Construction Phases of a 20-Story Tower

Project: Type: Mixed-use Tower
Location: San Francisco, CA
Year of Completion: Estimated 2025
Developer: Strada Investment Group
General Contractor: Swinerton
Marc Northstar’s role: Site visit, reverse engineering, study analysis

Marc Northstar's passion for construction is intricately intertwined with his artistic pursuits. This passion was ignited during his time as an architect at the Dubai International Financial Centre (DIFC) with Hopkins Architects, where he worked on-site during the construction of the iconic Burj Khalifa. These experiences have had a profound impact on his career in both art and architecture, a connection that may be appreciated by only a select few. In fact, his first solo art exhibition was appropriately named "Constructivism," reflecting the influence of his construction background on his artistic expression.

Now, let's delve into the fascinating process of building a 20-story structure in San Francisco. This journey begins with the initial excavation of the site and the necessary preparations to get the project underway.

PHASE 1 / DEMOLISHING

The demolition of the exciting 3 structures took place in November 2022. Silverado, renowned for their expertise in demolishing structures, successfully removed the older Bay Bridge in the past. During this phase, the demolition process was remarkably swift, taking approximately a 3 weeks to completely remove the old 3 buildings. A small team of only 5-8 people worked on-site to accomplish this task.

Despite heavy rain on December 31, 2022, the dedicated workers at the construction site in San Francisco persevered without taking a break. They braved the muddy conditions to ensure the progress of the project. During this stage, the remnants of the old three buildings were completely removed, and the next step, which involves excavating the earth, is set to begin soon.

PHASE 2 / ARRIVE OF HEAVY EQUIPMENTS

By February 17, 2023, the construction site was fully prepared to welcome a fleet of heavy machinery. Notably, a Crawler Crane, featured in this photo, arrived in separate pieces to be assembled on-site. Alongside it, storage containers for office use and a truck-mounted crane were also delivered. The majority of the equipment was expertly pieced together at the site, reminiscent of a toy set being meticulously assembled to create a temporary small village. The Crawler Crane possesses exceptional all-terrain capabilities, particularly on soft soils. With its specialized track system instead of wheels, it can operate effectively in challenging site conditions. You may notice the presence of steel plates beneath the tracks, providing both protection and stability during movement. Furthermore, this versatile crane boasts a 360-degree rotation capability.

Despite heavy rain, progress never halted at the construction site on March 2nd, 2023. The accompanying photo showcases the delivery of H-beams to the site. Pay close attention to the blue machine on the left, which is a pile driver. Its role is to vertically drive and hammer the H-beams deep into the ground along the perimeter of the site, creating a robust underground wall. This wall serves the dual purpose of protecting the neighboring buildings and enabling the excavation of the earth. The depth of the steel beams is meticulously calculated to guarantee the structural integrity of the 20-floor tower under construction.

On May 25th, 2023, the H-beam piles were completed. Temporary power distribution cables, easily identifiable by the black cables against the wall, were utilized to supply electricity to equipment and tools, fostering a vibrant construction environment akin to a bustling temporary village. Now, let's explore the purpose of the rounded steel beams. These beams are known as Waler Beams and serve a temporary function, to be removed upon completion of the extraction process. Waler Beams are connected to the H-beams, forming a cohesive unit along the perimeter wall, utilizing connectors to evenly distribute lateral forces and loads across the H-beams. This distribution prevents bending or buckling during excavation. Throughout the excavation process, the Waler beams and vertical H-beams collaborate, generating a secure retaining structure capable of withstanding the exerted soil forces. Once the excavation reaches completion, the Waler beams can be removed.

PHASE 3 / EXTRACTION OF EARTH

With the Waler Beams securely in place, the stage is set for the site's extraction process to commence. The enclosed image, taken on June 29th, 2023, showcases the remarkable dedication of the team as they meticulously remove the soil. The efficiency displayed throughout the extraction is commendable, with the excavated earth promptly loaded onto waiting trucks and swiftly transported to a predetermined location.

On July 11th, 2023, partially extracted areas has been completed and the ground has been flattened as well. We can notice black sheets on the wall, these are geomembrane sheets made of materials like high-density polyethylene (HDPE), polyvinyl chloride (PVC), or other flexible and impermeable materials. These sheets are used as waterproofing against water infiltration and erosion control to help stabilize the excavated walls and prevent erosion of the soil by acting as a protective barrier. Notably, this phase marks the initial introduction of concrete pouring for the construction of the new tower. Details regarding the concrete pouring phase will be discussed in subsequent updates.

PHASE 4 / FOUNDATION LAYER

Once the first pour of concrete, known as the curing phase, takes place, the construction phase commences. The photo captured on July 13th, 2023, shows progress as concrete is poured despite incomplete extraction. White sheets, called concrete curing blankets, are observed on top of the poured concrete. These blankets protect and facilitate proper curing, retaining moisture for optimal strength, minimizing cracks, and ensuring durability. Made of materials like polyethylene or polypropylene, curing blankets are durable, reusable, and resistant to outdoor conditions.

PHASE 5 / POURING CONCRETE

Around 2 AM on August 19, 2023, the night concrete pour was in progress with engineers and laborers on-site. The atmosphere was incredible, resembling the construction of a collaborative project. Pouring concrete at night was necessary to control temperature and minimize traffic disruption. The striking Boom Pumps, with their long, flexible arms, added an artistic touch to the process, efficiently delivering concrete to precise locations.

Marc will consistently provide updates to the site as the project progresses