Analysis of behaviour of clay under cyclic wetting and drying

1. 1

2. • Swell-shrink and collapse behaviour of the soils affect the stress
state in soil
• Formation of desiccation cracks on soil surface - natural phenomenon
• Cyclic expansion and shrinkage of clays and associated movements of
foundations cause cracking and fatigue to structures.
2

3. Residential Driveway
Damaged By Expansive Soils
Typical "Roller-coaster" Road
Caused By Expansive Soils
3

4.  To understand the effect of wetting-drying cycles on the initiation and
evolution of cracks in clay layer
 To understand the impact of cyclic wetting and drying on the swell and
collapse behaviour of soil specimen
 To analyze the soil microstructure before and after cyclic swelling
 To investigate the geometric characteristics of surface crack patterns
through image processing
4

5.  Swelling behaviour depends on
 Type and amount of clay mineral
 Soil structure
 Dry density and moisture content
 Shrinkage behaviour depends on
 Percentage of fine particles
 Initial water content
 Initial dry density
 Energy and process used in compaction
 Swelling pressures - heaving
 Shrinkage - differential settlement
 In cyclic expansion and Shrinkage :
Soil specimens are wetted, allowed to swell and then dried to its
initial water content at room temp and again this cycle is repeated.
5

6. Investigators concluded :
 Repeated wetting drying
cycles in clay specimens show
signs of fatigue after
each cycle.
 Exhibiting less expansion.
 That expansion reaches
equilibrium state after 3
to 5 cycles.
CONTD.
Variation in Swelling Potential with the
Number of Cycles (Chen; 1975) 6

7. This study investigates :
 The effect of W-D cycles on cracking behaviour
 The initiation and evolution of cracks on the specimen surface
 Structure evolution during the W-D cycle
 The geometric characteristics of surface crack patterns through
image processing
7

8. The Romainville clay was
used in this investigation
 Its considered responsible
for damages to structures
due to swelling shrinkage
and cracking phenomenon.
Physical properties Values
Density of the solid
phase of clay
2.79 Mg m-3
Liquid limit 77 %
Plastic limit 40 %
Plasticity index 37 %
USCS classification CH
Clay (<2μm) 79 %
Clay composition Illite and smectite
Specific surface area 340 m2/g
8

9.  Four specimens prepared
 The air-dried clay crushed and sieved at 2 mm
 Saturated slurry specimens - crushed powder + distilled water (170%)
 Slurry poured in cups and air bubbles removed by placing it on
vibrator device for 5 minutes
 Sealed with plastic membrane and left for atleast 3 days
 Thickness of final settled layer – 10mm
 Specimens were dried at constant room temperature until weight of
was stabilized (first W-D cycle)
9

10.  Water was provided to start
next W-D cycle without any
mixing
 Glass cups again sealed with
plastic membrane for at least 3
days
 Specimens exposed to room
temp to be dried again
 Procedure was repeated a total
of 5 W-D cycles
CONTD.
Schematic Drawing of Set-Up 10

11. Using image processing
 Crack Intensity Factor (CIF) :
the ratio of the area of cracks to the
total initial area of specimen
 CIF – to quantify the cracking extent
during drying
 The crack length – determined by
calculating the length of the mid - axis of
crack segment between two intersections
using skeletonising operation
Typical Desiccation Crack
Pattern of Specimen during the
First Drying Path
CONTD.
11

12. At the end of each W-D cycle other geometric parameters determined were :
 Number of intersections per unit area (Nint )
 Number of crack segments per unit area ( Nseg )
 Mean crack length (Lav )
 Mean crack width (Wav )
 Mean clod area (Aav )
 The clods are surrounded by cracks, and their areas are defined as Aav
 Final specimen thickness determined by using calliper to find the
thickness of eight clods selected in the end of each drying period
CONTD.
12

13. To find the volume shrinkage behaviour of specimens during drying :
 Four other identical specimens were prepared using same procedure
 Water contents (w) determined by selecting small clods at different time
 The clod volume was determined by immersing clods in a non-wetting
hydrocarbon liquid
 e and Sr of specimens can be determined using the equations:
e = { rs (1+0.01w) /r } -1
Sr = ( wrs ) / e
rs density of soild phase of the Romainville clay = 2.79 Mgm-3
CONTD.
13

14. Digital image processing - to analyse CIF, structure and geometric
characteristics of crack pattern
14
Procedure of Digital Image Processing. (Chao et al; 2011)

15. Procedure
1. The colour photograph of the crack pattern is changed to a grey level
image
2. Binarisation : black areas represent the crack networks, and the white
areas represent the aggregates
3. To determine the crack intersections and lengths, schematized
structure of crack network is created by skeletonising
4. Skeletonising - Medial axis transformation (MAT)
5. MAT - the middle line of crack segment was extracted as the skeleton
of crack network.
CONTD.
15

16. Evaporation, Shrinkage and Cracking Process
Desiccation Curves of the Specimens during the First Drying Path
(Chao et al; 2011) 16

