Project Details
Location: Aiea, Hawaii
Owner: Hawaii Department of Transportation
Contractor: Kieweit
Products Used
Project Overview
The H‑1 Freeway, which runs across Oahu, is the busiest roadway in the state of Hawaii. In 2019, Hawaii Department of Transportation completed improvements to H-1 through Pearl City, about ten miles northwest of Honolulu. The roadway surface was replaced with new pavement, and the shoulder lanes were widened. Two Reinforced Earth® mechanically stabilized earth (MSE) walls were installed along the highway on the existing slope to widen the road.
Both walls are 10 feet tall from foundation to roadway grade. Each wall added a length of highway shoulder about 500 feet long. The walls were built using concrete panel facing, steel soil reinforcements, and low-density cellular concrete (LDCC) for backfill.
Challenge: Weak Foundation
The existing foundation had bearing and settlement limitations. Although the proposed walls were not very tall, using granular soil or crushed stone backfill could make the foundation too heavy. Either the wall volume would have to be below a certain weight, or else the foundation would need improvement prior to installation of the wall.
Solution
To optimize project schedule and cost, the contractor considered factors such as the size of the walls, material availability, and installation speed. Geoquest’s engineering department did a calculation to show that the weight of the MSE wall volume with LDCC would be less than the original slope being replaced. The team chose lightweight backfill using Cell-Crete’s LDCC. The material had a unit weight of 36-lb per cubic-foot, which is about 70% lighter in weight than typical select granular backfill.
The use of low-density cellular concrete for MSE backfill is becoming more common across the country as a solution for weak foundations, or even simply for project constructability. In the case of the H-1 Freeway widening, it proved to be the best alternative to produce a new lightweight embankment with the strength to carry the highest volume of traffic in Hawaii.
