This project is the most northern leg of the TARP system. To date 7.315 km (24,000 LF) of 6.7 m (22 ft) diameter and 8.230 km (27,000 LF) of 9.14 m (30 ft) diameter rock tunnel has been mined by Jarva TBMs. In addition, 32 drop shafts and 2 work shafts have been completed. This paper presents a discussion of the tunnel and shaft operation with an emohasis on the tunnel TBM operation, tunnel muck handling system, and shaft downhole rock drill and clay seams encountered in a rock tunnel.
This contract is the most northerly portion of the Metropolitan Sanitary District of Greater Chicago's Tunnel and Reservoir Plan (TARP). The project begins at Addison Street in Chicago and proceeds northerly approximately ten miles to end at Wilmette Harbor and Lake Michigan. The project which consists of 2 work shafts, 32 drop shafts, 7.322 km (24,020 ft) of 6.7 m (22 ft) diameter circular rock tunnel, 8.458 km (27,750 ft) of 9.2 m (30 ft) diameter circular rock tunnel and miscellaneous rock bolting and grouting, was bid for a total cost of $63,140,480. The tunnel invert elevation varies from 65.5 m (215 ft) to 77.4 m (254 ft) below the ground surface, which places the tunnel in a rock formation of dolomite limestone. At the tunnel invert, the unconfined compressive strength of the limestone varies from 965 bar (14,000 psi) to 1516 bar (22,000 psi). The 6.7 (22 ft) diameter tunnel required the mining of 10.9 cu m (14.2 cyd) of rock per lineal foot of tunnel while the 9.2 m (30 ft) diameter tunnel required the mining of 20.1 cu m (26.3 cyd) of rock per lineal foot of tunnel. The total cubic meters of rock required to be excavated from both tunnels was 818,821 cu m (1,070,978 cyd). All of this will be mined by tunnel boring machines (TBM). These tunnels were not to be lined with concrete. The 32 drop shafts have upper portions that are cylindrical in the overburden and rock sections. They were divided into two groups, depending on diameter, with a different construction method for each group. The first group consisted of 23 of the smaller sized shafts, which ranged from 1.83 m (6 ft) to 3.34 m (11 ft) in diameter. The overburden portion of these shafts was drilled by a crane mounted auger, which placed a circular steel liner to retain the silts and clays. The depth of the overburden for these shafts varied from 17 m (56 ft) to 36 m (117 ft). The rock portion of these shafts ranged in depth from 27 m (90 ft) to 55 m (180 ft) and was drilled using a blind hole shaft drill. The second group of drop shafts consisted of nine of the largest sized shafts having a diameter that varied from 4.3 m (14 ft) to 5.2 m (17 ft). The overburden portion of these shafts was excavated by a clamp bucket mounted on a crane.