17. Variations of Surface Cracks Ratio RSC and Void
Ratio e with Water Content ( q / w ) during the
First Drying Path (Chao et al; 2011)
 The water contents
at AE and SL are
18% and 12%
 Rsc at different
water content
determined by
image processing
after dessication
cracks appeared on
surface of
specimen
CONTD.
17

18.  Cracking water content (wc/ qc ) : water content corresponding to the first
crack observed in specimen during drying
Cracking Water Content (qC /wC ) of the Specimens during each
Drying Path (Chao et al; 2011)
18

19. Surface Crack Ratio RSC after each W-D Cycle (Chao et al; 2011)
CONTD.
19

20. Mean Thickness hf of Specimen Layer after each W-D Cycle
(Chao et al; 2011)
CONTD.
20

21. Provide a way to investigate the essential mechanisms of cracking.
These parameters reflect material plasticity and mineral composition
After
W-D
cycle
Nint
(cm-2)
SD
Nint
Nseg
(cm-
2)
SD
Nseg
Lav
(mm)
SD of
Lav
Wav
(mm)
SD of
Wav
Aav
(cm2)
SD
Aav
First 1.09 0.17 1.78 0.12 8.43 4.50 1.01 0.63 1.18 1.20
Second 1.52 0.12 2.45 0.19 7.57 3.75 1.52 0.49 0.78 0.56
Third 1.37 0.08 2.13 0.11 8.12 3.42 1.86 0.42 0.69 0.53
Fourth 1.43 0.05 2.16 0.08 8.07 3.31 1.74 0.38 0.65 0.53
Fifth 1.44 0.07 2.22 0.05 8.22 2.75 1.73 0.37 0.65 0.49
Mean Values of Crack Quantitative Parameters and Corresponding Standard
Deviation after W-D Cycle (Chao et al; 2011)
21

22. Crack Pattern and Structure Evolution after W-D Cycles
Typical Desiccation Crack Patterns after each W-D Cycle(Chao et al; 2011)
22

23. After Ist cycle : clods - regular, crack segments - smooth & perpendicular
After IInd cycle : separated clods – irregular , crack segments - jagged
The geometric and morphologic characteristics of the crack patterns are
similar to each other after the third, fourth and fifth W-D cycle.
Cracking took place in three stages:
Stage 1: Main-cracks
Stage 2: Sub-cracks
Stage 3: The existing surface cracks just become wider until the
desiccation comes to the end.
CONTD.
23

24. Crack Pattern Evolution and Aggregate Formation during Wetting
Evolutions of Surface Cracks during the Second Wetting Path
(Chao et al; 2011) 24

25.  Wetting led to the immediate collapse of clods
 Collapse firstly occurred on the clods edges - rapid hydration firstly
occurred at these less stable positions
 Some new micro-cracks induced by wetting appeared on the surface
mainly due to differential swelling pressures
 Original dessication cracks fully closed after 2.5 min
 Edges of aggregates and micro cracks are clearly visible even after 72
hours
CONTD.
25

26. Evolutions of Surface Cracks during the
Third Wetting Path (Chao et al; 2011)
 Observations are
slightly different
from the second
wetting process
 No new micro-
cracks observed,
as in the second
wetting path
CONTD.
26

27.  Results shown concludes that the cracking behavior reached equilibrium
state after the specimens were subjected to the third cycle
 Number of cycles depend upon the material nature: Clay fraction
 Clayey soils with high plasticity need more W-D cycles to reach the
equilibrium state than silty or sandy soils.
27

28.  During the Ist drying path, evaporation process composed of two stages
 During the IInd and IIIrd wetting poured water caused rapid collapse of
clods
 After the IInd drying path, specimen homogeneity decreased
 The tested specimen, reached an equilibrium state after IIIrd W–D cycle
 Before equilibrium, θc, Rsc and hf increased with increasing cycles, but
after equilibrium it became insignificant
 Image processing provided information on the geometric characteristics
of crack patterns
28

29. This study investigates:
 The effect of cyclic swelling on the expansive characteristics of clays
 Soil micro structure before and after cyclic swelling
 The effect of cyclic wetting and drying on clay plasticity
29

30. Materials Used
 To accomplish the desired objectives six soils from various locations
in Irbid (a city in northern Jordan) were utilized in this study
 These soils were selected to cover the widest possible range of
plasticity
30

31. Properties of Test Soils (Al-Homound et al; 1995)
Property
Soil Series
A B C D E F
Depth of sampling (m) 4.0 6.0 6.0 3.5 3.0 2.5
Natural water content, w % 12.0 21.0 20.3 20.0 15.0 20.0
Initial dry unit weight (kN/m3) 16.0 17.0 16.0 27.0 16.8 17.2
Liquid limit,LL (%) 35 79 57 75 62 81
Plasticity index, PI (%) 22 27 15 37 34 38
Specific gravity of solids, G 2.56 2.70 2.64 2.71 2.65 2.68
Over consolidation ratio (OCR) 3.9 2.3 2.3 2.8 3.5 4.3
Sand (%) 32.0 8.0 38.0 30.0 20.0 5.0
Silt (%) 32.1 33.2 29.8 20.0 28.9 23.3
Clay (%) 37.9 58.8 32.2 77.0 51.1 71.7
Unified soil classification CL MH MH MH CH MH
31

