7. Effects of various conditions on
deformation and failure of rock‡：このマークが付してある著作物は、第三者が有する著作物ですので、同著作物の再使用、同著作物の二次的著作物の創作等については、著作権者より直接使用許諾を得る必要があります。

7.1 Loading rate

Strain rate of rock mass
Very slow strain rate by tectonic movements (10-16 s-1～1014 s-1） to very fast (around 103 s-1) by blasting
Strain rate affects deformability and strength significantly
Stability analysis should be based on deformability andstrength at a strain rate which is likely to occur.

Under compressive stress

UCS (MPa)

13012011010010-5 10-4 10-3 10-2 10-1-10.3

26
25

Poisson's ratio

Young's modulus (GPa)14024232221
20

10-5 10-4 10-3 10-2 10-1-1

0.2

0.1

010-5 10-4 10-3 10-2 10-1-1

Strain rate (s )Strain rate (s )Strain rate (s )UCSYoung's modulus

Poisson's ratio

Results of uniaxial compression tests forPombetsu sandstoneInada granite

Indirect tensile strength (MPa)Brazilian test

98765
10-8 10-7 10-6 10-5 10-4
Displacement rate (m/s)

Fracture toughness
0.6
0.5
1.5KCB (MPa m )Effect of loading rateon fracture toughnessof Shirahama
sandstone

0.4
0.3
0.2

Dry condition|r|=0.95

Wet condition|r|=0.95

0.1010-8 10-7 10-6 10-5 10-4 10-3
Displacing rate (m/s)

Cause of loading rate-dependency of strengthetc.
Rock whose strength is mainly due to such covalent bondas Si-O etc. (granite etc.)
Stress corrosion at crack tips.

Sandstone etc.
Stress corrosion at crack tips.
Loading rate-dependency of cementing clay materialSuction (negative pore pressure) due to dilatancy

7.2 Effects of water

Mineral particle

VoidGrain boundary

Pore water (free water)

Water in rock

Capillary water

制限資料

Chemically or physically adsorbed water
日本機械学会（1989）、岩石破壊力学とその応用、コロナ社、p. 25図2-18を修正

150
Dry
Stress (MPa)Stress-strain curves
in uniaxial
compression tests
for dry and wet
Kamisunagawa
sandstone.

100
Circumferential

Axial

50
Wet0-1-0.5

00.5-2

Strain (10 )1Mechanism of weakening by water
Decrease in friction between mineral prticles ⎛ − Eact + αK I ⎞V = V0 a(H 2 O) exp⎜⎟
Increase in stress corrosion rateRT⎠⎝
Decrease in fracture toughness
Example: surface energy of quartz (J/m2)
Fresh surface in vacuum: > 2
Bonded with hydroxyls: 0.48～0.69
Saturated by water:0.41～0.46
In water: 0.34～0.39（Parks, 1986）

CementDecrease in clay strength
Elusion of calcite

pH
There is a possibility that rock mass is subjected to waterof various pH
Acid water: organic acid water due to imperfect resolution of plant,
inorganic acid water around hot springs or due to such sulfide as
pyrite etc.
Alkali water: Getting mixed alkali hot spring or concrete.

Weakening of quartz under large pH (Atkinson,1984)ζ potential, NaCl etc.

7.3 Effects of temperatureTemperature
Rock mass can be subjected to various temperature
High temperature
Plate earthquake
Geothermal energy extraction
High level nuclear waste disposal (80～100oC)

Low temperature
Underground storage of LNG (0～−50oC)）
Steep cliffs in cold regions

Effects of high temperature
Differential stressstrain curves of abasalt underconfining pressureof 500 MPa(Griggs et al.,1960)

著作権処理の都合で、この場所に挿入されていた『山口梅太郎・西松裕一（1991）、岩石力学入門第3版、東京大学出版会、
p. 202図6.17a』
を省略させて頂きます。

