FIELD OF INVENTION
This invention relates to a method of producing a cavity for formation of engineered
aggregate piers. In particulars, this invention relates to a method of reinforcing of a
cavity by the step of soil stabilization.
BACKGROUND OF INVENTION
It is generally known that a foundation system for supporting a superstructure may
either be a deep or shallow system, the depth to width ratio generally defining said
system. The choice of the foundation is dependant on the load and as to whether the
soil can carry loads with adequate factor of safety with respect to shear and settlement.
Normally, if the soil does not have adequate supporting capacity to withstand the load, a
deep foundation system is preferred or ground improvement needs are followed even if
the load is not too considerable. Thus, the choice of the foundation system is not
dependant only on the load, but also on the supporting capacity of the soil with an
adequate factor of safety.

Deep foundations may be formed by driving a precast RCC or a steel pile.
Alternatively, tube or casing may be driven into the soil, and whereby the soil is
laterally displaced, and thereby resulting in a densification of the adjoining soil. A
reinforcement cage is introduced into the tube or casing and, thereafter, concrete is
poured into said tube or casing The casing or tube is slowly withdrawn by tamping with
a hammer.
Yet another method of forming a deep foundation system is to introduce an auger into
the soil. However, in such a method, the soil is removed and a temporary casing is
introduced so as to prevent a collapse of the wall of the formed cavity. Alternatively,
bentonite slurry may be circulated within the cavity. After lowering the reinforcement
cage, concrete is poured into the cavity to form cast in situ piles. Alternatively, precast
piles may be introduced into said cavity followed by grouting.
Shallow foundations are less complicated but have a limitation in withstanding the
load, unless soil resistance is substantial. Shallow foundations normally comprise
column footings or load bearing walls or raft foundations.
Yet another method of forming a foundation has been disclosed in U.S. Patent No.
5,249892. In the method of U.S. Patent No. 5,249,892, a cavity having a bottom and

side walls is formed. The soil in the proximity of the base or bottom of the cavity is
compacted so as to prestress and densify the adjacent soil. Such a step of compaction is
of importance as the bottom portion of the cavity is required to withstand the forces
exerted on the aggregates during the step of ramming. Such aggregates normally
consisting of stone are introduced in a stepwise manner such as to form a plurality of
layers disposed along the vertical axis to constitute an aggregate pier, each layer being
formed by introduction of such aggregates and then subjected to a step of ramming by a
tamping tool. As the force exerted by the tamping tool is eventually transferred to the
lowermost layer, it would be apparent that if the adjoining and bottom soil of the
lowermost layer is unable to withstand such a force, the adjoining soil within the
cavity does not get stiffened. Thus, one of the important steps disclosed in U.S.
Patent No. 5,249,892 is of compacting the soil in the vicinity of the bottom portion.
Thereafter, a plurality of layers, each having a predetermined height is formed by
introducing stone aggregates and then causing a compaction of each layer by a tamping
tool. It would be apparent that the step of ramming with high energy level results in
increase in lateral pressures with a limiting value being equal to passive pressure.

The present invention is essentially concerned with a stabilization of the cavity.
OBJECTS OF INVENTION:
An object of this invention is to provide a method of stabilization of the cavity for
aggregate piers.
Another object of this invention is to propose a method of stabilization of the
cavity without imparting any additional force other than that known in the art.
Yet another object of this invention is to provide a method for stabilization of the
cavity which is efficient.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a method of stabilizing and stiffening
the base material of bottom bulb/cavity of engineered aggregate piers by mixing
aggregates with a pre-determined quantity of soil stabilizing material such as
calcium chloride, a solidifier/binder such as sodium silicate and a tackifier such
as chrome lignin, cement, lime, a mixture of lime and pozzolonic material such as
fly ash, krilium and a carrier for said materials.
DESCRIPTION OF INVENTION:
According to this invention there is provided a method of stabilizing the soil of at
least the base of the cavity for formation of engineered aggregate piers which
comprises in introducing with the aggregate forming the lower most layer,
introducing soil stabilizing agents such as calcium chloride, a solidifier/binder
such as sodium silicate with or without calcium chloride, a tackifier such as
chrome lignin, cement, lime, a mixture of lime and pozzolonic material such as
flyash with or without calcium chloride, krilium and a carrier for said agents.

