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

**B. RATING** 

**58**

Strike and dip orientations

Ratings

Tunnels & mines

Foundations

Slopes **DETERMINED**

 **FROM TOTAL RATINGS**

100

81

I Very good

Good rock

 Fair rock

rock

I

20 yrs. for

1 year for 10 m

1 week for 5 m

10 hrs for 2.5 m span

> 15 m span

>400

>45

35–45

25–35

 300–400

 200–300

100–200

15–25

<100

<15

span

span

II

III

IV

V

30 min for 1 m span

II

III

 80

61

 60

 41

40

 21

IV

Poor rock

<21

V

Very poor rock

**C. ROCK MASS CLASSES** 

Rating Class number

Description **D. MEANING**

Class number

Average stand-up time

Cohesion of rock mass (kPa)

Friction angle of rock mass (deg)

**E.** 

**GUIDELINES**

Discontinuity

Rating

Separation (aperture)

Rating Roughness

Rating

 length

(persistence)

 **FOR** 

**CLASSIFICATION**

 **OF** 

**DISCONTINUITY**

<1m

6 None

6 Very rough

6

5

3

 Rough

 Slightly rough

5

4

<0.1 mm

 0.1–1.0 mm

4

2

 1–3m

 3–10 m

10–20 m

1 1–5 mm

1 Smooth

1

>20 m

0

>5 mm

0

Slickensided

0

 **conditions**

 **OF ROCK CLASSES**

0

�5

�25

0

�2

�7

**ADJUSTMENT**

 **FOR** 

**DISCONTINUITY**

Very favorable

0

�2

�5

 Favorable

 Fair

Unfavorable

�10

�15

�50

Very

Unfavorable

�12

*Slope Engineering*

�25

**ORIENTATIONS**

 **(See F)**


**1 Rock quality designation (RQD) RQD** A Very poor >27 joints per m<sup>3</sup> 0–25 B Poor 20–27 joints per m<sup>3</sup> 25–50 C Fair 13–19 joints per m<sup>3</sup> 50–75 D Good 8–12 joints per m<sup>3</sup> 75–90 E Excellent 0–7 joints per m3 90–100

*Note: i. Where RQD is reported, as* ≤*10 (including zero) the value 10 is used to assess the Q-value.*

**2 Jn values Jn** A Massive, no or few joints 0.5–0.1 B One joint set 2 C One joint set plus random joints 3 D Two joint sets 4 E Two joint sets plus random joints 6 F Three joint sets 9 G Three joint sets plus random joints 12 H Four joint sets, random, heavily jointed, "sugar cube", etc. 15 I Crushed rock, earth like 20

**3 Jr values Jr**

A Discontinuous joints 4 B Rough or irregular undulating 3 C Smooth undulating 2 D Slickensides, undulating 1.5 E Rough irregular planar 1.5 F Smooth planar 1 G Slickensides planar 0.5 Note: i. description refer to small scale features and intermediate scale features, in that order

H Zones containing clay minerals thick enough to prevent rock wall contact 1 I Sandy, gravely or crushed zone thick enough to prevent rock wall contact 1

*ii. RQD-intervals of 5 are adequately accurate.*

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

*Note: i. For tunnel intersection, use 3 Jn. ii. Far portals, use 2 Jn.*

*Joint set numbers (*Jn*) values [13].*

a. Rock-wall contact and

b. Rock-wall contact before 10 cm shear movement

c. No-rock wall contact when sheared

*Rock quality designation (*RQD*) and volumetric jointing [13].*

**Table 7.**

**Table 8.**

**61**

#### **Table 6.**

*Guidelines for excavation and support of 10 m span rock tunnels in accordance with the RMR system [1, 6].*

The second quotient *Jr Ja* communicates the unevenness and frictional features of the joint walls or infill materials. This measure is taken in favor of uneven, unchanged joints in direct interacted. The strength is reduced significantly in case where rock joints have coating of thin clay mineral and fillings. It defines the inter – block shear strength of rock mass.

