Advancing Geotechnical Practice with Design for Manufacture and Assembly (DfMA) Retaining Wall Construction

Abstract

This paper presents the application of Design for Manufacture and Assembly (DfMA) in the construction of a 52m long L-shaped retaining wall with a maximum height of 4.8m, founded on Completely Decomposed Granite, as part of the Relocation of Sha Tin Sewage Treatment Works into Caverns project. This initiative not only enhances sewage infrastructure but also mitigates environmental impact and frees up valuable land for sustainable urban development. The retaining wall supports a 500m access road to the Site Explosives Magazine, strategically designed for the supply of explosives for multiple blasts daily. By favoring DfMA over conventional in-situ methods, the project implemented an innovative design featuring precast steel beams encased in concrete, which were assembled on-site. This approach dramatically reduced construction time from 147 days to approximate 10 days, streamlined on-site activities from 70 to 21, and completely eliminated working-at-height risks, significantly enhancing safety and efficiency. A key to this success was collaboration among the RSS, contractors, subcontractors, and strong client support. Active engagement enabled the collective development of the DfMA strategy, leveraging on-site experience in design optimization and risk management. This approach facilitated early risk identification, ensuring DfMA strategies were well-resourced and successfully implemented.