95 State

95 State is a 25-story, 515,000 SF office tower built in Salt Lake City from 2019-21 by Okland Construction. It was designed by Skidmore, Owings & Merrill.

The foundation work on this building was fascinating. It was my first opportunity to experience the scale of a high-rise building's enormous foundation.
First, excavation takes the site down to about 30 feet below street level. You can see the shoring lining the site-large timbers span vertical steel beams which are tied back into the retained soil.
Once excavation is complete, piles are placed in the earth. I'm not exactly what kind of piles these are, but I'm assuming they are reinforced grout friction piles. A giant machine drills a deep 24-inch diameter hole into the earth, which is immediately filled with a cement slurry-basically concrete without the rock and gravel aggregate. Then, a cylindrical rebar cage is inserted in the slurry. Once the concrete hardens, 11 feet of the soil between the piles is excavated and the hardened slurry removed, exposing the top portion of reinforcing steel in the pile. The pile is then incorporated in the forms and reinforcing steel for the footings of the building. You can see the tops of these piles in the photo-small circles scattered throughout the rebar.
363 of these piles are drilled 110-115 feet deep down into a layer of dense gravel which can support the weight of the building above.

Rebar for the massive 11-foot-thick footings is assembled and formed up. Notice on the left side of the image-triangular shaped footings called "grade beam outriggers". I believe these are designed to transfer loads from the perimeter building columns into the stronger central core of the foundation. The cap of a pile is visible at bottom-center.
Space on a downtown job site is hard to come by, so construction materials are stored wherever there's space.

Concrete for the footings is poured. Vertical rebar clusters are the beginnings of vertical concrete columns. Horizontal rebar shows where grade beams with connect more footings together. The base of the building's concrete core is visible at the left, and formwork for the core is being assembled.
This building has 1 basement floor of below-ground parking on this south end and 2 levels on the north end which is all reinforced concrete. The rest of the building is a reinforced concrete core with steel structure and concrete floor deck with a glass curtain wall facade.

The concrete core-home to elevators, mechanical chases, and stairways, begins to rise. An intricate system of reinforcement assures the strength and durability of the 392-foot-tall structure.
The tower being located in a dense urban area means I can have great views of the construction. Pedestrian access remains constant around the site, so I can see all the work up close.

The core continues to rise. After a section is poured, the formwork is released and is jacked up one floor level. Rebar is assembled, concrete poured, and the process repeats.

Here we see embedded steel plates in the core. Additional steel connector plates will be welded to these-creating a place for the steel structure to attach to the concrete core.

The core continues to rise, followed by steel erection.

Photo from Loopnet
The finished tower. The first two levels above the lobby are a meetinghouse for the Church of Jesus Christ of Latter-Day Saints.

I learned a lot from this article in Structure Magazine.