City Creek Center - Block 76
- Location: Salt Lake City, UT
- Owner: Property Reserve, Inc.
- General Contractor: Okland Construction
- Technique(s) Utilized: Diaphragm Walls, Jet Grouting, Micropiles, Soil Nail Walls, Tieback Anchors
- Subsurface Conditions: Sand and Gravel over inter-bedded silt and clay over very dense sand and gravel
- Approximate Quantities: Diaphragm Wall - 45,000 square feet, Jet Grout Columns - 284, Micropiles - 103, Soil Nail Wall - 120,000 square feet, Tieback Anchors - 236
The Cross Roads Shopping Mall, located in downtown Salt Lake City, had been losing business to suburban retailers and experiencing major declines in sales since the 1990s. Upon losing another major retailer to a nearby shopping center, the Latter-Day Saints (LDS) Church stepped in and purchased the Cross Roads Mall, the nearby 22-story Key Bank Tower office building and a subsurface parking structure in 2003. The properties were purchased as part of a massive, $1 billion redevelopment project to revitalize the city and keep the areas surrounding Temple Square, the LDS Church's world headquarters, economically vibrant.
PROJECT BACKGROUND
The redevelopment project, named City Creek Center, includes up to three national department stores, new and newly refurbished office towers, new residential buildings, a full-service grocery store, a fountain, man-made streams, approximately six acres of gardens and an underground parking garage that accommodates approximately 5,600 vehicles.
The project spans more than 20 acres on three city blocks adjacent to Temple Square.
The first phase of the project, referred to as Block 76, required demolition, excavation and shoring in a 10-acre parcel to prepare it for new construction. Excavation was required to a depth of 65-feet below street level to accommodate the underground parking garage.
Further complicating the excavation was the site's close proximity to adjacent high-rise buildings with shallow foundations. The entire Block 76 project footprint required deep excavation through granular soils.
THE WORK
Nicholson provided the turnkey design-build earth retention system, which included 45,000 square feet of diaphragm walls and 120,000 feet of soil nail walls. The anchored diaphragm walls were installed in the areas immediately adjacent to existing buildings between nine and 20 stories high. These were considered the first anchored diaphragm walls used for earth retention in Salt Lake City.
The soil nail walls were used in the areas not supported by the diaphragm walls. They were also used directly below any nearby, existing structures. To provide additional support, and limit potential movements to one inch, an underpinning system, consisting of micropiles with an integral cap beam, was installed below the existing structures. Because of the site's closeness to groundwater, 700 linear feet of jet grout for water control was also installed.
As part of a joint venture, Nicholson also installed 1,040 24-inch diameter augercast piles as the deep foundations for a new structure that is rising out of a 65-foot deep excavation in the heart of Salt Lake City.
THE RESULT
City Creek Center, which is named after the snow-fed source of drinking and irrigation water that flowed through Salt Lake Valley, is a project of unprecedented scope and magnitude for Salt Lake City. The amount of earth retention for deep excavation accomplished in, around and below existing structures was truly unique.
Sustainable principles were applied to the design, construction and the future operation of this project.
The City Creek Center project is Leadership in Energy and Environmental Design for Neighborhood Development (LEED ND) certified, and is one of 60 pilot projects that will be used to help the United States Green Council to finalize its LEED ND process.
City Creek Center, which will officially open in 2012, will make Salt Lake City one of the few cities in the nation to have such vibrant, mixed development at its core.
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