Bobtail Road is a bypass along the steep mountain side which allowed traffic to get from one end of town to the other without having to drive thru the congested casino area. The original design was cast-in-place and complicated by the mountainous terrain, schedule requirements due to the approaching winter weather, and extreme safety risks due to 200’ cliffs below. Oldcastle’s engineering department was able to simplify the design and engineer a precast solution that received a quick approval from the project engineer. Each piece is 9’ wide x 15’ long x 14” thick with a monolithically poured wall that is 18” wide x 38” tall, weighing in at 33,000lbs each.
The precast design consisted of two different shapes, a rail slab that was square for straight runs, and slabs that had skewed ends to allow the slabs to be placed along the curvature of the road while maintaining minimal separation between each piece. The design also incorporated electrical conduit to be cast in and junction boxes for the electrician to run wires for the pedestrian lights and highway lights. The rail slabs were also designed to be impact resistant as required by state highway construction guidelines.
Project Manager for ACC, Grant Johns, stated that the precast solution reduced their project schedule by 45-50 days. Site conditions also proved that precast was the way to go, due to some pieces being cantilevered up to 2’ over the mountain side (the design allowed for up to 3’). Oldcastle produced 60’ of rail slab per day, or 65 tons of concrete, Close to 2,100 tons of rail slab were produced over a 63 day production schedule. Oldcastle was able to deliver an average of 90’ per day on 6 step-deck trucks. Scott Alexander of ACC stated they would have been lucky to pour half that per day, weather permitting. Jim Ford, the City of Black Hawk Project Manager, stated that the City is very pleased with the product and felt precast was a good fit. American Civil Construction also stated that they were very pleased with the design, quality and with the ease of installation. By utilizing precast, the project team was able to reduce inherent safety risks on site, reduce the overall project schedule, and provide a high quality product to the owner.
