Page - 95 - in Book of Full Papers - Symposium Hydro Engineering

The Interim RCC Foundation Replacement Concept described above was constructed during the 2017 construction season. As noted above, the Final Design solution for the RCC area of the FCO Spillway chute will include the following modifications during the 2018 construction season: a. The RCC side walls above the 4:1 chute surface will be removed following the 2017- 2018 Winter Flood Season so that new 6.1 meter (20-foot) high reinforced-concrete cantilever retaining walls can be added as the permanent chute walls. b. Permanent reinforced-concrete slabs will be placed over the RCC, including drainage and anchor design features, for the remaining portions of the chute. Key aspects of this work will include roughening the RCC surface to allow a better connection to the new reinforced concrete. 8. RCC DESIGN The initial estimated quantity of RCC was about 191,000 m3 (250,000 yd3), based on the initial topographic information from Station 29+00 to 39+00. This estimate was periodically revised during construction to account for changes in the foundation excavation, including the Arena Cut, which laid the upstream foundation area back to about Station 28+00 due to instabilities identified in the FCO Spillway upper chute foundation. Ultimately, the final RCC volume was about 268,000 m3 (350,000 yd3) that was placed during the 2017 construction season. The technical specification for RCC features were developed based on recently- completed RCC projects in California by members of the OER Spillway Task Force. The project specifications also included technical requirements for crushing on-site rock for the RCC. Key aspects of the project specifications included the following features:  RCC Mix Design  Unformed RCC 1:1 Slope for the abutment sides  Unformed RCC 4:1 Slope for the chute surface Each of these features of the RCC design are discussed in the following sections. RCC Mix Design: The intent for the RCC mix design was to use on-site materials for RCC aggregates, primarily rock eroded during the February 2017 incident that were later dredged from the Feather River. These eroded materials had been stockpiled in several areas around the project site. Initial investigations into the RCC mix design commenced shortly after the incident, using the dredged rock. These materials were crushed in several test programs, including preparation of RCC concrete cylinders. The results of these tests showed that an initial sorting process was necessary to remove fine-grained materials (silt, sand and gravel) finer than 1-inch in diameter. This provision was included in the final specification for the RCC Aggregates. To simplify the preparation of RCC aggregates, the specification was developed using only two types of aggregates: coarse and fine. The coarse aggregate was specified as ASTM C 33, Size Number 357 [8] with a maximum aggregate size of 38 mm (1.5 inches). The fine (sand) aggregate was a custom blend, initially established in the following table. In addition, the sand equivalent value requirement was set to be no less than 35 when tested in accordance with ASTM D 2419. 95