West Bay Builders (WBB) was awarded this Bureau of Reclamation project, which involved removal of an existing 20-ft.-tall concrete retaining wall for the installation of a new canal system. The challenge was finding a temporary shoring plan that would allow WBB to retain approximately 20 feet of water with a sheet pile cofferdam while the concrete wall was being removed. Though the Bureau provided AZ-26 sheet pile sections on-site to construct the cofferdam, there was no ability to tie back the sheet piles due to the depth of water being retained. The original civil engineer tasked by WBB with developing a cofferdam shoring system had developed a complex array of walers, struts, and sheet piles that had to be installed and removed in a six-stage sequence. Three of the walers consisted of 40-foot lengths of W 36 x 361, a significant piece of steel to handle in a confined space. The design was not approved by the Bureau, due to its complexity and cost.
Holdrege & Kull was then contacted to provide an alternative design in a short period of time. H&K’s design consisted of the original AZ-26 sheet pile wall but used a single W 18 x 50 waler and 1-inch wire ropes to tie the sheet pile wall to the existing concrete fish screen structures across a 50- to 85-foot span of water. H&K’s system was estimated to be 1/10 the cost of the original design, was constructed in less than a week, and eliminated the interference of steel shoring members during wall demolition. During other phases of the project, H&K provided additional shoring designs for excavations up to 25 feet deep and also prepared a cofferdam dewatering plan for construction of the concrete siphon beneath Red Bank Creek. The dewatering plan called for 24-inch-diameter well points, drilled on 50-foot centers to draw groundwater down, allowing construction of the siphon