AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY

FACULTY OF MINING AND GEOENGINEERING

DEPARTMENT OF GEOMECHANICS, CIVIL ENGINEERING AND GEOTECHNICS

CIVIL ENGINEERING

Underground Engineering

ROCK MASS CLASSIFICATION

Evaluation of the rock mass quality in the tunnel (chamber) area with the initial proposal for support

UNIVERSITY TEACHER: MSc Eng. Agnieszka Stopkowicz

AUTHOR: Katarzyna Ziobro

group: 3

number of project: 67

date: 2013-06-01

Introduction and design data

The tasks of the project

1. Defining indices of the RMR system (according to Bieniawski) and of Q (according to Barton, Lien and Lunde) and classification of rock mass.

2. Comparison of RMR and Q indices and comment on the rock mas quality and their correlations.

3. The initial proposal for lining the excavation site on the basis of the Q index.

Design data

No.	Parameter	Value or description
1.	Shape, dimensions and destination of tunnel (chamber)	road tunnel, circular cross-section with a 5,5 m radius
2.	Average depth [m]	85
3.	General characteristics of the rock mass in the area of tunnel (chamber) drilling	concise, block
4.	Average compressive strength of the surrounding rocks [MPa]	28
5.	Average tensile strength of the surrounding rocks [MPa]	3
6.	RQD [%], core diameter of 55 mm	as in the picture below
7.	Amount and average spacing of discontinuities	two discontinuity sets with an average spacing of 0.6 m
8.	Condition of discontinuities	rough, irregular, flat walls of a clay-filled joints (separation < 5 mm thick)
9.	Groundwater conditions	Large supply of water (more than 30l/min)
10.	Orientation of discontinuities relative to the direction of tunnel (chamber) drive	extension parallel to the long axis of the tunnel, dip 15 °
11.	Method of drilling	mechanical drilling

Rock Quality Designation (RQD) $\text{RQD} = \frac{\sum_{}^{}{\text{Length\ of\ core\ pieces\ } > \ 10\ \text{cm}\ }}{\text{Total\ length\ of\ core\ run}} \times 100\%$

$\text{RQD} = \frac{19 + 14 + 12 + 12 + 15 + 10}{94} \times 100\% = 87,23\%$

Rock mass classification based on RMR

Classification parameters and their ratings

1) Strength of intact rock material

uniaxial compressive strength is 28 MPa

rating: 4 /15

2) Drill core Quality RQD

the proportion of the intact core pieces longer than 100 mm to the total length of core is 87,23%

rating: 15/20

3) Spacing of discontinuities

two discontinuity sets with an average spacing of 0,6 m

rating: 10 /20

4) Condition of discontinuities

rough, irregular, flat walls of a clay-filled joints (separation < 5 mm thick)

rating: 15 /30

5) Groundwater

Large supply of water (more than 30l/min)

rating: 4 /15

Rating adjustment for discontinuity orientations

extension parallel to the long axis of the tunnel, dip 15 °– fair

rating: -5

Rock mass classes determined from total rating

total rating: 43/100

class number: III

description: fair rock

Modified RMR factor:

Factor	Note	Comments
AB (0,8-1,0) (Excavation method)	0,9	The medium value, because excavation is carried out by machines , which cause additional (minimal) failure of rock mass.
AS (0,6-1,2) (In – situ stress)	1,0	Rough separations, walls og a clay-filled joints.
S (0,7-1,0) (Condition of rock mass (joints))	0,7	Two sets of discontinuities with unfavourable spacing and shape.

A_B ^. A_S ^. S = 0,9 ^. 1,0 ^. 0,7 = 0.63 > 0.5

RMR_MODIFIED = RMR_BASIC ^. A_B ^. A_S ^. S = 43 ^. 0,9 ^. 1,0 ^. 0,7= 27,09

class number: IV

description: poor rock

Meaning of the rock class

average stand-up time: 10hours for2, 5 m span

cohesion of rock mass: 100-200 kPa

friction angle of rock mass: 15-25 deg

Prediction of in-situ deformation modulus E_m and of R_crm from rock mass classifications

Bieniawski and Serafim & Pereira:

E_m = 10^{(RMR − 10)/40} [GPa] for RMR < 50

Hoek & Brown:

$E_{m} = \frac{\sqrt{R_{c}}}{10}10^{(\text{RMR} - 10)/40}$

Verman:

$$E_{m} = 0,3H^{\propto}10^{\frac{\text{RMR} - 10}{40}}$$

∝ = 0, 22

Young’s module	For RMRBASIC	For RMRMODIFIED
Bieniawski and Serafim & Pereira	6,68 GPa	2,67 GPa
Hoek and Brown	4,72 GPa	1,89 GPa
Verman	6,58 GPa	3,41 GPa

Hoek:

$${R_{\text{crm}} = \sqrt{s}\ R_{c}}{s_{1} = e^{\frac{\text{RMR} - 100}{9}}}$$

Aydan & Kawamoto:

R_crm = 0, 0016 RMR^2, 5

Kalamaras & Bieniawski:

$R_{\text{crm}} = \frac{R_{c}}{2}\frac{\text{RMR} - 15}{85}$

Uniaxial compressive strenght of rock mass	For RMRBASIC	For RMRMODIFIED
Hoek	2,63 MPa	0,89 MPa
Aydan & Kawamoto	19,40 MPa	6,11 MPa
Kalamaras & Bieniawski	8,23 MPa	3,56 MPa

Rock mass classification based on Q

$$Q = \frac{\text{RQD}}{J_{n}} \times \frac{J_{r}}{J_{a}} \times \frac{J_{w}}{\text{SRF}}$$

where

RQD is the Rock Quality Designation

J_n is the joint set number

J_r is the joint roughness number

J_a is the joint alteration number

J_w is the joint water reduction factor

SRF is the stress reduction factor

Classification parameters and their ratings

1) Rock quality designation

The proportion of the intact core pieces longer than 100 mm to the total length of core is 0%, very poor. Where RQD is reported or measured as ≤ 10 (including 0), a nominal value of 10 is used to evaluate Q.

RQD  =  87

2) Joint set number

two discontinuity sets with an average spacing of 0.6 m

J_n = 4

3) Joint roughness number

rough, irregular

J_r = 1.5

4) Joint alteration number

flat walls of a clay-filled joints (separation < 5 mm thick)

J_a = 8.0

5) Joint water reduction

Large supply of water (more than 30l/min)

J_w = 0.33

6) Stress reduction factor

Medium stress

SRF = 1.0

Block size

$$\frac{\text{RQD}}{J_{n}} = \frac{87}{4} = 21,75$$

• represents the structure of rock mass

• crude measurement of block or particle size

Interblock shear strength

$$\frac{J_{r}}{J_{a}} = \frac{1,5}{8,0} = 0.188$$

• represents roughness and frictional characteristics of joint walls or infill material

Active stress

$$\frac{J_{w}}{\text{SRF}} = \frac{0.33}{1.0} = 0.33$$

• consists of two stress parameters

• SRF can be regarded as a total stress parameter of

  • loosening load in competent rock

  • rock stress in competent rock

  • squeezing loads in plastic incompetent rock

• J_w is a measure of water pressure

Rock Tunneling Quality Index Q

$Q = \frac{\text{RQD}}{J_{n}} \times \frac{J_{r}}{J_{a}} \times \frac{J_{w}}{\text{SRF}} = 21.75 \bullet 0.188 \bullet 0.33 = 1,35$

Rock support and reinforcement requirement

Excavation Support Ratio (ESR)

(D) Power stations, major road and railway tunnels, civil defense chambers, portal intersections.

ESR = 1.0

Equivalent Dimension D_e

Circular cross-section with a 5,5 m radius. Excavation span is 11 m.

$$D_{e} = \frac{Excavation\ span,\ diameter\ or\ height\ (m)}{\text{Excavation\ Support\ Ratio\ }\text{ESR}} = \frac{11\ m}{1.0} = 11\text{\ m}$$

Estimated support category based on the tunneling quality index Q

Description of the rock mass: Poor.

Reinforcement category:

(5) Fibre reinforced shotcrete, 50–90 mm, and bolting.

