Two-dimensional model of en-echelon jointed rock masses with multi-discontinuity geometry parameters. Technical note

Two-dimensional model of en-echelon jointed rock masses with multi-discontinuity geometry parameters. Technical note

68A is illustrated. The sensor, its mode of operation, and calibration using a pressure plate apparatus are described. Laboratory measurements can be ...

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68A is illustrated. The sensor, its mode of operation, and calibration using a pressure plate apparatus are described. Laboratory measurements can be compensated for effects of overburden pressure in the field. Interpretation of suction measurements applied to design of soil structures is briefly discussed.

902024 Characterisation of soil macroporosity with CT scanning Grevers, M C J; De Jong, E; Arnaud, R J S Can J Soil Sci V69, N3, Aug 1989, P629-637

Soil macroporosity images from thin sections and from computed tomography scanning were examined using an image analyser. Macroporosity measurements were comparable. The impregnation of resin into the soil to allow thin section preparation is seen to reduce macroporosity. The CT method is nondestructive, can identify boundaries of compacted layers to the nearest lmm, and allows preparation of three dimensional images. Resolution is limited to pore size above 750 microns.

902025 Interrelationship between chemical and mineral composition and aggregation and reaggregation of postlake cohesive soil Andrzejeszczak, B lnt Assoc Engng Goal Bull 1139, April 1989, P59-65

Aggregate and granulometric analysis was carried out on normally consolidated cohesive postlake soils. Chemical and mineralogical compositions were determined of the aggregates, the soil as a whole, and the clayey fraction. The interdependence was determined between the size of waterproof aggregates or the percentage content of the aggregate fraction and the composition of soil components which act in the structuring of the aggregates and counteract the dispersive effect of water.

902026 Microstrnctural investigation on laterite soils Malomo, S lnt Assoc Engng Geol Bull N39, April 1989, P105-108

Microstructures of lateritic soils from Brazil and Nigeria have been studied by optical and scanning electron microscopy. The development of the concretionary structure is a staged process involving the accumulation of sequioxides. They initially accumulate as amorphous implantations in pore space, then they crystallise, which leads to bonding between soil elements and concretion. The nature of the cementation in the concretionary structure is related to soil engineering properties.

902027 Three-dimensional statistical modelling of a fractured rock mass - an example from the Fanay-Augeres mine Billaux, D; Chiles, J P; Hestir, K; Long, J lnt J Rock Mech Min Sci 1/26, N3/4, July 1989, P281.299

The use of geostatistical techniques to represent the spatial features of a rock mass, such as variation of fracture density and fracture orientation, is described and illustrated using mapped data from two sections of a drift wall, one wet, the other dry. The conceptual model of the system, determination required of the model, numerical simulation, and measurement of connectivity in the simulations is presented. The wet section of the drift had a lower overall fracture density than the dry section, but a larger density of big fractures. Implications for interpretation of results are discussed.

902028 Coal examination on a mesoscopic scale Falkner, A J Sediment Petrol V59, N4, July 1989, P617-619

The use of a binocular microscope in the xl0-x40 magnification range with an incident light source is seen to be applicable to rapid appraisal of coal type. Individual facies can be further examined. The method is rapid,not hampered by subjective macroscopic brightness effects, and preserves the original structure and texture. 902029 Correlation between stress direction and extinction pattern of radial crystal fibres in synthetic quartz aggregates. Short note Luan, F J Struct Geol Vll, N6, 1989, P763-767

Synthetic quartz aggregates were prepared from silica gel particles of size less than 1 micron. The gel was cold pressed, then hot pressed at a variety of temperature/time combinations to produce different grain sizes. Some specimens were deformed immediately after hot pressing. A strong relation was seen between direction of applied stress and extension pattern of deformed radial fibres observed in the polarizing optical microscope. The pattern can be used to indicate the occurrence of deformation and infer the direction of the principal stress responsible. 902030 Strainscope: an optical device for field measurement of homogeneous finite strain. Short note Simon, J; Japas, M S; Amos, A J J Struct Geoi VII. N6, 1989. P769-774

A simple optical system of coupled astigmatic lenses producing simultaneous shortening and stretching within the plane of the lenses has been developed. It can be applied to examine objects of known original shape or to determine original shape when finite strain is known. Geological applications are examined. 902031 Mass physical properties of sediments from Bransfield Strait and Northern Weddel Sea Holler, P Marine Geotechnol VS, NI, 1989. PI-18

Mass physical properties of two different sedimentary environments in the Antarctic region are described. Sediments from a silled basin in the Bransfield Strait are characterised by abundant biogenic silica (microfossils), whereas more terrigenous materials, due to ice rafting, were deposited at the deeper site. High biogenic silica content was associated with generally higher water content and porosity, and lower shear strength, specific grain density, and wet bulk density. Only small, smooth variations were recorded with depth, due to consolidation processes, except for two cores containing turbidites. 902032 Two-dimensional model of en-echelon jointed rock masses with multi-discontinuity geometry parameters. Technical note Zhang Xing Rock Mech Rock Engng V22. N3, July-Sept 1989, P231-242

Properties of a rock mass depend not only on geometry and strength of individual joints but also on relative geometric positions of all joints. A method of describing all the joint geometric characteristics of a rock mass using only two parameters is presented. One, the individual joint geometry parameter, describes orientation, size, surface geometry, and

1990 Pergamon Press plc. Reproduction not permitted

69A aperture. The second, the multi joint geometry parameter, describes spacing, offset, persistence and overlap ratio. The method is used to model en-echelon jointed rock masses.

