Page 43

2013SumShotcreteEMag

Goin’ Underground shooting location to the next, the pumps withstood past performance before the program took effect, the abuse and operated successfully. was 40 yd3 (31 m3) of shotcrete placement per According to the specifications, all the large- volume shooting was to be done with wet-mix (refer to Fig. 3). Some smoothing or short patching was handled with dry-mix. For the most part, the dry-mix placement on the project employed full skid-mounted guns with pre- dampeners from Putzmeister. The dry-mix mate- rial supplier used, after a thorough vetting process, was King Packaged Materials Company. The crews had to understand more than just basic shotcrete (refer to Fig. 4). We used a sophis- ticated shotcrete mixture that included hydration control chemical dosing of concrete intended to sit for hours, yet remain plastic and pumpable without separation; be pumped up to and beyond 2000 ft (600 m); and make it to the nozzle without plugs despite being fiber-reinforced. Especially in overhead areas, the shotcrete material needed to have an accelerated set once sprayed, yet retain some plasticity for shaping or rough finishing. Each nozzleman could see firsthand how Fig. 5 important angle, velocity, mixture design, and equipment manipulation (such as man lifts) were to the overall success of the job. Our job was always made more diffi- cult by the requirement to add reinforce- ment to some of the rock substrate (refer to Fig. 5). Welded wire was attached to the rock bolts, and, on occasion, a metal mine strap was adhered to potentially loose rock material. These reinforcement requirements (overly reinforced in my humble opinion) likely reduced the bond of the fresh shotcrete to the rock substrate. Nozzle movements had to be perfect in and around a mine strap and where welded wire sheets overlapped, but we had virtually no access to the rock sub- strate behind the reinforcing material. In those few areas where the mesh over- lapped, we adeptly cut out the overlapping layer to allow proper shotcrete application and a good bond to the rock facing. current Status According to Sean Clevenstine, Gen- eral Superintendent of Concrete at Schia- vone Construction, who oversaw the shotcrete applications on the project: “Simple mathematics can be used to show the effectiveness of the program. In early 2011, our production goal based on Shotcrete • Summer 2013 41


2013SumShotcreteEMag
To see the actual publication please follow the link above