**4.2 Geological strength index (GSI)**

This classification system established and improved by Hoek and other researchers including the block size and its shear strength in order to estimate value of GSI quantitatively. The GSI index value for any rock mass is depend on the estimation techniques, expertise and reliability of these two input parameters. Sonmez and Ulusay developed the arithmetical basis for GSI value calculation and present quantitatively GSI chart as given in **Figure 5** [16]. Further research were carried out for quantification of GSI value by (Cai, et al.,2004), they present the assessment method for block size, joint and joints wall condition for GSI value quantification.

GSI system should not be considered as the replacement for other classification systems like RMR and Q-System, as this system cannot recommend any support system for stability of rock mass. This system can only be used in estimation of rock mass properties and input parameters for numerical modeling [15]. The comprehensive practice for estimation of input parameters for numerical analysis of stress condition and the remedial measures is presented in **Figure 5** (Hoek, 2013).

The GSI index may be estimated by subsequent various methods used for assessment of rock mass.

*Method A:* Using this method the GSI is estimated by skilled geologist or mining engineers from the data collected (observational data) at site and then the value of GSI is evaluated from chart [17].

carry the addition of a fresh parameter to Q-System named as excavation support ratio (ESR). The lower value of ESR symbolizes the necessity of great level firmness and vice versa. The ESR is used for the estimation of support system that can be set up to sustain the stability and also associated to the anticipated use of excavation. Incorporating various conditions, different values of ESR are summarized in **Table 14**. Based on the width and altitude of underground excavation, ESR shows

**6 SRF values SRF** N Mild swelling rock pressure 5–10 O Heavy swelling rock pressure 10–15

**Q-System values range Group Classes of rock mass** 0.001–0.01 3 Exceptionally Poor 0.01–0.1 Extremely Poor 0.1–1 2 Very Poor 1–4 Poor 4–10 Fair 10–40 1 Good 40–100 Very Good 100–400 Extremely Good 400–1000 Exceptionally Good

**Table 12.**

*Slope Engineering*

**Table 13.**

**Table 14.**

**64**

*Excavation support ratio (ESR) [13].*

*Stress reduction factor (SRF) values [13].*

*Rock mass classification based on Q-system [13].*

*De* <sup>¼</sup> width or altitude in meter

The support chart proposed by Bortan et al. (1974) as shown in **Figure 4**, is based on the Q-system ratings and equivalent dimension for the endorsement of permanent support system for underground excavations. This chart provides a

**7 Excavation types ESR values** A Temporary mine openings 3–5

B Permanent mine openings, water tunnels for hydro power (excluding high Pressure penstocks), pilot tunnels, drifts and headings for large excavations.

C Storage rooms, water treatment plants, minor road and railway tunnels, surge Chambers, access tunnels.

D Power stations, major road and railway tunnels, civil defense chambers, Portal intersections.

E Underground nuclear power stations, railway stations, sports and public Facilities, factories.

ESR (4)

1.6

1.3

1.0

0.8

the Equivalent dimension that is achieved by means of the Eq. (4) [13].

#### **Figure 5.** *Geological strength index chart [15].*

*Method B:* In this method the GSI index is estimated by using other classification systems like RQD and RMR etc. when limited data is available. The GSI can be estimate from the well-known relationship presented by various researchers [17].

*Method C:* The sonmez and Ulusay considered structure rating (SR) and surface condition rating (SCR) for approximation of GSI value [17].

The Cai et al. (2004) used block volume *(Vb)* and joint surface condition factor *(Jc)* to approximation the GSI. The block volume having greater number of joint sets indicated as:

$$Vb = \mathbf{S1} \times \mathbf{S2} \times \mathbf{S3} \tag{5}$$

analysis should be carried out for appropriate designing. The numerical methods are considered very useful to estimate the above parameters precisely and in minimum time as compared to other methods of design. Numerical methods used physical and strength properties of rock as input for analysis. For efficient and viable design the

Different researchers developed and present various numerical methods and models. These are divided into eight classes on the basis of four methods and two

The numerical methods of design uses in rock/soil engineering are grouped into

numerical and empirical methods are used in parallel [19–23].

**5.1 Numerical methods of modeling for rock/soil engineering**

three classes for modeling in rock mechanics as discussed above.

The different continuum methods of design are as under.

levels as shown in **Figure 7** [24, 25].

*Quantitative estimation of GSI chart [15].*

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

*5.1.1 Continuum methods*

**67**

**Figure 6.**

where, S is joint spacing.

The *Jc* defined by the roughness of joint, weathering and infilling, these are used to measure the joint surface condition factor by using the Eq. (6).

$$J\mathbf{c} = \mathbf{J}\mathbf{w} \times \mathbf{J}\mathbf{s}/\mathbf{l}\mathbf{a} \tag{6}$$

The*Vb* and *Jc* are used to precisely quantify the GSI value [17]. The quantitative chart for estimation of GSI suggested by sonmez and Ulusay [1999] is shown in **Figure 6**.

#### **5. Numerical methods of design**

The empirical methods of design do not estimate accurately the reliability supports, redistribution of stresses, rock mass deformation [18]. These parameters are very important in designing and analysis of any excavation therefore, numerical

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