The Kaneohe/Kailua Sewer Tunnel increased the reliability of the aging Windward Oahu sewerage system by conveying flows by gravity from the Kaneohe Wastewater Pre-Treatment Facility to the Kailua Regional Wastewater Treatment Plant, replacing an existing pump station and force main system. Additionally, the tunnel stores wet weather flows during heavy rain storms.
Eventually the Kaneohe plant will be decommissioned. The tunnel was constructed large enough to accommodate peak wet weather flows and also reduce the visual impact of a treatment facility and the possibility of spills.
JWF was the microtunnel subcontractor for the Southland/Mole, JV and installed 1,564 feet of 60-inch sewer pipe and steel casing in four drives of 178, 362, 439 and 585 feet at depths of 18 to 33 feet and 14 to 20 feet below the groundwater table .
Flows from the existing Kailua Regional Wastewater Treatment Plant were diverted to a new pump station by a new near-surface pipeline installed via microtunneling. The microtunneled pipeline was located under/near an existing DAFT Control building supported by shallow spread footings, existing 24-inch and 36-inch force mains and an existing diversion structure.
The soil conditions included highly variable ground consisting of primarily squeezing and flowing ground conditions. The soils included fill, alluvium,lagoonal deposits consisting mainly of saturated, highly compressible, soft to medium stiff clays and very loose to medium dense clayey coralline sands and gravel with extremely weathered basalt gravel and basalt. Based upon conditions identified in the geotechnical reports, the contractor performed jet grouting to stabilize the soils for tunneling.