Though the method of producing short aggregate piers is known from U.S. Patent No.
5,249,892, such a known process has the disadvantage of soil stability in the vicinity of
the base of the cavity. As described hereinabove, such a stability particularly at the base
of the cavity is of importance as the short aggregate piers disposed along the vertical
axis are supported on the bed or base of the cavity and consequentially any subsequent
displacement of the base or cavity wall forming the base portion can detrimentally affect
the stiffness characteristics of piers and matrix soil. Such a disadvantage is obviated by
the soil stabilization process of the present invention.
The soil stabilization process of the present invention comprises in a chemical treatment
of the soil with or without the known process of compacting the aggregates to densify
and laterally prestress the adjoining soil of the lowermost layer and, if required, that of
the walls of the cavity.
In accordance with this invention, the chemical treatment consists in introducing the
constituents individually or as an admixture.
The constituents comprise soil stabilizing agents such as calcium chloride and present
in an amount of 1-5% by weight of soil. The constituents further comprise a solidifier

or binder such as sodium silicate with or without calcium chloride and present in an
amount of 2 to 10%. Chrome lignin acts as a tackifier and present in an amount of
upto 10% by weight of soil and preferably 2 to 10%. The constituents further comprise
cement and/or hydrated lime which interacts with clay particles and binds the
particles. Lime is present in an amount of 2 to 4% by weight of soil. In the instance
of cement, it is present in an amount upto 15% by wt. of soil, and preferably 6 to 15%.
Pozzolonic material, such as flyash and lime is added in an amount of 2 to 5% in
combination or singularly with or without calcium chloride in an amount of 0.1 to 2%.
Resins such as vinsol or formaldehyde, may be added also as a constituent and present
in an amount of 1 to 10% by weight of soil. Such constituents are added individually or
as an admixture.
Reference is made herein to the constituents. Such constituents are introduced with a
carrier comprising a particulate material such as sand. Besides being a carrier, sand
has the additional advantage of filling the voids between adjacent aggregates and
thereby increasing the strength properties.

WE CLAIM;
1. A method of stabilizing and stiffening the base material of bottom
bulb/cavity of engineered aggregate piers by mixing aggregates with a
pre-determined quantity of soil stabilizing material such as calcium
chloride, a solidifier/binder such as sodium silicate and a tackifier such as
chrome lignin, cement, lime, a mixture of lime and pozzolonic material
such as fly ash, krilium and a carrier for said materials.
2. The method as claimed in claim 1, wherein calcium chloride is present in
an amount of 1 to 5% by wt. of soil.
3. The method as claimed in claim 1, wherein said pozzolonic material
comprises flyash and lime present in an amount of 2 to 5% by wt. of soil in
combination or singularly with or without calcium chloride.
4. The method as claimed in claim 1, wherein said cement is present in an
amount of upto 15% and preferably 6 to 15% by wt.
5. The method as claimed in claim 1, wherein said carrier is sand.
6. The method as claimed in claim 1, wherein said cement and /or hydrated
lime is present in an amount of 1 to 5% by wt. of soil.
7. The method as claimed in claim 1 wherein said binder or solidifier is
present in an amount of 2 to 5% by wt. of soil.

8. The method as claimed in claim 1 comprising resins such as vinsol or
formal dehyde.
9. The method as claimed in claim 1, wherein said tackifier is chrome lignin
and present in an amount of upto 1.0% by wt. of soil.
10. A method of stabilizing and stiffening the base material of bottom
bulb/cavity of engineered aggregate piers substantially as herein
described.
11. The method as claimed in claim 1, wherein the solidifier / binder such as
sodium silicate is with calcium chloride and the pozzolonic material such
as fly ash is with calcium chloride.
12. The method as claimed in claim 1, wherein the solidifier / binder such as
sodium silicate is without calcium chloride and the pozzolonic material
such as fly ash is without calcium chloride.

ABSTRACT

Title: A method of producing a cavity for formation of engineered aggregate piers.
A method of stabilizing and stiffening the base material of bottom bulb/cavity of
engineered aggregate piers by mixing aggregates with a pre-determined quantity
of soil stabilizing material such as calcium chloride, a solidifier/binder such as
sodium silicate and a tackifier such as chrome lignin, cement, lime, a mixture of
lime and pozzolonic material such as fly ash, krilium and a carrier for said
materials.