Mining Measurement Services Pty Ltd
103 Harding Road Macclesfield, Victoria. 3782, Australia. +61 3 5968 8220 +61 3 9015 6413
[email protected] Site www.mmsstress.com.au
ABN 94 008 914 167
USBM Cell a Useful Stress Measurement Tool MMS’s experience Background The USBM cell was used extensively in the 1970’s. In the early development stages of the CSIRO HI cell, it was used by CSIRO and others to validate the HI cell. The USBM cell is a two dimensional device and as such it only measures stresses in a plane perpendicular to the borehole. In order to measure the three dimensional stresses, measurements are required in a minimum of two non parallel boreholes. However, to confidently determine the three dimensional stresses, three non co-planar boreholes are required, with about three tests (overcores) in each borehole.
MMS initially acquired the USBM cell for use at a mine in Queensland to determine the 3D stress field, where a previous attempt at overcoring CSIRO HI Cells in the same rock unit failed. A satisfactory bond between the HI Cells and the pilot hole could not be achieved. MMS has developed software that can be used to determine the 3D stresses from USBM tests conducted in three holes. This code was checked against an independently developed code by the United States Bureau of Mines. Very good agreement was achieved by comparing stress outputs from the MMS and USBM codes.
MMS USBM VS HI ver1.2.doc
As the USBM cell is reusable and does not require grouting the instrument into the borehole, it can be quite a rapid testing tool. MMS has achieved four overcore tests and four biaxial tests in one day. Since using the USBM cell to determine the 3D stress field at the mine above, MMS has been using the USBM cell on a routine basis to gain more strain data at sites where MMS conducts CSIRO HI cell tests. This data is then included with the CSIRO HI cell data to determine the site 3D stress result. The USBM cell has also proved invaluable in obtaining more rock property data. In some cases where the HI cell core has broken and a biaxial test on this core was not possible, the USBM cell was inserted in the same core and biaxially tested. The modulus obtained was then used in the analysis to determine the stresses for the HI Cell. Another useful application of the USBM cell is when discing of the core is encountered. At one recent mine site we encountered discing of the core in a borehole to approximately 4 m depth. Two USBM tests were conducted immediately after the discing to determine the stresses that were required to cause discing of the core. The USBM cell may also be useful in pillars where only the 2D stress field is required, and rapid testing can be performed. MMS USBM Cell and CSIRO HI Cell Comparison Below is a comparison of the USBM cell data and CSIRO HI Cell data to date that have been conducted by MMS. As the USBM cell only measures the maximum and minimum stress normal to the borehole (magnitudes and directions), the CSIRO HI cell results have been rotated to obtain the maximum and minimum stresses in the borehole. To calculate the secondary principal stresses for the USBM cell, two formulas can be used; one which assumes zero stress in the borehole direction (plane stress condition) and the second, a more exact solution where the axial stress in the borehole is included (plane strain). In MMS’s comparisons we use the more exact solution. We are able to rotate the stresses obtained from the CSIRO HI cell results and determine the stress in the axial direction of the borehole and use this to calculate the secondary principal stresses for the USBM cell.
MMS USBM VS HI ver1.2.doc
Maximum Stress Direction
CSIRO HI Cell USBM Cell
50MPa
Looking in hole
Maximum and Minimum Magnitudes MAGNITUDES
50
HI1 HI2 HI3 US1 HI4 HI5
45
STRESS (MPa)
40 35 30 25 20 15 10 5 0
G MAX
MMS USBM VS HI ver1.2.doc
I MIN
SITE 1 Secondary Principal Stresses Around Hole DIRECTIONS 345 .
0
15
.
30
330 .
.
315.
45
.
300.
60
.
285.
HI Cell
.
75
270.
90
.
USBM Cell 255.
.
240.
105
120
.
225.
135
.
210 .
150
.
195 .
165
.
180
LOOKING INTO HOLE MAGNITUDES
40
TEST 1
35
TEST 2
STRESS (MPa)
30 TEST 3 25
USBM
20 15 10 5 0
G MAX
I MIN
YOUNG'S MODULUS
100 90 80 70
GPa
60 50 40 30 20 10 0 TEST 1
MMS USBM VS HI ver1.2.doc
TEST 2
TEST 3
USBM
SITE 2 Secondary Principal Stresses Around Hole DIRECTIONS 345.
0
.
15
330 .
.
30
315.
.
45
300.
.
285.
60
.
75
HI Cell 270.
USBM Cell
.
255.
.
240.
.
225.
.
210 .
.
195.
180
.
90
105
120
135
150
165
LOOKING INTO HOLE MAGNITUDES
80
TEST 1
70
USBM
STRESS (MPa)
60
TEST 2
50
TEST 3
40 30 20 10 0
G MAX
I MIN YOUNG'S MODULUS
140 120
GPa
100 80 60 40 20 0 TEST 1
MMS USBM VS HI ver1.2.doc
USBM 1
TEST 2
USBM 2
TEST 3
SITE 3 Secondary Principal Stresses Around Hole DIRECTIONS 345 .
0
.
15 30
330.
.
315.
45
.
300 .
.
285.
60 75
.
HI Cell 270.
USBM Cell
.
255.
90
105
.
240 .
.
225.
120
135
.
210.
150
.
195 .
180
.
