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Scattering attenuation and the fractal geometry of fracture systems
336A
Fracture processes 906105 Natural hydraulic fracturing Engelder, T; Lacazette, A Proc International Symposium on Rock Joints, Loen, 4-6 June 1990 P35-43. Pub/Rotterdam." A A Balkema, 1990 It is shown that joint development by N H F is theoretically possible within general theory of effective stress when crack driving stress arises from poroelastic behaviour of the rock. Surface morphology of crossfold joints in Ithaca siltstone is used to illustrate the possibility. Joint initiation takes place at l-3cm diameter flaws at pore pressures about 85% of overburden pressure. As the joint grows in volume, fluid pressure falls, and propagation ceases. It is reinstated at internal pressures below matrix pore pressure once the joint is longer than the initial flaw size. A pressure gradient is created maintaining flow from the matrix to the joint, continuously recharging fluid pressure.
906106 Scattering attenuation and the fractal geometry of fracture systems Main, I G; Peacock, S; Meredith, P G Pure Appl Geophys 11133, N2, April 1990, P283-304 The combined effects of stress concentration and stress corrosion produce stable quasi-static crack growth of fluid filled cracks in laboratory specimens at velocities much lower than those associated with dynamic rupture and mechanical crack growth. Extensive microcracking parallel to the maximum principal stress is also seen. This process is also proposed to account for fracture networks around faults in the earth crust. Based on the theory of Wu and Aki (1985) and a fractai fracture geometry, it is shown that the obtained frequency dependence of scattering attenuation of the earth crust in the range 1-25Hz is consistent with the presence of microcrack arrays formed in fluid filled cracks at sub-critical crack velocity.
906107 Analysis of random anisotropic damage mechanics problems of rock mass. Part 1 - probabilistic simulation Wohua, Z; Valliappan, S Rock Mech Rock Engng V23, N2, April-June 1990, P91-112 The primary elements which affect strength of engineering materials, and consequently crack growth bchaviour, are of statistical nature. Using the measured characteristics of random crack distribution on the surfaces of a rock specimen as a basis, a probabilistic distribution law of damage variables for the rock mass is presented as a Beta distribution, using the Monte Carlo statistical simulation method. Damage state and properties of a damaged rock mass will be evaluated in part 2.
906108 Relationship between fracture toughness and tensile strength for geomaterinis Haberfield, C M; Johnston, I W Proc 12th International Conference on Soil Mechanics and Foundation Engineeriq, Rio de Janeiro, 13-18 August 1989 VI, P47-52. Publ Rotterdam: A A Balkema, 1989 Tensile failure is often encountered in foundations in weak or weathered rocks. A realistic model, such as that based on fracture mechanics, is needed to accurately describe tensile failure. However, many geomaterials,particularly clays, are not sampled during site investigation to give specimens suitable for
fracture toughness testing. Plane strain (Mode I) fracture toughness of a synthetic material, Johnstone, was determined in the laboratory. This, and other data on Melbourne mudstone and other rocks and soils, is plotted against tensile strength values. Good correlation is seen, indicating fracture toughness may be inferred from tensile strength data.
Time dependent behaviour See also." 906284 9O6109 Screw plate measurement of soil creep Brown, P T; Abdel-Latif, M F Aust Geomech N18, Jan 1990, P17-18 Time dcpendent deformation of soft silty soils should be evaluated at the site investigation stages. Although oedometer tests simulate deformation under a fill, it is suggested that screw plate tests be used for foundation design, whcrc high shear stresses will be found at the edge of the foundation. Results of screw plate, model footing, and oedometer tests on a soft estuarine silt arc presented. Young's modulus values from screw plate and footings tests are vcry similar. Oedometer results undcrpredicted settlement.
906110 Laboratory measurement of the creep of Texsol (In French) Blivet, J C Bull Liaison Labs Pouts Chaussees N165, Jan-Feb 1990, P4144 Texsol, soil reinforced by polymer thread, is used in many civil engineering applications. Laboratory creep tests have been carried out on Texsol under uniaxial compression and under triaxial stress at 60 deg C, in order to accelerate creep of the polymer. Texsol is less sensitive to creep than the polymer alone, and if a logarithmic creep law is assumed, creep may be neglected for practical purposes.
906111 Deformation rate in quasi static tests. Technical note (In French) Sahli, M Rev Fr Geotech II51, 1990, P69-73 Quasi static constant strain rate tests are normally used in the laboratory. Deformation mechanisms for rocks are briefly outlined, and results are presented from simple compression tests on a molassic sandstone. The influence of strain rate on strength and Young's modulus is illustrated.
906112 Shear creep of swelling soils Meschyan, S R; Airoyan, S G Soil Mech Found Engng II26, N4, July-Aug 1989, P162-166 Sand-bentonite samples were tested under different densitywater content states. Data are presented for shear creep, shear strength, and swelling pressure. Results indicate that scatter of shear creep deformation data from samples with different properties does not exceed that from tests on one series of twin samples. To determine the shear creep of swelling soils under different density-water content states, it is, therefore, sufficient to determine only one family of curves under any state.
