thermal failure in soil
TRANSCRIPT
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1
THERMAL FAILURE IN SOIL
Prof: Samirsinh P Parmar (CE-14103277)
Research Scholar, Department of Civil Engineering IIT Kanpur
Special Thanks to: Vadigalla Chinasivunnaidu and Viswanath Parol
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2 SCOPE
Thermal failure analysis of soils is essential in case of
Underground Structures exposed to heat
Energy storage in soils using geo-structures
such as piles, walls
Oil recovery from reservoirs
Underground nuclear disposal facilities
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3 LAYOUT
EXPERIMENT
THERMAL FAILURE MODELS
CAM CLAY MODEL EXTENSION BY T. HUECKEL et. al.
A GENERAL MODEL BY C. ZHOU & C.W.W.Ng
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4 EXPERIMENT
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5 EXPERIMENTAL SETUP
Taken from Can. Geotech. J. 29, 1095-1 102 (1992)
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6 SOIL USED
Boom Clay Pasquasia clay
PROPERTIES
240m depth soft & highly plastic
22% smectite, 19% illite, 29% kaolinite
160m depth Mediumplasticity
cemented clay 10-15% kaolinite,
<5% smectite, 20-25% calcite, 15-20% quartz,
NCC - 1OCC - 2 Only OCC Samples used
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7 PROCEDURE
Undrained isotropic loading
Stabilization of ‘U’
Consolidation
Heating in stages till failure
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8 NCC
• Initial temperature –
21oC
• Confining – 5.75MPa
• Consolidated
• Deviatoric stress given
– 2MPa
• Heated in stages
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9
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10 OCC
22.5oC 60oC 22.5oC 100oC
ΔU = 0.86MPa ΔU = 1.25MPa
@64oC the axial strain shoots up by 5.4 % Later stabilized by U development
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11
Boom Clay
The other OCC sample was given q = 1MPa & P= 1.98MPa, the cycle of temperature was between 59oC & 29oC
• Result - ΔU was smaller
Pasquasia clay
The OCC sample was given q = 2MPa & P= 3MPa• The plastic strain is higher
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12 CONCLUSIONS OF EXPT.
Under constant effective stress the yield surface shrinks with temperature
Upon the completion of the thermal cycle a substantial negative pore-pressure difference may be induced in clay
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13
THERMAL FAILURE EXPERIMENT AND
MODELLING BY HUECKEL et. al.
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14 Evolution of yield locus
adapted from Hueckel, 1992
• On the basis of these observations, the elasticity domain is thought of as temperature dependent, shrinking when soil is heated and expanding during cooling
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15Prager’s Consistency Condition requires ,
flow rule is assumed to be associated
Giving in consistency condition
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16 At any constant effective stress during heating along with continuing plastic yielding, the plastic strain increment per increment of temperature is
This equation represents thermo plastic strain- hardening. Then according to consistency condition ,
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17
q = 0 q ≠ 0 , p’ > p’co /2.718
q ≠ 0 , p’ < p’co /2.718 > p’co /2.718
q ≠ 0 , p’co /2.718 < p’ < p’co /2.718
Cam Clay yield locus
adapted from Hueckel, 2009
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18
CD TEST ON OCC
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19For 0.2 MPa
1 - 22oC2 - 98oC
adapted from Hueckel, 2009
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20 Multiple loading
adapted from Hueckel, 2009
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21 The coefficient M, and hence the internal friction angle, are both dependent on ∆T .
But pre-consolidation pressure and M are independent of each other
The evolution of both the yield locus and failure is critically dependent on the history of thermo mechanical loading, especially the stress state and drainage condition in which the heating is performed.
Conclusions from test
adapted from Hueckel, 2009
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22
THERMAL MODEL BY C. Zhou and C.W.W. Ng
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23 IMPORTANCE
Size and shape of the bounding surface allowed to change
with temperature
Degradation of shear modulus with smaller strains are
incorporated
This model measures volume change in heating and cooling
It predicts both drained and undrained behavior of soil
It has been evaluated only for OCC
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24 MATHEMATICAL FORMULATION
Volumetric strain increment Shear strain increment
Considering temperature dependency
Flow rule
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25
Normally Consolidation LineSpecific volume relations
are as following
from C. Zhou and C.W.W. Ng (2014)
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26 CSLSpecific volume relations are as following
Bounding Surface equation is
Where:
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27
Variation of shape of yield surface with parameters n and r
from C. Zhou and C.W.W. Ng (2014)
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28 INCORPORATING HARDENING
condition of consistency can be expressed as
Rearranging
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29 Calibration of model
Ten parameters defined in the model
Out of ten, five are that of Cam Clay Model
Parameters are,
Two parameters are used for shape of bounding surface
Three parameters are used for simulating thermal effect
of soil. They are expressed below
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30 RESULTS
Comparisons between measured and computed results of Un-drained triaxial compression tests on illitic clay
from C. Zhou and C.W.W. Ng (2014)
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31
Comparisons between measured and computed results of shear modulus degradation curve, obtained from undrained triaxial compression tests on illitic clay
from C. Zhou and C.W.W. Ng (2014)
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32
Comparisons between measured and computed results of undrained triaxial compression tests on reconstituted kaolin clay:
from C. Zhou and C.W.W. Ng (2014)
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33
Comparisons between measured and computed results of drained triaxial tests on compacted silt with different confining pressures
from C. Zhou and C.W.W. Ng (2014)
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34 CONCLUSIONS
There are lot of contradictions on the behavior of soil in
heating between different authors
The experiment results needed for validation are limited
SCOPE
As studies has shown that in vijoint dam(Italy) failure,
temperature rise due to slip also played a part for failure, it is
important to apply thermal behavior in slope stability
Since in many cases temperature increases when exposed to
chemicals, So the coupled effect of thermal and chemical has
to be understood properly
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35 REFERENCE
C. Zhou and C.W.W. Ng (2014) “A thermo mechanical model for
saturated soil at small and large strains”, Can. Geotech. J. 52:
1101–1110
T. Hueckel, B. Francois and L. Laloui (2009) “Explaining thermal
failure in saturated clays”, Geotechnique 59, No. 3, 197–212
T. Hueckel, R. Pellegrini (1992) “Effective stress and water
pressure in saturated clays during heating-cooling cycles”, Can.
Geotech. J. 29, 1095-1 102
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36
THANK YOU
Question Please?