The third quotient *Jw SRF* incorporates two stress related parameters. SRF is a degree of 1) untying load when the excavation passes through clay bearing rock and shear zones, 2) rock stress when the excavation is within competent rock, and 3) squeezing loads in plastic weak rock masses. It is also as a total stress parameter. The Jw parameter is amount of water pressure, adversely affect the shear strength of joints as it reduces the effective normal stress. In addition, presence of water may create softening and ultimately the possibility of outwash when clay infill the joints. It generally shows the active stress component and that is determined empirically. The comprehensive and detail system of determining the values of the Q-System parameters (Rock quality designation *(RQD),* Number of joints *(Jn)*, Roughness number for joint *(Jr),* Joint alteration number *(Ja),* Joint water reduction factor *(Jw),* Surface reduction factor *(SRF)* are given in **Tables 7**–**12**. The extreme value exemplifies good class of rock and the inferior value signifies poor class of rock.

The values achieved for the different parameters using the above cited tables are then used for the determination of the value of the Q- system. Based on the Value of Q-System the Bortan et al. (1974) classify the quality of rock into nine different groups as shown in **Table 13**.

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


*Note: i. Where RQD is reported, as* ≤*10 (including zero) the value 10 is used to assess the Q-value. ii. RQD-intervals of 5 are adequately accurate.*

#### **Table 7.**

*Rock quality designation (*RQD*) and volumetric jointing [13].*


#### **Table 8.**

The second quotient *Jr*

blasting.

**Rock mass class**

*Slope Engineering*

I. Very good rock *RMR*: 81–100

II. Good rock *RMR*: 61–80

III. Fair rock *RMR*: 41–60

IV. Poor rock *RMR*: 21–40

V. Very poor rock *RMR*: < 20

**Table 6.**

**Excavation Rock bolts**

Full face, 3 m advance. Generally no

Full face, 1–1.5 m advance. Complete support 20 m

Top heading and bench 1.5– 3 m advance in top heading. Commence support after each blast. Complete support 10 m from face.

Top heading and bench 1.0–1.5 m advance in top heading. Install support concurrently with excavation, 10 m from face.

Multiple drifts 0.5–1.5 m advance in lop heading. Install support concurrently with excavation Shotcrete as soon as possible after

from face.

**(20 mm diameter, fully grouted)**

support required except spot boiling.

Locally, bolts in crown 3 m long, spaced 2.5 m wi1n occasional wire mesh.

Systematic bolts 4 m long, spaced 1.5–2 m in crown and walls with wire mesh in crown.

Systematic bolts 4– 5 m long, spaced 1– 1.5 m in crown and walls with wire mesh.

Systematic bolts 5– 6 m long, spaced 1– 1.5 m in crown and walls with wire mesh. Bolt invert.

**Shotcrete Steel sets**

None.

None.

Light to medium ribs spaced 1.5 m where required.

Medium to heavy ribs spaced 0.75 m with steel lagging and forepoling if required. Close invert.

50 mm in crown where required.

50–100 mm in crown and 30 mm in sides.

100–150 mm in crown and 100 mm in sides.

150–200 mm in crown, 150 mm in sides, and 50 mm on face.

The third quotient *Jw*

groups as shown in **Table 13**.

**60**

inter – block shear strength of rock mass.

*Ja* communicates the unevenness and frictional features of

*SRF* incorporates two stress related parameters. SRF is a degree

the joint walls or infill materials. This measure is taken in favor of uneven, unchanged joints in direct interacted. The strength is reduced significantly in case where rock joints have coating of thin clay mineral and fillings. It defines the

of 1) untying load when the excavation passes through clay bearing rock and shear zones, 2) rock stress when the excavation is within competent rock, and 3) squeezing loads in plastic weak rock masses. It is also as a total stress parameter. The Jw parameter is amount of water pressure, adversely affect the shear strength of joints as it reduces the effective normal stress. In addition, presence of water may create softening and ultimately the possibility of outwash when clay infill the joints. It generally shows the active stress component and that is determined empirically. The comprehensive and detail system of determining the values of the Q-System parameters (Rock quality designation *(RQD),* Number of joints *(Jn)*, Roughness number for joint *(Jr),* Joint alteration number *(Ja),* Joint water reduction factor *(Jw),* Surface reduction factor *(SRF)* are given in **Tables 7**–**12**. The extreme value exemplifies good class of rock and the inferior value signifies poor class of rock. The values achieved for the different parameters using the above cited tables are then used for the determination of the value of the Q- system. Based on the Value of Q-System the Bortan et al. (1974) classify the quality of rock into nine different

