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Analysis of geomechanic characteristics of rock masses using Lugeon-type water injection tests (in French)
165A meability is described. Auth.
Fracture processes See also: 845092 845018 Stress corrosion and acoustic emission during tensile crack propagation in Whin Sill dolerite and other basic rocks Meredith, P G; Atkinson, B K Geophys J R Astr Soc V75, N1, Oct 1983, P1-22 Double torsion tests in ambient air and liquid water have been used to establish critical stress intensity factors and stress intensity factor-crack velocity diagrams for propagation of single tensile cracks in Whin Sill dolerite and Ralston intrusive rock. Acoustic response was monitored during experiments on the Whin Sill dolerite. The results sugges[ that the detailed mechanism of crack growth is strongly dependent on crack tip environment and that the acoustic response can be used to monitor the humidity of this environment. 845019 Micrucrack connectivity in rocks: a renormulization group approach to the critical phenomena of conduction and failure in crystalline rocks Madden, T g J Geopltys Res V88, NB1, 10 Jan 1983, P585-592 A study is made of the critical phenomena associated with the onset of conductivity and the onset of failure in a rock with a random distribution of microcracks using a renormalization group theory approach. The predictions of the model agree well with SEM data on the microcrack populations of stressed and unstressed samples. 845020 On the stability of shear cracks and the calculation of compressive strength Dienes, J K J Geophys ICes V88, NB2, 10 Feb 1983, Pl173-1179 Griffith's 1921 theory of crack stability is extended to account for the frictional energy dissipation associated with interracial sliding when the crack faces are in contact. The most critical crack orientation is found and the theoretical strength defined as the critical stress for that orientation. Following this, the heating due to interfacial sliding is found by a one-dimensional thermoclastic analysis. It is concluded that under normal conditions, the stress field acting on the crack faces is only slightly affected by frictional heating. 845021 Communicating elements for the simulation of crack growing processes in rock masses Gross, H Proc 5th Congress of the International Society for Rock Mechanics, Melbourne, 10-15 April 1983 V2, PF19-F24. Publ Rotterdam: A. A. Balkema, 1983 The knowledge of joint openings and crack propagations is important for the exploitation of natural resources out of deep rock. The Finite Element Method in standard form either leads to too inexact solutions or requires too large systems of equations. Therefore an iteration procedure based on the Finite Element Method is introduced. At critical positions a net refinement is carried out automatically. Although the system of equations retains its original size, the same solution is nevertheless obtained by the use of the appropriate fine net. A proof of convergence follows.
845022 In-situ stress variations and hydraulic fracture propagation in layered rock - observations from a mineback experiment Teufel, T W; Warpinski, N R Proc 5th Congress of the International Society for Rock Mechanics, Melbourne, 10-15 April 1983 V2, PF43-F48. Publ Rotterdam: A. A. Balkema, 1983 In situ experiments, which were accessible for direct observations by mineback, have been conducted to determine the effect that material property interfaces and in situ stress differences have on hydraulic fracture propagation and the resultant overall fracture geometry. Fractures were observed to terminate only in regions of high minimum principal in situ stress. It was shown that a factor of 5 difference in elastic modulus between adjacent layers was insufficient to arrest fracture at an interface. It is concluded that the minimum principal in situ stress is the predominant controlling factor in fracture propagation. The results indicate the determination of in situ stresses can be used to assess the potential success of fracture treatment of lowpermeability gas reservoirs.
