1. Stone Columns: An Overview
by
S.V. Abhishek & V. Tarachand
Department of Civil Engineering
College of Engineering (A)
Andhra University
Visakhapatnam

2.  Amongst
Stone Columns
various techniques for improving
in-situ ground conditions, stone columns are
probably the most versatile, due to their ability to
perform a variety of important geotechnical
functions.
 Origin
Germany (1950s)
 In India, the use of stone columns began in the
early 1970s.
 Load bearing columns of well compacted coarse
aggregate installed in the ground to serve various
purposes such as reinforcement, densification
and drainage.

3. Applicable Soil Types
Soft,
Non-Compactible, Weak Soils
Granular
Soils with High Fines
Content (in excess of 15%)
Organic Soils
Marine/Alluvial Clays
Liquefiable Soils
Waste Fills
Reclaimed Fly Ash/Pond Ash Ponds

4. Functions
 Improve
the bearing capacity of weak soils.
 Carry
high shear stresses by acting as stiff
elements and hence increase the stability of
embankments founded on soft ground.
 Facilitate
radial drainage (by acting as vertical
drains) and dissipate rapidly the excess pore water
pressure leading to acceleration of consolidation
process and reduced post-construction settlements.
 Mitigate
the potential for liquefaction and damage
by preventing build up of high pore pressure,
providing a drainage path and increasing the
strength and stiffness of the ground.

5. Due to high angle of internal friction and stiffness of stone
column when compared to that of in-situ weak soil,
majority of applied load is transferred to stone column.
As a result, less load is transferred to surrounding weak
soil which leads to reduction in settlement.

6. Installation Patterns
Area of Influence = (√3/2)S2
De = 1.05S
Area of Influence = S2
De = 1.13S
Time required for consolidation is directly proportional
to square of the drainage path.

7. Load Carrying Mechanism
Lateral earth pressure/radial confining
stress against bulging from surrounding
soil.
Surface resistance or frictional
resistance developed between the
column material and surrounding weak
soil acting upwards within the critical
length.
Passive resistance mobilized by
column material.
Load carrying capacity of stone
columns = 100 to 400 kN.
Note: End bearing is not considered in
estimation of load carrying capacity
because load carrying mechanism is
local perimeter shear.

8. Estimation of Load Carrying Capacity
 Assumed
that foundation loads are carried only
by the stone columns with no contribution from
the intermediate ground.
K p (4c + σ 'r )
 Hughes & Withers (1974)
qa =
F.S.
where,
qa = allowable bearing capacity of stone column
Kp = coefficient of passive earth pressure
= tan2(45+φ/2)
c = cohesion of soil
σr’ = average effective radial stress over a depth
of ‘4d’ where ‘d’ is the diameter of the column
F.S. = factor of safety = 1.5 to 3.0

9. Settlement Control
 Stone
columns should extend through weak
soil to harder firm strata to control
settlements.
 Provision of stone columns does not reduce
the entire consolidation settlement. The
reduction depends on the spacing of stone
columns (generally 2.0 to 3.0 m c/c over the
site).
 Maximum percentage reduction of settlement
is 75%.

10. Drainage Function of Stone Columns
 Load
carrying capacity of stone columns is
generated by the top section of the column
which extends to about 4 times the diameter
of the stone column.
 The
length below 4d allows for radial
drainage and acceleration of settlements.
 To
retain continuity of drainage path, it is
necessary to provide a 150 mm thick drainage
blanket on top of the stone columns.

11. Failure Mechanism (IS: 15284 Part 1 – 2003)

12. Installation Techniques
1. Rammed Stone Column Technique
2. Vibro-Replacement
Wet Top-Feed Method
Dry Bottom-Feed Method

13. Rammed Stone Column by Cased Borehole Method
(Datye and Nagaraju, 1975)

14. Vibro-Replacement
The Depth Vibrator Principle:
Extension Tube
Coupling
Air or
Water
Supply
Motor
Excentric
Weight
Tip

15. Depth Vibrator (Courtesy of Keller Group)
Air Chamber and Lock
Extension Tube
Flexible Coupling
Electric Motor
Stone Feeder Pipe
Eccentric Weight
Top-Feed Vibrator
Bottom-Feed Vibrator

16. Wet Top-Feed Method
(Courtesy of Keller Group)

17. Dry Bottom-Feed Method with Leader
Supported Rig (Courtesy of Keller Group)

18. Vibrocat (Courtesy of Keller Group)

19. Dry Bottom-Feed Crane Hung System
(Courtesy of Keller Group)

20. Quality Control - Production Monitoring
On-board M4 Computer: Depth, Compaction,
Length of Pull, Re-penetration, Increase in Power
Consumption, Column Diameter

22. Stone Column after Installation

23. Post-Installation Quality Control (Load Test)

24. Applications in Civil Engineering
 Rail
and Road Embankments
 Bridge Approaches and Abutments
 Offshore Bridge Abutments
 Airport Runways and Taxiways
 Storage Tanks (LNG, Crude Oil, LPG etc)
 Power Plants

25. Ipoh-Rawang Electrified Double Track
(Malaysia)

26. Ipoh-Rawang Electrified Double Track
(Malaysia)

27. KVMRT Kajang Maintenance Depot
(Malaysia)

28. Bridge Approaches and Abutments
Putrajaya, Malaysia

29. Putrajaya Bridge Approach
Embankment
R.C. Structure
RL +32.0
Top of Bridge Deck
Water Lev. RL +21.5
Embankment
RL +12.0
Pile cap
Stone columns
Bored piles
Stone columns

30. Offshore Bridge Abutments
Johor Bahru, Malaysia

31. Airport Runways and Taxiways
Alor Setar Airport Project, Malaysia

32. Storage Tanks
Hazira LNG Terminal, Gujarat

33. Case History of Highway
Embankment on Stone Column
Treated Ground in Queensland,
Australia (Oh et al. 2007)

35. Subsoil Properties

36. 520 mm
Untreated
495 mm
SC @ 3m c/c
SC @ 2m c/c
390 mm

37. Lateral Displacement Profiles

38. Conclusions
Stone Columns are one of the most versatile
techniques for engineering the ground.
 They can be installed to improve a variety of
ground conditions through several variants of the
technique such as rammed stone columns and
vibro-replacement (wet top-feed and dry bottomfeed methods).
 The in-situ ground is improved by reinforcement,
densification and drainage functions performed by
the stone columns.
 From the case history, the embankment treated
with stone columns spaced at 2 m centre to centre
experienced the least settlement and lateral
displacement when compared to the other cases.


39. Acknowledgments
Prof. M.R. Madhav
Professor Emeritus, JNTU
Visiting Professor, IIT Hyderabad
Dr. V.R. Raju
Managing Director
Keller Asia

40. Earthquake Rose
Thank
You