Relocation of Sha Tin STW to Caverns — Effluent Discharge Pipe-Jacking Works (DC/2020/05)

This project forms a critical component of the 'Relocation of Sha Tin Sewage Treatment Works to Caverns' programme (Contract DC/2020/05), involving the construction of two effluent discharge pipes — each approximately 2.2 m in diameter and 320 m in length — to convey treated effluent from the new cavern-based facilities to Sha Tin Hoi for discharge.

Site constraints posed one of the greatest challenges. The available work area was extremely limited, ruling out conventional equipment staging. Access routes were narrow with steep gradients, requiring bespoke mobilisation plans for each major plant item — including disassembly for transport and on-site reassembly.

Geologically, the pipe alignment traversed predominantly unweathered granite classified at Grade V with a rock hardness rating of 5. Driving a 2.2 m diameter pipe through such high-strength rock by pipe-jacking placed exceptional demands on TBM cutter selection, thrust calculation and boring parameter control.

At 320 m per drive, the alignment fell within the long-distance pipe-jacking category, where deviation risk increases substantially. The project team deployed a high-precision guidance system coupled with real-time attitude monitoring to maintain axial deviation strictly within tolerance, achieving accurate breakthrough on both drives.

For environmental management, a complete slurry treatment system was installed to process excavated slurry through multi-stage separation, converting it into clean water and reusable aggregate — minimising impact on surrounding water bodies and ecology, and meeting green construction objectives.