Thermal failure in soil

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

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

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

4 EXPERIMENT

5 EXPERIMENTAL SETUP

Taken from Can. Geotech. J. 29, 1095-1 102 (1992)

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

7 PROCEDURE

Undrained isotropic loading

Stabilization of ‘U’

Consolidation

Heating in stages till failure

8 NCC

• Initial temperature –

21oC

• Confining – 5.75MPa

• Consolidated

• Deviatoric stress given

– 2MPa

• Heated in stages

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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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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

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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THERMAL FAILURE EXPERIMENT AND

MODELLING BY HUECKEL et. al.

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

15Prager’s Consistency Condition requires ,

flow rule is assumed to be associated

Giving in consistency condition

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 ,

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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CD TEST ON OCC

19For 0.2 MPa

1 - 22oC2 - 98oC

adapted from Hueckel, 2009

20 Multiple loading

adapted from Hueckel, 2009

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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THERMAL MODEL BY C. Zhou and C.W.W. Ng

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

24 MATHEMATICAL FORMULATION

Volumetric strain increment Shear strain increment

Considering temperature dependency

Flow rule

25

Normally Consolidation LineSpecific volume relations

are as following

from C. Zhou and C.W.W. Ng (2014)

26 CSLSpecific volume relations are as following

Bounding Surface equation is

Where:

27

Variation of shape of yield surface with parameters n and r

from C. Zhou and C.W.W. Ng (2014)

28 INCORPORATING HARDENING

condition of consistency can be expressed as

Rearranging

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

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)

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)

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)

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)

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

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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THANK YOU

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