Innovative Foundation for expansive clays

1. 1
Innovative Foundations to Stabilize Expansive Clays
Dept. of Civil Engineering
Indian Institute of Technology
Hyderabad

2.  Introduction
 Granular pile Anchor (GPA) and mechanism involved in GPA
 Experimental Procedure
 Materials used
 Results and Discussions
 Conclusions
2
Outline of the presentation

3.  Vertisol soils or Shrink Swell soils.
 Swells in monsoon seasons.
 Shrinks in dry seasons.
Introduction: What are Expansive Soils?
Process is reversible, and causes
alternate expansion and contraction
of the soil.
3

4. 4
Introduction: Damage Done?
Cracks formed in expansive
soils.
 Several Billion U.S. Dollars world wide.

5. 5
Introduction: Damages caused
Damages caused to
structures by expansive soils.
Heave in pavements.

6. 6
Introduction: Foundations in Expansive Soil
Existing Foundation Practices

7. 7
Introduction: Existing foundations in expansive soil
Under Reamed Piles
3 m
Expansive soil
2 m
Expansive soil
1 m
CNS layer
CNS layer
Sand cushion method

8. 8
Granular Pile Anchor (GPA) and Mechanism Involved
 Granular pile is a particulate medium, it
cannot counteract the tensile uplift force
caused by swelling soils on foundations.
Solution:
 Granular pile can be modified into a GPA
by providing an anchor.
 Now, the pile becomes tension-resistant
and can counteract tensile uplift forces.
 Anchorage can be provided through an
axial anchor rod attached to an anchor
plate.

9. Phanikumar 1997
Phanikumar et al. 2004
Rao et al. 2007, 2008
Phanikumar et al. 2008
Madhav et al. 2007 – compared the displacements of GPAs.
Sharma et al. 2004 - presented the compressive load response of geogrid-
encased granular pile in soft clays.
9
Studies pertaining to GPA
Presented the heave, pullout and compression
studies of GPAs in expansive soils.

10. The objectives of the study are as follows:
 To assess the performance of expansive clay beds reinforced with GPAs
and geogrid-encased GPAs.
 To study the size and scale effects of GPAs and geogrid-encased GPAs on
heave of expansive clays.
10
Objectives of the Study

11. 11
Materials used
Soil: Expansive Clay collected at a depth of 1.50 m below GL from Amalapuram.
Granular Materials: A mixture of
20% metal chips - 6 mm to 10 mm and
80% coarse sand - 2.4 mm and 4.8 mm.
Anchor Rod Anchor Plate:
4 mm dia. mild steel rod and diameter = diameter of GPA.
length = length of GPA. thickness = 5 mm.
Geogrid: PVC coated glass fiber geogrid with aperture size 10 mm x 10 mm
having tensile strength of 10 kN/m was used in the tests.

12. 12
Properties of the soil
Property Value
Specific Gravity 2.69
Sand (%) 13.33
Silt (%) 35.4
Clay (%) 51.27
Liquid Limit (%) 90
Plastic Limit (%) 35.2
Plasticity Index (%) 54.8
Free Swell Index (%) 140
USCS Classification CH
Index Properties of the Soil

13. 13
Shear properties
 Shear parameters
When clay and granular material as interface
cohesion (c’) = 13 kPa
angle of internal friction (Ø’) = 30o
 Shear parameters
When clay, geogrid and granular material as interface
cohesion (c’) = 13.3 kPa
angle of internal friction (Ø’) = 35o

14. 14
GPA
Heave of expansive
clay beds was
reduced up on
installation of GPAs
in both small and
large moulds.
l/d ratio
of GPA
As the l/d ratio of the
GPA increases heave
of the expansive clay
beds reduced
significantly.
Geogrid-encased
GPA
 Heave further
reduced when GPA is
encased with geogrid.
 It was reduced by
92.5% and 98.3% in
small and large
moulds respectively.
Conclusions

15. 15
Rate of
development
of heave with
GPA
Requires 10080 min.
for unreinforced clay
bed in large mould
and got reduced to
3240 min. upon
installation of GPA
with l/d = 3.23.
Rate of
development of
heave with
geogrid-encased
GPA
There is no effect in
time in case of GPAs
encased with geogrid.
% reduction in
heave
The % reduction in heave
are 97.6%, 98.0% and
98.3% with l / d = 1.63,
2.43 and 3.23 respectively
when reinforced with
geogrid-encased GPAs in
case of large mould.
Conclusions

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Thank you
for your attention
Queries??

17. 17
Conclusions
The following are the main conclusions that can be drawn from the experimental study:
1. Heave of the expansive clay beds decreased when they were reinforced by GPAs. Heave further decreased with
increasing in l/d ratio of the GPAs. Reduction in heave was even more when the GPAs were encased with a geogrid.
2. Heave decreased by 92.5% and 98.3% respectively in the case of GPAs encased with geogrid in small and large
moulds.
3. The time periods required for equilibrium heave also decreased when the clay beds were reinforced with GPAs.
For example, the unreinforced expansive clay bed attained the equilibrium heave in 3600 and 10080 minutes of
continuous wetting respectively when the test was performed in small and large moulds. However, when the clay
beds were reinforced with GPAs required much less time to attain equilibrium heave.
4. Further, it was found that, as the GPA length increased, the time required to attain final equilibrium further
decreased.