View
221
Download
0
Category
Preview:
Citation preview
8/14/2019 Rockmass Strength Properties
1/32
D.J. Hutchison - 2000
Rock and Rockmass Properties
Lecture 4
Earth 691B: Rock EngineeringMaterials used with kind permission
of Dr Jean Hutchison, Queens U
8/14/2019 Rockmass Strength Properties
2/32
D.J. Hutchison - 2000
Rockmass
Strength
Stope
Hutchinson and Diederichs, 1996
Hutchinson, 2000
8/14/2019 Rockmass Strength Properties
3/32
D.J. Hutchison - 2000
Hoek, 2000
s=1
8/14/2019 Rockmass Strength Properties
4/32
D.J. Hutchison - 2000
Hoek-Brown Failure Criterion
a
ci
bci sm
3
31
'''
Generalized Hoek-Brown failure criterion for jointed rock masses:
Where:
1and 3are maximum and minimum effective stresses at failure
mbis the value of the Hoek-Brown constant m for the rockmass
s and a are constants which depend upon the rockmass characteristicsciis the uniaxial compressive strength of the intact rock pieces
(11.1)
8/14/2019 Rockmass Strength Properties
5/32
D.J. Hutchison - 2000
Generation of Mohr-Coulomb parameters
from the Hoek-Brown failure criterion
Use Equation 11.1 to generate triaxial test results
Statistical curve fitting of data, using Equation 11.2:B
ci
tmn
ciA
'(11.2)
Where:
A andB are material constants
nis the normal effective stress
tmis the tensile strength of the rockmass (Equation 11.3), reflecting
the fact that the rock particles are interlocked and not free to dilate
smmbb
ci
tm 4
2
2 (11.3)
8/14/2019 Rockmass Strength Properties
6/32
D.J. Hutchison - 2000
Estimation of Rockmass Strength
Three rockmass properties are required:ci: uniaxial compressive strength of the
intact rock pieces
mi: value of Hoek-Brown constant mfor
these intact rock pieces
GSIfor the rockmass
8/14/2019 Rockmass Strength Properties
7/32D.J. Hutchison - 2000
Intact Rock Strength
For intact rock, Equation 11.1 simplifies to:5.0
331 1
'''
ci
ici m
(11.4)
For tests conducted in the range of
0 < 3< 0.5ciand at least 5 tests
on each rock type
Hoek, 2000
8/14/2019 Rockmass Strength Properties
8/32D.J. Hutchison - 2000
Testing UCS for Weak Rock
Generally very difficult to do as sampleswill contain several discontinuities within
their volume.
Very high skill level and specializedequipment only available in a few places in
the world is required.
Use Point Load Test where load is appliednormal to the bedding plane orientations. If
the rock is very weak, and the platens indent
the rock, these tests are invalid.
8/14/2019 Rockmass Strength Properties
9/32D.J. Hutchison - 2000
Hoek, 2000
Foliated rocks displayan anisotropic response
to triaxial testing
8/14/2019 Rockmass Strength Properties
10/32D.J. Hutchison - 2000
Influence of Sample SizeHoek, 2000
18.0
50
50
dccd
8/14/2019 Rockmass Strength Properties
11/32D.J. Hutchison - 2000
Grade
*
Term UCS
(MPa)
Point
Load
Index
MPa
Field estimate of strength Examples
R6 Extremelystrong
> 250 > 10 Specimen can only be chipped with ageological hammer
Fresh basalt, chert, diabase, gneiss,granite, quartzite
R5 Very strong 100 to 250 4 to 10 Specimen requires many blows of a
geological hammer to fracture it
Amphibolite, sandstone, basalt,
gabbro, gneiss, granodiorite,
limestone, marble, rhyolite, tuff
R4 Strong 50 to 100 2 to 4 Specimen requires more than one
blow of a geological hammer to
fracture it
Limestone, marble, phyllite,
sandstone, schist, shale
R3 Medium
strong
25 to 50 1 to 2 Cannot be scraped with a pocket
knife, specimen can be fractured with
a single blow from a geological
hammer
Claystone, coal, concrete, schist,
shale, siltstone
R2 Weak 5 to 25 ** Can be peeled with a pocket knife
with difficulty, shallow indentation
made by firm blow with point of a
geological hammer
Chalk, rocksalt, potash
R1 Very weak 1 to 5 ** Crumbles under firm blows with point
of a geological hammer, can be
peeled by a pocket knife
Highly weathered or altered rock
R0 Extremely
weak
0.25 to 1 ** Indented by thumbnail Stiff fault gouge
** Point load tests on rocks with a uniaxial compressive strength < 25 MPa are likely to yield highly ambiguous results.
Table 11.2: Field estimates of uniaxial compressive strength
* Grade according to Brown (1981).
