I am sorry that I may sound rude, but dear Manasa all those parameters are explained in full detail by the original Authors and others in a number of articles. You can find much of this literature in "Hoek's Corner" at www.rocscience.com. It will be useful if you start with the Practical Rock Engineering notes by Dr E. Hoek on Rock Mass Classification and Rock Mass Properties at https://www.rocscience.com/learning/hoek-s-corner/books.  Finally, please note that it is the nature of rock types and their mineralogy (e.g. m), strength (e.g. UCS) and stress history that provide all the initial input to derive Hoek-Brown criterion related parameters (e.g. a and s).

Dear Sir,

Thank you for your suggestion.

Hi Manasa

It is the bi-linear relationship between shear stress and normal stress. The main difference in failure criteria theory between rock and soli is change in direction of normal stress.

Rock mass index rating was practiced in rock mechanics to find parameters which affect  the behavior of rock.

We should turn the original question around - does the behaviour of weak rock to some degree match its description by H-B parameters, using the non-linear shear strength (an improvement on linear M-C) and when the above is applied as a potential model of constitutive behaviour in e.g. an FEM code such as Phase 2? So far incontestable diplomacy. The problem then arises - are the modelled results consistent with the observed behaviour (displacement, failure-proximity etc.). They may not be, because, depending on the scale of the problem, there may be progressive failure tendencies. If this applies, we are unlikely to be justified in assuming simultaneous mobilization of the cohesive strength components and the frictional strength components: the typical c + sigma n x tan phi of linear M-C, or of non-linear H-B.

The various resisting media along the potential multiple-failure-mode 'surfaces' - may include'intact bridges' where capable rock joints are missing, the probably larger areas of capable rock joints, and a possible mix of weaker clay-bearing discontinuities due to weathering etc. Big slopes can be monitored, and failure can occur in stages, without loss of life in e.g. large open pits....because 'c' breaks at smaller strain and friction remains requiring larger displacements to eventually reach lower residual strength and perhaps failure. If one has to perform continuum modelling, degrade cohesion and mobilize friction so c and phi are not being added when respective peak values are reached. Discrete element modelling with non-linear strength UDEC-BB might give more insight, with numerically 'glued' intact bridges which fail when over-stressed. A nice fracture mechanics code FRACOD might be good if the weak rock is more 'intact' than assumed above.

Thank you for your kind response Mr.K.Nagappan and Mr.N.Barton.