Strength characteristics See also: 845316 845023 Possibilities and limitations of finite elements for limit analysis De Borst, R; Vermeer, P A Geoteclmiqne V34, N2, June 1984, P199-210 The ability of the 15-noded displacement based finite element to assess accurately collapse loads of soil structures is examined for high friction angles and non-associated flow rules. Solutions are presented for strip and circular footings, for the trap door problem and for the cone penetration test. The last two problems arc introduced in order to demonstrate that the method can be used to generate realistic solutions for problems that cannot be solved analytically. The footing problems are treated in order to assess the accuracy and stability of the numerical scheme. The accuracy is shown to be very high, but stability problems occur when non-associated flow rules are applied. In soil mechanics, this constitutes a fundamental problem since this type of instability is of a physical nature rather than of a numerical nature. Auth. 845O24 Probabilistic characterization of shear strength using results of direct shear tests. Technical note Miller, S M; Borgman, L E Geoteclmique V34, N2, June 1984, P273-276 Probabilistic geotechnical analyses require a statistical description of material shear strengths, particularly along discontinuities. Direct shear testing of discontinuities in oriented rock specimens provide data for analysis by nonlinear regression techniques. 845025 Analysis of geomechanic characteristics of rock masses using Lugeon-type water injection tests (In French) Foyo Marcos, A Int Assoc Engng Geoi Bull N26-27, Dec 1982-June 1983, P411-414 (Paper to the International Symposium on Soil and Rock Investigations by In Situ Testing, Paris, 18-20 May 1983) By performing Lugeon permeability tests with a defined sequence of increasing and decreasing water pressures, it is possible to find the threshold fracturing pressure which defines the tensile strength of the rock. The results of tests performed in
166A some Spanish dam foundations are analysed and the tensile strength parameters of the foundations determined. A normalized permeability test programme is proposed, which depends on the parameters to be determined, such as permeability and strength. 845026 Some studies of low temperature rock strength. Technical note Inada, Y; Yokota, K lnt J Rock Mech Min Sci V21, N3, June 1984, P145-153 Uniaxial compression and Brazilian tests were carried out on 'wet' and 'dry' samples of several granites and andesites at very low temperatures. Microscopic observations of the mineral texture in the rocks were also made at -160 deg C and room temperature. It was concluded that: (1) the compressive and tensile strengths of the rocks increased with decrease in temperature; (2) the compressive strength of wet specimens was less than that of dry specimens, but the tensile strength was greater for the wet specimens; (3) the number of microcracks induced in the andesite was greater than in the granite; (4) the temperatureinduced strain was greater in the granite than in the andesite, and greater in the wet specimens, and (5) there was an increase in elastic wave velocity with temperature decrease.
845030 Shear strength of rock joints with reference to cautious blasting Maki, K; Holmberg, R In: Rock Mechanics: Caverns and Pressure Shafts (papers to the I S R M Symposium, Aachen, 26-28 May 1982) V1, P85-95. Publ Rotterdam: A. A. Balkema, 1982 A model has been developed for predicting the extent of the zone of damage in the remaining rock after blasting. The shear strength of rock joints with blast damage has been investigated in the laboratory using a specially designed direct shear apparatus. 845031 Comparison of shear strength measurements using two sizes of shearbox Brady, K C; Awcock, I; Wightman, N R Transport and Road Research Laboratory report N1105, 1983, 25P
845027 Vane shear data on undrained residual strength. Technical note Pyles, M R J Geotech Engng Div ASCE VIlO, NGT4, April 1984, P543547
The results of tests on a uniformly graded medium sand using 60mm and 300ram shearboxes are presented. From both shear boxes the results showed that the angle of friction of the sand could be broken down into two parts; a constant volume component and a particle interlock component. The constant volume component was approximately 33.6 deg. The maximum value of the particle interlock component was governed by the initial density of the specimens and could be related to the maximum value of the ratio of the rate of vertical to the rate of horizontal movement.
The laboratory and field vane testing reported was undertaken to determine the variation of ultimate undrained residual strength as a function of one-dimensional consolidation pressure, using undisturbed samples of San Francisco Bay mud.
