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of 10 seconds (+/- 4 seconds) when tested in accordance with ASTM C 1170, Procedure B [12]. The trial placement was also used for physical testing as well, including trenching through fresh RCC (anticipated for the installation of foundation drains); installation of contraction joints; installation and testing of foundation anchors; and two types of demolition (blasting and hoe-ram). Enriched RCC Mix Design: An enriched RCC overlay material was developed for use as a surficial wearing surface on the FCO Spillway chute surface between Stations 28+35 and 39+00, where the RCC would be exposed only for the 2017-2018 Winter Flood Season. This material was required to have an early strength higher than the base mix to allow flows on the FCO Spillway chute as early as November 1, 2017. Based on cylinder testing during the full- scale trial placement, the enriched RCC mix design was established as 178/103 kg/m3 (300/175 lb/yd3) of cement/fly ash, which was expected to produce RCC with an unconfined compressive strength of about 27.6 MPa (4,000 lb/in2) at 28 days and about 41.4 to 51.2 MPa (6,000 to 8,000 lb/in2) at one year. Unformed RCC 1:1 Slopes: A key factor in the RCC design was construction simplicity in order to provide for timely future recovery at the Oroville Dam’s spillways during the 2018 construction season. For the FCO Spillway chute, the outside slopes of the foundation replacement were designed to be unformed at a 1:1 slope (see Fig. 7) in order to expedite and simplify construction. The RCC structural section provides a stable and robust structure against static and dynamic loads, including potential overtopping of walls during the interim 2017-2018 Winter Flood Season (temporary RCC walls are shorter than the permanent reinforced-concrete walls). Unformed 1:1 RCC slopes have been used successfully at other RCC projects, including the foundation replacement shaping blocks at Olivenhain Dam (San Diego, California, 2004). This previous history of RCC construction gave credibility for the mix design to regulatory agencies and the OER’s independent Board of Consultants. Figure 7 Unformed 1:1 Slope of RCC Structure 97