Beyond the straight and narrow

The first curved microtunnelling project in the United States was successfully completed in late May.

Northeast Remsco Construction has completed construction on a curved microtunnel in Hartford, the capital of Connecticut. According to the company, this is the first curved microtunnel to be planned in the United States.

The tunnel boring machine (TBM) undertook a curve of 414.2 m radius for a length of 48.8 m, and reached the receiving shaft with horizontal and vertical breakthrough accuracy less than 1.3 cm.

The 182.9 m tunnel was constructed on behalf of the Metropolitan District Commission, and forms part of Hartford’s $US1.6 billion “˜Clean Water Project’, which aims to reduce overflows in the local sanitary sewer system.

Microtunnelling was used to construct a section located between shafts MHD and MHK, due to the density of surrounding utility services. Following a detailed study of the route and potential obstacles, it was established that the drive would need to be curved.

The route was designed by AECOM, and who had to modify the precise alignment on several occasions due to the complexity of the obstacles.

The TBM used for the drive was a Herrenknecht AVND 1800AB MTBM, equipped with a SLS Microtunnelling LT guidance system supplied by VMT GmbH. VMT also supplied an experienced engineer to oversee the guidance of the machine.

The machine reached the receiving shaft after nine days of tunnelling, and the project was successfully completed on 19 May.

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