The mass of rock interrupted by discontinuities with each constitute discrete block having intact rock properties is known as Rock mass.
Rock mass are heterogeneous because of different rock type ,presence of discontinuities, and varying degrees of weathering.The Stability and deformability of rock is dependent on the strength and the deformability of the rock mass. Bedding Planes, foliation, joints,faults,and fault zones are all forms of discontinuities.
Rock mass= Intact Rock + Discontinuities
During the the feasibility and preliminary design instead of a project, when very little detailed information on the rock mass and its stress and hydrologic characteristics is available, the use of rock classification scheme can be of considerable benefit. Different classification system place different emphases on the various parameter, and it is recommended that at least two method be used at any site during the early stage of a project.
Rock Mass Classifi....Show More
The mass of rock interrupted by discontinuities with each constitute discrete block having intact rock properties is known as Rock mass.
Rock mass are heterogeneous because of different rock type ,presence of discontinuities, and varying degrees of weathering.The Stability and deformability of rock is dependent on the strength and the deformability of the rock mass. Bedding Planes, foliation, joints,faults,and fault zones are all forms of discontinuities.
Rock mass= Intact Rock + Discontinuities
During the the feasibility and preliminary design instead of a project, when very little detailed information on the rock mass and its stress and hydrologic characteristics is available, the use of rock classification scheme can be of considerable benefit. Different classification system place different emphases on the various parameter, and it is recommended that at least two method be used at any site during the early stage of a project.
Rock Mass Classification is the process of placing a rock mass into groups or classes on defined relationships (Bieniawski, 1989) and assigning a unique description (or number) to it on the basis of similar properties/characteristics such that the behavior of the rock mass can be predicted. The Rock mass classification system at
Terzaghis Rock mass classification
Rock quality designation index (RQD)
Geomechanical classification/ RMR classification
Rock tunneling quality index(Q-index)
Geomechanical classification/ RMR classification
Bieniawski published the details of a rock mass classification called the geomechanics classification and widely known as rock mass rating (RMR) system.This system combines the most significant geologic parameters and represent them with one overall comprehensive index of Rock quality, which is used for the design and construction of exhibition in rock, such as tunnels, mines and foundations.
The following 6 parameters are used to classify a rock mass using RMR system.
Uniaxial compressive strength of rocks,
RQD,
Spacing of discontinuities,
Condition of discontinuities,
Orientation of discontinuities,
Groundwater conditions.
According to Bieniawski (1993), the objectives of rock mass characterization and classification are:
to identify the most significant parameters influencing the behavior of a rock mass;
to divide a particular rock mass formation into a number of rock mass classes of varying quality;
to provide a basis for understanding the characteristics of each rock mass class;
to derive quantitative data for engineering design;
to recommend support guidelines for tunnels and mines;
to provide a common basis for communication between engineers and geologists;
to relate the experience on rock conditions at one site to the conditions encountered and experience gained at other
Advantage of Rock mass Classification System:
Classification of rock mass improves the quality of site investigations by calling for a systematic identification and quantification of input data. A rational, quantified assessment is more valuable than a personal (non-agreed) assessment. Classification provides a checklist of key parameters for each rock mass type (domain) i.e. it guides the rock mass characterization process. Classification results in quantitative information for design purposes and enables better engineering judgment and more effective communication on a project (Bieniawski, 1993). A quantified classification assists proper and effective communication as a foundation for sound engineering judgment on a given project (Hoek, 2007). Correlations between rock mass quality and mechanical properties of the rock mass have been established and are used to determine and estimate its mechanical properties and its squeezing or swelling behavior.
Disadvantages of rock mass classification:
According to Bieniawski (1993), the major pitfalls of rock mass classification systems arise when:
using rock mass classifications as the ultimate empirical cook book, i.e. ignoring analytical and observational design methods;
using one rock mass classification system only, i.e. without cross-checking the results with at least one other system;
using rock mass classifications without enough input data;
using rock mass classifications without full realization of their conservative nature and their limits arising from the database on which they were developed.
Some people are of the opinion that
natural materials cannot be described by a single number,
other important (often dominating) factors are not considered
results of rock mass classification are prone to misuse (e.g., claims for changed conditions)
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