Award-winning Work on the Haiwee Penstock in California




Project Info

Client
Los Angeles Department of Water and Power; & Barnard Construction Company, Inc.

Location
California, USA

Description

A key part of the aqueduct system supplying the city of Los Angeles with water and electrical power is more secure because Golder helped design a replacement section of the Haiwee penstock.

The work on the design build project led by Barnard Construction was recognized when the Haiwee Power Plant Penstock Replacement Project, in which Golder participated, won ENR California’s 2019 Best Projects Award in the Water/Environment category. The project was subsequently named one of 20 winners in ENR’s Best of Best Projects nationwide, selected from more than 900 entries. The project team will be recognized at ENR’s 55th Award of Excellence Gala on April 2, 2020.

The story of the Aqueduct goes back to the early 1900s, when the growing city of Los Angeles, in near-desert conditions, needed a reliable supply of water. Public officials planned an aqueduct system to carry water from the High Sierra Mountains, the major snow-capped mountain range in California, some 370 km (230 miles) south to where it was needed. City officials soon realized that the water could do double duty – the fall of water from the mountains to Los Angeles could also be used to generate electricity to meet the city’s need for power.

Expanded and updated over the last 100 years, the Los Angeles Aqueduct system is still a vital source of water and electrical power for the ever-expanding, large urban area.

Designing a pipe to meet high pressures and earthquake loads

 In 2017, the Los Angeles Department of Water and Power (LADWP) re-issued a tender to replace a three-kilometer (10,000 foot) section of 2.6-meter (104 inch) steel penstock. This penstock carries water from LADWP’s South Haiwee reservoir, to the Haiwee hydroelectric plant. The new pipe was to replace the old steel pipe with one made of a fiber-reinforced polymer (FRCP) composite.

One of the design considerations was California’s well-deserved reputation as earthquake country.

Accordingly, Golder assembled a team of professionals with a wide range of skills, drawn from offices around California as well as Florida, Oregon, Arizona and Ontario, Canada. This group worked with other service providers to complete the Design-Build contract.

Golder’s design effort included hydraulic sizing for the penstock pipe—including selection of the final pipe diameter, pressure rating, and wall thickness—as well as all pipe mechanical and civil design. Golder also helped review manufacturer’s calculations and documentation and provide technical support during the construction and installation of the new FRPC penstock.

The field geotechnical program indicated a potential for up to 76 cm (30 inches) of subsidence for the on-surface pipe section from soil liquefaction during the design-level earthquake. This created design challenges in determining the expected pipeline movement and ensuring the pipe was not over-stressed if the earthquake-induced subsidence occurred.

For the buried pipeline section, the client opted to use controlled low strength backfill to ensure proper and consistent soil properties around the pipeline. Golder developed a mix recipe, which maximized reuse of the native soils to minimize total incurred cost for the project.

Within three months of completion, the pipeline’s integrity was “tested” by Mother Nature when a magnitude M7+ earthquake struck nearby. The penstock pipe had no issues withstanding the shaking from this major earthquake, and continues to deliver water, supporting LADWP’s mission to provide reliable, high-quality water to 4 million Los Angeles residents.


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