City: Honolulu
State:  Hawaii
General Contractor: Hawaiian Dredging Construction Company

Jet Grouting Solutions for Sanitary Sewer Line Upgrades

The development of nearby residential and commercial properties in Honolulu, HI, required upgrading 500 feet of an existing sanitary sewer line. The sewer line was located below the water table in soft, lagoon deposits prone to settlement, posing significant challenges for excavation and construction.

Challenge

Since the existing sewer line was constructed below the water table in soft, lagoonal deposits, it was unstable and prone to settling. To properly install the new sewer line, two main solutions were needed: cutting off groundwater infiltration and structural support. The excavation reached about 26 feet deep, so a strong foundation was required to support the sewer line and prevent further settlement.

Solution

Schnabel was contracted by Hawaiian Dredging Construction Company to design and install jet grout columns. The scope of work included:

• 450 jet grout side and cradle columns (19 feet deep) to create watertight sidewalls and a 5-foot thick structural cradle.
• 75 structural jet grout support columns (26 feet deep) to extend to the coral formation below.
• 35 additional 26-foot columns around manholes and utilities for sealing.

Conclusion

Schnabel completed the jet grouting work on schedule, creating a stable and watertight environment for the sewer line upgrade. Using advanced jet grouting techniques, Schnabel delivered a solution that addressed the groundwater control issues and provided the necessary structural support to facilitate the continued development of the residential and commercial properties.