845032 In-situ shear strength tester for coal Handy, R L; Engle, L E; Pitt, J M US Bureau of Mines report OFR 197-83, 10 May 1976, 125P
845O7.8 Shear failure in granular media Bora, P K J Geotech Engng Div ASCE VIIO, NGT5, May 1984, P582598
The objective of this research was to develop a lightweight, portable device for rapid in situ measurement of rock shearing strength and to compare the results with those obtained by other test methods. The rock borehole shear test (RBST) operates by expansion of two opposed steel plates against rock in the periphery of a 76ram (13in) diameter borehole, followed by axial movement of the plates. Small teeth on the contact plates cause shearing to occur with the rock itself. Several tests were conducted at different applied expansion pressures to generate a failure envelope of shearing strength versus applied normal stress. The envelope is plotted while the test is being conducted; a complete envelope may be generated by four tests in about 45 rain. The slope of the envelope is the angle of internal friction, and the extrapolated shearing strength at zero normal stress is the cohesion. Analogous data are obtained for the residual shear strength, or strength along the induced fractures. The device also indicates whether dilatancy, or rock volume expansion, occurs during shearing. Comparative RBST versus triaxial and other tests indicate close agreement of friction angles but somewhat lower cohesions caused by disturbance by the shear plate teeth. Auth.
The concept of 'effective confining contact stress', the product of porosity and effective confining stress, has been used to analyse shear test results on several sands and on steel balls. A plot of the effective angle of shearing resistance versus the log of effective confining contact stress at failure yields a linear relationship for dilatant granular soils. This has made it possible to formulate a method by which the effective angle of shearing resistance can be predicted from the results of 2 or 3 drained tests. The method does not involve separation of the dilatancy component of shear strength for 'energy correction' or correlation. Particle breakdown in the shearing process does not influence its effectiveness. 845029 Continuous failure state direct shear tests Tisa, A; Kovari, K Rock Mech Rock Engng I117, N2, April-June 1984, P83-95 The concept of a 'continuous failure state' (CFS) direct shear test is shown to furnish the exact failure envelope for the residual shear strength. The determination of the peak strength envelope for rough surfaces or those with teeth is also possible provided that only a small amount of slip per unit shear stress is permitted during the tests. Tests on 2 different materials, brick and cement mortar, have shown encouraging results. The new shear test apparatus for combined use with a servo-controlled loading machine has proved very useful in conducting the CFS direct shear tests.
Avail: NTIS, Springfield, Va 22161 USA (PB 84-126481) D e f o r m a t i o n characteristics
See also: 845068, 845082 845033 Design and construction of a block test in closely jointed rock Black, M T; Cramer, M L Bull Assoc Engng Geol V21, N1, Feb 1984, P39-45
Fracture processes See also: 845092 845018 Stress corrosion and acoustic emission during tensile crack propagation in Whin Sill dolerite and other basic rocks Meredith, P G; Atkinson, B K Geophys J R Astr Soc V75, N1, Oct 1983, P1-22 Double torsion tests in ambient air and liquid water have been used to establish critical stress intensity factors and stress intensity factor-crack velocity diagrams for propagation of single tensile cracks in Whin Sill dolerite and Ralston intrusive rock. Acoustic response was monitored during experiments on the Whin Sill dolerite. The results sugges[ that the detailed mechanism of crack growth is strongly dependent on crack tip environment and that the acoustic response can be used to monitor the humidity of this environment. 845019 Micrucrack connectivity in rocks: a renormulization group approach to the critical phenomena of conduction and failure in crystalline rocks Madden, T g J Geopltys Res V88, NB1, 10 Jan 1983, P585-592 A study is made of the critical phenomena associated with the onset of conductivity and the onset of failure in a rock with a random distribution of microcracks using a renormalization group theory approach. The predictions of the model agree well with SEM data on the microcrack populations of stressed and unstressed samples. 845020 On the stability of shear cracks and the calculation of compressive strength Dienes, J K J Geophys ICes V88, NB2, 10 Feb 1983, Pl173-1179 Griffith's 1921 theory of crack stability is extended to account for the frictional energy dissipation associated with interracial sliding when the crack faces are in contact. The most critical crack orientation is found and the theoretical strength defined as the critical stress for that orientation. Following this, the heating due to interfacial sliding is found by a one-dimensional thermoclastic analysis. It is concluded that under normal conditions, the stress field acting on the crack faces is only slightly affected by frictional heating. 845021 Communicating elements for the simulation of crack growing processes in rock masses Gross, H Proc 5th Congress of the International Society for Rock Mechanics, Melbourne, 10-15 April 1983 V2, PF19-F24. Publ Rotterdam: A. A. Balkema, 1983 The knowledge of joint openings and crack propagations is important for the exploitation of natural resources out of deep rock. The Finite Element Method in standard form either leads to too inexact solutions or requires too large systems of equations. Therefore an iteration procedure based on the Finite Element Method is introduced. At critical positions a net refinement is carried out automatically. Although the system of equations retains its original size, the same solution is nevertheless obtained by the use of the appropriate fine net. A proof of convergence follows.
