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2017SpringShotcreteEMag

Fig. 5: Reinforced beam section in upper-level arch of TT#1 structure REINFORCING BAR Some areas of the project contained extremely heavy and congested reinforcing bar layouts, including the upper level of TT#1. This structure was the intersection of four tunnel segments and an intersecting cross passage with an arch that contained a double mat of No. 11 and No. 9 (No. 36M and No. 29M) bars at 6 in. (150 mm) spacing and four beam sections. The combination of lap lengths, stirrups, and bars transitioning from the inner to outer mats at the interfaces in this reinforcing bar design forced the shotcrete to be placed in one lift. SHOOTING Shooting this area in one lift required the constant movement of the nozzleman shooting from different angles through the reinforcing bar as well as an adjacent worker with an air lance to constantly remove rebound and material from the outer layer of reinforcing bar to achieve proper consolidation. This was especially important in the reinforced beam section where concrete depths from the face were up to 24 in. (600 mm). It was also necessary to untie select reinforcement from the outer reinforcing bar mat when shooting the inner mat to provide good access for shotcrete placement, especially during placement in the beam sections. The untying of selected reinforcing bars, especially in the areas adjacent to the beams, gave the nozzlemen better shooting angles and the ability to place the nozzle further past the outer reinforcement layer. After the shotcrete was properly consolidated and placed beyond the inner mat, the reinforcing bar was reinstalled and the placement in that area continued. The use of universal ring lock scaffolding provided a continuous and extremely stable platform for the overhead shotcrete operations. A rubber float finish was provided on the approximately 1500 ft2 (140 m2) surface area of these placements. ADDITIONAL MAJOR STRUCTURES The tunnels and cavern arches were two additional major structures on the project that benefited from the use of Fig. 6: Upper-level arch of TT#1 structure, tunnel, and crosspassage interface Fig. 7: Upper-level arch of TT#1 structure, tunnel, and crosspassage interface (opposite view) Fig. 8: Shotcrete wireman installing z-bars and pencil rod for grade control on running tunnel section shotcrete. The tunnels that used shotcrete placement were located on the upper level of the project between two major caverns. Their isolated location made shotcrete the perfect process for placing the structural liners because the forms could not easily reach this area. The tunnel sections had an arc length from invert to invert of 52 ft (16 m) with No. 6 and No. 7 (No. 19M and No. 22M) reinforcing bars spaced at 12 in. (300 mm). www.shotcrete.org Spring 2017 | Shotcrete 13


2017SpringShotcreteEMag
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