What is ‘jack and bore’ and how is it holding up the 187-million-pound Salt Lake Temple?
Part of the seismic upgrade, crews dig by hand under the foundation so 96 pipes 4 feet round and 20-40 feet long can be inserted
What is a “jack and bore” and why is it important to the Salt Lake Temple renovation?
With the use of reinforced steel tubes, the jack-and-bore process is key to the seismic upgrade of the temple, suspending the 187-million-pound building while crews excavate 20 feet below its nearly 170-year-old foundation in downtown Salt Lake City.
And the result is a new foundation to give strength, stability and mobility to the temple during an earthquake. The planning is high-tech, but the digging under the foundation is tedious — done by hand, an inch at a time, moving in and out of 4-foot-diameter steel pipes.
The jack-and-bore process is featured in a nearly seven-minute video and accompanying update published Friday, Aug. 26, on ChurchofJesusChrist.org about the Temple Square renovation project, now in its third year.
What is jack and bore?
Jacking is the pushing of the pipe into place with hydraulic rams, and boring is the digging — usually done with large augers. However, because of the large rocks being found in the foundation and the need for precision, the boring is being done by hand — hand-measured, hand-dug and then laser-confirmed.
For the Salt Lake Temple project, the jack and bore will place 96 pipes ranging from 20 to 40 feet under the temple. The pipes join the cables, rods, trusses and transfer bases and are tied to the spires, roof and building so that the temple moves as a solid structure in an earthquake.
Grouting done several times fills the gaps and voids between the pipes and foundation. Long, cylinder-like rebar cages are later inserted into each pipe, with the cages specifically designed for each pipe and each site according to the representative weight of the temple above in that area. The cages add strength to the pipes.
Later, additional excavation will be done to prepare for 98 base isolation units as part of the seismic upgrade.
Elsewhere in the project, grounds and areas surrounding Temple Square are being remodeled, with the new landscape desire better integrating the temple grounds with the Main Street Plaza, the Church Office Building plaza and the northwest areas surrounding the temple.
Main Street Plaza
Renovation of the Main Street Plaza began in April, with the gardens, reflection pool and decorative landscaping removed in order to repair and add waterproofing to the decking that covers the underground employee parking garage.
Church Office Building plaza
On the Church Office Building plaza, new stonework is being installed, with the walking area receiving new pavers.
Grounds northwest of the temple
Progress is being made on a newly designed contemplative garden area northwest of the Salt Lake Temple. The area will include additional restroom facilities for visitors to Temple Square and attendees at events in the Tabernacle and Assembly Hall.
West Temple crosswalk
With the mid-block West Temple crosswalk blocked for several months, new planter boxes are being built as part of the future crosswalk between Temple Square and the Church History Museum.