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.

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 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.

How is rock mass rating calculated?

RMR is determined as an algebraic sum of ratings for all of the parameters. On the basis of RMR values for a given engineering structure, the rock mass is sorted into five classes: very good (RMR 100–81), good (80–61), fair (60–41), poor (40–21), and very poor (<20).

What does rock strength depend on?

Strength of a given rock type is strongly influenced by physical parameters such as temperature, confining pressure, fluid pressure, and the length of time the stress is applied.

What is MPa in rock?

Rock mass classification The vertical stress is about 1.0 MPa, and the horizontal stress is about 3.4 MPa. The major principal stress is horizontal with a magnitude of 3.4 MPa, and the compressive strength of the rock types is 53 MPa for the shale and 71 MPa for the basalt.

How do you calculate RMR for rocks?

The groundwater rating accounts for 15% of total ratings. The final RMR value of the rock is calculated as follows:(1) R M R = R 1 + R 2 + R 3 + R 4 + R 5 + R 6 where R1, R2, …, R6 are the ratings corresponding to six rock parameters as depicted in Table 2.

What is RMR and Q system?

Although the rating methods of RMR and Q-system are additive and multiplicative, respectively, the basic concepts of both schemes are similar. Both schemes allocate the ratings to the properties that influence the rock mass behavior and then quantitative figures such as total-RMR and Q-value are produced.

What is Q value of rock?

The rock mass quality (Q) is a very sensitive index and its value varies from 0.001 to 1000. Use of the Q-system is specifically recommended for tunnels and caverns with an arched roof.

Which Three methods are commonly used to classify rock mass?

This system forms the foundation for the development of three most common rock mass classification schemes i.e. Q, RMR, and GSI. This conservative method has been modified and improved over time and is still used today to aid in the design of tunnels.

How deep is the rock mass at Hoek & Brown?

The station has cover depth of approximately 10 m over the crown. The rock mass is locally known as Athenian schist which is a term erroneously used to describe a HOEK & BROWN – PRACTICAL ESTIMATES OF ROCK MASS STRENGTH17

When was Hoek and brown’s rock mass estimate published?

Published in the International Journal of Rock Mechanics and Mining Sciences, Vol 34, No 8, 1997, pages 1165-1186 HOEK & BROWN – PRACTICAL ESTIMATES OF ROCK MASS STRENGTH1

How to determine the uniaxial and Hoek-Brown constant of a rock?

Determination of the intact rock uniaxial compressive strength s ciand the Hoek-Brown constant m ishould be carried out by triaxial testing wherever possible. The tests should be carried out over a confining stress range from zero to one half of the uniaxial compressive strength.

When can the rock mass be treated as Hoek-Brown material?

When the slope or underground excavation is large and the block size small in comparison, the rock mass can be treated as a Hoek-Brown material. 0 50 100 150 200 250 300 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 n i a x i a l