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Norman H. Sleep - One of the best experts on this subject based on the ideXlab platform.

  • Rate‐ and state‐dependent friction of Intact Rock and gouge
    Journal of Geophysical Research, 1999
    Co-Authors: Norman H. Sleep
    Abstract:

    The shear traction during frictional sliding depends on the instantaneous sliding strain rate e and on a state variable ψ which represents the previous history of the sample. A formulation of rate and state friction covers the continuum between gouge and Intact Rock, as well as the behavior at high and low normal tractions. A traditional formula for the instantaneous coefficient of friction is retained, μ = μ 0 + a In(e/e 0 ) + b In(ψ/ψ 0 ), where μ 0 is the steady state coefficient of friction at the reference strain rate e 0 , and a and b are small constants. The normalizing ψ 0 for isothermal conditions is ΔP N /ΔP 0 N , where AP is the effective normal traction, ΔP 0 is a reference normal traction, and N is an exponent. The coefficient of friction of Intact Rock is approximately μ close -bN In(ΔP/ΔP close ), where the coefficient of friction is μ close , at the normal traction ΔP close where essentially all the pore space is closed during steady state sliding. The formulation provides an acceptable fit to the observed coefficient of friction of Westerly Granite at normal tractions up to 1500 MPa including steady sliding and Intact Rock failure.

  • rate and state dependent friction of Intact Rock and gouge
    Journal of Geophysical Research, 1999
    Co-Authors: Norman H. Sleep
    Abstract:

    The shear traction during frictional sliding depends on the instantaneous sliding strain rate e and on a state variable ψ which represents the previous history of the sample. A formulation of rate and state friction covers the continuum between gouge and Intact Rock, as well as the behavior at high and low normal tractions. A traditional formula for the instantaneous coefficient of friction is retained, μ = μ 0 + a In(e/e 0 ) + b In(ψ/ψ 0 ), where μ 0 is the steady state coefficient of friction at the reference strain rate e 0 , and a and b are small constants. The normalizing ψ 0 for isothermal conditions is ΔP N /ΔP 0 N , where AP is the effective normal traction, ΔP 0 is a reference normal traction, and N is an exponent. The coefficient of friction of Intact Rock is approximately μ close -bN In(ΔP/ΔP close ), where the coefficient of friction is μ close , at the normal traction ΔP close where essentially all the pore space is closed during steady state sliding. The formulation provides an acceptable fit to the observed coefficient of friction of Westerly Granite at normal tractions up to 1500 MPa including steady sliding and Intact Rock failure.

Abigail Hackston - One of the best experts on this subject based on the ideXlab platform.

  • The Mohr-Coulomb criterion for Intact Rock strength and friction – a re-evaluation and consideration of failure under polyaxial stresses.
    Solid Earth, 2016
    Co-Authors: Abigail Hackston, Ernest Rutter
    Abstract:

    Abstract. Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr–Coulomb failure criterion under axisymmetric shortening conditions, provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compressive stress direction in the two loading configurations. The normals to the Mohr–Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined saw cuts and failure surfaces produced in Intact Rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both Rock types. Friction data for these and other porous sandstones accord well with the Byerlee (1978) generalization about Rock friction being largely independent of Rock type. For engineering and geodynamic modelling purposes, the stress-state-dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other Rock types.

  • the mohr coulomb criterion for Intact Rock strength and friction a re evaluation and consideration of failure under polyaxial stresses
    Solid Earth, 2016
    Co-Authors: Abigail Hackston, E H Rutter
    Abstract:

    Abstract. Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr–Coulomb failure criterion under axisymmetric shortening conditions, provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compressive stress direction in the two loading configurations. The normals to the Mohr–Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined saw cuts and failure surfaces produced in Intact Rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both Rock types. Friction data for these and other porous sandstones accord well with the Byerlee (1978) generalization about Rock friction being largely independent of Rock type. For engineering and geodynamic modelling purposes, the stress-state-dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other Rock types.

  • The Mohr–Coulomb criterion for Intact Rock strength and friction – a re-evaluation and consideration of failure under polyaxial stresses
    Solid Earth Discussions, 2015
    Co-Authors: Abigail Hackston, Ernest Rutter
    Abstract:

    Abstract. Abstract Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr–Coulomb failure criterion under axisymmetric compression conditions provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compression direction in the two loading configurations. The normals to the Mohr–Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined sawcuts and failure surfaces produced in Intact Rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both Rock types and could be reconciled by a variant on the Mogi (1967) failure criterion. Friction data for these and other porous sandstones accord well with the Byerlee (1977) generalization about Rock friction being largely independent of Rock type. For engineering and geodynamic modelling purposes, the stress-state dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other Rock types.

Elia Rigo - One of the best experts on this subject based on the ideXlab platform.

  • 3D Stress–Strain Analysis of a Failed Limestone Wedge Influenced by an Intact Rock Bridge
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Paolo Paronuzzi, Alberto Bolla, Elia Rigo
    Abstract:

    This paper presents a back-analysis of a Rock wedge failure (volume = 25–30 m^3) that involved a limestone scarp in the Rosandra valley (Trieste karst, NE Italy). Thanks to the mechanical survey of the detachment surface, a single Rock bridge having a size of about 15 cm × 30 cm has been ascertained. A 3D stress–strain analysis has been performed to examine the influence of the Rock bridge on the block stability (initial unweathered condition: strength reduction factor SRF equal to 1.14). The shear strength provided by the basal and lateral joints represents the main contributing factor for the wedge stability (about 60–75 % of the whole resisting system). However, the equilibrium of the wedge was temporarily attained thanks to the strength contribution provided by the Rock bridge (25–40 %) until the acting forces locally exceeded the resisting forces, thus determining the bridge rupture and, as a consequence, the wedge collapse. The mean shear stress acting on the Rock bridge at failure ranges from about 3.5 to 5 MPa. Calculated block displacements up to failure vary from 0.6 to 1.5 mm, depending on the different elastic modulus assumed for the wedge ( E  = 30, 10, and 4 GPa). Pre-collapse block displacements increase as a result of the shear strength decrease that was initially caused by the weathering of the delimiting Rock joints and, further, by the progressive failure of the Rock bridge. The cohesion at failure of the Rock bridge ranges from 2.1 to 2.6 MPa (friction angle of Intact Rock φ  = 40°).

