227A illustration of the onset of unstable crack propagation and/or flaw coalescence when irreversible microcracking is generated by vibratory loading. 876O83 Fracture toughness determination with the modified ring test Thiercelin, M; Roegiers, J C Proe International Symposium on Engineering in Complex
Rock Formations, Beijing, 3-7 November, 1986 P284-290. Publ Beijing: Science Press. 1986 The modified ring test, based on hollow cylinder geometry with diametrically opposed flat loading surfaces, has been developed to allow accurate determination of fracture toughness in soft or heterogeneous rock. It uses core based specimens, and prevents the formation of a large process zone ahead of the crack tip, employs the concept of critical crack length, and considers a sufficiently long crack to be able to neglect subcritical propagation. 876084 Mechanics of crack propagation in stiff clays Vallejo, L E Proc Symposium on Geotechnical Aspects of Stiff and Hard
Clays, Seattle, 9 April 1986 P14-27. Publ New York: ASCE, I986 Cracks in stiff fissured clays in natural slopes and earth dams may propagate under gravitationally induced stresses. A theoretical analysis, using linear elastic fracture mechanics, of fracture propagation under field conditions is undertaken, and the maximum tangential stress criterion for crack propagation is developed. Laboratory uniaxial compression tests on a stiff kaolinite clay with pre-existing cracks give results in accordance with the proposed analysis.
Time dependent behaviour See also: 876005, 876321, 876384, 876385 876085 Time dependent behaviour of the Boom clay at great depth an application to the construction of a waste disposal facility De Bruyn, D; Neerdael. B; Gonze, P; Rossion, J P; Rousset, G
Comput Geotech V3, N1, 1987, P3-20 Rheology of the Boom clay formation in Belgium has been studied using laboratory triaxial creep tests and in situ tests in an underground laboratory at depth 223m. Results have been used to simulate excavations of large galleries at depth. A finite element program using Vyalov's creep law was chosen as a first approach. Simulation of shaft and gallery excavations will allow evaluation of the creep parameters to predict clay and lining behaviour of large diameter excavations. 876086 Time-deflection behaviour of a rigid under-reamed anchor ifia deep clay layer Small, J C; Booker, J R lnt J Num Anal Ateth Geomech VII, N3, May-June 1987,
P269-281 A method is presented to analyse the time-deflection behaviour of an impermeable, rigid or flexible, circular underreamed anchor in an isotropic soil, due to soil consolidation• It uses numerical inversion of transformed solutions, and accurate solutions are more easily obtained than with numerical
techniques such as finite element anal.vsis. Results of the proposed method are compared with published and recomputed finite element analysis. Behaviour is seen to be relatively insensitive to Poisson's ratio for the soil. 876087 Creep bending of rock beams Singh, J G; Upadhyay, P C
Min Sci Technol I/5, N2, Juh" 1987, P163-I69 The creep bending under constant loading of a rock beam, represented by a Burger's model, has been analysed. The differing creep rates of rock under tensile and compressive loading are included in the analysis. Results are expressed in terms of non-dimensional parameters, some of which are of significant influence. The movement of the neutral axis has been qualitatively verified by experiment. 876088 Creep parameters of rocks on an engineering scale Han-Ping Chin; Rogers, J D
Rock 34ech Rock Engng ~ 0 . N2, April-June 1987, P137-146 To study creep deformation of carbonate shale, tuff, and weathered limestone for a hydropower project, vertical shafts of 137cm diameter were excavated and the change in diameter with time under constant radial pressure recorded. Three rheologic models were examined for best fit against experimental results. The power law yielded good data fit. It was found that discontinuous field rocks have higher plasticities than small, intact laboratory specimens, and in situ measured viscosities are much smaller than those from laboratory tests. 876089 Upper limits of power law creep of rocks Tsenn, M C; Carter, N L
Tectonophysics V136, N1/2, 1 May I987. P1-26 At depths over of few kilometers, most rocks deform in the steady state by diffusion assisted dislocation c r o p , and strain rate is proportional to a tow power of deviatoric stress. At high stress levels this power law breaks down. Methods by which the breakdown may be estimated are examined for metals, alloys, ceramics, non-silicate rocks, and silicates. For silicates at high stress levels there is an exponential dependence of strain rate on stress, and the deformation mechanism is generally lattice controlled dislocation glide and mechanical tvdnning. Breakdown stresses for silicates are effectiveIy strain rate insensitive, and extrapolated values suggest that low temperature, high stress plasticity may be suppressed in geological formations. The breakdown stress for olivine rich rocks and deformation of wet and dry olivine polycrystals are discussed. 876O9O Prevision of convergency in highway tunnels using dilatometer tests in Liege (Belgium) Delapierre, J; Pohl, E; Funcken, R; Nomerange. J: Marchal, J P; Latour, F Proc International Symposium on Large Rock Carerns, Helsinki, 25-28 August 1986 V2, P921-927. Publ Oxford:
Pergamon Press, 1986 Dilatometer creep tests were among those carried out during site investigation. Assuming the rock to be a Burgers body, viscoelastic parameters of the rocks encountered are evaluated and compared with previous work. Predictions are made of the convergence of lined and unlined tunnels in very fractured sandstone, to assess behaviour between excavation and lining, and after lining.
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