interceptor projects.