Sakai City to Expand “Detailed Design with Construction” System to Medium and Large-Diameter Sewer Pipes in FY2025
October 3, 2025 – Government & Organizations
The Sakai City Waterworks and Sewerage Bureau is advancing efforts to efficiently renovate and improve the earthquake resistance of its aging sewer pipes by trialing a “detailed design with construction” contracting system. Starting in fiscal year 2025, the scheme will be expanded from small-diameter pipes to also cover medium- and large-diameter pipelines. Through effect verification and phased expansion, the bureau aims to put the system into full-scale operation as soon as possible.
Traditionally, detailed design and construction were tendered separately. Under the new method, both are commissioned together in a single package—an adaptation of the Design-Build (DB) system for sewer pipe renewal and seismic strengthening projects.
The bureau first introduced this system in FY2023, requiring joint ventures (JVs) of contractors and construction consultants. To date, three projects have been tendered, reducing the coordination burden between design and construction, improving efficiency for both client and contractors, and helping to address on-site labor shortages. Each tender attracted around ten bidders, ensuring sufficient competition.
In the first project, the Sunamichi-cho Sewer Pipe Seismic Reinforcement Work, the total design and construction schedule—including bidding and contracting procedures—was reduced by about seven months compared to the two years typically required. Currently, two small-diameter projects are underway as part of the FY2024 trial, including the Miyayamadai Sewer Pipe Seismic Reinforcement Work (approx. 2.2 km, 200–500 mm diameter).
With sewer pipe deterioration a nationwide challenge for municipalities, Sakai’s approach has drawn considerable attention, with many cities sending inquiries and conducting site visits.
A bureau official stated:
“This fiscal year, we plan to expand the system to cover medium- and large-diameter pipelines and increase the number of projects. Based on lessons learned from the trials, we will refine the system and contribute to solving the broader national policy challenge of sewer infrastructure renewal.”