© 1990 Pergamon Press pie. Reproduction not permitted
Fracture processes 906105 Natural hydraulic fracturing Engelder, T; Lacazette, A Proc International Symposium on Rock Joints, Loen, 4-6 June 1990 P35-43. Pub/Rotterdam." A A Balkema, 1990 It is shown that joint development by N H F is theoretically possible within general theory of effective stress when crack driving stress arises from poroelastic behaviour of the rock. Surface morphology of crossfold joints in Ithaca siltstone is used to illustrate the possibility. Joint initiation takes place at l-3cm diameter flaws at pore pressures about 85% of overburden pressure. As the joint grows in volume, fluid pressure falls, and propagation ceases. It is reinstated at internal pressures below matrix pore pressure once the joint is longer than the initial flaw size. A pressure gradient is created maintaining flow from the matrix to the joint, continuously recharging fluid pressure.
906106 Scattering attenuation and the fractal geometry of fracture systems Main, I G; Peacock, S; Meredith, P G Pure Appl Geophys 11133, N2, April 1990, P283-304 The combined effects of stress concentration and stress corrosion produce stable quasi-static crack growth of fluid filled cracks in laboratory specimens at velocities much lower than those associated with dynamic rupture and mechanical crack growth. Extensive microcracking parallel to the maximum principal stress is also seen. This process is also proposed to account for fracture networks around faults in the earth crust. Based on the theory of Wu and Aki (1985) and a fractai fracture geometry, it is shown that the obtained frequency dependence of scattering attenuation of the earth crust in the range 1-25Hz is consistent with the presence of microcrack arrays formed in fluid filled cracks at sub-critical crack velocity.
906107 Analysis of random anisotropic damage mechanics problems of rock mass. Part 1 - probabilistic simulation Wohua, Z; Valliappan, S Rock Mech Rock Engng V23, N2, April-June 1990, P91-112 The primary elements which affect strength of engineering materials, and consequently crack growth bchaviour, are of statistical nature. Using the measured characteristics of random crack distribution on the surfaces of a rock specimen as a basis, a probabilistic distribution law of damage variables for the rock mass is presented as a Beta distribution, using the Monte Carlo statistical simulation method. Damage state and properties of a damaged rock mass will be evaluated in part 2.
906108 Relationship between fracture toughness and tensile strength for geomaterinis Haberfield, C M; Johnston, I W Proc 12th International Conference on Soil Mechanics and Foundation Engineeriq, Rio de Janeiro, 13-18 August 1989 VI, P47-52. Publ Rotterdam: A A Balkema, 1989 Tensile failure is often encountered in foundations in weak or weathered rocks. A realistic model, such as that based on fracture mechanics, is needed to accurately describe tensile failure. However, many geomaterials,particularly clays, are not sampled during site investigation to give specimens suitable for
fracture toughness testing. Plane strain (Mode I) fracture toughness of a synthetic material, Johnstone, was determined in the laboratory. This, and other data on Melbourne mudstone and other rocks and soils, is plotted against tensile strength values. Good correlation is seen, indicating fracture toughness may be inferred from tensile strength data.
Time dependent behaviour See also." 906284 9O6109 Screw plate measurement of soil creep Brown, P T; Abdel-Latif, M F Aust Geomech N18, Jan 1990, P17-18 Time dcpendent deformation of soft silty soils should be evaluated at the site investigation stages. Although oedometer tests simulate deformation under a fill, it is suggested that screw plate tests be used for foundation design, whcrc high shear stresses will be found at the edge of the foundation. Results of screw plate, model footing, and oedometer tests on a soft estuarine silt arc presented. Young's modulus values from screw plate and footings tests are vcry similar. Oedometer results undcrpredicted settlement.
906110 Laboratory measurement of the creep of Texsol (In French) Blivet, J C Bull Liaison Labs Pouts Chaussees N165, Jan-Feb 1990, P4144 Texsol, soil reinforced by polymer thread, is used in many civil engineering applications. Laboratory creep tests have been carried out on Texsol under uniaxial compression and under triaxial stress at 60 deg C, in order to accelerate creep of the polymer. Texsol is less sensitive to creep than the polymer alone, and if a logarithmic creep law is assumed, creep may be neglected for practical purposes.
906111 Deformation rate in quasi static tests. Technical note (In French) Sahli, M Rev Fr Geotech II51, 1990, P69-73 Quasi static constant strain rate tests are normally used in the laboratory. Deformation mechanisms for rocks are briefly outlined, and results are presented from simple compression tests on a molassic sandstone. The influence of strain rate on strength and Young's modulus is illustrated.
906112 Shear creep of swelling soils Meschyan, S R; Airoyan, S G Soil Mech Found Engng II26, N4, July-Aug 1989, P162-166 Sand-bentonite samples were tested under different densitywater content states. Data are presented for shear creep, shear strength, and swelling pressure. Results indicate that scatter of shear creep deformation data from samples with different properties does not exceed that from tests on one series of twin samples. To determine the shear creep of swelling soils under different density-water content states, it is, therefore, sufficient to determine only one family of curves under any state.
© 1990 Pergamon Press pie. Reproduction not permitted