Project Spotlight: Oahu Region reconstructs deteriorating seawall on the island’s scenic Poka‘i Bay

GBI PARC Seawall - Ohau

Goodfellow Bros. (GBI) worked with client, U.S. Army Corps of Engineers Honolulu District on the $4 million emergency repair of the seawall at the Pililaau Army Recreation Center (PARC) in Waianae, Oahu, Hawaii.

Located on Oahu’s scenic Poka‘i Bay, the PARC is home to a seawall that had deteriorated and was in dire need of repair. The seawall runs parallel to a public beach and its poor condition posed a safety hazard to PARC users and beachgoers alike.

GBI PARC Seawall (2)GBI was tasked with reconstructing approximately 677 lineal feet of concrete rubble masonry seawall behind the existing damaged seawall. The repair and replacement work required replacing the existing seawall, including demolishing damaged sections, excavating, removing and disposing of the debris and seawall fragments which collapsed and separated from the remaining seawall, and to reconstruct a taller, deeper seawall.

The lower portion of the newly constructed 15-foot-high seawall is comprised of a unique marine mattress system, including a one-foot-thick layer of crushed rock retained by a synthetic geoweb to protect petroglyphs carved into the top of the hard sand layer. Because petroglyphs were present in the coral layer, a qualified archaeologist was always present to monitor ground-disturbing activities to ensure they were protected during construction. In addition to the seawall, a sidewalk and streetlights were relocated to beautify the beach area.

The project had several challenges. Among other things, the crew worked within a very tight space surrounded by pedestrian traffic while performing delicate excavation to maintain the integrity of the petroglyphs.

GBI PARC Seawall (1) During the construction of the marine mattress system, careful excavation took place to protect the petroglyphs. The lower portion of the seawall, marine mattress, and boulder base were constructed in 20 to 60 foot increments depending on three factors: tidal influence, the condition of the existing seawall, and the proximity to existing structures. The area behind the existing seawall was excavated to elevation five to create a working bench for the equipment and personnel. Sections of steel shoring—each 20 feet long and eight feet high with 12-foot-wide spreaders—were placed in the new seawall footprint. An excavator was then used to remove the material within the shoring until elevation two. Based on the boring logs, the hardpan layer was between an elevation of one to two feet; the bottom of the excavation was probed with a hammer and rebar to determine the exact elevation.

The excavated material was loaded directly onto trucks and transported to the laydown area to be used to backfill the new wall. The last foot of material on the hardpan was either removed using shovels, with the assistance of a vacuum truck, or with a rubber bucket edge. The marine mattress was then filled with aggregate, transported to the excavation, and placed with an excavator. Rocks for the seawall were delivered to the site and staged at the construction area because space along the seawall was limited. A loader was used to transport the rock to the seawall and the rocks were then placed with an excavator or by hand. Prior to the placement of the three-foot boulders, an excavator installed steel plates at both ends of the shoring system. Following the placement of the three-foot boulders and geotextile, a pump truck was used to place the concrete between the boulders and the gap between the shoring and boulders. Smaller rocks were placed by hand and concrete was mixed within the construction area. Once the wall reached elevation five, the shoring system was removed, and the wall was backfilled as construction continued.

There is a coral reef at the north end of the project, so extra care was taken during excavation to minimize impact to coral growth and prevent any damage to the petroglyphs. In place of hand-digging, GBI used a rubber bucket edge to expedite the sand excavation processes as crew members got closer to the hard coral layer that contained the petroglyphs. On-site personnel learned how to identify endangered species and were instructed to stop working if they spotted any endangered species near the work area. GBI also worked closely with the client and all regulatory state and federal agencies to ensure there were no adverse environmental impacts.

Additionally, GBI used GPS technology to assist with the excavation and backfill of the new seawall. A survey team brought points into the project that tied into our GPS system and as a result, the project was constructed as designed and there was live data available anywhere on the project site at any time for the client and stakeholders.

Because the project was located next to a public beach, pedestrian traffic posed an additional challenge as the crew moved from one end of the site to the other. Keeping the community safe was of utmost priority; crew members were tasked with ensuring the public was a safe distance from the work zone, 24 hours a day, seven days a week. By the time the project was complete, it had accrued more than 7,800 worker-hours and zero safety incidents. Rebuilding the seawall and beautifying the surrounding beach area of Poka’i Bay was a great example of how Goodfellow Bros. seeks to live our mission and improve our communities where we live and work.

GBI PARC Seawall (11)

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