Download - Friction coefficient shear displacement
Friction coefficient β shear displacement curve of kaolinite in different slip rate
Presenter : Yi-Chia Chiang
Advisor : Prof. Jia-Jyun Dong
Date : 2020.03.27
Outline
1. Introduction
2. Methodology
3. Preliminary results
4. Preliminary conclusions
5. Future works
Introduction
β’ The strength of sliding surface will be strongly affected by the slip rate and the sliding distance when the landslide occurs. (e.g., Tika and Hutchinson, 1999; Yang et al., 2014; Alonso et al., 2016).
Introduction Methodology Results Conclusions Future work
1
Introduction
β’ Slip-dependence friction law
Introduction Methodology Results Conclusions Future work
2
Slip-strengthening
Slip-weakening
Lowslip rate
Intermediate slip rate
High slip rate
Introduction
β’ Shear rate-dependence friction law
Introduction Methodology Results Conclusions Future work
3
Displacement (m)
Fric
tio
n c
oef
fici
en
t (-
)
Rate-strengthening
Rate-weakening
Shear rate V
The steady-state friction coefficient
πππ
The steady-state friction coefficient
πππ
Shear rate
π
Shear rate
π
Shear rate V
π1
π2
π3
π½π > π½π > π½ππ½π > π½π > π½π
Purpose
1. Find out the reason that makes the difference of the strength measurement by rotary shear test.
2. Investigate the friction coefficient - shear displacement curve under different shear rate, and try to define the friction coefficient in more.
Introduction Methodology Results Conclusions Future work
4
Rotary shear test
Introduction Methodology Results Conclusions Future work
Rotational side
Stational side
ππ
β’ A low to high rotary-shear frictional testing apparatus
5
Experiment conditions
β’ Pre-consolidated : 1MPa
β’ Normal stress : 1MPa (shear tests)
0.5~2MPa (Teflon calibration)
β’ Shear rate : 10β7 ~ 1 m/s
β’ Material : Kaolinite clay
β’ Water condition : Room humidity
Introduction Methodology Results Conclusions Future work
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Introduction Methodology Results Conclusions Future work
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The reasons that make the difference of the strength measurement by rotary shear test.
Is shear displacement enough?
The way used to calculate πππ ?
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.39πππ= 0.28πππ= 0.29
Is it steady-state ?
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.59 πππ= 0.40 πππ= 0.40
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.49 πππ= 0.41 πππ= 0.48
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.60 πππ= 0.46 πππ= 0.79
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.81 πππ= 0.57 πππ= 0.70
Shear rate : ππβπm/s
Introduction Methodology Results Conclusions Future work
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πππ= 0.82 πππ= 0.74 πππ= 0.90
Steady-state friction coefficient
Introduction Methodology Results Conclusions Future work
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Introduction Methodology Results Conclusions Future work
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π- Displacement Curve pattern
Lowslip rate
Intermediate slip rate
High slip rate
Displacement (m)
Fric
tio
n c
oef
fici
ent
(-)
ππβπ, ππβπm/s ππβπ, ππβπ, π m/s
Increase to 1st peak and weaken to residual value
ππβπ, ππβπm/sππβπ, ππβπm/s
Shear rate V
Rate-strengthening
Displacement (m)
Fric
tio
n c
oef
fici
en
t (-
)
Increase to 1st peak and weaken to residual value
Rate-strengthening
Rate-weakening
ππβπ~ππβπm/s
ππβπ~π m/s
ππβπ, ππβπ, π m/sππβπ, ππβπ, π m/sππβπ, ππβπ, π m/sShear rate V
Shear rate V
Displacement (m)
Fric
tio
n c
oef
fici
ent
(-)
ππβπ, ππβπ, ππβπm/s
Shear rate V
Two peaks appear before the friction coefficient reaches a steady state value
Rate-strengthening
Introduction Methodology Results Conclusions Future work
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What is the reason that we need much longer shear displacement to reach the steady-state?
Rotary shear test vs Ring shear test
V=0 Vmax Vmin Vmax
Introduction Methodology Results Conclusions Future work
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(Doung et al.,2018)
STEP 1
β’Defined the curve of shear stress versus shear displacement
β’Get ππ, ππ, π·π, π·π
Introduction Methodology Results Conclusions Future work
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Introduction Methodology Results Conclusions Future work
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STEP 1
β’Defined the curve of shear stress versus shear displacement
β’Get ππ, ππ, π·π, π·π
Shear rate V
STEP 2
β’Cut the shear plane into 5 rings
β’Calculate the shear rate of each ring
Introduction Methodology Results Conclusions Future work
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V=0 Vmax
The shear rate and shear displacementon the shear plane are not uniformly
distributed from the outside to the inside
ππ
ππ
ππ
ππ
ππ
ππ π½π π½ππ½π π½π
STEP 2
β’Cut the shear plane into 5 rings
β’Calculate the shear rate of each ring
Introduction Methodology Results Conclusions Future work
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Shear rate V
Set πππ = 10β4m/s
ππππ₯ = 10β4m/s π0 = 0m/s
V1 9.0 Γ 10β5m/s
V2 7.0 Γ 10β5m/s
V3 5.0 Γ 10β5m/s
V4 3.0 Γ 10β5m/s
V5 1.0 Γ 10β5m/sππ π½π π½ππ½π π½π
STEP 3
β’Calculate the shear stress of each ring
β’Transform to the shear stress of the whole plane
Introduction Methodology Results Conclusions Future work
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ππππ =π=1π=5
ππ π Γ π΄π π
π΄πππ
πππππ =π=1π=5
πππ π Γ π΄π π
π΄πππΟRi : Shear stress of RiARi : Area of Ri
π¨π
π¨π
π¨π
π¨π
π¨π
Preliminary conclusions1. At the low (10β7, 10β6m/s) and high (10β2~1m/s) shear rates, the
friction coefficient increases with the increasing shear displacement
to a peak and then weakens to a steady state.
Introduction Methodology Results Conclusions Future work
23Displacement (m)
Fric
tio
n c
oef
fici
ent
(-)
ππβπ, ππβπm/sππβπ, ππβπm/sππβπ, ππβπm/s
Shear rate V
ππβπ, ππβπ, π m/s
Displacement (m)
Fric
tio
n c
oef
fici
ent
(-)
ππβπ, ππβπ, π m/sππβπ, ππβπ, π m/sππβπ, ππβπ, π m/sShear rate V
Shear rate V
Preliminary conclusions2. The friction coefficient-shear displacement curve obtained from the
rotary shear test actually reflects the results of the weighted
average of different shear rates and displacements covered by the
sliding surface.
The complexity of the obtained results under medium shear rate is related to
this limitation of the rotary shear test.
Introduction Methodology Results Conclusions Future work
24Displacement (m)
Fric
tio
n c
oef
fici
ent
(-)
ππβπ, ππβπ, ππβπm/s
Shear rate V
πππ½π π½ππ½π π½π
Future works
β’ To do more calculation using the strength measurement results by
ring shear test at different slip rate.
β’ To discuss the reasons that make the complexity of the obtained
results under medium shear rate .
Introduction Methodology Results Conclusions Future work
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Thank you