Stone Columns: An Overview
S.V. Abhishek & V. Tarachand
Department of Civil Engineering
College of Engineering (A)
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
In India, the use of stone columns began in the
Load bearing columns of well compacted coarse
aggregate installed in the ground to serve various
purposes such as reinforcement, densification
Applicable Soil Types
Non-Compactible, Weak Soils
Soils with High Fines
Content (in excess of 15%)
Reclaimed Fly Ash/Pond Ash Ponds
the bearing capacity of weak soils.
high shear stresses by acting as stiff
elements and hence increase the stability of
embankments founded on soft ground.
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.
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.
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.
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.
Load Carrying Mechanism
Lateral earth pressure/radial confining
stress against bulging from surrounding
Surface resistance or frictional
resistance developed between the
column material and surrounding weak
soil acting upwards within the critical
Passive resistance mobilized by
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.
Estimation of Load Carrying Capacity
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 = allowable bearing capacity of stone column
Kp = coefficient of passive earth pressure
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
columns should extend through weak
soil to harder firm strata to control
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
Maximum percentage reduction of settlement
Drainage Function of Stone Columns
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.
length below 4d allows for radial
drainage and acceleration of settlements.
retain continuity of drainage path, it is
necessary to provide a 150 mm thick drainage
blanket on top of the stone columns.
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.
Prof. M.R. Madhav
Professor Emeritus, JNTU
Visiting Professor, IIT Hyderabad
Dr. V.R. Raju