Granite Construction was awarded the contract for Phase 3 of the Folsom Dam Auxiliary Spillway project. The project included the installation of 1”- to 3”-diameter rock bolts capable of supporting loads of up to 745,000 pounds. Preliminary plans from the Army Corps of Engineers (Corps) specified over 150 3”-diameter bolts designed with a 25’ bond length and an unbonded length of 30’. The Corps’s design required a 5.5”- diameter coupling, which in turn required a costly 7”-diameter drilled hole.
H&K was asked to review the preliminary design and provide an alternative rock bolt design. Our analysis determined that the most likely failure point of the bolts would be between the grout and the bolt, rather than the rock itself, and we provided an alternative design with a reduced bond length. Our design not only reduced the bolt length (and drilling) by 12 feet, but also the need for couplings. In the absence of couplings, the drilled-hole diameter was reduced to 5.5”, further reducing drilling time and expense. H&K continues to work with the installation contractor to provide bolt testing protocols and design of test loading equipment for the project. H&K also continues to provide on-call engineering services for temporary fill slope configurations, temporary heavy equipment pads, and slope monitoring, as requested by the contractor.