165
LOOKING INTO HOLE
MAGNITUDES
50
STRESS (MPa)
45 40
TEST 1
35
TEST 2
30
TEST 3
25
USBM
20 15 10 5 0
G MAX
I MIN
YOUNG'S MODULUS
90 80 70
GPa
60 50 40 30 20 10 0 TEST 1
MMS USBM VS HI ver1.2.doc
TEST 2
TEST 3
TEST USBM1
SITE 4 Secondary Principal Stresses Around Hole DIRECTIONS 345 .
0
15
.
30
330 .
.
315.
45
.
300.
60
.
285.
.
75
HI Cell 270.
USBM Cell
90
.
255.
.
240.
105
120
.
225.
135
.
210 .
150
.
195 .
165
.
180
LOOKING INTO HOLE MAGNITUDES
STRESS (MPa)
50 45
TEST 1
40
TEST 2
35
TEST 3
30
USBM
25 20 15 10 5 0
G MAX
I MIN YOUNG'S MODULUS
160 140 120
GPa
100 80 60 40 20 0 TEST 1
MMS USBM VS HI ver1.2.doc
TEST 2
TEST 3
USBM
SITE 5 Secondary Principal Stresses Around Hole DIRECTIONS 345.
0
.
15
330 .
.
30
315.
.
45
300.
.
285.
60
.
75
HI Cell 270.
USBM Cell
.
255.
.
240.
.
225.
.
210 .
.
195.
180
.
90
105
120
135
150
165
LOOKING INTO HOLE MAGNITUDES
70
Test 1 60
Test 2
STRESS (MPa)
USBM 50
Test 3 Test 4
40 30 20 10 0
G MAX
I MIN YOUNG'S MODULUS
90 80 70
GPa
60 50 40 30 20 10 0 Test 1
MMS USBM VS HI ver1.2.doc
Test 2
USBM
Test 3
SITE 6 Secondary Principal Stresses Around Hole 345 .
DIRECTIONS 0
15
.
330 .
.
30
315 .
45
.
300.
.
60
285
HI Cell
75
.
27
USBM Cell
.
255
105
.
240.
.
225 .
TESTS at 5m (Not Virgin)
90
120
135
.
210 .
.
195 .
180
150
165
.
TESTS at 5m (Not Virgin)
LOOKING INTO HOLE MAGNITUDES
60
TEST U1 TEST U2 TEST U3 TEST H1 TEST U4 TEST U5 TEST H2 TEST H3 TEST U6 TEST H4 TEST U7
STRESS (MPa)
50 40 30 20 10 0
G MAX
100
I MIN
YOUNG'S MODULUS
90 80 70 GPa
60 50 40 30 20 10
TE ST U1 TE ST U TE 2 ST TE u3 ST TE hi1 ST U TE HI ST U4 TE ST U5 TE ST H2 TE ST H3 TE ST U6 TE ST H4 TE ST U7
0
MMS USBM VS HI ver1.2.doc
SITE 7 Secondary Principal Stresses Around Hole
HI Cell USBM Cell
LOOKING INTO HOLE
MAGNITUDES
50
HI1 HI2 HI3 US1 HI4 HI5
45
STRESS (MPa)
40 35 30 25 20 15 10 5 0
I MIN
G MAX YOUNG'S MODULUS
90 80 70
GPa
60 50 40 30 20 10 0 HI1
MMS USBM VS HI ver1.2.doc
HI2
HI3
US1
HI4
HI5
SITE
SITE 8 Secondary Principal Stresses Around Hole
HI Cell USBM Cell
LOOKING INTO HOLE MAGNITUDES
50
1 2 US1 3 4
45
STRESS (MPa)
40 35 30 25 20 15 10 5 0
I MIN
G MAX
YOUNG'S MODULUS
60 50
GPa
40 30 20 10 0 1
MMS USBM VS HI ver1.2.doc
2
US1
3
4
SITE
SITE 9 Secondary Principal Stresses Around Hole
HI Cell USBM Cell
LOOKING INTO HOLE MAGNITUDES
50
1
45
2
STRESS (MPa)
40
3
35
4
30
US1
25 20 15 10 5 0
I MIN
G MAX
YOUNG'S MODULUS 120 100
GPa
80 60 40 20 0 1
MMS USBM VS HI ver1.2.doc
2
3
4
US1
SITE
SITE 10 Secondary Principal Stresses Around Hole
HI Cell USBM Cell
LOOKING INTO HOLE MAGNITUDES
40
HI1 HI2 HI3 HI4 HI5 US1
STRESS (MPa)
35 30 25 20 15 10 5 0
I MIN
G MAX
YOUNG'S MODULUS
60
50
GPa
40
30
20
10
0 HI1
HI2
MMS USBM VS HI ver1.2.doc
HI3
HI4
USB9.4
HI5
US1
SITE
SITE 11 Secondary Principal Stresses Around Hole
HI Cell USBM Cell
LOOKING INTO HOLE MAGNITUDES
35
HI 1 30
STRESS (MPa)
HI 2 25
HI 3
20
US 1
15 10 5 0
I MIN
G MAX YOUNG'S MODULUS
90 80 70
GPa
60 50 40 30 20 10 0 HI 1
MMS USBM VS HI ver1.2.doc
HI 2
HI 3
US 1
SITE
