Design and Construction for the First Semi-Cavern Building in Hong Kong – A Case Study in Tseung Kwan O – Lam Tin Tunnel

The Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) has been commissioned since December 2022, which is a new truck road linking Tseung Kwan O and Kowloon urban area, with about 2.2 km long rock tunnels. This tunnel connects the Cross Bay Link in the east, and the Trunk Road T2 in the west, forming the integrated part of future Route 6, servicing the second tunnel for TKO residents to Kowloon with shortened travelling time. At the TKO Portal, two large-span caverns were designed and constructed to accommodate a semi-cavern tunnel ventilation buildings. This idea was proposed to reduce the surface footprint of ventilation building by placing its significant portion into the caverns. With this innovative semi-cavern building scheme, the slope cutting and stabilization works have been minimised, the disposal of excavated materials and tree felling have been reduced, it also improves the visual impact of the ventilation building and enhanced the construction programme. With portion of ventilation building inside the caverns, it could provide stable environment for E&M equipment with regard to weather protection, steady temperature and humidity. The challenges in terms of geology, hydrogeology and geotechnical engineering have been overcome successfully throughout the project implementation. This innovative engineering solution also provided significant benefits to the project in terms of cost effectiveness, sustainability and energy efficient aspects in the construction and operation stages of the project. This semi-cavern building scheme is a perfect example that the industry is utilising underground space and promoting rock cavern development in Hong Kong. This paper presents a successful case study for the rock semi-cavern works in TKO-LTT from the planning, detailed design to construction stages.