frost heave properties in ballast tracks tc202/archive... · lead sphere +tc 0 ℃ frozen fringe ts...
TRANSCRIPT
Frost Heave Properties in Ballast Tracks Field Observations and Laboratory Experiments
Satoshi AKAGAWA Cryosphere Engineering Laboratory
1/41 Cryosphere Engineering Laboratory
Topics
What is Frost Heaving
Field Works Monitoring at railway tracks
Laboratory Works Frost heave tests of crushed rock with different fines content
2/41 Cryosphere Engineering Laboratory
Topics
What is Frost Heaving
Field Works Monitoring at railway tracks
Laboratory Works Frost heave tests of crushed rock with different fines content
Cryosphere Engineering Laboratory 3/41
What is frost heaving.
Cryosphere Engineering Laboratory 4/41
Ice Lens Segregates at Negative Temp.
Cryosphere Engineering Laboratory
Frozen
Unfrozen
Surface of
Segregating Ice Lens
Lead sphere +TC
0 ℃ Frozen Fringe
Ts
5/41
Crystal Structure of Ice Lens
Cryosphere Engineering Laboratory 6/41
Schematic Drawing of Ice Lens
Cryosphere Engineering Laboratory 7/41
How Pore Water Freezes
Cryosphere Engineering Laboratory 8/41
Distribution and Thickness of Unfrozen Water
Cryosphere Engineering Laboratory 9/41
Field Observation
Cryosphere Engineering Laboratory 10/41
Our Test Fields
Cryosphere Engineering Laboratory 11/41
Ballast Track Structure
Cryosphere Engineering Laboratory 12/41
What is the uncertainty?
Dose ballast which contains fines frost heave?
Cryosphere Engineering Laboratory 13/41
Temperature Measurement in Railway Track Layers
Cryosphere Engineering Laboratory 14/41
Frost Heave Measurement in Railway Track Layers
Truncated cone
Cryosphere Engineering Laboratory 15/41
What items have monitored
Cryosphere Engineering Laboratory 16/41
Frost Heave Monitored in Ballast Track
Data of Furen Cryosphere Engineering Laboratory
17/41
Laboratory Observation
Cryosphere Engineering Laboratory 18/41
Grain Size Distribution of Ballast Track
Fhuren
Shizukuishi
12/20 Cryosphere Engineering Laboratory
19/41
Textures of Real Ballast
Cryosphere Engineering Laboratory 20/41
Mineral compositions of ballast and subgrade at Fhuren and Shizukuishi
Cryosphere Engineering Laboratory 21/41
Frost Heave Test Results (Shizukuishi)
Cryosphere Engineering Laboratory 22/41
A Model for Prediction
of Ballast Frost Susceptibility
Cryosphere Engineering Laboratory 23/41
An Empirical Formula has been used in Japan
for Frost Heave Susceptibility Prediction
,
,
0
0
1 0UU
where, ; heave ratio,
; confining pressure,
; freezing speed,
; test constants
U
0
0
0U
h
H Original
height
Heave amount
Hh
Cryosphere Engineering Laboratory 24/41
How the Ballast Layer Frost Heaves
17/20
Cryosphere Engineering Laboratory 25/41
Confirmation of
Proposed Formula
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Utilized Ideal Ballast which contains Fines
Kaolinite Gs=2.54 g/cm3 Crushed Rock I Grain Size Distribution; 2.5mm to 5.0mm Crushed Rock II Grain Size Distribution; 13mm to 20mm
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Frost Heave Test Apparatus−I
Thermal Bath
Valve
LVDT
Valve
Pt Temp.
Φ=200mm
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Frost Heave Test Apparatus−II
ϕ=50mm
L=20 to 100mm LVDT
Weight
Thermal Bath
Φ=50mm
Pt Temp.
Valve for PW
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Frost Heave Test Conditions
Overburden Pressure:33.9(kPa)
Pore Water Pressure:0kPa
Confining Pressure
Height:38~47(mm)
Diameter:50(mm)
Specimen Size
Height:92~111(mm)
Diameter:200(mm)
Temperature Gradient:
2.4
0
-2.4
Tw
Tc
0 48
Freezing Speed:0.10(cm/hr)
Thermal Condition
Example: Specimen Height = 48 mm
Apparatus I
Apparatus II
0.5(℃/cm)
Time (hr) Bo
un
dar
y T
emp
. (o
C)
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Frost Heave Tests Result
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How the Ballast Layer Frost Heaves
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Anticipated Result F
rost
Heave R
ate
(ξ)
Because of the unsaturated
pore condition with fines, frost
heave of the fines may not
contribute the macroscopic frost
heave in CASE-3.
In the CASE-3, steeper reduction of HEAVE RATE was expected.
Pores are not saturated with fines
Pore
3
V
V fCASE-3
Finds
Ballast
Piece of ballasts are floating in the pore fines
CASE-2
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Vertical Section of frozen Fines (CASE-1) H
eat
Flo
w D
irection
Horizontally elongated ice lenses
which are normal to the heat flow are
observed. Vertical ice veins which are
developed by the shrinkage due to
pore water pressure depression in
frozen fringe is also observed.
Normal frost heaving has happend
Cryosphere Engineering Laboratory 34/41
Vertical section of frozen Ballast (CASE-3)
⇒Even in the CASE-3, pores are filled with fines and ice lenses but no frozen balk water.
Mac
rosc
opi
c H
eat
Flo
w D
irection
57.03 =V
V f÷÷ø
öççè
æ= 19.0
V
V f
Cryosphere Engineering Laboratory 35/41
Fines between Piece of Ballasts
may Segregate Thick Ice Lenses M
acro
scopi
c H
eat
Flo
w D
irection
0 isotherm in rock advances faster.
Thermal conductivity of rock is
higher than soil.
Thick ice lens may segregate.
Heave at the rock-fines boundary last
longer.
Thick ice lenses have developed
at the upper part of piece of
ballasts (=cold side of piece of
ballasts)
Cryosphere Engineering Laboratory 36/41
Fins in pores frost heave higher than
total heave M
acro
scopi
c H
eat
Flo
w
Direction
Fines in pores show higher
frost heave ratio.
Microscopic heat flow
may meander due to
inhomogeneity of thermal
conductivity
Microscopic frost heave
ratio along the white dotted
line was 32%, whereas
average was 14%.
Cryosphere Engineering Laboratory
37/41
Cause of Thick Ice Lenses in Pore in CASE-3 M
acro
scopi
c H
eat
Flo
w D
irection
Then fins suffer almost no
confinement.
Initially total stress was supported
by rock skeleton.
Heave rate of fines under very low
confinement is very high.
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Again what was happened
Rock
Fines
Initial Condition
Final Condition
Ice Lens
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One Evidence
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Conclusions
Ballast which contains fines may frost heave.
Proposed empirical formula provides frost heave susceptibility of ballast which contains fines.
However farther researches will be required to refine the reliability of the proposed formula.
Cryosphere Engineering Laboratory 41/41
Thank you for your attention
Cryosphere Engineering Laboratory