Brittle Fracture of Rocks
Most rocks specimens fail violently and uncontrollably at their peak strength when tested under unconfined stress conditions in conventional hydraulic loading systems. At failure their resitance to carry load rapidly drops to zero. This behaviour is commonly known as the “brittle” behaviour of rocks. Only recently it was recognized that such a behaviour is largely due to the rapid release of stored strain energy from the specimen-machine system (COOK 1965; HUGES and CHAPMAN 1966; BIENIAWSKI 1967). The understanding of this problem made possible a considerable progress in studying the fracture processes in rocks in laboratory testing. WAWERSIK (1968) showed in one of the most comprehensive fracture studies up to date by using a “stiff” loading system that fracture of rock may be considered as a continuous progressive and controllable breakdown process occurring over the entire deformation range, from initial loading to the complete disintegration. The concept of the application of such “stiff” loading systems related to rock testing is shown in Fig. 1 for a soft (K1), a relatively stiff (K2) and a very stiff (K3) system (K are the stiffnesses, defined as the ratio between the drop in force, ΔF, and the corresponding platen displacement).
KeywordsBrittle Fracture Rock Specimen Store Strain Energy Griffith Crack Typical Stress Strain Curve
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- W. Wawersik (1968): A detailed analysis of rock failure in laboratory compression tests. PhD thesis, Univ. of Minn.Google Scholar
- N.G.W. Cook (1965): The failure of rock. Int. J. Rock Mech. Minn. Sci., Vol. 2, 4.Google Scholar
- B.P. Huges and Chapman (1966): The complete stress-strain curve for concrete in direct tension. Bull. Rilem. No. 30.Google Scholar
- Z.T. Bieniawski (1967): Determination of rock properties. South Afr. CSIR Rep., No. Meg. 518Google Scholar
- F. Rummel and Fairhurst (1970): Determination of the post-failure behaviour of brittle rock using a servo-controlled testing machine Rock Mech. 2, 189 - 204.Google Scholar
- L. Fairhurst (1971): Fundamental considerations relating to the strength or rock. Coll. Fracture Mechanisms in Rocks, Bochum, 1971 Veröff. Inst. Bochum etc. Felsmech., Univ. Karlsruhe 1972, Heft 55.Google Scholar
- J. Hudson et al. (1972): Soft, stiff and servo-controlled testing machines, a reviw. Eng. Geol., 6 (3).Google Scholar
- [81.C. Fairhurst (1973): Estimation of the mechanical properties of rock masses. ARPA-Report, Univ. Minn.Google Scholar
- K.V. Terzaghi (1929): Effect of minor geol. de on safety of dams. T.P. 215, ALME.Google Scholar
- K.V. Terzaghi (1945): Stress conditions for the failure of saturated concrete and rock. Proc. ASTM 45.Google Scholar
- C.B. Raileigh and J. Handin (1972): Manmade earthquakes and earthquake control. Conf. Flow in Fiss. Rocks, Stuttgart.Google Scholar
- Raileigh and Dieterich: pers. comìn. (1972).Google Scholar