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2014SumShotcreteEMag

Goin’ Underground Due to safety concerns over having crews shotcrete pumps and in the event that there was working directly below freshly applied shotcrete an issue with the wet-mix material supply. while installing the inside layer of WWR, it was decided to apply all overhead shotcrete in two Summary passes. Using this approach, the inside WWR of The project provided an opportunity to learn a round was installed during the outside mesh and about the challenges of applying shotcrete on girder installation of the following round. Identi- frozen ground. Using WWR, No. 7 (No. 22M) cally, the second shotcrete pass of a round was reinforcing bar, and lattice girders, it was possible applied immediately after placing the initial pass to shotcrete an initial self-supporting shell that on the following round. Using this approach, the could support the structural shotcrete thickness next operation following shotcreting was excava- and prevent any loss of ground (Fig. 4). tion and no personnel—only the stick of the excavator—was exposed to potential shotcrete fallout (Fig. 3). Shotcrete was applied using a small track- Paul H. Madsen received his mounted robot, except for the invert shotcrete in the BSc in civil and construction center drift, which was applied using a 2 in. (50 mm) engineering at the Engineering hand nozzle suspended from the stick of the exca- College of Copenhagen, Copen- vator. This solution was required to properly shoot hagen, Denmark, and his MSc the tight areas at the connection points to the lower in soil and rock mechanics at sidewall drifts below the temporary sidewalls. Heriot Watt University, Edin- The shotcrete was pumped from the surface to burgh, Scotland. He has over the headings through a 4 in. (100 mm) slick line 20 years of underground experience as a contrac- using shotcrete pumps with an integrated accel- tor’s Geotechnical and Tunnel Engineer as well erator dosing system. This setup allows for proper as Tunnel Superintendent and Project Manager quality control of the accelerator dosing and ulti- with Kiewit Infrastructure Co. Projects include mately the strength performance of the mixture. Storebaelt Tunnel in Denmark, Devil’s Slide in A dry-mix shotcrete setup using bagged California, and recently the Northern Boulevard materials was kept as backup for the two wet-mix Crossing in New York. Fig. 4: Completed tunnel Shotcrete • Summer 2014 45


2014SumShotcreteEMag
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