Second Stage of Big Walnut Interceptor Tunnel Breaks Through in OhioThe Big Walnut Augmentation/Rickenbacker Interceptor (BWARI) project is part of an overall programme for the City of Columbus, Ohio, intended to significantly increase the capacity of its sanitary sewer system. The BWARI tunnel project includes approximately 11.2 kilometres of earth pressure balance tunnelling and is made up of two parts. Part 1 of the BWARI project was awarded in September 2003 to a joint venture of Jay Dee, Michels and Traylor. Click here. Part 2, which is also known as the Big Walnut Outfall Augmentation Sewer (BWOAS), was awarded to the McNally-Kiewit Construction joint venture in October 2004. Both tunnel contracts and the associated southerly waste water treatment plant are expected to accept flow in July 2008. The Lovat RME167SE series 21500 TBM, owned by the McNally-Kiewit joint venture, has broken through the Big Walnut Outfall Augmentation Sewer (BWOAS). The 4.2 m-diameter mixed face, earth pressure balance TBM attained daily production rates of up to 24 rings erected during excavation of the 4,084 m-long tunnel. Weekly performance of up to 79 rings was achieved, with best mining and ring build times of eight minutes and 17 minutes, respectively. Visit www.lovat.com, www.mcnallycorp.com or www.mcnallytunneling.com and www.kiewit.comGeological conditions consisted primarily of two types of soil deposits, glacial-till and glacio-fluvial / outwash materials, with uniform fine sands also encountered. Gravel, cobbles, and boulders were also present during portions of the alignment, located below the groundwater table for its entire duration. As the tunnels were classified "potentially gassy", the TBM was designed in compliance with regulations for operation in a Class I, Division II hazardous location.The Part 2 (BWOAS) project included the construction of a launch shaft, four intermediate shafts and the main shaft site. The main site was prepared for the arrival of the TBM by late summer 2005.The BWOAS innovative segments are a "hybrid" design using both steel fibres and standard steel reinforcement in combination to provide the strength required for the tunnel structure. These segments have been manufactured by the North American Segment Company, a McNally company. Click us/39. 38/07.