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Weak rocks in Brazil
337A 916046 Stiffness of granular soils from field performance. Technical note Berardi, R; Lancellotta, R Geoteclmique V41, N1, March 1991, P149-157 Empirical approaches are still widely used for engineering design in granular soils. Because of sampling problems for cohesionless materials, correlations are made between observed settlements and results of penetration, pressuremeter, or plate loading tests. Results of over 200 cases originally studied by Burland and Burbidge (1985) have been re-examined in order to determine whether an operational stiffness can be obtained from the empirical approach for use in a continuum mechanics approach for evaluating settlement. 916047 Weak rocks in Brazil Dobereiner, L lnt Assoc Engng Geol Bull N42, Oct 1990, P21-29 Weak rocks are widely distributed in Brazil, primarily in the Parana, Amazon, and Parnaiba sedimentary basins. The stratigraphy of these basins is outlined and the index parameters, deformability, and permeability described. Major projects in these rocks are listed. Laboratory and field investigation techniques are described, including drilling and sampling and seismic surveys. The largest weak rock engineering project in Brazil, the Pereira-Barreto canal, was excavated in weak sandstone by ripping, following blasting to loosen the rock mass. 916048 View on some soft rock experiences in Belgium Huergo, P J lnt Assoe Engng Geol Bull N42, Oct 1990, P45-53 Several rock engineering problems have been encountered recently in tunnelling and construction projects in soft rock sequences in southern Belgium. Case histories are outlined of works in Silurian shales, Carboniferous fissured layers of shales, greystone, and mudstone, and Cretaceous chalk. Rock mechanical properties are described. Slope stability at tunnel portals and construction of a waste disposal facility are described in some detail. 916049 Correlating Schmidt hardness with compressive strength and Young's modulus of carbonate rocks Sachpazis, C I lnt Assoc Engng Geol Bull N42, Oct 1990, P75-83 The Schmidt hammer index test is widely used as it is simple, rapid, and low cost. Schmidt hammer rebound values were measured in the laboratory on blocks of size approximately 25cm by 25cm by 20cm of 29 carbonate rocks from Greece and 4 from England. Tangent Young's modulus and uniaxial compressive strength were also measured. Regression analysis indicated strong correlation between the three mechanical parameters. 916050 Numerical analysis of the shape effect on the tensile strength evaluation of axisymmetric specimens Zhang, L C lnt J Num Anal Meth Geomech II15, N4, April 1991, P241250 The effect of shape of axisymmetric rock specimens on measured tensile strength is analysed using an improved adaptive dynamic relaxation method (IDRM). Numerical results for spheroidal specimens reveal variations in stress distribution along the loading axes. It is suggested that loading along the
shorter principal axis be used for strength determination. The accuracy of the IDRM is demonstrated by comparing its output to other experimental and analytical data. An empirical formula based on the failure criterion of maximum tensile stress is proposed to evaluate the tensile strength of specimen materials. 916051 Effects of porosity on the brittle-ductile transition in sandstones Scott, T E; Nielsen, K C J Geophys Res V96, NB1, Jan 1991, P405-414 Sandstone samples with porosities from 6.0-27.6% were deformed under triaxial conditions at a range of confining pressures from 0.1-130MPa. Two sets of samples were used, intact cores and cores containing a 35 deg sawcut. Deformation and failure mechanisms from brittle shear to ductile cataclastic were studied. The brittle ductile transition occurred at similar confining pressures for both sets of samples, and is dependent on initial porosity. Increased confining pressures move the transition to lower porosities. 916052 Faulting associated with the olivine to spinel transformation in germanium olivine and its implications for deep-focus earthquakes Burnley, P C; Green, H W J Geophys Res V96, NB1, Jan 1991, P425-443 Samples of a germanium olivine were tested in the laboratory under triaxial stress. The metastable material fails by faulting when loaded at a temperature where incoherent nucleation of grains of the stable spinel structure just becomes possible. At lower temperatures the transformation is inhibited and the material is ductile and strong, at higher temperatures the transformation is rapid and the material becomes ductile and weak. A new type of transformation microstructure is seen in specimens which failed. The very small grain size suggests the possibility of superplasticity. Implications for deep-focus earthquakes are considered. 