845022 In-situ stress variations and hydraulic fracture propagation in layered rock - observations from a mineback experiment Teufel, T W; Warpinski, N R Proc 5th Congress of the International Society for Rock Mechanics, Melbourne, 10-15 April 1983 V2, PF43-F48. Publ Rotterdam: A. A. Balkema, 1983 In situ experiments, which were accessible for direct observations by mineback, have been conducted to determine the effect that material property interfaces and in situ stress differences have on hydraulic fracture propagation and the resultant overall fracture geometry. Fractures were observed to terminate only in regions of high minimum principal in situ stress. It was shown that a factor of 5 difference in elastic modulus between adjacent layers was insufficient to arrest fracture at an interface. It is concluded that the minimum principal in situ stress is the predominant controlling factor in fracture propagation. The results indicate the determination of in situ stresses can be used to assess the potential success of fracture treatment of lowpermeability gas reservoirs.
Strength characteristics See also: 845316 845023 Possibilities and limitations of finite elements for limit analysis De Borst, R; Vermeer, P A Geoteclmiqne V34, N2, June 1984, P199-210 The ability of the 15-noded displacement based finite element to assess accurately collapse loads of soil structures is examined for high friction angles and non-associated flow rules. Solutions are presented for strip and circular footings, for the trap door problem and for the cone penetration test. The last two problems arc introduced in order to demonstrate that the method can be used to generate realistic solutions for problems that cannot be solved analytically. The footing problems are treated in order to assess the accuracy and stability of the numerical scheme. The accuracy is shown to be very high, but stability problems occur when non-associated flow rules are applied. In soil mechanics, this constitutes a fundamental problem since this type of instability is of a physical nature rather than of a numerical nature. Auth. 845O24 Probabilistic characterization of shear strength using results of direct shear tests. Technical note Miller, S M; Borgman, L E Geoteclmique V34, N2, June 1984, P273-276 Probabilistic geotechnical analyses require a statistical description of material shear strengths, particularly along discontinuities. Direct shear testing of discontinuities in oriented rock specimens provide data for analysis by nonlinear regression techniques. 845025 Analysis of geomechanic characteristics of rock masses using Lugeon-type water injection tests (In French) Foyo Marcos, A Int Assoc Engng Geoi Bull N26-27, Dec 1982-June 1983, P411-414 (Paper to the International Symposium on Soil and Rock Investigations by In Situ Testing, Paris, 18-20 May 1983) By performing Lugeon permeability tests with a defined sequence of increasing and decreasing water pressures, it is possible to find the threshold fracturing pressure which defines the tensile strength of the rock. The results of tests performed in
166A some Spanish dam foundations are analysed and the tensile strength parameters of the foundations determined. A normalized permeability test programme is proposed, which depends on the parameters to be determined, such as permeability and strength. 845026 Some studies of low temperature rock strength. Technical note Inada, Y; Yokota, K lnt J Rock Mech Min Sci V21, N3, June 1984, P145-153 Uniaxial compression and Brazilian tests were carried out on 'wet' and 'dry' samples of several granites and andesites at very low temperatures. Microscopic observations of the mineral texture in the rocks were also made at -160 deg C and room temperature. It was concluded that: (1) the compressive and tensile strengths of the rocks increased with decrease in temperature; (2) the compressive strength of wet specimens was less than that of dry specimens, but the tensile strength was greater for the wet specimens; (3) the number of microcracks induced in the andesite was greater than in the granite; (4) the temperatureinduced strain was greater in the granite than in the andesite, and greater in the wet specimens, and (5) there was an increase in elastic wave velocity with temperature decrease.
