Replacing Coastal Culvert Along Hawaii’s Salt Laden Shoreline

Along the salt-kissed coastline of Pokai Bay on Oahu’s west side, the City and County of Honolulu discovered a couple of bridges quietly deteriorating beneath the roadway.

The old cast-in-place structures had broken down beyond repair after decades of exposure to salt-laden air and daily traffic, putting them at risk of collapse. The bridge crossings also spanned drainage trenches, meaning the culvert beneath played a vital role carrying stormwater runoff safely toward the ocean.

To restore long-term reliability along the coastal thoroughfare, local officials moved forward with a replacement project designed to improve both structural integrity and public safety. Jensen Infrastructure partnered with Island Construction & Demolition to help restore the roadway by supplying custom precast concrete box culvert systems.

This project had two specific goals: build a structure capable of surviving Hawaii’s aggressive coastal environment while also tying cleanly into the existing drainage trench system beneath the roadway.

Replacing aging culvert just steps from the Pacific Ocean meant designing for constant exposure to sea-sprayed air, moisture, and daily traffic loading. The new structures also needed to meet demanding AASHTO HL-93 loading requirements for vehicular traffic above.

Because the structures served both drainage and roadway functions, the replacement culvert needed to connect directly into the existing trench configuration without disrupting stormwater flow or requiring a full rebuild of the surrounding infrastructure.

Jensen Infrastructure supplied two precast concrete box culvert systems engineered specifically for the project’s structural and environmental demands.

One culvert utilized a Type 1 configuration measuring 96” by 54” with a total installed length of 36’, while the second utilized a larger Type 3 configuration measuring 166” by 40” with a total installed length of 48.5’.

To improve long-term durability in the aggressive coastal environment, the culvert was manufactured using stainless steel reinforcing bar, corrosion-inhibiting concrete admixtures, and microfiber reinforcement within the concrete mix.

The end sections were also manufactured with exposed reinforcing steel, allowing the new precast structures to tie directly into the existing drainage trench system on-site.

Precast concrete allowed the culvert to be manufactured off-site while field work progressed, helping streamline installation and reduce roadway disruption along the busy coastal corridor.