What is the role of the disturbance factor D in the Hoek-Brown strength criterion?
Experience in the design of slopes in large open pit mines has shown that the Hoek-Brown criterion for rock masses in situ undisturbed (D = 0) determines properties of the rock mass that are too optimistic.
What is the value of constant A for poor quality rock in Hoek and Brown failure criterion?
≈ 0.5
It will be noted that, for intact rock, only two variables are needed to define the Hoek–Brown failure envelope with a tension cut-off. These are the unconfined compressive strength of the intact rock, , and the material parameter, mi. For hard intact rock, the parameter s is always equal to 1 and the constant a ≈ 0.5.
What is Mi in Hoek-Brown?
The m i is an important parameter in the use of the Hoek-Brown failure criterion. It can be estimated using a triaxial compressive strength test but in many projects there is no actual test result for the parameter. An estimation of m i comes from a reference table giving a constant value.
Which parameters determine how rock responds to mining?
Stress concentration, seismicity, water pressure and temperature are the main hazards of fracturing in deep underground mines. These parameters can have influences on the behaviour of hard rock and cause violent failures such as rockburst, brittle failure, fault burst and spalling.
What is RMR in geology?
The rock mass rating (RMR) is a geomechanical classification system for rocks, developed by Z. T. Bieniawski between 1972 and 1973.
What is rock mass properties?
The properties Em and σcm are the rock mass values of deformation modulus and compressive strength respectively. These designations and parameters are all discussed in detail by Hoek et al. (1995). The terms σ[field], Vp and Vs are the (in-situ) field stresses and P- and S-wave acoustic velocities within the rock mass.
What is meant by rock strength?
Rock strength is defined by stress/strain relationships, pore fluid pressure, and confining pressure. Stronger, more dense rocks are not as likely to be involved in a rock slide or landslide than porous less dense rocks that can be easily saturated with water.
How does weathering affect rock and rock mass properties?
The influence of weathering is quite clear in the decrease of intact rock strength over the complete sequence from fresh to completely weathered rock masses and for the decrease in discontinuity spacing and condition of discontinuities …
What is intact rock strength?
Intact rock strength is mostly defined as the strength of the rock material between the discontinuities. Strength values used are often from laboratory unconfined compressive strength (UCS) tests.
What are the factors that affect the strength of rock explain?
The principal factors controlling the strength of solid rocks are: I) mineral composition, structure and texture; 2) bedding, jointing and anisotropy; 3) water content; 4) state of stress in the rock mass.
What are rock parameters?
Rock physical properties include density, porosity, and permeability, etc. Rock mechanical properties mainly include elastic modulus, Poisson’s ratio, and rock strength. These parameters can be obtained by lab experiments of core samples or by in-situ tests.
What is RQD and RMR?
RQD is determined from rock cores or volumetric joint count; it is the percentage of rock cores in one meter of drill run. RMR is determined as an algebraic sum of ratings for all of the parameters.
What is the Hoek–Brown criteria?
Introduction The Hoek–Brown criterion was derived from the results of research into the brittle failure of intact rock by Hoek (1965) and on model studies of jointed rock mass behaviour by Brown (1970).
What are the input parameters to calculate the Hoek-Brown?
The other input parameters to calculate the Hoek-Brown are: Uniaxial compressive strength (\\(\\sigma_{ci}\\))
How is the Hoek-Brown failure criteria related to the Mohr-Coulomb failure criteria?
The Hoek-Brown Failure Criteria is related to the Mohr-Coulomb Failure Criteria by fitting a straight line on an range given by the following limits: $$\\sigma_{t} < \\sigma_{3}^{‘} < \\sigma_{3max}$$
How to analyse triaxial test results using the Hoek–Brown criterion?
When the Hoek–Brown criterion was introduced, it was recommended that triaxial test results should be analysed by linear regression of the following version of Eq. (1) ( Hoek, 1983 ): (11) ( σ 1 − σ 3) 2 = m i σ ci σ 3 + σ ci 2