Underpinning the Salt Lake Temple-Paper

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The Salt Lake Temple, dedicated in 1893, is undergoing a major seismic retrofit that will place its historic stone structure on base isolators. The approximately 187-million-pound building rests on massive, unreinforced stacked-stone foundations. Installing the new foundations required excavation up to 18 feet below the existing footings, so a temporary support system was needed to limit movement and protect the structure.<br /><br />Because conventional underpinning was impractical, the perimeter foundations were supported on confined soil “columns.” Secant piles formed the exterior shoring walls, while closely spaced micropiles and shotcrete formed interior walls. Tie rods and tieback anchors restrained the walls, limiting lateral soil movement and settlement. The stone foundations were first strengthened through consolidation grouting and tensioned rods.<br /><br />Four large corner openings were created for construction access and the new structural system. Each required sequential hand-dug underpinning piers, reinforced concrete beams, steel girders, and needle beams to support the walls while sections of the original foundations were removed. Micropiles and load-transfer frames also supported interior structural elements.<br /><br />Installation was complicated by dense gravel, cobbles, restricted access, tight clearances, and the need to maintain building services. Careful sequencing, trial drilling, survey controls, and Building Information Modeling (BIM) helped coordinate temporary works with the permanent foundations and reduce construction clashes. Soil-structure interaction analyses informed the sequence and anticipated movement.<br /><br />After excavation, the permanent system—concrete-filled steel pipes connected to reinforced-concrete transfer beams and supported on base isolators—was built beneath the Temple. Once the building’s weight is transferred to this system, soil beneath the walls and pipes can be removed, allowing the structure to move freely during an earthquake. The project demonstrates how varied underpinning and shoring techniques, supported by close multidisciplinary coordination, enabled complex foundation construction while protecting a major historic building.
Keywords
Salt Lake Temple
seismic retrofit
base isolators
underpinning
micropiles
secant piles
shotcrete
foundation excavation
historic building preservation
soil-structure interaction