32.  Remoulded specimens - prepared by compacting in the consolidation ring
 The compacted soil sample placed in a consolidation cell at confining
pressure of 7kPa
 For each soil considered, two identical samples were prepared
 The first specimen - to determine the swell percent
 The second - to assess the swell pressure
32

33.  To determine the percent swell
 sample inundated with distilled water to fully swell for at least 48 hr
 At this stage, the water removed and the consolidation cell dismantled
 The test sample - then allowed to air-dry to its initial water content within
the laboratory environment
 To estimate swell pressure - constant volume swell test.
 After the application of the surcharge load - the specimens fully inundated
with distilled water.
CONTD.
33

34.  As swelling commences, vertical deformation prevented by continously
adding loads at every vertical expansion
 void ratio kept unchanged
 The loads - sand added to a plastic bag hung off the loading arm
 The loads - continually added until no expansion was observed
 Swell pressure was calculated as the load required to retain zero swell
divided by the specimen area
CONTD.
34

35. Variation of Swell Percent with Time after W-D
Cycles
Swell Percent with Time for: (a) Cycle I (b) Cycle V for Test Soils
(Al-Homound et al; 1995)
35

36. Vertical Swell and Shrinkage with Time for: (a) Soil A (b) Soil F
(Al-Homound et al; 1995) 36
Vertical Swell and Shrinkage with Time after W-D Cycles

37. Variation of Swell potential and swell pressure with Time after W-D Cycles
Change of Swell Potential and Swell Pressure with Cycle
Number for Test Soils (Al-Homound et al; 1995) 37

38. Photomicrograph Showing Microstructure of Soil Sample F
(a) Initial Remoulded Sample; (b) after First Cycle; (c) after Fifth Cycle
(Al-Homound et al; 1995) 38

39. CONTD.
 Image analysis proved - decrease of swelling characteristics was due to
change in clay microstructure
 Soil sample F may be considered here as an example
 In addition to SEM analysis basic properties of the soil estimated for the
initial soil and at the end of the equilibrium cycle
 Cyclic wetting and drying decreases the clay content and reduces clay
plasticity
 Reason - particle aggregation caused by drying leading to a decrease in
specific surface area available for interaction with water
39

40. CLAY CONTENT CONSISTENCY LIMITS
Liquid Limit Plasticity Index
Intial
cycle
Final
cycle
%
reduction
Intial
cycle
Final
cycle
%
reduction
Intial
cycle
Final
cycle
%
reduction
A 37.9 30.1 20.6 53 42 20.7 22.4 13.1 41.5
B 58.8 47.9 18.5 79 65 17.7 36.5 32.9 9.9
C 32.2 26.3 18.3 57 49 14 15.3 11.6 24.2
D 77 66.7 13.4 75 65 13.3 37.1 29.2 36.7
E 51.1 46.8 8.4 62 48 22.6 33.5 23.5 29.9
F 71.7 52.1 27.3 81 67 17.3 37.6 32.6 13.3
Change of Clay Content and Consistency Limits before and after
Cyclic Swelling (Al-Homound et al; 1995)
40
CONTD.

41. The soils show sign of fatigue after each W- D cycle which decreased
swelling ability
The first cycle causes the most reduction in swelling potential.
Till the equilibrioum state the swelling potential decreases after which it
seem to level off
Scanning electron micrographs showed a continuous rearrangement of
particles during W-D cycles
Reduction in clay content and plasticity shows that Cyclic W-D causes
particle aggregation thus reducing swelling characteristics
41

42.  Image processing can quantitatively analyze geometric characteristics of
crack patterns
 The soils show sign of fatigue after each W- D cycle
 Cracking takes place in three stages
 SEM analysis - rearrangement of particles during cyclic W-D
 Multiple W-D cycles result in changes in clay structure and cracking
 Attention should be paid to the engineering fields where swelling clays
are involved
 Especially during construction of low permeable structures
42

43. 1. Tang Sheng Chao et al. (2011) , “Desiccation And Cracking Behavior Of
Clay Layer From Slurry State Under Wetting - Drying Cycles”, Science
Direct, Geoderma, Volume 166, Issue 1, 111–118
2. Al-Homound A.S et al.(1995), “Cyclic Swelling Behavior OF Clays ”,
ASCE ,Journal of Geotechnical Engineering , Vol.121, No.7, 562–565.
3. Chao Sheng Tang et al. (2008), “Influencing Factors of Geometrical
Structure of Surface Shrinkage Cracks in Clayey Soils ”, Science Direct ,
Engineering Geology 101, 204–217. 43

44. 4. Chao Sheng Tang et al.(2011), “Experimental Investigation of the
Desiccation Cracking Behavior of Soil Layers during Drying ”, ASCE,
Journal of Materials in Civil Engineering, Vol. 23, 873-878.