By rosebell
While on July 22, TBM Mary erected the landmark ring, just 193 rings was leaved to go before breakthrough on the second of the twin-bore tunnels. The scheduled date for completing excavation is the autumn.
Considering that TBM Mary is boring the uphill climb to the South Island, it is encountering fine grained soils, such as clay, as the Virginia Department of Transportation (VDOT) says in its latest project update.
The TBM record was installing 66 rings during one week in June, that achieved in large part because of the work of Katherine the Slurry Treatment Plant. Katherine processes approximately 600 tons of soil per ring before the spoils are transferred to barges for disposal.
According to the VDOT: “Katherine was able to make quick work of the coarse-grained sandy soils found deep beneath the bay bottom. The top layers of the bay stretch Katherine and her limits to quickly process spoils, removing soil particles half the thickness of a human hair in size. These fine particles require more time to separate from the slurry and result in a more moderate pace as Mary reaches the end of her work.”
Thanks to TBM Mary’s steady pace, the second bore may be completed faster than the 51 weeks taken to completing the first tunnel.
The concrete pours for the TBM cradle where the cutterhead and shield is due to rest in the receiving pit after breakthrough, has been commenced by Hampton Roads Connector Partner crews on South Island.
Also the process of completing tie-ins to the mega-trestle connecting the tunnels to the Norfolk shoreline, is undergoing by Island and trestle crews.
While the fit-out works inside the HRBT’s first bored tunnel continue, since June crews have completed placement of the tunnel’s roadway base along the entire length of the tunnel, allowing completion of the tube’s new egress structures and drainage systems.
In order to supporting the collection of water, as well as the pumping of water back to the surface for treatment, over than 610m of pipe has been laid in the new tunnel, whereas aater main and fire main installations are also progressing steadily. In addition, over 1,500m of L-wall and more than 610m of plenum wall have been constructed to support the tunnel’s emergency egress corridors.
On the new eastbound tunnel TBM Mary is currently boring, phase one of ballast placement is nearly 20% complete.
