CONCLUSIONS For the investigated limestone rock, the effect of confining pressure on KIC and KIIC is much more significant than the effect of temperature. KIC increased by 274% under σ3 = 28 MPa, but the corresponding value at T = 116°C was 24%. KIIC increased by 137% under σ3 = 28 MPa, but the corresponding value at T = 116°C was only 9%. Also, the effect of confining pressure on KIC is much more significant than its effect on KIIC. The above observations lead to the conclusion that the Mode-II component may be the most critical mode controlling failure at high values of temperature and confining pressure. ACKNOWLEDGEMENTS The authors acknowledge the support of King Fahd University of Petroleum and Minerals for providing computing and laboratory facilities. REFERENCES 1. Whittaker, B. N., Singh, R. N. and Sun, G. (1992), “Rock Fracture Mechanics; Principles, Design and Applications”, Developments in Geotechnical Engineering, Elsevier Publishers, Netherlands. 2. Lim, I. L., Johnston, I. W. and Choi, S. K., Assessment of mixed mode fracture toughness Testing methods for rock., Int. J. Rock Mech. Min. Sci. & Geomech. Abstr., Vol. 31, No. 3,. pp. 265-272 (1994). 3. Atkinson, C., Smelser, R. E. and Sanchez, J. (1982), “Combined Mode Fracture via the Cracked Brazilian Disk”, Intl. Journal of Fracture, Vol. 18, pp. 279-291. 4. Huang, J. and Wang, S. (1985), “An Experimental Investigation Concerning the Comprehensive Fracture Toughness of Some Brittle Rocks”, Int. J. Rock Mech. Min. Sci. and Geomech. Abstr., Vol. 22, No. 2, pp. 99-104. 5. Sun, G.X. (1990), Application of Fracture Mechanics to Mine Design, PhD Thesis, Dept. of Mining Engineering, University of Nottingham, England. 6. Awaji, H. and Sato, S. (1978), “Combined Mode Fracture Toughness Measurement by the Disk Test”, Journal of Engineering Materials and Technology, Vol. 100, pp. 175-182. 7. Lim, I. L., Johnston, I. W., Choi, S. K. and Boland, J. N. (1994), “Fracture Testing of a Soft Rock with Semicircular Specimens Under Three Point Bending-Part 1”, Int. J.Rock Mech. Min. Sci & Geomech. Abstr., Vol. 31, No. 3, pp. 185-197. 8. Khan, K., and Al-Shayea, N. A., “Effects of Specimen Geometry and Testing Method on MixedMode I-II Fracture Toughness of a Limestone Rock from Saudi Arabia”, Rock Mechanics and Rock Engineering, July-Sept. 2000, 33 (3), 179-206. 9. Al-Shayea, N. A., Khan, K. and Abduljauwad, S.N., “Efffects of Confining Pressure and Temperature on Mixed-Mode (I-II) Fracture toughness of a Limestone Rock Formation”, International Journal of Rock Mechanics and Rock Sciences, June 2000, 37 (4), 629-643.
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