Strengthening the side walls of the under-sea tunnel on the Tokyo Port number 2 route using the post-construction reinforcement-embedment method for shear strengthening

Toru KOBAYASHI¹, Osamu KIYOMIYA², Yukio OKUDAIRA³
1. Nippon Civic Consulting Engineers Co., Ltd. ; 2. Waseda University;
3. Tokyo Metropolitan Ports & Harbour Authority
Civil Engineering Construction Technical Symposium, 2003 proceedings, July 2003

Key words: immersed tunnel, road tunnel, Tokyo Port, shear strengthening, Hanshin Earthquake, specification, post-construction reinforcement-embedment method, seismic resistance, shear strengthening

Background
The conventional method of seismic reinforcing of existing structures is to encase the weak member with a steel plate or cable or to increase the thickness of the member. For tunnels, though, the internal cross-section opening needs to be preserved as much as possible. The Tokyo Port number 2 route sub-sea tunnel is an immersed-tube road tunnel opened in 1980. Twenty years on, the need to strengthen the tunnel to resist seismic forces equivalent to the Great Hanshin Earthquake (Japan level 2 earthquake intensity) was identified. The "post-construction reinforcement-embedment method", in which deformed reinforcement is embedded in the target members, was proposed as the construction method so as not to reduce the internal cross-section of the road tunnel.

Research Summary
Before using the proposed method on the actual site, its strengthening effect was confirmed in 12 indoor tests using a test beam member (30 cm x 46 cm x 240 cm). Based on the results, specifications were subsequently prepared addressing important considerations for design and construction.