**4.1 Rock mass classification systems**

Rock mass classification is a tool for the assessment of the rock behavior and performance based on the essential inherent and structural parameters [9]. Rock mass classification systems are the most and widely used empirical methods of design Different rock mass classification systems are RMR, Q-System, RQD, RSR, GSI etc. [6]. Rocks have been classified on the basis of origin, mineralogical compositions and distinct physical properties and ground condition. Rock Classification provides a mutual basis of communication to recognize rock mass in a category having same and well define characterization and basic input parameters for rock engineering design. For designing purposes in several attempts were made to classify rock based on rock and site characterization. Such simplified classification systems have served to understand the upper bound response of the rocks [10]. Rock mass classification systems effectively combined the results comes observation, experience and other engineering judgment for providing a quantitative evaluation of rock mass situations. Rock mass classification systems has the below mentioned purposes in tunneling design [5].


Up till now different rock mass classification systems have been proposed by Terzaghi (1946), Lauffer (1958), Deere (1964), Wickham, Tiedemann, and Skinner (1972), Bieniawski (1973), and Barton, Lien, and Lunde (1974), (Bieniawski Z. T. 1990). The different classification systems used for the design purposes are assembled in **Table 1**.

3.Blocky and seamy rock: Such rocks consist of chemically intact or almost intact rock fragments which are totally detached from each other and erroneously

**Originator Origin**

1 Rock Load Terzaghi, 1946 USA Tunnels with steel

2 Stand-up time Lauffer, 1958 Australia Tunneling

5 Rock Structure Rating (RSR) Wickham et al., 1972 USA Tunneling

8 Strength- Block Size Franklin, 1975 Canada Tunneling 9 Rock Mass Strength (RMS) Stille et al., 1982 Sweden Metal Mining

12 Basic Geotechnical Classification ISRM, 1981 International General

13 Geological strength index (GSI) Hoek et al. 1995 Mines and Tunnels

Rock Mass Quality (Q) Barton et al., 1974

Bieniawski 1973 (List modified, 1989-USA) Özkan and Ünal, 1990

(Last modified 2002)

**country**

Pacher et al., 1964 Austria Tunneling

Deer et al., 1967 USA Core logging,

Williamson, 1984 USA General

Singh, 1986 India Coal Mining

South Africa Turkey

**Application areas**

support

Tunneling

Mining

Foundations

Communication

Norway Tunnels, Mines,

Tunnels, Mines, (Slopes, Foundations)

4.Crushed rock: such rocks are chemically intact rock but have the characteristic of crusher outing. If maximum or completely all the fragments are as small as fine sand particles and no cementation has taken place, crushed rock below the

5.Squeezing rock: Squeezing rock gradually progresses into the tunnel without noticeable increase in volume. An obligation for squeeze is a high percentage of microscopic and sub-microscopic elements of micaceous minerals or clay

6. Swelling rock: Such rock moves inside the tunnel mainly because of expansion. The capability to swell seems to be insufficient to those rocks that have clay

Lauffer (1958) anticipated that stand up time for an excavation span is associated with the quality of rock mass in which the width is mined. The Unsupported span may be defined as the width of the tunnel or the distance between the face and the adjacent support, if such is grater that the tunnels width. Laufer's (1958)

minerals such as montmorillonite, with a high swelling capability.

joined. In such rock, vertical walls may need sides support.

water table demonstrate the properties of water-bearing sand.

minerals with a low swelling capability.

**S. No**

**system**

(RQD)

(M-RMR)

**Rock mass classification**

*Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*

3 New Austrian Tunneling Method (NATM)

4 Rock Quality Designation

6 Rock Mass Rating (RMR) Modified Rock Mass Rating

10 Unified Rock Mass Classification

11 Weakening Coefficient System

*Most widely used rock mass classification systems [6, 10].*

System (URMC)

(WCS)

**Table 1.**

**51**

*4.1.2 Classifications containing stand-up time*

#### *4.1.1 Terzaghi's rock mass classification*

A well-known classification system for support of tunnels. This explanatory system was developed in the U.S.A in 1946. Terzaghi's (1946) formulate the first rational method of evaluating the rock loads suitable to the design of steel sets. This classification is appropriate for the estimating rock loads for steel arch supported tunnels. It is not so suitable for modern tunneling methods using shotcrete and rock bolts [5].

Terzaghi's classify rocks as under [11]:

1.*Intact Rock*: Rocks that's having no joints and cracks, it breaks crossways a sound rock or loose block may drops off the top for many hours and days due to blasting. It is called sapling condition.

Stratified rock: that rock composed those distinct sections having slightly or no confrontation to parting beside the margins stuck between the strata. In such rock the spalling condition is generally happened.

2.*Moderately jointed rock:* That rock having joints and hair cracks, but the blocks among joints are locally developed collectively or so closely joined that perpendicular walls do not need on the sides support. In this type of rock, both spalling and popping conditions may be happened.

## *Design Techniques in Rock and Soil Engineering DOI: http://dx.doi.org/10.5772/intechopen.90195*


#### **Table 1.**

**4.1 Rock mass classification systems**

*Slope Engineering*

1.Group rock masses having similar behaviors.

assembled in **Table 1**.

**50**

*4.1.1 Terzaghi's rock mass classification*

Terzaghi's classify rocks as under [11]:

to blasting. It is called sapling condition.

rock the spalling condition is generally happened.

spalling and popping conditions may be happened.

Rock mass classification is a tool for the assessment of the rock behavior and performance based on the essential inherent and structural parameters [9]. Rock mass classification systems are the most and widely used empirical methods of design Different rock mass classification systems are RMR, Q-System, RQD, RSR, GSI etc. [6]. Rocks have been classified on the basis of origin, mineralogical compositions and distinct physical properties and ground condition. Rock Classification provides a mutual basis of communication to recognize rock mass in a category having same and well define characterization and basic input parameters for rock engineering design. For designing purposes in several attempts were made to classify rock based on rock and site characterization. Such simplified classification systems have served to understand the upper bound response of the rocks [10]. Rock mass classification systems effectively combined the results comes observation, experience and other engineering judgment for providing a quantitative evaluation of rock mass situations. Rock mass classification systems has the below mentioned purposes in tunneling design [5].

2.Provides the root for understanding the characteristics of independent groups.

3.Helps in planning and designing of excavation in rock and provide quantifiable

4.A common understanding agenda for all the related people in the project.

Up till now different rock mass classification systems have been proposed by Terzaghi (1946), Lauffer (1958), Deere (1964), Wickham, Tiedemann, and Skinner (1972), Bieniawski (1973), and Barton, Lien, and Lunde (1974), (Bieniawski Z. T. 1990). The different classification systems used for the design purposes are

A well-known classification system for support of tunnels. This explanatory system was developed in the U.S.A in 1946. Terzaghi's (1946) formulate the first rational method of evaluating the rock loads suitable to the design of steel sets. This classification is appropriate for the estimating rock loads for steel arch supported tunnels. It is not so suitable for modern tunneling methods using shotcrete and rock bolts [5].

1.*Intact Rock*: Rocks that's having no joints and cracks, it breaks crossways a sound rock or loose block may drops off the top for many hours and days due

2.*Moderately jointed rock:* That rock having joints and hair cracks, but the blocks among joints are locally developed collectively or so closely joined that perpendicular walls do not need on the sides support. In this type of rock, both

Stratified rock: that rock composed those distinct sections having slightly or no confrontation to parting beside the margins stuck between the strata. In such

data for the design of complex engineering complications.

*Most widely used rock mass classification systems [6, 10].*

