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What are Microtunneling Wet Retrievals?

Find out more about this unique process

Microtunneling is a remote-controlled system for the trenchless installation of an underground passageway. Because it is a closed-face system, it can be successfully operated from a shaft on land to a pre-determined underwater endpoint. It can be used to mine outfall and intake pipes.

Here are five terms to help you learn about this operation, known as a wet retrieval.  

Microtunneling - Microtunneling is the installation of casing pipe with a remotely controlled, steerable machine. Despite its name, microtunnel projects are not tiny. Actually, Michels’ most recent microtunneling projects have averaged more than 80 inches – or 6 ½ feet – in diameter. However, mictrotunneling is smaller than conventional tunneling, which can create passages larger than 50 feet in diameter.

Wet Retrieval - Once a tunnel is completed, the machine is pressurized, disconnected from the pipe and pulled out of the water with a crane. The crane can be located on a barge or on land, depending on how far the tunnel extends from shore.

Casing - A casing pipe is able to withstand jacking forces and other construction forces. Steel casing pipes are common in the microtuneling industry.

Drive - A drive is a section of casing pipe installed from a jacking (launch) shaft to a receiving shaft.

Bulkhead - Bulkheads are temporarily installed between the mictrotunnel boring machine (MTBM) and the end of the casing to stop water from flooding the casing after the MTBM is removed.

Interested in learning more about the winning project and seeing the wet retrieval from the surface? Watch this video.

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