Weakening mechanisms under hightemperature
Thermal stress

Increase in stress corrosion rate
Decrease in viscosity of water⎛ − Eact + αK I ⎞V = V0 a(H 2 O) exp⎜
⎟RT⎠⎝

Viscosity (10-3 Pa・s)

Thermal cracks
Increase in stress intensity factor

1.5
10.5
0020 40 60 80 100
Temperature (oC)Tem perature
increase

T herm alactivation

T herm al stressincrease

Stressintensity
factor increase

Stresscorrosion
rate increase

Strain rate increase
Weakening

Viscosity
decrease

Increase in diffusion
rate of w ater

Increase in viscous defof clay m inerals

SurfacedecreaseenergyFracture
decrease

toughnessEffects of lowtemperature
UCS vs. temperature forsome rocks (Denchuken,1987)

著作権処理の都合で、この場所に挿入されていた『電力中央研究所（1987）、低温化、高温化での岩石・岩盤の特性調査、電力中央研究所報告、U87010, p.2,Fig. 1.1』を省略させて頂きます。

Strengthen mechanism under low temperature
Adherence of cracks, voids etc. by freezing
Activity of water decreases
Thermal activation is inhibited⎛ − Eact + αK I ⎞V = V0 a(H 2 O) exp⎜
⎟RT⎠⎝

Near surface of rock slope
in cold regions etc.
Fractures grow by
freezing pressure
Rock mass is not
weakened by freezing
Rock fall may occur whenrock mass thaws
Repeated rock fall
Formation of overhang
Giant rock slope
collapse

Indirect tensile strength (MPa)Freeze-thaw cycle
0.7
0.6
0.5
0.4
0.3
0.2

020 40 60 80 100

Number of freeze-thaw cycles

Indirect tensile strength of
Takinosawa hyaloclastite in freezethaw cycles (Fujii et al., 2002）

7.4 AnisotropyAnisotropy
Anisotropy of triaxial
strength for a slate(Goodman, 1980)
ψσ1

著作権処理の都合で、この場所に挿入されていた『Goodman (1980), Introduction toRock Mechancs, John Wiley andSons, p. 89, Fig. 3.23a』
σ3を省略させて頂きます。

Cause of anisotropy in strength
Mineral particles are anisotropic
Rock is a composition of mineral particles
Texture and structure of rock (foliation, sedimentary plane,flat particles, oriented microcracks, etc.) is more importantin an engineering point of view than anisotropy of mineralparticles

7.5 Scale effects

著作権処理の都合で、この場所に挿入されていた『Goodman (1980), Introduction to Rock Mechancs, John
Wiley and Sons, p. 86, Fig. 3.21』を省略させて頂きます。

UCS vs. specimen length (Goodman, 1980)

Large scale uniaxial
compression test(Goodman, 1980)

著作権処理の都合で、この場所に挿入されていた『Goodman (1980), Introduction toRock Mechancs, John Wiley and Sons,
p. 87, Fig. 3.22』を省略させて頂きます。

7.6 Shape effects

200
180
UCS (MPa)

UCS ofPombetsu
sandstone

160140
120
100

0.5

1Length / Diameter7.7 WeatheringPhysical weathering
Freeze-thaw cycle
Cyclic thermal stress
Repeated drying and moistening

Chemical weathering
Water-mineral reaction
Ex. Pyrite in a rock is oxidized and sulfate is generated. Calcite is dissolved bythe sulfuric acid and gypsum is created or illite is decomposed by the sulfuric
acid and jarosite is created (Okada et al., 2003)
4FeS2 + 15O2 + 10H2O → 4FeOOH（limonite） + 8H2SO4
CaCO3 + H2SO4 + 2H2O → CaSO42H2O + H2O + CO24(KAl2Si3O8(OH)2) + 12FeSO4 + 48H2O → 4(KFe3(OH)6(SO4)2 + 8Al(OH)3 +12Si(OH)4 + 4H2SO4