Rock Mass Mapping Assignment
CSMM130 – Excavation & Geomechanics
Student Number: 640046848
Lecturer: Lewis Meyer
November 2014
640046848
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Contents
1.
Introduction ..................................................................................................................................... 1
2.
Data Collected.................................................................................................................................. 2
3.
2.1.
Scanline Setup ......................................................................................................................... 2
2.2.
Geological Analysis.................................................................................................................. 2
Results.............................................................................................................................................. 3
3.1.
DIPS Data................................................................................................................................. 3
3.2.
RQD & Q Data ......................................................................................................................... 4
3.3.
Schmidt Hammer Data ............................................................................................................ 4
4.
Estimation of Q ................................................................................................................................ 4
5.
RMR and GSI Estimation .................................................................................................................. 5
5.1.
RMR System ............................................................................................................................ 5
5.2.
Geological Strength Index ....................................................................................................... 5
6.
Conclusions ...................................................................................................................................... 5
7.
Works Cited ..................................................................................................................................... 6
8.
Appendix .......................................................................................................................................... 6
Figure 1 - Holman's Mine Entrance .......................................................................................................... 1
Figure 2 - Scanline Locations .................................................................................................................... 1
Figure 3 - Rock Bolts at Intersection ......................................................................................................... 2
Figure 4 – Collective DIPS Data ................................................................................................................. 3
Figure 5 - Collective Rosette Diagram ...................................................................................................... 3
Figure 6 - Scanline Orientation vs Joint Sets (Rocscience Inc., 2014) ....................................................... 4
Figure 7 - Rock Mass Quality and Rock Support (NGI, 2013) .................................................................... 4
Figure 8 - GSI Index Chart ......................................................................................................................... 5
Equation 1 - Q Value Formula (Barton, et al., 1974) ................................................................................ 4
Equation 2 - Worst Case Q Value of Scanline 2 ........................................................................................ 4
Equation 3 - Bolt Length Calculation (Barton, et al., 1974) ...................................................................... 5
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1. Introduction
This report details the findings following a rock mass mapping exercise on several drives in granite within Holman’s Test Mine,
Cornwall. Initial observations saw a clear presence of multiple joint sets (Figure 1, Left), resulting in a blocky texture and imposing
a potential threat of unsafe rock in areas of the mine ceiling. Reinforcement to counteract this can be seen throughout the mine,
primarily with rock bolts regularly spaced throughout the roof. Several sections have been further reinforced with a wire mesh,
and shotcrete has been utilized around the mine entrances (Figure 1, Right).
F IGURE 1 - HOLMAN 'S MINE E NTRANCE
Several scanlines within the mine were mapped separately, to allow for more accurate results via collaboratively using the data
collected. Figure 2 shows the layout of the mine including the locations for all 8 scanlines mapped. This report is focused around
scanline 2, shown in yellow on the map.
F IGURE 2 - S CANLINE L OCATIONS
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A fault was identified during the mapping, also highlighted in Figure 2 – orientated WNW/ESE. This could potentially influence
conclusions from the Q-System, as the SRF was read as 5, up from 2.5, due to the loss in structural strength at the fault line.
2. Data Collected
2.1. Scanline Setup
The selected scanline (2) runs in a south west to north east direction, with a bearing of 50o.
The drive section was first walked through for a quick inspection to identify the general
geological setup of the wall, with an additional purpose of evaluating the environment for
potential hazards. The present support, in the form of multiple rock bolts, was also identified
– especially focused at intersections (Figure 3). The width and height of the tunnel were
measured at 5m intervals along the scanline, with averages of 3.2m and 2.6m respectively
(Appendix Table A).
F IGURE 3 - R OCK B OLTS AT
I NTERSECTION
2.2.Geological Analysis
To begin the inspection, a 30m tape measure was laid out along one side for clearer logging
of details. A Clar Compass was used to obtain orientation data (dip, dip direction) of discontinuities. A Schmidt Hammer was
utilized according to the ISRM guidelines (Aydin, 2008) to establish values for the rebound hardness of the rock. Additionally,
further data was collected to allow for the evaluation of the rock using Q and RMR analysis:



Roughness, taken both by gauging the surface type of the discontinuity (stepped, undulating or planar), and to what
degree – in addition to the JRC roughness method; rating roughness on a range from 0 (smooth) to 20 (severely rough).