T bl 11 3 (H k 2000) V l f f i t t k b k V l i th i ti t
8/14/2019 Rockmass Strength Properties
12/32D.J. Hutchison - 2000
Coarse Very fine
Conglomerate Claystone
(22) 4
Breccia
(20)
Marble
9Migmatite
(30)
Gneiss Slate
33 9
Granite
33
Granodiorite
(30)Diorite
(28)
Gabbro
27
Norite
22
Agglomerate
(20)
Sandstone Siltstone
19 9
* These values are for intact rock specimens tested normal to bedding or foliation. The value of m iwill be significantly different if
failure occurs along a weakness plane.
Table 11.3 (Hoek, 2000): Values of m ifor intact rock, by rock group. Values in parenthesis are estimates.
Rock type Class GroupMedium Fine
Texture
Greywacke
Spartic
(10)
Gypstone
7
Chalk
(18)
Coal
(8 to 21)
16
Hornfels
(19)Amphibolite
25 to 31
Schist
4 to 8
Rhyolite
(16)
Dolerite
(19)
Breccia
(18)
Micritic
8
Anhydrite
13
Quartzite
24Mylonite
(6)
Phyllite
(10)
Obsidian
17
(19)
Dacite
(17)Andesite
Tuff
(15)
Clastic
Non-clastic
Organic
Carbonate
Chemical
19
Basalt
Sedimentary
Metamorphic
Non foliated
Slightly foliated
Foliated*
Igneous
Light
Dark
Extrusive pyroclastic type
Rock Texture
8/14/2019 Rockmass Strength Properties
13/32D.J. Hutchison - 2000
Very fineClaystone
4+/-2
Shale
(6+/-2)
Marl
(7+/-2)
Dolomite
(9+/-3)
Chalk
7+/-2
Slate
7+/-4
Peridotite
(25+/-5)
Siltstone
7+/-2
Gypsum
(29+/-3)
* Conglomerate and breccia may have a wide range of m ivalues, depending upon the nature of the cementing material, and
the degree of cementation. Hence their values may range from values similar to that of sandstone to those of fine grained
sediments (even < 10).
Rock
typeClass Group
Fine
Texture
Gabbro
Granite
32+/-3 25+/-5
(8+/-2)
Marble
9+/-3
Amphibolite
26+/-6
Migmatite
Hornfels
(19+/-4)
Metasandstone
(19+/-3)
Diorite
Schist
12+/-3
(29+/-3)
Granodiorite
Micritic Limestone
(9+/-2)Anhydrite
12+/-2
Quartzite
20+/-3
Gneiss
28+/-5Phyllite
(7+/-3)
Tuff
(13+/-5)
Clastic
Non-Clastic
Carbonate
Slightly foliated
Foliated**
Organic
Non foliated
Hypabyssal
Volcanic
Lava
Pyroclastic
Greywacke
(18+/-3)
Evaporite
Breccia
*
Crystalline
Limestone
(12+/-3)
Spartic Limestone
(10+/-2)
22
Dark27+/-3
Dolerite
(16+/-5)
Norite
Coarse MediumSandstone
17+/-4
Conglomerate
*
Porphyry
(20+/-5)
Diabase
(15+/-5)
Rhyolite
(25+/-5)
Andesite
25+/-5
Dacite
25+/-3
Basalt
(25+/-5)
** These values are for intact rock specimens tested normal to bedding or foliation. The value of m iwill be significantly
different if failure occurs along a weakness plane.
