Study on application of displacement measurement method in 3-D physical model tests of cavern complex

AUTHORS: 
Zhu, W.S., Zhang, Q.B., Sun, L.F., Zhang, L., Li, S.C., Zhang, Q.Y., and Ma, Q.S
Geotechnical & Structural Engineering Research Center, Shandong University, Jinan, Shandong 250061, P. R. China

ABSTRACT:
Using the Shuangjiangkou hydropower station on the Dadu River in China as a background, another new physical model test of an underground cavern complex in a true 3D stress state has been conducted based on a quasi-three dimensional model test which was performed in 2007. The original experimental techniques used in last model test have been significantly developed, and some new measuring techniques have been implemented in the new model test. In order to solve the problem in measurement of small displacements in the surrounding rock masses, the digital speckle correlation method (DSCM) and special displacement sensing bars based on fiber Bragg grating (FBG) technology are adopted. Mini multi-point extensometers with high-precision grating scales are developed as transducers for displacement monitoring. We also conducted a numerical simulation with almost the same conditions, and compared the results of the model test and the numerical approaches. The study shows that the research and application of the displacement measurement methods used in the surrounding rock masses for large-scale model tests of cavern complex under 3-D stress field have achieved satisfactory results. 

REFERENCES:
1. Zhu, W.S., Y. Li, L. Zhang, et al. 2008. Model test and numerical analyses on the stability of a cavern complex. In the 42nd US Rock Mechanics Symposium and 2nd U.S.-Canada Rock Mechanics Symposium, San Francisco, June 29-July 2, 2008. ARMA 08-194.
2. Zhu, W.S., Y. Li, L. Zhang, et al. 2008. Geomechanical model test on stability of cavern group under high geostress. Chinese Journal of Rock Mechanics and Engineering 27(7): 1308-1314. (in Chinese)
3. Li, Z.K., H. Liu, R. Dai, et al. 2005. Application of numerical analysis principles and key technology for high fidelity simulation to 3-D physical model tests for underground caverns. Tunnelling and Underground Space Technology 20(4): 390-399.
4. Nagai, T., S. Kunimura, and J. Sun. 1996.  Behaviour of jointed rock masses around an underground opening under excavation using large-scale physical model tests. In Proceedings of the Symposium on Rock Mechanics. 27:116-120.
5. Meguid, M.A., O. Saada, M.A. Nunes, et al. 2008. Physical modeling of tunnels in soft ground: A review. Tunnelling and Underground Space Technology 23(2): 185-198.
6.  Sterpi, D. and A. Cividini1. 2004. A Physical and Numerical Investigation on the Stability of Shallow Tunnels in Strain Softening Media. Rock Mechanics and Rock Engineering 37(4): 277-298.
7. Tiwari, R.P. and K.S. Rao. 2004. Physical modeling of a rock mass under a true triaxial stress state. International Journal of Rock Mechanics and Mining Sciences 41(Supplement 1): 396-401.
8. Seki, S., S. Kaise, Y. Morisaki, et al., 2008. Model experiments for examining heaving phenomenon in tunnels. Tunnelling and Underground Space Technology 23(2): 128-138.
9. Lee, Y.J. and R.H. Bassett. 2006. Application of a photogrammetric technique to a model tunnel. Tunnelling and Underground Space Technology 21(1): 79-95.
10. Li, Y.H., H.H. Zhu, K. Ueno, et al. 2004. Deformation field measurement for granular soil model using image analysis. Chinese Journal of Geotechnical Engineering 26(1):36-41. (in Chinese)
11. Zhao, Y. and Y. Liao. 2004. Discrimination methods and demodulation techniques for fiber Bragg grating sensors. Optics and Lasers in Engineering 41(1): 1-18.
12. Yin, J.H., H.H. Zhu, W. Jin, et al. 2007. Performance evaluation of electrical straingauges and optical fiber sensors in field soil nail pullout tests. Geotechnical Advancements in Hong Kong since 1970s, The HKIE Geotechnical Division 27th Annual Seminar. Hong Kong, 249-254.
13. Chan, T.H.T., L. Yu, H.Y. Tam,  et al., 2006. Fiber Bragg grating sensors for structural health monitoring of Tsing Ma bridge: Background and experimental observation. Engineering Structures 28(5): 648-659.
14. Chu, L. M.  and J. H. Yin. 2005. A laboratory device to test the pull out behavior of soil nails. ASTM Geotechnical Testing Journal  28(5):1-15.
15. Itasca Consulting Group, Inc. Flac 3D version 3.0. Minneapolis (MN, USA). 2002.