Published on July 1st, 2014 | by UC&D Magazine0
In The Trenches, July 14
Few infrastructure projects in the entire State of Utah are as critical to local residents as the multi-phase, $42 million Terminal Reservoir Replacement Project (TRRP) currently underway near the top of 33rd South and directly west of I-215 in Salt Lake City.
In addition to the reservoir being more than 60 years old – it was originally part of the Provo River Project and placed into service in 1951 – its location directly above businesses and residents on the City’s east side, and the fact it sits directly on the Wasatch Fault, add to its importance.
Wayne Winsor, Engineering and Maintenance Manager for the Metropolitan Water District of Salt Lake & Sandy (MWDSLS), said this is the District’s current major Capital Improvement project, and had to be built in a multi-phase process to ensure that 40 MG (54 MG reservoir capacity) of water remain available to customers throughout the construction process.
“The District is obligated to continue supplying water throughout the construction period and maintain a minimum of 75% of the total original storage at the site,” said Winsor. “These constraints necessitated that the project be divided into five phases, to be completed sequentially by a single contractor over an extended time period.”
The planned seven-year (2011-2018), five-phase project consists of removing 40 MG of potable water storage and replacing it with a total of 48 MG in three cells (9 MG, 28 MG, 11 MG). The existing 40 MG storage was designed by the Bureau of Reclamation as part of the Provo River Project – Aqueduct Division and placed into service in 1951.
Alder Construction of Murray has been the general contractor on the project since November 2011, having completed the 9 MG cell already and currently in the midst of building the 28 MG cell. During peak activity, Alder has between 40-50 workers on site and is pouring on average between 100-150 cu. yds. per day, especially as walls and columns started rising in early July.
The concrete mix design has a low water content to limit shrinkage and cracking, and includes the additive Eclipse to help with workability.
“The slopes are very challenging to finish because the concrete sets up so fast, which is why the workers are on it so quickly,” said Charley Alger, Quality Control Field Engineer for Alder. “It can present a challenge getting a quality finish but our guys are good. It’s starting to get really technical right now as we get rebar set and plumb and keeping it plumb while we’re pouring concrete.”
Alder Project Superintendent Paul Huff said keeping 40 MG on site is one of the more unique aspects of this project.
“The challenge with this job is schedule, and having to maintain 40 MG on site,” said Huff. “We’ve already built one reservoir, had to tear this one down and build a new one, and once it’s online we’ll tear down the last one and rebuild another one…so it’s an interesting process. There is a lot of activity happening right now.”
As of mid-July, approximately 15,000 cu. yds. of concrete have been placed on the project, including nearly 3,000 this year. Crews have removed 3,200 ft. of old piping and will install 8,000 ft. of underground pipe ranging from 4 in. to 72 in., in addition to 20 new valves that are 16 in. to 72 in. in diameter.
The contract allows up to seven years for completion, but Alder is already a year ahead of the schedule, Winsor said, and on target to finish the entire project by July 2017.
Stringent Seismic Design
The TRRP location is approximately2.5 miles east of the East Bench fault line, within the Wasatch Fault Zone. In this location, the reservoirs are subject to potential earthquake forces as large as any anticipated in the State of Utah, according to Greg Loscher, Project Engineer for Bowen Collins & Associates of Draper. The project is designed for projected forces from a Magnitude 7 event with consideration
for the proximity to the fault and the site- specific geology. A site-specific analysis was performed to give engineers the best and most current data available for design.
Loscher said the two old 20 MG reservoirs would likely have remained functional for many more years, but weren’t seismically sound, which necessitated the replacement.
“A good concrete reservoir should last circa 100 years; the old one was designed when there were no seismic codes, and as designed it would not hold up,” said Loscher. “In terms of being sound and holding water, it works fine.”
He added that the design criteria used is similar to that used for most major facilities under the International Building Code (IBC). However, the District’s more stringent criteria include the requirement that this facility be usable after a 7.0 earthquake. While there is no such thing as an “earthquake-proof” structure, these reservoirs have been designed to a performance level intended to ensure their continued utility in one of the most active seismic zones in the United States.