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Fig. 3: Overhead load applied to the tunnel Fig. 4: Waterproofing and ring girders being installed the conversion was accomplished with minimal down time. Temporary support of the overhead structures, which had a pile foundation that would be interrupted by the tunnel, would eventually be replaced by steel tube ring girders installed to permanently carry the load of the overhead structures once the transfer occurred. The shotcrete encapsulation of the ring girders was the first issue and we proved our methods were accurately represented during the mockup for the project. Due to the size of the girders, we used a layering method and encapsulated the backs of ring girders ahead of the reinforcement being installed. We then shot the remaining thicknesses during a follow-on mobilization (refer to Fig. 5(a) and (b) and 6). Another challenge, which was proven at the mockup stage, was the encapsulation of the No. 11 (#36M) reinforcing bar splices, which were (a) (b) Fig. 5: Mockup of ring girder shoot Fig. 6: Shooting the mockup lapped, leaving us only a 3.5 in. (90 mm) opening to shoot through. The next challenge was shooting a 36 in. (0.9 m) thick structural liner from spring line to spring line, mostly in the overhead position and finishing the project in less than 5 days. We attacked the project by working two crews per shift and two long shifts per day, with a cleanup and maintenance shift in between, with the wall segments being installed first, then moving to shooting the overhead areas. Due to the thickness of this liner, we used several methods to assist us in encapsulating all of the reinforcement. We placed the shotcrete with unique techniques developed by our team specifically for this application (refer to Fig. 7 and 8). All in all, Superior shot 1463 yd3 (1118 m3) and finished the tunnel with two shifts to spare. From the complexity of the tunnel reinforcement system, the large thickness, and the overhead Shotcrete • Winter 2016 35


2016WinterShotcreteEMag
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