Patillas Dam Safety Seismic Retrofit Project Overview.pdf

PATILLAS DAM SEISMIC RETROFIT PROJECT OVERVIEW

The Patillas Dam Safety Seismic Modification Project requires the construction of a large earthen berm and extension of the outlet works conduit, both on the downstream side of the existing dam. Patillas Dam is a semi-hydraulic fill dam and was completed in 1914. The dam impounds Lake Patillas, which is used for critical power generation at a downstream station. Reservoir water is also used for municipal water supply.

The semi-hydraulic fill construction method and associated materials create a vulnerability which, when combined with Puerto Rico's significant seismic hazard, present a significant risk to the public. The reservoir has operated at a restricted maximum reservoir elevation for over a decade to reduce seismic risks. The modifications are currently in the Final Design phase, with design being performed by the Bureau of Reclamation.

The overlay berm will be a zoned earthfill structure with a total fill volume of approximately 600,000 cubic yards. The various material zones will be commercially sourced from nearby quarries. Sand and gravel filter zones will provide drainage to a 24-inch HDPE toe drain system. A key trench at the downstream toe will extend to approximately 30 feet deep and will require dewatering of the foundation materials. Construction will also include temporary and permanent instrumentation installments, including inclinometers, vibrating wire pressure transducers, piezometers and settlement monitoring points.

Extension of the outlet works conduit will require a diver-installed bulkhead at the base of the gate tower. This will be installed by passing through a 24-inch square manhole at a depth of over 90 feet. The bulkhead will be Contractor designed based on high-resolution 3-dimensional photogrammetric scans and dive report. The existing discharge and conveyance features at the downstream end of the system will be demolished. This will include the outlet works conduit, forebays, canal overflow, as well as the abandoned power generating building. The abandoned portion of the outlet works will be replaced with a new 54-inch concrete encased steel conduit with 36-inch steel bifurcation to make canal releases. The first approximately 320-feet of 54-inch outlet works demolition and construction takes place in the existing 20-foot diameter horseshoe shaped tunnel which will then be backfilled with controlled low strength material (CLSM). Two new concrete buildings will house a pair of gates for the 54-inch conduit and valves for the 36-inch.

However, a Contractor designed temporary bypass is required to provide up to 25 cfs of uninterrupted canal deliveries from when the bulkhead is installed until the new outlet works is commissioned and operating.

PROJECT SITE

TUNNEL SECTION

PROJECT RENDERING FOR STRUCTURAL FEATURES

PROJECT EMBANKMENT CROSS SECTION

“NOTICE: This is not a solicitation of any offers or bids. Funds are not presently available for this effort. No award will be made under this solicitation until funds are available. The Government reserves the right to cancel this solicitation, either before or after the closing date. In the event the project is cancelled, there is no obligation to reimburse an offeror for any costs.”