  • 3d stress strain analysis of a failed limestone wedge influenced by an Intact Rock bridge
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Paolo Paronuzzi, Alberto Bolla, Elia Rigo
    Abstract:

    This paper presents a back-analysis of a Rock wedge failure (volume = 25–30 m3) that involved a limestone scarp in the Rosandra valley (Trieste karst, NE Italy). Thanks to the mechanical survey of the detachment surface, a single Rock bridge having a size of about 15 cm × 30 cm has been ascertained. A 3D stress–strain analysis has been performed to examine the influence of the Rock bridge on the block stability (initial unweathered condition: strength reduction factor SRF equal to 1.14). The shear strength provided by the basal and lateral joints represents the main contributing factor for the wedge stability (about 60–75 % of the whole resisting system). However, the equilibrium of the wedge was temporarily attained thanks to the strength contribution provided by the Rock bridge (25–40 %) until the acting forces locally exceeded the resisting forces, thus determining the bridge rupture and, as a consequence, the wedge collapse. The mean shear stress acting on the Rock bridge at failure ranges from about 3.5 to 5 MPa. Calculated block displacements up to failure vary from 0.6 to 1.5 mm, depending on the different elastic modulus assumed for the wedge (E = 30, 10, and 4 GPa). Pre-collapse block displacements increase as a result of the shear strength decrease that was initially caused by the weathering of the delimiting Rock joints and, further, by the progressive failure of the Rock bridge. The cohesion at failure of the Rock bridge ranges from 2.1 to 2.6 MPa (friction angle of Intact Rock φ = 40°).

Paolo Paronuzzi - One of the best experts on this subject based on the ideXlab platform.

  • 3D Stress–Strain Analysis of a Failed Limestone Wedge Influenced by an Intact Rock Bridge
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Paolo Paronuzzi, Alberto Bolla, Elia Rigo
    Abstract:

    This paper presents a back-analysis of a Rock wedge failure (volume = 25–30 m^3) that involved a limestone scarp in the Rosandra valley (Trieste karst, NE Italy). Thanks to the mechanical survey of the detachment surface, a single Rock bridge having a size of about 15 cm × 30 cm has been ascertained. A 3D stress–strain analysis has been performed to examine the influence of the Rock bridge on the block stability (initial unweathered condition: strength reduction factor SRF equal to 1.14). The shear strength provided by the basal and lateral joints represents the main contributing factor for the wedge stability (about 60–75 % of the whole resisting system). However, the equilibrium of the wedge was temporarily attained thanks to the strength contribution provided by the Rock bridge (25–40 %) until the acting forces locally exceeded the resisting forces, thus determining the bridge rupture and, as a consequence, the wedge collapse. The mean shear stress acting on the Rock bridge at failure ranges from about 3.5 to 5 MPa. Calculated block displacements up to failure vary from 0.6 to 1.5 mm, depending on the different elastic modulus assumed for the wedge ( E  = 30, 10, and 4 GPa). Pre-collapse block displacements increase as a result of the shear strength decrease that was initially caused by the weathering of the delimiting Rock joints and, further, by the progressive failure of the Rock bridge. The cohesion at failure of the Rock bridge ranges from 2.1 to 2.6 MPa (friction angle of Intact Rock φ  = 40°).

  • 3d stress strain analysis of a failed limestone wedge influenced by an Intact Rock bridge
    Rock Mechanics and Rock Engineering, 2016
    Co-Authors: Paolo Paronuzzi, Alberto Bolla, Elia Rigo
    Abstract:

    This paper presents a back-analysis of a Rock wedge failure (volume = 25–30 m3) that involved a limestone scarp in the Rosandra valley (Trieste karst, NE Italy). Thanks to the mechanical survey of the detachment surface, a single Rock bridge having a size of about 15 cm × 30 cm has been ascertained. A 3D stress–strain analysis has been performed to examine the influence of the Rock bridge on the block stability (initial unweathered condition: strength reduction factor SRF equal to 1.14). The shear strength provided by the basal and lateral joints represents the main contributing factor for the wedge stability (about 60–75 % of the whole resisting system). However, the equilibrium of the wedge was temporarily attained thanks to the strength contribution provided by the Rock bridge (25–40 %) until the acting forces locally exceeded the resisting forces, thus determining the bridge rupture and, as a consequence, the wedge collapse. The mean shear stress acting on the Rock bridge at failure ranges from about 3.5 to 5 MPa. Calculated block displacements up to failure vary from 0.6 to 1.5 mm, depending on the different elastic modulus assumed for the wedge (E = 30, 10, and 4 GPa). Pre-collapse block displacements increase as a result of the shear strength decrease that was initially caused by the weathering of the delimiting Rock joints and, further, by the progressive failure of the Rock bridge. The cohesion at failure of the Rock bridge ranges from 2.1 to 2.6 MPa (friction angle of Intact Rock φ = 40°).

Lars Jacobsson - One of the best experts on this subject based on the ideXlab platform.