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US breakthrough marks completion tunnel machine’s 12th scheme

Sak Construction has celebrated breakthrough on construction of a new 945m hard rock tunnel in the US but the tunnel boring machine (TBM) has now clocked up more than 40km of tunnels.

The 3.4m diameter Robbins Main Beam TBM was originally bought for a hydroelectric scheme in Austria in 1981 and the work in St Louis, Missouri was its 12th scheme.

Before starting work on the Lemay Redundant Force Main in February this year the machine was refurbished to cope with driving the tunnel through the limestone and dolerite rock at St Louis. Despite rock strengths of up to 130MPa, the machine achieved rates of 39m in one day and up to 158m in one week during the drive.

Support for the excavated tunnel is provided by two 1.4m long resin encased rock bolts installed at 1.2m intervals and 1.2m by 1.2m wire mesh panels and steel straps installed in the crown where ground conditions were more challenging.

Work is now underway to install a secondary lining and completion of the work will enable Lemay Wastewater Treatment Plant to accept a higher volume of wastewater and enable the existing force main to be inspected for the first time since its construction in the 1960s.

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