845030 Shear strength of rock joints with reference to cautious blasting Maki, K; Holmberg, R In: Rock Mechanics: Caverns and Pressure Shafts (papers to the I S R M Symposium, Aachen, 26-28 May 1982) V1, P85-95. Publ Rotterdam: A. A. Balkema, 1982 A model has been developed for predicting the extent of the zone of damage in the remaining rock after blasting. The shear strength of rock joints with blast damage has been investigated in the laboratory using a specially designed direct shear apparatus. 845031 Comparison of shear strength measurements using two sizes of shearbox Brady, K C; Awcock, I; Wightman, N R Transport and Road Research Laboratory report N1105, 1983, 25P
845027 Vane shear data on undrained residual strength. Technical note Pyles, M R J Geotech Engng Div ASCE VIlO, NGT4, April 1984, P543547
The results of tests on a uniformly graded medium sand using 60mm and 300ram shearboxes are presented. From both shear boxes the results showed that the angle of friction of the sand could be broken down into two parts; a constant volume component and a particle interlock component. The constant volume component was approximately 33.6 deg. The maximum value of the particle interlock component was governed by the initial density of the specimens and could be related to the maximum value of the ratio of the rate of vertical to the rate of horizontal movement.
The laboratory and field vane testing reported was undertaken to determine the variation of ultimate undrained residual strength as a function of one-dimensional consolidation pressure, using undisturbed samples of San Francisco Bay mud.
845032 In-situ shear strength tester for coal Handy, R L; Engle, L E; Pitt, J M US Bureau of Mines report OFR 197-83, 10 May 1976, 125P
845O7.8 Shear failure in granular media Bora, P K J Geotech Engng Div ASCE VIIO, NGT5, May 1984, P582598
The objective of this research was to develop a lightweight, portable device for rapid in situ measurement of rock shearing strength and to compare the results with those obtained by other test methods. The rock borehole shear test (RBST) operates by expansion of two opposed steel plates against rock in the periphery of a 76ram (13in) diameter borehole, followed by axial movement of the plates. Small teeth on the contact plates cause shearing to occur with the rock itself. Several tests were conducted at different applied expansion pressures to generate a failure envelope of shearing strength versus applied normal stress. The envelope is plotted while the test is being conducted; a complete envelope may be generated by four tests in about 45 rain. The slope of the envelope is the angle of internal friction, and the extrapolated shearing strength at zero normal stress is the cohesion. Analogous data are obtained for the residual shear strength, or strength along the induced fractures. The device also indicates whether dilatancy, or rock volume expansion, occurs during shearing. Comparative RBST versus triaxial and other tests indicate close agreement of friction angles but somewhat lower cohesions caused by disturbance by the shear plate teeth. Auth.
The concept of 'effective confining contact stress', the product of porosity and effective confining stress, has been used to analyse shear test results on several sands and on steel balls. A plot of the effective angle of shearing resistance versus the log of effective confining contact stress at failure yields a linear relationship for dilatant granular soils. This has made it possible to formulate a method by which the effective angle of shearing resistance can be predicted from the results of 2 or 3 drained tests. The method does not involve separation of the dilatancy component of shear strength for 'energy correction' or correlation. Particle breakdown in the shearing process does not influence its effectiveness. 845029 Continuous failure state direct shear tests Tisa, A; Kovari, K Rock Mech Rock Engng I117, N2, April-June 1984, P83-95 The concept of a 'continuous failure state' (CFS) direct shear test is shown to furnish the exact failure envelope for the residual shear strength. The determination of the peak strength envelope for rough surfaces or those with teeth is also possible provided that only a small amount of slip per unit shear stress is permitted during the tests. Tests on 2 different materials, brick and cement mortar, have shown encouraging results. The new shear test apparatus for combined use with a servo-controlled loading machine has proved very useful in conducting the CFS direct shear tests.
Avail: NTIS, Springfield, Va 22161 USA (PB 84-126481) D e f o r m a t i o n characteristics
See also: 845068, 845082 845033 Design and construction of a block test in closely jointed rock Black, M T; Cramer, M L Bull Assoc Engng Geol V21, N1, Feb 1984, P39-45