The Study On Adjoining Rock Stability And Support Pattern Of Deep-lying Tunnel

As a kind of important hydraulic structure, hydraulic tunnel is very useful at many aspects such as conveyance, diversion and flood discharge. Many conveyance and hydropower projects including many hydraulic tunnels are built since 1949. A lot of experiences at the construction of tunnel are accumulated. But to deep-lying diversion runnel, there are a lot of problems to be resolved not only hi design theory but also in techniques. Tunnel construction is very difficult hi region with high geotectonic stress and high subsurface water pressure. Few deep-lying tunnels are constructed in civil conveyance and hydropower engineering up to now.The structure of Jinping Cascade 2 Hydropower Station is a high-head and high discharge diversion tunnel with low crown gate. The key technique of this project is the design and construction of four deep-lying long runnels. Their length, diameter and maximum bury-depth are 18 km, llm, 2500 m. The high geotectonic stress at the construction region and the activity subsurface water will have important effects on construction and operation. Excavation of tunnel will lead to local geotectonic stress release and redistribution around tunnel; the appearance of new outlet boundary will lead to outlet seepage of subsurface water and the change of mountain seepage field. The problems to be resolved are the stability analysis considering the influence of so many loads and how to reach the stability requirement by choosing reasonable support patterns.This thesis tries to solve the problems in the design and construction of Jinping Cascade 2 Hydropower Station. A typical section is selected to analysis seepage, seepage control and FEM numerical simulation. The influence of different plans of excavation and support on seepage field of subsurface water and stability of adjoining rock are studied .The homologous support pattern is suggested according to the research results.