Influence of nonlinear material properties and resistance to bending on the development of internal structures

192A efficiencies compared. The Salamon and Wiebols procedures performed best but areas for further development are outlined. 856199 Instantaneous outbursts of coal and gas with reference to geological structures and lateral stresses in collieries Shepherd, J; Blackwood, R L; Rixon, L K Proc 1st International Congress on Roekharsts and Seismicity in Mines, Johannesburg, Sept 1982 P97-106. Publ Johannesburg: SAIMM, 1984 The roles of geological structure and lateral stress are analysed with respect to certain gas outbursts in Australia. The 'dynamic theory' is developed to explain outbursts at two sites where excess lateral stresses overloaded gassy coal ahead of the faces. An energy balance hypothesis is outlined numerically to explain face failure close to minor strike-slip faults. A qualitative, mechanistic model accounts for the development of conical cavities. The outbursts can be considered as having been initiated in a manner similar to the origin of geological kink bands. Comments are made on outbursts in a region of low seismic activity. 856200 Shrinkage and Atterherg limits in relation to other properties of principal soil types in Israel Smith, C W; Hadas, A; Dan, J; Koyumdjisky, H Geoderma V35, N1, April 1985, P47-65 Soil samples from 32 sites were used to study the relationships between mechanical properties (Atterberg limits, coefficient of linear expansion (COLE) and physical and chemical properties (specific surface area, chemical composition, cation exchange capacity (CEC) and exchangeable sodium percentage (ESP). It was concluded that mechanical properties may be estimated as a first approximation from knowledge of clay mineralogical status and texture. Many secondary factors are shown to introduce complicating effects to the simple predictive model. 856201 Influence of nonlinear material properties and resistance to bending on the development of internal structures Latham, J P J Struct Geoi V7• N2, 1985, P225-236 A reexamination of Biot's internal instability analysis, including the effects of bending resistance and nonlinear material properties, shows that internal buckling and oblique localized shearing into bands are the two end-member processes associated with internal instability. A power-law elastic model was used to illustrate the most important mechanical effects of nonlinear properties, effects that are probably typical of many elastic-plastic strain-hardening rocks. The effective modulus equations are derived for a simple bilaminate consisting of layers with properties described by the power-law elastic model. These equations define the mechanical properties of a homogeneous anisotropic continuum. Solutions for the dominant characteristic direction for shearing are derived and presented graphically in terms of the degree of incremental anisotropy and the bending coefficient. 856202 Numerical investigation and geological discussion of the relationship between folding, kinking and faulting Latham, J P J Struct Geol V7. N2, 1985, P237-249 The layer-parallel compression of a regular bilaminate consisting of layers with materials described by an incompressible power-law elastic model is considered. The average mechanical properties of this idealised multilayer are then represented by those of an equivalent anisotropic continuum with internal

resistance to bending. Estimates of nonlinear material properties from reported experiments on the behaviour of various rocks in the time-dependent deformation regime, and geometric parameters such as the volume fraction of each material and the number of confined layers are considered. Results suggest that for typical properties of sedimentary multilayers, kinking is strongly favoured over repetitive buckling where the weaker material occupies only a very small volume fraction of the multilayer. The effect of significant imperfections leading to slippage between layers is discussed. A simple classification of structure genesis is proposed in which the mechanical relationships between apparently diverse structures is illustrated. 856203 Study of house foundations at Elizabeth East, South Australia Pile, K C Proc 4th Australia-New Zealand Conference on Geomechanics, Perth, Western Australia, 14-18 May 1984 V2. P466-470. Publ Barton: lnst qf Engineers. 1984 Results of observations extending over 17 years on the foundations of 16 houses are presented. It is concluded that the movements of external walls are mainly due to soil moisture changes resulting from domestic activities and that the pattern and magnitude of movements are unpredictable. An attempt is made to assess the relevance of the currently used methods for footing design proposed by Walsh and Mitchell. These do not model the observed long-term soil deformation accurately. Nevertheless, for the soil deformations at the 16 sites in the study, footings properly designed by either of the above methods would perform satisfactorily. 856204 Criterion for quasibrittle crack growth Margolin, L G; Smith, B W In: Rock Mechanics in Productivity and Protection (paper to the 25th Symposium on Rock Mechanics, Evanston, Illinois, 25-27 June 1984) P21-28. Publ New York: AIME, 1984 An expression is derived to predict the onset of crack growth in a quasibrittle material. The Griffith energy criterion is applied to the elastic-plastic crack of Olesiak and Wnuk (1968) which is a three dimensional generalisation of the Dugdale crack. The expression differs in several respects from the criterion for crack growth in a brittle material but its predictions are in qualitative agreement with experimental data: 856205 Development of fracture regions in brittle materials Vailejo, L E: Pramono, E In: Rock Mechanics in Productivity and Protection (paper to the 25th Symposium on Rock Mechanics, Evanston, Illinois, 25-27 June 1984) P47-54. Publ New York." A1ME, 1984 Theoretical analysis and model tests were used to examine the mechanics of growth and interaction of inclined cracks (left stepping, right stepping, non-stepping) under uniaxiat compression. 8562O6 Fracture analysis of subsize, charcoal granite specimens Labuz, J F; Shah, S P; Dowding, C H In: Rock Mechanics in Productivity and Protection (paper to the 25th Symposium on Rock Mechanics, Evanston, Illinois, 25-27 June 1984) P77-86. Pub/New York: AIME, 1984 Closed-loop, strain-controlled fracture tests were carried out using double-edge-notched plates of Charcoal granite. The specimens were observed to act as single-edge-notched plates for crack lengths 20-45mm. This was verified optically, by strain gauge data and compliance calculations. The extent of the nonlinear region in subsize specimens of Charcoal granite is shown