Rock mass classification

In geotechnical engineering, the first major rock mass classification system was proposed about 60 years ago for tunnelling with steel support. Later classification systems were developed for non-steel support underground excavation, slope and foundation engineering. Considering the three main design approaches for excavation in rock – analytical, observational and empirical – the most predominant design approach is the empirical design method. Indeed, on many underground or surface construction and mining projects, rock mass classifications have been providing the only systematic design aid in an otherwise haphazard "trial-and-error" procedure.

Objectives

Rock mass classifications were developed to create some order out of the chaos in site investigation procedures. They were not intended to replace analytical studies, field observations, measurements or engineering judgement.

The objectives of rock mass classifications are to:

# Identify the most significant parameters influencing the behaviour of a rock mass.
# Divide a particular rock mass formulation into groups of similar behaviour – rock mass classes of varying quality.
# Provide a basis of understanding the characteristics of each rock mass class
# Relate the experience of rock conditions at one site to the conditions and experience encountered at others
# Derive quantitative data and guidelines for engineering design
# Provide common basis for communication between engineers and geologists

And main benefits of rock mass classifications:

# Improving the quality of site investigations by calling for the minimum input data as classification parameters.
# Providing quantitative information for design purposes.
# Enabling better engineering judgement and more effective communication on a project.

List of rock mass classifications

*Rock load classification method
**It was the first rational method of rock classification. It was developed for tunnels driven in 50 – years supported by steel sets by Karl von Terzaghi. It is not suitable for modern tunneling methods using shotcrete and rockbolts. This classification was too general to permit objective prick
*Stand-up time classification
**The main significance of this method is that an increase in tunnel span leads to a major reduction in the stand up time. This method has influenced the development of more recent rock mass classification systems.
*Rock Quality Designation (RQD)
*Rock Structure Rating (RSR)
*Rock Mass Rating system (RMR)
*Q-system
*Size Strength classification
*ISRM classification

Classification systems for slope engineering:
*Slope Stability Probability Classification (SSPC) [http://www.xs4all.nl/~hack/WORKHack/Publications/2003%20sspc/SSPC%20ver%20web.pdf]
*Slope Mass Rating (SMR)