Displacement of Underground around Existing Tunnel Affected by Adjacent Slope Excavation Step in a Jointed Rock Mass

초록

In these days, construction adjacent to the existing structure has been growing in order to construct parallel tunnel, cross tunnel, embankment, cutting and structure foundation above existing tunnel, slop excavation, and so on. Especially, when the rock slope is excavated adjacent to a tunnel in order to construct road or new parallel tunnel, the stability of the existing tunnel would be influenced and plastic zone could be developed or expanded around the existing tunnel. Behavior of the existing tunnel would be greatly influenced by not only slope angle but also joint condition. Therefore, the safety of existing tunnel should be analyzed under the consideration of joint condition of rock mass and excavation conditions (slope, reinforcement method, etc.). However, it is not easy to find out examples or studies on slope or tunnel excavation adjacent to an existing tunnel. Only a few studies could be found, but they are mostly limited to homogeneous ground. In the jointed ground, therefore, construction is often undertaken based on the judgment of engineer’s experiences for the homogeneous ground. In this study, the effects of joints on the ground displacement around existing tunnel during the ground excavation close to a tunnel was investigated through large scale model tests in the biaxial test facility (3.1m x 3.1m x 0.50m (width x height x length)). Test ground with regular joints were built with concrete blocks. Model tunnel in 1/10 scale (0.6 m in diameter) was built up. Joint dips were varied from vertical to horizontal (0°-90°), while the angle of excavated slope was varied 60°~90°. Behavior of ground displacement was measured and analyzed under the consideration of joint dip, slope angle, and slope excavation.