Tunnel Business Magazine

OCT 2018

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TUNNELINGONLINE.COM 1 5 TBM: TUNNEL BUSINESS MAGAZINE // OCTOBER 2018 further 17 million gallons of overflow can be diverted through an Enhanced High Rate Treatment (EHRT) process that will allow the water to be directly released into the Little Cuyahoga. The EHRT is a separate project that will be completed in the future. The tunnel will pull from nine main regulators referred to as racks (overflow spots) along a narrow corridor to achieve the water storage, while the city's other overflow spots are being controlled through storage basins, sewer separations, maximizing conveyance and green infrastructure. Unique TBM Design The Crossov - signed for the project's geology, which transitioned from soil to partial face shale to full face shale rock. The Cross- over XRE included features of both EPB and Hard Ro es, with a versatile cutterhead that could be configured for hard rock or soft ground conditions. The cutterhead design was built to specifically address a major problem for mixed gr t of abnormal flat and multi-flat cutter wear, resulting in the cutter wearing flat on part of its surface. Abnormal wear is a consequence of the soft ground encountered, which cannot provide sufficient rolling force for cutters to overcome the pre-torque of cutter b tterhead was equipped with 56 housings that could be dressed with either knife bits/rippers or 17-in. disc cutters. Due to geologic variability, the contractor JV of Kenny/ Obayashi and Robbins decided that disc cutters would be beneficial from the outset, and launched the machine with a full dressing of discs. In consideration of the 65% drive in rock, the cutterhead was also dressed with Hardox 450 faceplates to reduce the risk of abrasive wear. When boring in soft ground, it was decided to reduce the pre-torque of the cutter bearings by 25% to require less rolling force for each cutter to rotate evenly. Furthermore, in order to avoid hyperbaric intervention in the first 1,610 ft of boring, sacrificial rippers were welded to intervene in case of ring wear greater than 0.6 in. In the event a cutter becomes blocked, rippers enable continued cutting of the face until the machine reaches a section where it can operate in open mode. The screw conveyor was another customized comp is a shaft-type design, 64.5 ft long, 47 in. in diameter, with a tapered front nose to 30 in. In consideration for the OCIT geology and the necessity to muck out shale bedrock, the single shaft-type screw conveyor required a much higher speed than would normally be provided. The hydraulic power unit had an output of 5x110 kW, which brought the max theoretical speed of the conveyor to 16 rpm at a limited torq In both rock mode and mixed ground, and to a lesser degree in EPB mode as well, the auger and the casings were in contact with abrasive material creating wear. The screw conveyor was designed for an abrasive environment, with the leading face of the front auger flight and the outside diameter covered with welded-in wear plates made of Chromeweld 600 – a premium grade of chromium carbide wear plate – and hardfacing in a crosshatch pattern. The auger shaft was also covered in a crosshatch pattern of hardfacing. In addition, the inside diameter of the casing was similarly reinforced with Chromeweld 600 for the first 1/3 of the casing, followed by hardfacing in the remaining 2/3 of its length. Ports in the screw enabled injection of foam, bentonite, or other lubricants. Landmark Conveyor System Behind the Crossov obbins Continuous Conveyor system for muck re- The 30.4 ft diameter Robbins Crossover TBM was designed and built in Robbins' Solon, Ohio, USA facility. C O V E R S T O R Y

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