Fibre reinforced shotcrete 90 mm

Bolt spacing in shotcreted area: 2.50 m

Length of the bolts

roof:

$$L = \frac{2 + 0.15s}{\text{ESR}} = \frac{2 + 0.15 \bullet 11\ m}{1.0} = 3,65\ m \approx 3.7\ m$$

walls:

$$L = \frac{2 + 0.15H}{\text{ESR}} = \frac{2 + 0.15 \bullet 11\ m}{1.0} = 3.625\ m \approx 3.7\ m$$

Young’s modulus:

$$E = 10^{3}\sqrt[3]{Q\frac{R_{c}}{3}} = 10^{3}\sqrt[3]{1,39 \bullet \frac{50}{3}} = 2,85\ \text{GPa}$$

Analysis and comparison of the results

	RMR	Q
Value	27,09 /100	1,39 /1000
Description of the rock mass	poor	poor
Young’s modulus (E) [GPa] according to Bieniawski and Serafim &Pereira	2,67	2,85

RMR-Q Correlation

RMRbasic = 43

RMRmod = 27, 09

Q = 1, 35

Source of case studies	Correlation	RMR(Q)	Comments
New Zealand	RMR = 13.5 log Q + 43	44,76	Civil engineering tunnels
Diverse origin	RMR = 9 ln Q + 44	45,17	Civil engineering tunnels
Spain	RMR = 12.5 log Q + 55.2	56,83	Civil engineering tunnels
S. Africa	RMR = 5 ln Q + 60.8	61,45	Civil engineering tunnels
Spain	RMR = 43.89 – 9.19 ln Q	42,69	Mining tunnels, soft rock
Spain	RMR = 10.5 ln Q + 41.8	43,16	Mining tunnels, soft rock
Canada	RMR = 12.11 log Q + 50.81	52,39	Mining tunnels, hard rock
Canada	RMR = 8.7 ln Q + 38	39,13	Civil engineering tunnels
Canada	RMR = 10 ln Q + 39	40,30	Mining tunnels, hard rock
India	RMR = 21,8 ln Q + 31	33,84	Coal mines, civil engineering tunnels

Conclusions

Section 2.E.:

The first difference calculations appear with the use of different methods of calculation modules Young and the uniaxial compressive strenght of rock mass. Maximum differences oscillate between 2GPa (Young's modulus for both the basic RMR and modified). The calculation of uniaxial compression, you will see a clear difference in the obtained values ​​depend on the method of calculation. The maximum difference shows a comparison of methods Hoek by Aydan and Kawamoto-is 17MPa (for RMR modified-difference of 5 MPa, but it is because the values ​​obtained are much smaller). The most comparable methods for the Young's modulus are the methods of time Bieniawskiego vs Verma.

Section 3.:

In this section we classify the rock on the basis of Q. To calculate the value of Q, we need to define other parameters, and on the basis of the coefficients, which are often determined based on experience and subjective assessments of the rock mass parameters. Finally, after selecting the appropriate parameters, our rock is classified as poor , and has been adapted housing tunnel (Fibre reinforced shotcrete 90 mm; bolt spacing in shotcreted area: 2.50 m). Young's modulus calculated based on the value of the Q parameter is similar to that obtained by using the RMR Bieniawskiego modified. Compared to E obtained from RMR basic, values ​​significantly different from each other (approximately 2.5 fold).

Section 4.:

The correlation between RMR and Q shows us that our conditions are similar to those in Spain in mining tunnels with soft rock. RMR (Q) is compared to a basic RMR (not RMR modified).

ALL:

Despite the differences in calculation and testing methods used, the final statement of the quality of the rock is the same both by Q and RMR. Although we have received similar features rocks can not be equated with these two methods together. Each method takes into account the different characteristics of the rock mass (eg, number of cracks in the Q when you do not take into RMR). In the assessment of the rock mass and the award of points for a particular trait given table are helpful, but in some cases are not clear such determination slightly, on average they are not related to a specific defined ranges of values, because subjectivity is a key element of this value. To properly reflect the assessment of the rock mass at the points, you have a lot of experience. At the design stage using the same calculation, the values ​​obtained approached with reserve and distance, and treat them as an aid to further design.