The International Information Center for Geotechnical Engineers

Tuesday, 20 November 2018 01:00

TBM breaks through hard granitic rock on Atlanta water tunnel

TBM breaks through very hard rock on Atlanta water tunnel TBM breaks through very hard rock on Atlanta water tunnel.

The Tunnel Boring Machine (TBM) that was used to achieve Atlanta's water supply tunnel overcame extreme hard rock conditions.

The 3.8-meter diameter Robbins Main Beam TBM completed its 8 kilometers mission on October 4, 2018. The new tunnel is expected to increase the water capacity of Atlanta by 30-90 days depending on the daily usage. 

The TBM was ready to operate by October 2016. It was assembled at a quarry using Onsite First Time Assembly (OFTA) with help of Robbins stuff that worked under high temperatures and extreme humidity. "The guys built everything per the specs to help with scheduling. It was a challenge but there was no negativity during the process," said Larry Weslowski, Tunnel Superintendent for the PC Russell JV.

The advance of the machine was highly challenged by hard granitic rock. In order to overcame the stiff rock-mass, 19-inch disc cutters were used. Weslowski stated: "There was ground so hard that it would take eight hours to go 1.5 m. It was between 117 and 310 MPa UCS (Uniaxial Compression Strength). The beginning of the job was tough." However, once the team adapted to the characteristics of the excavation, "they started breaking project records left and right towards the end. We got a best day of 38.4 meters. Rates just kept increasing." The project also faced some issues with contamination of the groundwater but they were addressed successfully.

Bob Huie, Project Director of the PC Russell JV, the Construction Manager at Risk (CMAR) for the project stated: "Our schedule for the project was very aggressive but the project team stayed together to overcome issues related to the mining of the tunnel." Personnel is responsible for the success of the project. "I'm proud of our team. They had obstacles and challenges and challenging ground, but they stuck together and didn't give up, and they were successful. There was great leadership and supervision all around," Weslowski added.

The $300 million facility is now heading to its completion. The inactive Bellwood quarry will be transformed into a 9.1-billion-liter water storage facility.

Source: Canadian Underground

Read 343 times Last modified on Tuesday, 20 November 2018 15:10

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