S
edimentary
Metamorphic
Light
Plutonic
Igne
ous
Agglomerate
(19+/-3)
Breccia
19+/-5
Hoek and Marinos, 2000
8/14/2019 Rockmass Strength Properties
14/32D.J. Hutchison - 2000
Geological Strength
Index: GSI
Hoek, 2000Strength of jointed rockmass
depends on:
properties of intact rock
pieces, and
upon the freedom of thesepieces to slide and rotate
under different stress
conditions,
controlled by the
geometrical shape of the
intact rock pieces as well as
the condition of the
discontinuities separating the
pieces
8/14/2019 Rockmass Strength Properties
15/32
8/14/2019 Rockmass Strength Properties
16/32D.J. Hutchison - 2000
Mohr-Coulomb Parameters
Hoek, 2000
Hoek, 2000
8/14/2019 Rockmass Strength Properties
17/32D.J. Hutchison - 2000
Cohesive and Frictional Strength
Hoek, 2000
8/14/2019 Rockmass Strength Properties
18/32D.J. Hutchison - 2000
Deformation Modulus
For poor quality rockmasses, where ci< 100:
4010
10
100
GSI
ci
mE
8/14/2019 Rockmass Strength Properties
19/32D.J. Hutchison - 2000
Effect of water on rockmass strength
Reduction in strength of rock, particularlyshale and siltstone.
Pressure: why?
This may not be much of a problem duringexcavation, because water pressures in the
surrounding rock are reduced to negligible
levels. If groundwater pressures are re-established after the completion of the final
lining, then consider in design.
Water handling.
H k 2000
8/14/2019 Rockmass Strength Properties
20/32D.J. Hutchison - 2000
Post-failure Behaviour:
Very Good Quality HardRockmass
Hoek, 2000
H k 2000
8/14/2019 Rockmass Strength Properties
21/32D.J. Hutchison - 2000
Post-failure Behaviour:
Average Quality Rockmass
Hoek, 2000
8/14/2019 Rockmass Strength Properties
22/32
D.J. Hutchison - 2000
Post-failure Behaviour:
Very Poor QualityRockmass
Hoek, 2000
8/14/2019 Rockmass Strength Properties
23/32
D.J. Hutchison - 2000
Uncertainty in
Rockmass
StrengthEstimates:
INPUTHoek, 2000
8/14/2019 Rockmass Strength Properties
24/32
D.J. Hutchison - 2000
Uncertainty in
Rockmass Strength
Estimates: OUTPUT
Hoek, 2000
8/14/2019 Rockmass Strength Properties
25/32
D.J. Hutchison - 2000
Practical Examples of Rockmass Property Estimates:
Massive Weak Rock, Braden Breccia, El Teniente Mine
Hoek, 2000
Hoek, 2000
8/14/2019 Rockmass Strength Properties
26/32
D.J. Hutchison - 2000
Massive Strong Rockmasses,
Rio Grande Pumped Storage Scheme
Hoek, 2000
8/14/2019 Rockmass Strength Properties
27/32
D.J. Hutchison - 2000 Hoek, 2000
Average Quality Rockmass, Nathpa Jhakri Hydroelectric
Partially completed 20 m
span, 42.5 m high
underground powerhouse
cavern of the Nathpa Jhakri
Hydroelectric Project inHimachel Pradesh, India.
The cavern is approximately
300 m below the surface.
8/14/2019 Rockmass Strength Properties
28/32
D.J. Hutchison - 2000
Average Quality Rockmass, Nathpa Jhakri Hydroelectric
Hoek, 2000
8/14/2019 Rockmass Strength Properties
29/32
D.J. Hutchison - 2000
Poor Quality Rockmass at Shallow Depth: Athens Metro
Hoek, 2000
8/14/2019 Rockmass Strength Properties
30/32
D.J. Hutchison - 2000
Poor Quality Rockmass at Shallow Depth: Athens Metro
Hoek, 2000
Hoek, 2000
8/14/2019 Rockmass Strength Properties
31/32
D.J. Hutchison - 2000
Poor Quality
Rockmass underHigh Stress
8/14/2019 Rockmass Strength Properties
32/32
Poor Quality Rockmass under High Stress
Hoek, 2000
Figure 11.28: Results of a numerical
analysis of the failure of the rock mass
surrounding the Yacambu-Quibor tunnel
when excavated in graphitic phyllite at ad h f b 600 b l f
Figure 11.29: Displacements in the rock
mass surrounding the Yacambu-Quibor
tunnel. The maximum calculated
displacement is 258 mm with no supportd 106 i h
Recommended