Design and Construction of the Upstream Geomembrane Facing System for the San Vicente RCC Dam Raise

The San Vicente Dam Raise (SVDR) Project for the San Diego County Water Authority (SDCWA) is the highest dam raise in the world using roller compacted concrete (RCC). The dam was originally built by the City of San Diego to a height of 220 feet (67m), between 1941 to 1943, as a key water supply reservoir. The 117 foot (36m) high RCC raise will make the new height of the dam 337 feet (103 m), resulting in a 152,000 AF (187,489,239 m³) increase in reservoir storage capacity. The 117 foot (36m) raise was accomplished with a placement of more than 600,000 cubic yards (459,000 m³) of RCC. The primary design objective is for the dam to survive a large seismic event, remaining fully operational to provide an emergency supply of water to the San Diego region. To meet this objective, designers selected a flexible exposed PVC geomembrane system for installation over the raised portion of the upstream face of the dam as one of its principal design features.
The exposed geomembrane liner includes an integral drainage system between the exposed PVC membrane and the concrete face of the dam. The geomembrane liner and integral drainage layer act as a seepage barrier to the RCC at the upstream face, eliminating the need for internal formed drains and waterstops at contraction joints in the raised portion of the dam. The elimination of formed internal drains and contraction joint waterstops simplified construction and saved construction costs. The drainage system of the exposed geomembrane liner is connected to the original dam’s drainage system, so that any seepage water would be collected in the drainage gallery for monitoring. With this system, any damage to the exposed liner system would be evident and can be repaired. The dam is designed to remain stable in case of any damage to the exposed geomembrane liner system.
This paper discusses the selection, design, and construction of the upstream facing system for the SVDR. This represents the world’s first geomembrane facing system ever installed on a RCC dam raise. The selection process included evaluating 7 different upstream facing systems that have been used worldwide for RCC dams. The exposed geomembrane system was determined to be the highest rated upstream facing system based on a number of criteria, including seismic survivability, seepage control, constructability, appearance, durability and cost. Of particular importance for the SDCWA was the excellent performance of the same PVC geomembrane system installed on SDCWA’s Olivenhain Dam in 2003. The paper also includes a discussion of the performance of Olivenhain Dam’s upstream geomembrane system and its precedence for again selecting the exposed PVC geomembrane system for the SVDR Project.