A two-stage model of fracture of rocks

PROPERTIES:FRACTURE 968096 Strain softening and shear band form&ion and sand in multi-axial testing J. Chu, S.-C. R. Lo & I. K. Lee, Geotechnique, 46(l), 1996, pp 63-82. The strain softening of a granular soil under a or’ # ai # cr3’ condition and along a wide spectrum of paths was investigated experimentally. Strain softening was found to be pathdependent. It can take the form of shear band formation, or it can occur without the development of any non-homogeneity. Shear band formation is not necessarily a consequence of boundary imperfections, but can occur as the inevitable response of a sample to certain stress states and shear paths. The conditions for shear band formation were established and three types of strain softening identified. (from Authors) 968097 Angles of friction and dilatancy of sand T. Schanz & P. A. Vermeer, Geotechnique, 46(l), 1996, pp 145-151. The strength of sand is usually characterized by the peak friction angle &, and the critical state friction angle &. It is generally realized that the peak friction angle depends not only on density but also on the stress path, including differences between plane strain and triaxial testing conditions. Indeed, plane strain and triaxial strain angles can differ by more than 5” for a dense sand. For a loose sand at the critical density it is often suggested that similar differences occur. This note presents data on a unique critical state angle. The implication is that the failure criterion of a very loose sand is accurately described by the Mohr-Coulomb condition, which gives the known six-sided pyramid in principal stress space. (from Authors) Exact prescribed displacement field solutions in Mohr Coulomb elastoplnsticity Pankaj & K. Moin, Engineering Computations, 13(l), 1996, pp 4-14. Exact solutions in computational elastoplasticity cannot be used directly as they often pertain to solutions that are valid only for specific cases. However, these solutions can be used as benchmark tests to check the validity of finite element codes and accuracy of numerical solution procedures. Here exact solutions for Mohr-Coulomb elastoplasticity are developed, detailed expressions derived and three dimensional examples considered. (from Authors) 968099 Inclusion of specific water volume witbin an elnsto-plastic model for unsaturated soil S. J. Wheeler, Canadian Geotechnicul Journal, 33(l), 1996, pp 42-57. An existing elastoplastic model has been extended to include relationships describing the variation of specific water volume. The proposed form of the variation of specific water volume was based on consideration of the soil fabric, resulting in a coupled form of elasto-plastic behaviour. Normal compression lines for specific water volume at different values of suction were well predicted, as was the variation of specific water volume during wetting. Critical state values of specific water volume were slightly underestimated, but test paths for both drained and undrained shearing were predicted with reasonable success. (from Author) 96lilOO In situ tests in Brasilia porous clay J. A. R. Ortigao, R. P. Cunha & L. S. Alves, Canadian Geotechnicul Journal, 33(l). 1996, pp 189-198. An in situ testing programme was carried out in 1992 aimed at obtaining design parameters for the construction of the Brasilia Underground line. The top layer of soil consisted of an unsaturated and collapsible soft porous clay layer 5-30 m thick followed by residual soils from slate and interlayered

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metasiltstones and quart&es. A series of Marchetti dilatometer (DMT) logging tests results were compared with Menard pressuremeter (PMT) and horizontal plate loading (PLH) tests. The DMT yielded very good results: excellent repeatability, low cost, and results that agree with other in situ tests and laboratory data. (from Authors) 968101 Geological characteristics and economic appraisal of Jinojiping granite deposit in Hanyuan, Sicbuan (in Cbinese) Xiao Yuanfu, Sun Yan, Mao Yanshi & Xia Jun, Journal Chengdu Institute of Technology, 22(3), 1995, pp 65-69. The paper describes in detail the geological characteristics of the Jiaojiping granite deposit in Hanyuan County, Sichuan and makes a geological economic appraisal of the commodity features and the quality of dimension stone in the deposit. The physical properties of the dimension stone come up to the indexes of granitic stone required by American Institute of Stone Industry. So the deposit is one of the highquality red granite deposits in China. (English summary) 968102 The distribution and geotecbnical properties of loess soils, lateritic soils and clayey soils in China Guorui Gao, Engineering Geology, 42(l), 1996, pp 95-104. The special geotechnical properties of Chinese soils are briefly described. It is shown that the special geotechnical properties of these soils depend mainly on their material component and microstructural features. The distribution of these soils is studied in relation to geographical environment and climatic conditions. It is suggested that the formation of the geotechnical properties of these soils have undergone three different development stages. (from Authors)

Fracture processes 968103 Modelowanie procesu niszczenia gorotworu oraz analiza stabihrosci mas sknlnych (Modelling of fracture processes and an analysis of stability of rock masses) K. Wanat, Publications - Institute of Geophysics, Poltih Academy of Sciences, series M, M-19(281), 1995, pp 103-l 13. Within a fracture mechanics framework, a notion of effective fracture tensor and effective seismic moment tensor is introduced A method of summing up of fracture tensors is given. The algorithms to calculate resultant displacements in rock mass and the change in stress state generated by a sequence of seismic events are described. An analysis of rock mass stability, based on fracture mechanics, is also presented. (from English summary) 968104 A two-stage model of fracture of rocks V. Kuksenko, N. Tomilin, E. Damaskinskaya & D. Lockner, Pure & Applied Geophysics, 146(2), 1996, pp 253-263. The paper proposes a two-stage model of rock fracture. In the first stage, cracks or local regions of failure are uncorrelated and occur randomly throughout the rock in response to loading of pre-existing flaws. As damage accumulates in the rock, there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop. The proposed model incorporates notions of the kinetic (and therefore time-dependent) nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation. (from Authors) 968105 Experimental study of meso-fractures in rock and its implication for understanding seismic activities (in Chinese) Zhao Yong-Hong, Huang Jie-Fan, Hou Jian-Jun & Wang Ren, Acta Geophysicu Sinicu, 38(5), 1995, pp 627-638.