SALT LAKE CITY — The Salt Lake Temple is enormous. For the first time, we know just how mountainous the landmark is.
“Well, the temple, it weighs about 187 million pounds,” Brandan Rowley said in a video recently released by The Church of Jesus Christ of Latter-day Saints.
Rowley is a superintendent on the four-year project to renovate, restore and — most vitally — give the temple’s foundation a monumental seismic upgrade.
The project boils down to a single, staggering question: How do you shore up pioneer-era stone foundations to protect a cherished 100,000-ton landmark from high-magnitude earthquakes so it will last hundreds of additional years?
The answer is emerging into literal view as the church prepares for its 190th Semiannual General Conference on Saturday and Sunday. Excavation work recently uncovered much of the stone foundation set in place in 1853. Temple Square will be closed during conference, a church spokesman said, but passersby now can see that huge slab of history with their own eyes from North and South Temple streets.
“We’re exposing some of the historic foundation stones that were originally laid for the construction of the temple,” Andy Kirby, the church’s director of historic temple renovations, said in the video. “It strengthens the perspective of what a sacrifice it was to lay this foundation for future generations of the church. It’s awe-inspiring to me.”
Exposing the foundations is crucial to strengthening them, which is happening in three major ways. One of them will be the most important and most difficult part of the project.
Filling the voids
First, workers have spent the past two months drilling 3-inch-wide holes at different angles into the foundation footings on the north side of the temple. They are drilling 8 to 14 feet deep into the north walls and will do the same on the south over the next few months.
They will drill 10 to 35 feet deep into the east and west walls because the temple’s tower foundations are larger.
Crews fill each hole with high-strength grout, which also pushes farther into voids and will consolidate the foundations.
The same work is continuing out of sight inside the temple’s walls, where workers also are exposing the foundation so it can be strengthened by core drilling from the middle of the foundation as well.
Retaining wall around the temple
Second, crews are excavating 40 to 60 feet deep around the temple and building a sturdy retaining wall underground around the temple site.
To make way for the excavation, crews spent the summer demolishing and removing most of the improvements added around the temple in the 1960s, including the north entrance, the north chapel, the cafeteria, locker rooms and the sealing room addition.
Now, massive augurs are drilling holes for columns to support a retaining wall around the construction site and another around the temple’s foundation.
In each case, the augur drills a hole 40 to 60 feet below ground and then a crew puts a pipelike segment casing down the hole. Then the crew members place a steel beam down the center of the hole, fill the hole with concrete and remove the casing. Each vertical column of steel and concrete is called a soldier pile.
Soldier piles have been installed on the north side of the temple and now are being added on the west side. The concrete beams are being connected to steel cables and lagging — 4-inch-thick pieces of wood — to hold the earth back. The retaining walls are crucial to keeping the earth around the excavation site from collapsing into the site and to keep the foundation firm and in place.
“We don’t want to have any opportunity for material to flow out from underneath the foundations that would create cracking or settlement,” Malcolm Drilling vice president Scott Chambers said in the video.
The base isolation system
Third, project managers are preparing to install the base isolation system that will allow the temple to move without damage during a major earthquake.
“The next stage is probably the hardest,” Kirby said.
This is also where the temple’s weight comes into play. Workers will place 98 base isolators underneath the temple’s foundations. A base isolator is shaped like a hockey puck with a top and bottom plate. In the center is a dished plate of stainless steel with a ball bearing inside, Rowley said.
Each base isolator can hold 9 million pounds of pressure, which means the combination of the base isolation system can hold five times the colossal weight of the temple during a high-magnitude earthquake.
“The dished plate will allow the temple to just sort of float and slow the building down as it starts to settle back down,” Rowley said.
The church has installed base isolation systems under new temples in areas with frequent earthquakes. Those systems have successfully protected at least one of those temples during a high-magnitude quake, Brent Roberts, the church’s special projects director, previously told the Deseret News.
A temple with a base isolation system will still experience a 7.3-magnitude earthquake at the level of a 5.1 or 5.2, so reinforcing the temple’s walls and towers is vital, said David Hart, past executive director of the Utah Capitol Preservation Board, in a previous interview.
In fact, said Rowley, who worked on the base isolation installed under the Utah Capitol during the 2004-08 renovation, the grout being infused in the temple’s walls and foundations are part of the base isolation system.
Once the grout is infused, teams will drill new holes to install metal rods into the foundation and help pin the foundation together. Then the team will install transfer beams.
“That will help the foundation take the stress of actually sitting on top of the isolators,” Rowley said.
Utah deemed construction work essential during the pandemic, so COVID-19 has not slowed the project. However, a 5.7-magnitude earthquake on March 18 stopped work for about a week while safety assessments were conducted.
The reviews led to the expedited removal of the temple spires, or finials, and the removal of the statue of the Angel Moroni, which lost its trumpet in the quake. A crane removed the statue on May 18.
Work crews are also focused on reducing the amount of debris sent to landfills.
They are recycling copper, aluminum, steel, stone and concrete. For example, workers break up concrete and separate the rebar and reinforced steel. The concrete and stone go to a crusher for reuse in other Utah construction projects.
“We’re proud of our efforts to be good stewards,” Kirby said.