Design and Construction of The Upstream Geomembrane Facing System for Grindstone Canyon RCC Dam

摘要

The Grindstone Canyon Dam near Ruidoso, New Mexico was built using roller compacted concrete (RCC) in 1986, with a height of 123 feet, a 1300-foot-long dam crest, and a vertical upstream face. The pool level in Grindstone Canyon Reservoir had been restricted by the New Mexico Office of State Engineer NMOSE since 2010 to an elevation of 6903.5 representing 11% of the dam height in an effort to mitigate seepage and stability concerns. The primary design objective was to reduce seepage that had been occurring at the dam since first filling so that the full reservoir height could be utilized. To meet this objective, designers selected a flexible PVC geocomposite membrane system for installation over the majority of the upstream face of the dam. The facing area lined for this project was approximately 59,000 square feet, approximately the upper half of the face height or 61% of the total upstream face area. A geocomposite membrane system was selected as the preferred alternative for a cost-effective and viable waterproofing solution. The selected membrane was a Sibelon CNT 4400, which is a 120 mil (3mm) thick PVC membrane with a 15oz per square yard (500-gram per square meter) non-woven geotextile heat-bonded to the back of the membrane. Because the RCC was porous and fractured and the fractures reflected through the upstream face to vertical rustication joints, significant interconnected seepage paths across the lower liner seal were likely. A urethane grout curtain was installed behind the dam face to cut off potential seepage paths around the lower seal of the geocomposite system. Also, cracks at the base of vertical rustication joints beneath the liner and where the joints crossed under the lower seal were grouted to cut off potential seepage paths. A drainage system was installed across the base of the membrane installation just above the lower submersible seal. The system included three drains cored horizontally through the dam, and downstream piping, which carries seepage to the spillway stilling basin. The subsequent liner drain flow data will be presented to better understand the seepage after installation at Grindstone Canyon Dam to determine liner system effectiveness. From this data, it is apparent that the liner is performing well with drain seepage flow rates approaching zero about one year after the liner was installed.