RQD measurements were taken along the length of the scanline in 1m intervals and averaged. Vertical readings were also
taken every 5m (Appendix Table B).
Data for Q-Value analysis, specifically values for the joint set (Jn), roughness (Jr), alteration (Ja), water reduction (Jw), and
the stress reduction factor (SRF).
The data collected was analysed using DIPS software (Rocscience Inc., 2014) to establish a clear visualization of the joint
discontinuities. Data from the other scanlines was also included to establish a group data file, increasing the reliability of the
results and allowing for conclusions to be drawn about the mine as a whole, not just from one section.
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3. Results
3.1. DIPS Data
The results for all 8 scanlines are shown in Figure 4 below. The program highlights two main discontinuities, with the primary
labelled as Discontinuity 1 and the other as Discontinuity 2; at orientations of 290o and 359o respectively. A further horizontal
discontinuity can be seen in the set at the centre of the diagram; Discontinuity 3. The fourth discontinuity has been taken as a
random due to the lower density concentration of poles. These discontinuities are highlighted in the rosette diagram (Figure 5).
F IGURE 4 – C OLLECTIVE DIPS DATA
F IGURE 5 - C OLLECTIVE ROSETTE D IAGRAM
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3.2.RQD & Q Data
The RQD value was found to be 91% for the total scanline (Appendix Table B), representing a ‘good’ rock mass quality. With regards
to the DIPS results discussed, Jn – the amount of joint sets in the rock – was taken as 12. This represents three key joint sets, as
can be seen in Figure 5, with the inclusion of a random – the somewhat present fourth discontinuity. Jr has been taken as 3,
representing an undulating rough and irregular roughness. Similarly, J a was found to have a common value of 1, representing
unaltered joint walls with only surface staining. Despite some pooling on the floor, the mine was relatively dry – thus Jw was taken
as 1. Finally, the stress reduction factor was taken as 2.5 to represent a single shear zone, although there was a reading of 5, this
was a unique occurrence from being in the fault zone.
3.3.Schmidt Hammer Data
A Schmidt hammer was used throughout the entirety of the scanline. To ensure accuracy, 10 separate locations were tested, 10
times each – averaging only the 5 highest readings for each location (in accordance with ISRM guidelines), returning an average
value of 59.2. The Schmidt hammer data can be seen in Table C in the Appendix, with the average then used with the appropriate
chart (Appendix Figure A) to provide a UCS of just less than 230 MPa.
4. Estimation of Q
The formula for Q is shown in Equation 1, with values then incorporated to give a Q value of 9.
Q=
RQD Jr Jw
90 3 1
x x
=
x x
=9
Jn Ja SRF 12 1 2.5
E QUATION 1 - Q VALUE FORMULA (BARTON , ET AL ., 1974)
It should be noted however that the Q system relies upon a human assessment of the recorded
data. Alternatively, a decision could be made to take the maximum values, i.e. taking J a and SRF as
2 and 5 respectively.
Q=
90 3 1
x x = 2.25
12 2 5
E QUATION 2 - WORST CASE Q VALUE OF S CANLINE 2
The resulting Q value of 2.25 is substantially lower than the original value of 9, potentially requiring
different reinforcement; highlighting the influence of judgement on results. A further influence
could be on the interpretation of scanline data, demonstrated in Figure 6. In this situation, many
more joint sets would be recorded for Set A than Set C – potentially resulting in an incorrect Jn.
Figure B (Appendix) shows only the data for scanline 2. This could be taken as having additional
disorientation sets; another appears adjacent to the North:South discontinuity. This extra set would
increase Jn to 15, significantly decreasing the Q value. While Terzaghi’s principle (Terzaghi, 1946)
would help amend this, the collaborated data from multiple scanline orientations negates this
effect.
F IGURE 6 - S CANLINE
O RIENTATION VS J OINT SETS
(ROCSCIENCE INC ., 2014)
The Q value for the mapped scanline with a span of 3.2m, and for a proposed excavation of 10m span is shown in Figure 7. The
ESR, or excavation support ratio, has been taken as 1.6 (permanent opening).
Current Excavation
Proposed Excavation
F IGURE 7 - R OCK MASS QUALITY AND R OCK SUPPORT (NGI, 2013)
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The graph indicates that the current excavation does not require support, but that the proposed excavation would need systematic
bolting in addition to a 5-6mm shotcrete layer. The length of the bolts required has been calculated in accordance with the Q
system; and is shown in Equation 3 – resulting in a desired length of 2.9m.
