Abstract: The 2×2 lane Yuzhou Tunnel was extended to 4×4 lane tunnel in Chongqing airport road. Taking this project as an engineering background, the influences of in situ extension of the tunnel excavation on adjacent buildings and blasting effect on adjacent buildings are studied. The main study methods include the literature research, numerical analysis, monitoring measurement and blasting monitoring. The main conclusions are drawn as follows. (1) Unilateral expansion, both sides extension and around extension are the three tunnel extension method in situ, by construction mechanics analysis, the unilateral extension is optimal; (2) maximum surface settlement curves of extension tunnel are similar with neighborhood tunnel; (3) radius of surface settlement trough curve is about 40 m; (4) the max surface settlement differential is about 10 m and 30 m distance from the center line. The building settlement meets the specifications, and the buildings are safe; (5) blasting vibration monitoring data indicate that the vibration speed of the near building and tunnel is below the specification limit, which indicates that the free face of the existing tunnel absorbs and releases most of blasting vibration energy. The research results provide a reference for similar tunnels in situ extension project.

Key words: tunnel, expansion in situ, settlement, numerical analysis, monitoring measurement, blasting monitoring