Stability Analysis Of Underground Cavern Based On Load/unload Of In-situ Stress Field

The stability of underground cavern is very complicated. In this paper, load/unload response ratio(LURR) theory is applied in analysis of stability of underground cavern. Through load/unload test of rock specimens, physical model experiment and numerical analysis,conclusions can be drawn as follows.1) Two types of load –unload path are designated, one is load-unload of axial stress with constant confining pressure, the other is load/unload of confining pressure with constant axial stress. Through MTS system,the experimental results show that, under the first stress path, LURR of axial strain vs. axial stress presents sharp increase while close to the peak stress. Under the second stress path, LURR of axial strain vs. confining pressure and circumferential strain vs. confining pressure is studied, the similar results are found. These results reflect that LURR can be adopted in prediction of rock failure.2) The stability of tunnel using LURR theory is studied through the physical model test. Research shows that LURR of crown displacement and surrounding rock pressure can well reflect stability of tunnel. With vertical in-situ stress increase, LURR of the two parameters grows sharply close to tunnel instability. During load/unload of vertical in-situ stress, AE events and location are researched, While close to instability of tunnel failure, AE events locate intensively at the failure crack close to sidewall of the tunnel.3) A numerical model is set up in order to compared with physical model through RFPA software. Failure of the tunnel locates at the similar position, also LURR of crown displacement vs. vertical in-situ stress presents similar characteristics with physical model results.