(Q) 5. Geomechenics
The stability factor for all pillars throughout the Quinsam Mine is well above 2.0 according to C. Mark using Analysis of Retreat Mining Pillar Stability (ARMPS).
The engineering rock properties for Quinsam Mine are as follows. These are extracted from the data provided by CANMET.
Sandstone
Mudstone
A. Uniaxial Loading
Unit
Average
Std. Dev.
Average
Std. Dev.
Unconfined Compressive Strength
(MPa)
68.63
24.51
57.13
15.98
Young's Modulus (Static)
(GPa)
6.51
0.02
10.66
3.22
Poisson's Ratio (Static)
35.18
0.02
0.20
0.09
Young's Modulus (Dynamic)
(GPa)
13.95
7.60
20.54
14.91
Shear Modulus (Dynamic)
(GPa)
0.26
3.17
8.19
5.74
Poisson's Ratio (Dynamic)
4.07
0.02
0.24
0.04
P-wave velocity
(km/s)
2.31
0.35
2.89
0.96
S-wave velocity
(km/s)
0.24
1.66
0.49
B. Point Loading*
Is (Axial)
(MPa)
4.55
1.23
3.11
1.96
Is(50) (Axial)
(MPa)
1.88
0.48
1.33
0.78
Is (Diametrical)
(MPa)
1.63
1.18
0.84
0.62
Is(50) (Diametrical)
(MPa)
1.63
0.84
0.91
0.48
*Note: - The Is values are calculated directly from the CANMET testing data.
- The standardized Point Load Strength Index, Is(50) is determined by calibration against the 50mm loading distance using calibration curves.
- In the case of axial loading tests, the loading distance is only 10 ~ 12mm, outside the range of the available calibration curves. The Is(50) is determined by extrapolation.
- Based on the data provided, all the Point Load test specimens had diameter of about 35mm. The length was 10 ~ 12mm for axial loading and 28 ~ 40mm for diametrical loading. The specimen dimensions for axial loading did not meet the requirements, which require a loading distance (the length) of about 1.1 times the diameter. Therefore, the results of axial loading tests may be questionable and can only be used as a reference.
The details of CANMET test data are given in these three files: (Q)compression, (Q)point-axial and (Q)point-diametrical.
Rock type
RMR
Q
CMRR
CMRS
General quality description
Coal #1 Seam
37
2.1
Fair to poor
Dirt band
21
0.1
27
Poor to very poor
Coal #1 rider
35
40
Fair to poor
Siltstone (weak)
18
0.1
24
Poor to very poor
Siltstone (competent)
54
0.5
35
35
Fair to poor
Sandstone
69
16.3
78
81
Good
From the report of C. Mark, the RQD of the mudstone overlying the #1 Seam is 60 with a fracture spacing of 10cm. The RQD of the siltier upper mudstone is 90 (overall) with a fracture spacing of 30cm. The data from borehole QM2 reveal that the fine to very fine-grained siltstone interbedded with mudstone overlying the #1 Seam. Figure Q2 shows maximum RQD of 96% for a single layer in this borehole.
No data of in situ stress measurement are available. At Quinsam Coal, the depth of cover is relatively shallow (about 120m or 400 feet at present) and therefore the in situ vertical stresses are small. However, vertical stresses at the pillar line can be much greater. In addition, vertical stresses can be altered by the presence of faults creating hanging and footwall situations.
According to the mine report, there is little sign of high in situ horizontal stress at Quinsam Coal.