Chaotic behaviour of frictional shear instabilities

Chaotic behaviour of frictional shear instabilities

17A 921125 Relative performance of compacted and uncompacted rockfiil Matheson, G M Rock Mechanics Contributions and Challenges: Proc 31st US Symposiu...

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17A 921125 Relative performance of compacted and uncompacted rockfiil Matheson, G M Rock Mechanics Contributions and Challenges: Proc 31st US Symposium, Golden, 18-20 June 1990 P989-995. Publ Rotterdam: A A Balkema, 1990

921129 Chaotic behaviour of frictional shear instabifities Hobbs, B E Proe 2nd International Symposium on Rockbursts and Seismicity in Mines, Minneapolis, 8-10 June 1988 P87-91. Publ Rotterdam: A A Balkema, 1990

Results of monitoring several large valley embankment fills for periods up to 95 months are presented. One fill was completed in two stages, part compacted and part uncompacted. Comparison of settlements and settlement rates is made. Compaction reduces potential for settlement by a factor of up to 5. The majority of settlement of the compacted fill is achieved in 12 months. Uncompacted fill will reduce to 12 month settlement rate for compacted fill after about 45 months. Deformation moduli were estimated for one fill on the basis of compression due to additional fill load.

Stick slip motion on pre-existing fractures is one common mechanism for rockburst. It is widely held that such events should be periodic in time. The stability of a simple springslider system, with rate and state dependent frictional constitutive laws and effect of inertia included, is examined by the distinct element method. As spring constant progressively decreases, behaviour changes from periodic/decreasing limit cycles to periodic/sustained limit cycles, to small stick slip events increasing in amplitude with decreasing K, to period doubling and finally chaos.

921126 MechanicaI-AE/MA correlation Cristescu, N Proc 4th Conference on Acoustic Emission/Microseismic Activity in Geological Structures and Materials, Pennsylvania, 22-24 October 1985 P559-567. Publ Clausthal-Zellerfeld." Trans Tech Publications. 1989

Physico-chemical properties

An elastic-viscoplastic constitutive relation is presented (Cristescu, 1985) which can describe dilatancy and damage. Correlation between acoustic emission observed during laboratory tests and deformational behaviour as described by this law is examined. As the law can adequately predict the onset of dilatancy, it should be possible to detect the change to dilatant state of rock around underground openings by monitoring in situ AE count rates. More laboratory data are essential to establish a general invariant form of the correlation between AE and constitutive behaviour.

Surface properties 921127 Joint profiles and their roughness parameters. Technical note Xianbin Yu; Vayssade, B int J Rock Mech Min Sci V28, N4, July 1991, P333-336 The correlation between Barton's JRC and several numerical parameters has been evaluated. Four parameters, those of Myers and of Sayles and Thomas, Real Profile Length, and Standard Deviation of Angle show strong correlation. For these, sensitivity to sampling interval was examined, using Barton's 10 typical profiles, digitised with different sampling intervals. Need to take account of sampling interval when estimating JRC by numerical methods is discussed.

921128 Model for steady state friction Lomnitz-Adler, J J Geophys Res I1"96, NB4, April 1991, P6121-6131 A model for steady state friction between two rough surfaces subjected to constant normal stress is presented in which the friction force results from momentum being transferred from the horizontal to the vertical direction by collisions between asperities. The friction law is independent of the detailed mechanism of energy dissipation. Velocity dependence of the law is evaluated for non-fractal and self-similar surfaces. In the latter case, the existence of stick-slip instability is implied.

See also: 921289 921130 Experimental simple shear deformation of magnetic remanence Kodama, K P; Goldstein, A G Earth Planet Sci Lett VI04, NI, May 1991, P80-88 Shear box tests were carried out on analogue materials to investigate how the magnetic remanence vector behaves during simple shear strain. Samples were given an anhysteretic remanence at various angles to the shear plane and deformed to discover whether the magnetization deformed as a passive line marker or as if carried by actively rotating rigid grains. The majority of these tests, supported by numerical modelling results, suggest the latter mechanism, although there is uncertainty about application of the laboratory conclusions to real rocks. 921131 Mathematical model of a Hot Dry Rock system Heuer, N; Kupper, T; Windelberg, D Geophys J VI05. N3, June 1991, P659-664 A mathematical model is presented which can be used to determine the evolution of temperature in a HDR geothermal reservoir. The solution is available analytically, which allows long term prediction of temperature evolution and evaluation of the effect of critical operational parameters. Although the model contains many simplifying assumptions, it provides a good basis for study, management, and efficiency calculations of a HDR system. 921132 Thermal conductivity and well logs: a case study in the Paris basin Demongodin, L; Pinoteau, B; Vasseur, G; Gable, R Geophys J VI05, N3, June 1991, P675-691 An approach is presented whereby well logs are interpreted in terms of mineralogic composition and porosity, and in situ thermal conductivity estimated using mixing formulae. It has been verified in the laboratory for isotropic samples, but not under in situ conditions. Temperature data recorded at equilibrium for two wells in the Paris basin are used to this purpose. This allows refinement of the conductivity model with emphasis on the contribution of clay minerals. An empirical model where bulk conductivity is expressed directly as a function of well logs is tested, and its shortcomings discussed.

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