902033 Stratigraphical and geotechnicai correlated properties of Belgian loess Huergo, P J; Crespo, E Q Proc International Conference on Engineering Problems of Regional Soils, Beijing, 11-15 August 1988 P241-246. Publ Beijing: International Academic Publishers, 1989 Origin, geological and stratigraphic descriptions of loess soils in Belgium are presented. Grain size distribution, plasticity, activity, compressibility, consolidation, and collapse properties and their variation with depth have been determined. Comparison of the two data sets indicates that stratigraphic data can be used to assess geotechnical properties. All sediments are preconsolidated, with degree varying with age. Several geotechnical mapping units are defined, but verification of local stratigraphy is necessary before they can be used in engineering work.

902034 Naturally occurring gravels for road construction Hight, D W; Toll, D G; Grace, H Proc 2nd International Conference on Geomeehanics in Tropical Soils, Singapore, 12-14 December 1988 VI, P405412. Publ Rotterdam: A A Balkema, 1988 A laboratory study into the natural laterite and quartz gravels used as road bases in Kenya was undertaken to identify key factors responsible for good performance. Grain size distribution, Atterberg limits and clay activity, fabric, suction, permeability and strength were analysed. It seems the gravels offer good performance as they are widely graded and show dilatant behaviour under shear for most densities and good compactability.

Deformation and strength characteristics See also: 902204. 902205, 902220, 902242, 902243, 902245, 902246, 902035 Strength of frozen sand containing tetrahydrofuran hydrate. Note Parameswaran, V R; Paradis, M; Handa, Y P Can Geotech J V26, N3, Aug 1989, P479-483 Frozen hydrates are encountered in gas and oil fields in arctic regions. Their physical and mechanical properties are little known. Tetrahydrofuran hydrate is easily formed in the laboratory. Cylindrical samples of sand containing frozen T H F hydrate and ice were tested under uniaxial compression at various strain rates. The sand containing THF was the stronger at low strain rates but its strain rate sensitivity is such that as strain rate is increased, the two frozen soils show comparable strengths.

902036 Thin-sample technique of residual strength measurement. Technical note Chandler, R J; Hardie, T N Geotechnique 1/39, N3, Sept 1989, P527-531 Thin sample techniques, which use widely available apparatus, have been largely abandoned since the advent of the ring shear apparatus. Results are presented for tests on 60mm square

samples in a direct shear apparatus. Samples were consolidated in stages between porous stones. Over and normally consolidated specimens of thickness 1.5-10mm were tested. The influence of inaccurate centring of the specimen was studied. Results indicate these tests provide quick and accurate determinations of residual strength, more satisfactory than those from 10-20mm thick specimens.

902037 Crystalline calcite in till: engineering implications. Technical note

Little, J A Geotechnique 1/39. N3, Sept 1989, P533-541 Two glacial tills from the UK, one a chalky till containing crystalline calcite and the other from a naturally decalcified horizon, are compared. Mineralogy and elemental composition were determined by x-ray analysis. Oedometer compression characteristics for reconstituted and undisturbed samples, variation of undrained strength with liquidity index, and scanning electron microscopy of the tills are illustrated. Results are discussed with reference to soil pedogenesis and engineering properties.

902038 Elastic-plastic response of a circular hole to repeated loading Senseny, P E; Lindberg, H E; Schwer, L E lnt J Num Anal Meth Geomech VI3, N5, Sept-Oct 1989, P459-476 An analytical solution is obtained to the problem of repeated axisymmetric loading of an infinite Mohr-Coulomb material containing a circular hole. After application of an initial farfield load, pressure is reduced to zero then increased up to and above the pressure at which the cycle began. The solution is used to predict results of tests on a rock-like material containing a reinforced hole. Closure is influenced by internal pressure, working load, and friction angle and compressive strength of the material. Closure increments per load cycle at small closures are small compared to initial closure, comparable and cumulative.

902039 Pore pressure predictions in finite element analysis Pacheco, M P; Altschaeffl, A G; Chameau, J L lnt J Num Anal Meth Geomech V13, N5, Sept-Oct 1989, P477-491 A pore pressure model including simultaneous effects of shear and mean confining stress is presented. As it is difficult to determine strains using the FEM at sufficient accuracy to ensure satisfactory pore pressure predictions, the proposed model uses a pore pressure function coupled to a potential and a loading function in an elasto-plastic constitutive model. Assumptions made and limitations of the procedure are discussed. The advantages of the model for pore pressure prediction during undrained loading are demonstrated.

902040 Strain-path analyses for arbitrary three-dimensional penetrometers Huang, A B lnt J Num Anal Meth Geomech VI3, NS, Sept-Oct 1989, P551-564 A numerical technique based on the theory of potential flow and the panel method is presented. It is used to model the 'flow' of soil due to the penetration of a cone and a flat Marchetti dilatometer. Results show the responses of soils to these two types of penetrometer are fundamentally different.

© 1990 Pergamon Press plc. Reproduction not permitted RMMS 27 2--F