916053 Microstructures in water-weakened single crystals of quartz FitzGerald, J D; Boland, J N; Mclaren, A C; Ord, A; Hobbs, B E d Geophys Res V96, NB2, Feb 1991, P2139-2155 Single crystals of quartz were deformed in a solid medium apparatus under conditions of controlled oxygen, hydrogen, and water fugacity. Detailed optical and transmission electron micropy studies of the deformed specimens were made, and aspects relating primarily to the chemical environment examined. These features, together with the correlation between location of plastic strain and regions of earlier fracture, suggested the relation between strength and chemical environment is not simply due to water weakening as a result of high point defect concentrations. Other mechanisms are proposed and discussed. 916054 Effects of porosity on fault reactivation in sandstones Scott, T E; Nielsen, K C J Geophys Res V96, NB2, Feb 1991, P2253-2262 Reactivation of pre-existing weakness in rock is governed by the relation between coefficients of sliding and internal friction and the orientation of the applied stress field. Limiting angles for fault reactivation were determined for 7 sandstones with porosities 6-28%. Whole core and sawcut samples were tested under triaxial stress in the saturated, drained state. Mohr failure envelopes and sliding friction lines were generated in order
© 1991 Pergamon Press plc. Reproduction not permitted
shorter principal axis be used for strength determination. The accuracy of the IDRM is demonstrated by comparing its output to other experimental and analytical data. An empirical formula based on the failure criterion of maximum tensile stress is proposed to evaluate the tensile strength of specimen materials. 916051 Effects of porosity on the brittle-ductile transition in sandstones Scott, T E; Nielsen, K C J Geophys Res V96, NB1, Jan 1991, P405-414 Sandstone samples with porosities from 6.0-27.6% were deformed under triaxial conditions at a range of confining pressures from 0.1-130MPa. Two sets of samples were used, intact cores and cores containing a 35 deg sawcut. Deformation and failure mechanisms from brittle shear to ductile cataclastic were studied. The brittle ductile transition occurred at similar confining pressures for both sets of samples, and is dependent on initial porosity. Increased confining pressures move the transition to lower porosities. 916052 Faulting associated with the olivine to spinel transformation in germanium olivine and its implications for deep-focus earthquakes Burnley, P C; Green, H W J Geophys Res V96, NB1, Jan 1991, P425-443 Samples of a germanium olivine were tested in the laboratory under triaxial stress. The metastable material fails by faulting when loaded at a temperature where incoherent nucleation of grains of the stable spinel structure just becomes possible. At lower temperatures the transformation is inhibited and the material is ductile and strong, at higher temperatures the transformation is rapid and the material becomes ductile and weak. A new type of transformation microstructure is seen in specimens which failed. The very small grain size suggests the possibility of superplasticity. Implications for deep-focus earthquakes are considered. 916053 Microstructures in water-weakened single crystals of quartz FitzGerald, J D; Boland, J N; Mclaren, A C; Ord, A; Hobbs, B E d Geophys Res V96, NB2, Feb 1991, P2139-2155 Single crystals of quartz were deformed in a solid medium apparatus under conditions of controlled oxygen, hydrogen, and water fugacity. Detailed optical and transmission electron micropy studies of the deformed specimens were made, and aspects relating primarily to the chemical environment examined. These features, together with the correlation between location of plastic strain and regions of earlier fracture, suggested the relation between strength and chemical environment is not simply due to water weakening as a result of high point defect concentrations. Other mechanisms are proposed and discussed. 916054 Effects of porosity on fault reactivation in sandstones Scott, T E; Nielsen, K C J Geophys Res V96, NB2, Feb 1991, P2253-2262 Reactivation of pre-existing weakness in rock is governed by the relation between coefficients of sliding and internal friction and the orientation of the applied stress field. Limiting angles for fault reactivation were determined for 7 sandstones with porosities 6-28%. Whole core and sawcut samples were tested under triaxial stress in the saturated, drained state. Mohr failure envelopes and sliding friction lines were generated in order
© 1991 Pergamon Press plc. Reproduction not permitted