Mt. St. Helens Sediment Retention Structure Spillway Elevation Project


The Mount St. Helens project was an effort to reduce flood damage to the communities along the lower Cowlitz River. The U.S. Army Corps of Engineers, Portland District (Corps), has proposed to raise the spillway of the existing sediment retention structure (SRS) by up to 10 feet to increase its sediment storage capacity. This action was needed to increase the efficiency of sediment deposition above the SRS and decrease the volume of sediment available for deposition in the lower Cowlitz River and to maintain required flood risk reduction benefits to communities along the lower Cowlitz River.

Fall Line performed the RCC/Bedding mix design program for the project for aggregates testing, curing, and testing of RCC. The Mix Design included vebe testing, compressive strength testing, final aggregate sieve sizes, final weights for each constituent for the bedding/mortar mix including slump, water retarding mixture, and compressive strength.