Bolt length = 2 + (0.15 ∗
Width
) = 2 + (0.15 ∗ 6.25) = 2.9m
ESR
E QUATION 3 - BOLT LENGTH CALCULATION (BARTON , ET AL ., 1974)
5. RMR and GSI Estimation
5.1.RMR System
In addition to classifying the rock with the Q-System, the rock quality has been
assessed using the rock mass rating system (Bieniawski, 1989). Table 1 shows
the recorded variables from the mapping.
The resulting total of 77 classifies the rock quality as “good rock”. This implies
that a full face excavation can be carried out, with an advance between 1 and
1.5m meters – support being completed 20m from the working face
(Bieniawski, 1989). 3m long rock bolts are recommended, with 2.5m spacing.
Occasional use of wire mesh is recommended. It should be noted that these
recommendations are for a 10m span tunnel, and are therefore appropriate
for the proposed excavation but likely an overestimation for the 3m span.
These conclusions correlate well with those drawn from the Q system
analysis; requiring the same length of rock bolts for the proposed excavation,
but requiring little to no reinforcement for the actual scanline.
Parameter
Value
RMR Rating
UCS (Mpa.)
230
12
RQD
92%
20
Spacing (m)
0.30
15
Discon. Conditions
Good
25
Groundwater
Dry
10
Joint Orientation
Fair
-5
Total
77
T ABLE 1 - RMR A NALYSIS
5.2.Geological Strength Index
The Geological Strength Index (GSI) of a rock mass can be
calculated in 2 main ways; first by obtaining a GSI value through
the use of Figure 8 – assessing the quality of the rock structure
and surface quality. In this case, the rock consists of a reasonably
blocky structure due to the number of discontinuities running
through it. The discontinuity conditions were identified as rough
and slightly weathered, but overall “good” in the RMR analysis.
This would return a value between around 70-80.
An additional method of finding a GSI can be used if an RMR
value has already been found. This is simply to minus 5 from the
given number, in this case returning a GSI of 72; relatively close
to the value found from the chart - proving a good degree of
accuracy.
6. Conclusions





The mine consists of 3 joint sets, though one is
horizontal and is not overly structural significant. An
additional random joint set is also present.
RMQ and RMR systems have produced similar values.
Generally not requiring current support for the scanline
but would require support for a 10m span expansion
(systematic 3m rock bolts, shotcrete).
RMR is set to a 10m span standard, whereas RMQ can
be adapted to any span.
From the above, RMR can be argued as better design
case – it provides bolt spacing and shotcrete depth.
RMQ does however
While both systems assess rock quality – they do not
identify possible failure mechanisms such as block or
wedge failures.
F IGURE 8 - GSI INDEX C HART
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7. Works Cited
Aydin, A., 2008. ISRM Suggested Method for Determination of the Schmidt Hammer Rebound Hardness, Lisbon: ISRM.
Barton, N., Lien, R. & Lunde, J., 1974. Engineering classification of rock masses for the. Rock Mechanics, Vol 6, No. 4, pp. 189236.
Bieniawski, Z. T., 1989. Engineering rock mass classifications, New York: Wiley.
EnviroTools, 2014. Geologist's Compass. [Online]
Available at: http://www.envirotools.hu/geologists_compass.html
NGI, 2013. Q System. [Online]
Available at: http://www.ngi.no/en/Contentboxes-and-structures/Reference-Projects/Reference-projects/Q-method/
[Accessed 10 November 2014].
Rocscience Inc., 2014. Dips. [Online]
Available at: https://www.rocscience.com/products/1/Dips
[Accessed 10 November 2014].
Terzaghi, K., 1946. Rock defects and loads on tunnel supports, Youngston, Ohio: Commercial Shearing and Stamping Co..
8. Appendix
T ABLE A – TUNNEL MEASUREMENTS
T ABLE B - RQD DATA
T ABLE C - S CHMIDT HAMMER DATA
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F IGURE A - S CHMIDT HAMMER CONVERSION C HART
F IGURE B - S CANLINE 2 DIPS DATA
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CSMM130
Number Chainage Dip Direction Quantity Scan No.