*Guidelines for excavation and support of 10 m span rock tunnels in accordance with the RMR system [1, 6].*

*Joint set numbers (*Jn*) values [13].*



iii. Jr. = 0.5 can be used for planar, slickensides joints having lineation, provided that the lineation are oriented for minimum strength.

**5 Jw values Jw** A Dry excavation or minor inflow (humid or a few drips) 1.0 B Medium inflow, infrequent outwash of joint filling (many drips/"rain") 0.66 C Jet inflow or higher pressure in competent rock with unfilled joints 0.5 D Large inflow or higher pressure, considerable outwash of joint fillings 0.33

0.2–0.1

0.1–0.05

10

7.5

5

2.5

0.01–0.3 1

10–5 0.3–0.4 0.5–2 2–5\*

5–3 0.5–0.65 5–50

σΘ / σc SRF

SRF

10

E Exceptionally high inflow continuing without perceptible decay. Causes outwash of material and possibly cave in

F Exceptionally high inflow continuing without perceptible decay. Causes outwash of material and possibly cave in

A Multiple occurrences of weak zones within a short section containing clay or chemically disturbed very loose surrounding rock at any depth, or long section with incompetent rock.

B Multiple shear zones within a short section in competent day-free rock with weak surrounding rock at any depth.

C Single weak zone with or without clay or chemical disintegrated rock with depth less than or equal to 50 m.

E Single weak zones with or without clay or chemical disintegrated rock with depth greater than 50 m

G Medium stress, favorable stress condition 200–

Suggest SRF increase from 2.5 to 5 for such cases (see H). c. Squeezing rock: plastic deformation in incompetent rock under the influence

H High stress, very tight structure. Usually good for stability. Depending on stress orientation it may be unfavorable to stability.

I Moderate spalling land/slabbing after greater than one hour in massive rock

d. Swelling rock: chemical swelling activity depending on the

of high pressure

presence of water

**63**

D Loose, open joints, heavily jointed at any depth 5

Note: i. Reduce these values of SRF by 25–50% if the weak zones but do not intersect the underground opening b. Competent massive rock with stress problems σc / σ1 σΘ / σc SRF F Low stress, near surface, open joints >200 <0.01 2.5

J Spalling or rock burst after a few minutes in massive rock 3–2 0.65–1 50–200 K Heavy rock burst and instant active deformation in massive rock <2 >1 200–400 Note: ii. For strongly anisotropic virgin stress field (if measured): when 5 ≤ σ1 / σ3 ≤ 10 reduce σc to 0.8 σc, and σΘ to 0.8 σΘ, when σ1 / σ3 > 10 reduce σc to 0.5 σc, and σΘ to 0.5 σΘ. iii. Few case records available where depth of crown below surface is less than span width

L Mild squeezing rock pressure 1–5 5–10 M Heavy squeezing rock pressure >5 10–20

**6 SRF values SRF** a. Weak zones crossing the underground excavation, which may cause loosening of rock mass

**Table 11.**

*Joint water reduction factor (Jw) values [13].*

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

#### **Table 9.**

*Joint roughness number (*Jr*) values [13].*


#### **Table 10.**

*Joint alteration (Ja) values [13].*

High professionalism is required for estimation of the values of parameter used in this system. The poor professional users may face trouble while approximating the score of the parameters and may approximate the lesser value for Q-System, which is considered the weakness of this classification system [14].

The width and altitude of the underground excavations mainly depend on the class of rock mass and considered as significant elements in design of underground excavations. The facet of width or altitude directly disturbs the stability when amplified or declined. To highlight the safety obligation, Bortan et al. (1974) further
