Rock failure in compression

IliA A probabilistic model of the fracture processes unifying the phenomenological study of long term strength of materials, fracture mechanics and statistical approaches to fracture is briefly outlined. The general framework of irreversible thermodynamics is employed to model the deterministic side of the failure phenomenon. The stochastic calculus is used to account for the failure mechanisms controlled by chance, particularly, the random roughness of fracture surfaces. Auth. 854019 Rock failure in compression Nemat-Nasser, S; Horii, H lnt J Engng Sci V22, N8-10, 1984, P999-1011 (paper to the Proceedings on Media with Microstructure and Wave Propagation, Houghton, Michigan, 24-25 Jan 1983) Failure mechanisms for rock in compression were studied. Analytical models were constructed and model testing using a brittle polymer was carried out. Axial splitting of uniaxially compressed rock is shown to occur through unstable growth of tension cracks which propagate from the tips of pre-existing cracks and curve towards the direction of maximum compression. Shear failure of triaxially compressed rock is due to sudden growth of tension cracks at tips of a suitably arranged intersecting set of microcracks. The variation of ultimate strength and orientation of the overall fault plane with confining pressure is estimated and the brittle-ductile transition is discussed. 854020 Numerical simulation of unsteady fluid flow and propagation of a circular hydraulic fracture Cleary, M P; Wong, S K lnt J Num Anal Meth Geomech V9, NI, Jan-Feb 1985, P1-14 An hydraulic fracture is modelled as a circular crack propagating under the action of frac-fluid being pumped in at a central wellbore. The coupling between elasticity and fluid flow is dealt with numerically, by two different algorithms: one iterates on crack tip velocity, the other varies the time step size until it agrees with the chosen increment in crack length. The velocity algorithm is found to be computationally more efficient and stable. The model allows detailed tracing of pressure distribution and fluid flow in the fracture. 854021 Theoretical study on the stability of a reservoir created by the intersection of a fluid-filled crack with an oblique joint for the extraction of geothermal heat Abe, H; Hayashi, K; Arima, S lnt J Num Anal Meth Geomech I/9, N1, Jan-Feb 1985. P1527 The stress intensity factors are evaluated for discussing crack kinking at the upper joint tip, and the conditions are obtained for the inclination of the joint and the length between the upper joint tip and point of intersection to keep a fluid-filled crack stable just beneath a joint. The volume of the stable reservoir created by using a joint is much larger than that of a fluid-filled crack in a jointless rock mass, even if the joint is oblique and is opened up by the fluid pressure. 854022 Experimental analysis of crack propagation in granite Labuz, J F; Shah, S P; Dowding, C H lnt J Rock Mech Min Sci V22, N2, April 1985, P85-98 An experimental approach is used to demonstrate the concept of an effective crack length with double-edge-notched (DEN) specimens of Charcoal and Rockville granite, and the importance of including the fracture process zone (a region analogous to the plastic zone in metals) when calculating the fracture resistance of subsize specimens. Twenty closed loop,

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strain controlled fracture tests and eight tensile tests were conducted. A J-integral expression was derived for the DEN geometry in terms of the area under the load-displacement record. Results and discussion are presented. 854023 Experimental investigation concerning the comprehensive fracture toughness of some brittle rocks Huang Jian-An; Wang Sijing lnt J Rock Mech Min Sci V22, N2, April 1985. P99-104 An experimental investigation of comprehensive fracture toughness of syenite and basalt rocks by using a testing procedure which consists of three-point bending, asymmetric threepoint bending and four-point shear tests. Experimental data can be correlated with various physico-mechanical properties. Results show that the curve of rock fracture toughness of various fracture modes can be approximated by an empirical quadratic equation. Various characteristics of rock fracture such as the critical stress intensity factors, notch displacement, fracture toughness ratio and fracture angle are found to be dependent upon the petrological composition and grain size. 854024 J-integral method in analysis of stress intensity factor using boundary elements Kishitani, K; Hirai, T; Murakami, K J Fac Engng Unit Tokyo Set B V37, N3. March 1984. P529547 The Boundary Element Method may be beneficially used in calculating numerical solutions to engineering problems such as elastic analysis of crack propagation. There are two methods for formulating BEM, direct and indirect, the latter of which is superior with respect to accuracy when developing a BEM program which can be applied to arbitrary boundary conditions. A crack analysis technique using the indirect method of formulation has been derived and applied to a number of crack problems with arbitrary boundary conditions.

Strength characteristics 854025 Cyclic triaxial behaviour of Monterey number 0 and number 0•30 sands. Technical note Charlie, W A; Muzzy, M W; Tiedemann, D A: Doehring, D O Geotech Test J V7, N4, Dec 1984, P211-215 Results of a testing program to compare the cyclic triaxial behaviour of Monterey No 0 and No 0/30 sands are presented. Tested under identical conditions, the Monterey No 0 3 0 sand yielded higher cyclic strengths than did Monterey No 0 sand. 854026 Residual strength of clays in landslides, folded strata and the laboratory Skempton, A W Geotechnique 1135, N1, March 1985, P3-18 An account of the special lecture to the British Geotechnical Society, at the Institution of Civil Engineers. A summary on the subject of residual strength. Descriptions of the development of residual strength; field residual strength for landslides and for clays; comparison of field residual and ring shear tests: relation between residual strength and clay fraction; and rate effects are presented.