Award of Merit: Water Structures Category
Emergency Repair of a Cast-in-Place Concrete Penstock
Near San Jose, Costa Rica
Submitted by QuakeWrap, Inc.
Ghella SpA Sucursal
San Jose, Costa Rica
FRP Construction, LLC
A newly constructed large-diameter cast-in-place penstock located at the El Encanto Hydroelectric Power Plant in Costa Rica (approximately 75 miles [120 km] northwest of San Jose) conducts water from a dam to a turbine building. The prevalent mountainous topography forced significant variations on the penstock layout which, along with the difference in elevation between the dam and the turbine building, caused the water flow to be pressurized.
In early 2009, the penstock was subjected to a pressurized flow test and extensive leaking was observed from surface cracks along the entire length of the structure. The penstock was dewatered and all visible cracks were sealed with traditional leak repair products; when the penstock was repressurized, however, the cracks reopened and leaking continued.
The repair alternative that was selected required the installation of a single layer of glass fiber-reinforced polymer (GFRP) structural liner to the entire inner surface of the penstock. Nearly 150,000 square feet (14,000 square meters) of GFRP liner was installed in 15 days by a locally trained 40-man crew divided into four installation fronts.
Each installation front achieved installation rates of over 300 square feet (27.9 square meters) per hour in a typical 8-hour workday.
Among the unique challenges in this repair project were design and installation complexities caused by variable horizontal and vertical alignment of the penstock, installation labor with no prior experience with FRP projects, limited access to the interior of the penstock, extensive prep work required due to inner-surface nonuniformity caused by cast-in-place construction, and meeting a very tight project schedule to not delay the incorporation of the power plant into the national electrical grid.
The GFRP liner installation was completed in July 2009—1 week ahead of schedule—and the penstock was successfully repressurized shortly thereafter. This was the world’s largest FRP pipeline retrofit project on record that was completed in a single phase.