Road Tunnel Excavations Beneath Existing Metro Lines: Tseung Kwan O – Lam Tin Tunnel Available to Purchase

Tseung Kwan O - Lam Tin Tunnel project will be developed to improve connectivity between the Central and Eastern Kowloon areas of Hong Kong. The twin tube road tunnel is 2.6 km long requiring excavation spans ranging from 16 m to 34 m. The underlying geology of the site is dominated by jointed granite and highly fractured volcanic tuff. The rock will be excavated using drill and blast techniques, but with the appropriate restrictions applicable to the urban area setting. At Lam Tin Interchange (LTI) Portal, a 9 m span pilot adit, enlarged to a permanent portal span of 25 m is required to obtain early access one of the main tunnel drives. The key challenge at this location, is that the adit and main drive junction pass directly beneath existing metro lines, with vertical separation less than 10 m at the closest point. What further complicates matters is that in this particular zone there is a mapped fault running through this location. It is a requirement of the rail authority, Mass Transit Railway, MTR, that any tunnel excavation induced deformation and vibration within the existing metro is monitored and controlled to pre-determined levels. If these allowable limits are exceeded, tunnelling works are suspended. This paper presents the detailed construction impact assessment which was carried out using advanced numerical modelling techniques to predict the potential effects on the metro tunnels. A comparison between the predicted and measured ground conditions and ground response to the tunnelling is presented to compare actual with predicted observations. The paper will serve as a useful reference for analytical techniques employed at critical existing infrastructure locations where impacts must be tightly controlled to ensure acceptable ongoing operational and safety measures are maintained.