1
0.35
60
305
1
2
2
0.4
65
279
1
2
3
0.6
87
082
1
2
4
0.8
82
222
1
2
5
0.8
10
141
1
2
6
0.8
45
275
1
2
7
1.1
80
104
1
2
8
1.1
90
291
1
2
9
1.1
10
201
1
2
10
1.7
40
274
1
2
11
1.4
68
258
1
2
12
1.8
85
098
1
2
13
1.2
60
350
1
2
14
2
55
294
1
2
15
2.1
58
290
1
2
16
2.3
75
145
1
2
17
2.35
70
332
1
2
18
2.4
55
349
1
2
19
1.8
30
280
1
2
20
2.65
89
298
1
2
21
2.65
55
358
1
2
22
2.3
70
161
1
2
23
3
75
350
1
2
24
3.4
20
329
1
2
25
3.95
62
310
1
2
26
4.8
72
326
1
2
27
4.3
88
300
1
2
28
5.2
88
110
1
2
29
6.4
60
296
1
2
30
5.65
55
172
1
2
31
6.8
90
176
1
2
32
6.5
58
358
1
2
33
7
38
334
1
2
34
6.7
78
158
1
2
35
7
85
157
1
2
36
7.4
84
104
1
2
37
8
79
101
1
2
38
8.6
15
276
1
2
39
7.95
25
280
1
2
40
8.6
80
118
1
2
41
8.2
42
159
1
2
42
8.1
85
122
1
2
43
8.5
54
200
1
2
44
8.7
75
054
1
2
45
9
83
152
1
2
46
9.3
85
150
1
2
47
9.3
25
293
1
2
48
10.3
85
152
1
2
49
10.7
82
002
1
2
50
12.3
87
148
1
2
Type
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
F
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
JRC
8
10
5
5
7
5
4
4
6
4
6
8
6
6
6
4
4
8
5
6
6
5
5
9
8
7
6
5
6
8
5
5
6
6
4
4
3
5
5
5
7
5
4
6
5
4
6
6
5
5
Roughness
IV
IV
VII
V
IV
V
VII
VII
IV
VII
VII
I
IV
IV
I
VII
VIII
IV
V
IV
IV
V
V
IV
IV
IV
IV
VII
IV
IV
VII
V
IV
VII
VII
VII
VII
IV
IV
VII
IV
IV
VII
IV
VII
VII
IV
I
IV
II
Jr
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Ja
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Jw
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
SRF
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Comments
10cm dist.
10cm dist.
15cm sep.
15cm sep.
70cm width
T ABLE E - MAPPING DATA 1
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CSMM130
Number Chainage Dip Direction Quantity Scan No.
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
13.6
14.3
13.8
14.6
14.8
15.8
15.7
16.4
15.9
16.6
16.2
16.6
17
17.3
18
18.3
18.6
19.1
12.7
19.8
20.5
21.4
21
22.6
23.2
23.2
23.4
23.6
24
24.4
24.7
24.7
24.7
25.2
25.5
25.8
26.2
26.5
26.8
27
27.5
28.4
28
27.8
29.5
28.8
29.9
30
30.2
27.6
61
20
85
55
89
45
45
84
45
35
85
86
88
60
88
60
58
89
53
75
85
80
30
88
82
80
89
86
86
75
18
86
90
90
80
90
86
75
65
86
5
79
87
80
80
14
80
85
33
20
147
294
163
346
155
310
172
104
288
275
098
183
286
176
110
316
186
286
000
278
264
356
208
189
356
234
077
255
260
178
346
288
195
080
263
260
178
014
226
252
276
316
002
122
288
231
278
176
282
312
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Type
JRC
Roughness
Jr
Ja
Jw
SRF
Comments
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
F
F
F
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
J
8
9
5
8
5
7
4
6
5
7
10
8
8
3
6
6
8
5
6
5
6
8
5
6
9
9
8
4
4
7
9
8
5
9
6
5
6
5
6
4
5
7
6
4
5
6
5
7
6
8
IV
IV
II
IV
II
IV
VII
IV
I
IV
I
IV
II
VIII
IV
IV
IV
I
IV
VII
IV
IV
IV
IV
IV
IV
I
IV
IV
IV
IV
II
VII
I
IV
VII
I
IV
IV
VII
IV
IV
IV
VII
IV
IV
VII
IV
IV
IV
3
3
3
3
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
3
3
3
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Shear zone
Shear zone
Shear zone
20cm sep. perp.
Outcropping block
Outcropping block
Outcropping block
T ABLE F - MAPPING DATA 2
640046848
9
CSMM130