Atlanta Builds West Area CSO Tunnels The West Area CSO tunnel in Atlanta will collect, convey and store up to 567.8 million litres of combined sewer overflow from the Clear Creek, Tanyard and North Avenue CSO drainage basins to a new dedicated CSO treatment facility at the R.M. Clayton Water Reclamation Center on Bolton Road. The alignment of the tunnel was determined so that wastewater flow could be intercepted from the existing trunk and relief sewers in the three drainage basins. The overflows will be stored in a large underground tunnel in bedrock. The geology is mylonite and gneiss. When a storm is over, the captured CSO volume is conveyed to a separate treatment system for removal of pollutants and reduction of harmful bacteria before discharge into the Chattahoochee River. The City of Atlanta is under a federal court mandate to have these tunnels operational by the end of 2007. The West Area CSO tunnel project comprises two legs, the Clear Creek tunnel and the North Avenue tunnel awarded in 2004 by the Department of Watershed Management to Atlanta CSO Constructors, a JV of Obayashi and MassAna. The construction manager is the JDH JV including Jordan, Jones & Goulding, Delon Hampton and Associates, and Hatch Mott MacDonald. Visit www.obayashi.co.jp/english, www.jjg.com, www.delonhampton.com and www.hatchmott.comThe Clear Creek tunnel consists of approximately 6,436 m of TBM tunnel, 8.2 m excavated diameter, 7.3 m finished diameter, and approximately 440 m of drill/blast tunnel, 3.35 to 7.3 m diameter. The North Avenue tunnel and pumping station includes approximately 7.2 km of TBM tunnel, with the same diameter, and approximately 540 m of drill/blast tunnel. The drill/blast connecting tunnels and pumping station are subcontracted to W.L. Hailey & Co.Other underground structures within the project include a 20.1 m-diameter 67 m-deep pumping station shaft, the 12.2 m-diameter 45.7 m-deep Clear Creek construction shaft, the 12.2 m-diameter 65.6 m-deep North Avenue construction shaft, a 7.3 m-diameter 45.7 m-deep overflow shaft, various raisebore shafts, up to 6.1 m in diameter, and three interceptor structures constructed using cut-and-cover techniques (through soil and rock), the largest at Clear Creek being 152.5 m long , 26 m deep and 12.2 m wide.The top headings for drill/blast connecting tunnels are being excavated using Reedrill MK65 two-boom jumbos and the benches are drilled using a Tamrock Commando 300. Mucking-out is done via Wagner ST-6 LHD. Visit www.reedrill.com and www.tamrock.sandvik.comTwo Herrenknecht 1,285-tonne hard rock TBMs are used for the TBM-driven tunnels. The length with back-up is 100 m (26 m without). The total installed main drive power is 3,150 kW and the total installed power is 4,200 kW. The expected compressive strength is 195 MPa, the highest expected being 340 MPa. The maximum rotation speed is 7.6 rpm, the maximum torque 9,472 MNm and the maximum thrust force 26.1 kN. The 8,230 mm-diameter cutter head is equipped with 52 19" cutters.The first TBM, christened 'Rocky', cuts the Clear Creek CSO tunnel from the 95 m-deep Rockdale launch shaft to the 45 m-deep Clear Creek reception shaft. The machine commenced its job at the end of July, with 13.8 cu m muck boxes. The TBM has begun mining with conveyors set-up. Currently 412 m has been tunnelled but a stretch of ground requiring full-ring steel ribs has been encountered. The second TBM, named 'Rocksanne', drives the North Avenue CSO tunnel from the R.M. Clayton access shaft to the 65 m-deep North Avenue reception shaft. That machine commenced working in mid-September. In early October, it had already bored 137 m. Tunnelling has been temporarily suspended on 10th October for approximately six weeks to allow installation of the conveyor belt. It is anticipated that machine will re-start mining shortly. Visit www.herrenknecht.comThe initial rock support consists of pattern rock bolts in Type A ground (RMR > 60); pattern bolts, welded wire fabric supplied by DSI and rolled channels for Type B (60 > RMR > 40); and rolled steel ribs/lagging in Type C ground (RMR < 40). The rock bolts are fully cement grouted 3 m CT-bolts supplied by Orsta Staal. The rolled channel/steel ribs are from American Commercial. Visit www.dsigroundsupport.com, www.ct-bolt.com and www.americancommercial.comOnce tunnelling of each tunnel is completed, a 7.32 m-diameter unreinforced concrete lining will be placed through an estimated 50% of the tunnel. Formwork will be provided by Wausau Everest.The rock haulage equipment includes 25-tonne Plymouth locomotives from Mining Equipment, horizontal conveyor systems supplied by DBT America and vertical belts supplied by FKC LakeShore. Visit www.miningequipmentinc.com, www.dbtamerica.com and www.frontier-kemper.com/lakeshore.html. Read E-News Weekly 13/2004. Click us/84. Visit www.cleanwateratlanta.org/CSOTunnels/default.htm 47/05. Click to enlarge image