Related to my FYP2 (Undrained Shear Strength Of Soft Clay Installed in Encapsulated Bottom Ash Column)

1. © FKASA PROCEDIA CIVIL ENGINEERING | 2014
Undrained Shear Strength of Soft Clay Reinforced with
10mm and 16mm Diameter Single Encapsulated Bottom
Ash Columns
Suzillco Suki, Dr. Muzamir Hasan*
Abstract
Stone column is one of the most commonly used in soil improvement technique around the world which
capable to increase the bearing capacity of soft clay and able to reduce the settlement of superstructure
constructed on them. Due to its higher value of strength and stiffness, it can sustain larger proportion of
the applied load which improves the performance of foundation beds. The substantial amount of bottom
ash disposed in the landfills have causes a serious environment pollution. As the bottom ash is part of the
non-combustile residue of combustion and also the by-product produced in a furnace of the power plant.
Hence, by reutilize the bottom ash as granular material in vertical granular column, the cost of
construction can be reduced and able to achieve more sustainable development in construction industry
This paper focuses on the use of bottom ash which has the potential to be used as a substitution to
replace sand in the vertical granular column. This study aimed to determine the improvement in the shear
strength of soft clay after being reinforced with a single encapsulated bottom ash column. The first stage
of the study was determine the physical and mechanical properties of the material used such as soft clay
and bottom ash. The results shows that kaolin can be classified as silty soil while the properties of bottom
ash has relatively similar characteristic with sand. At the second stage, remoulded specimens of 50mm in
diameter and 100mm in height soft kaolin clay with single encapsulated bottom ash columns was
subsequently tested under Unconfined Compression Test. The diameter of the encapsulated bottom ash
column is 10mm and 16mm. It can be concluded that the shear strength parameters shows some
significant improvement on encased and non-encased bottom ash columns and were affected by the
diameter and height of the column.
KEYWORDS | soft soil, bottom ash, shear strength, geotextile
*Corresponding author: suzillcosuki@gmail.com | muzamir@ump.edu.my
INTRODUCTION
In Malaysia, rapid urbanisation and growth of
infrastructure has dramatically increased the
demand for land space. Meanwhile, soft soils
has created a challenge for the engineer
especially towards the construction industry
because of the characteristic of the soil usually
characterized by a low permeability and shear
strength together with a high compressibility and
low bearing capacity. Due to these factors, the
buildings that constructed on this type of soils
pose a formidable challenge to the engineer.
Soft clay is a problematic soil since it has low
bearing capacity, low permeability and high
compressibility characteristics. The weak soft
soil is not suitable for structure construction. So
ground improvement is necessary to modify and
improve the soil properties and increase the
shear strength of soft soil.
Bottom ash is produced as a result of burning
coal in a dry bottom pulverized coal boiler. The
basic properties of bottom ash are porous,
glassy and dark grey material with a grain size
similar to the sand or gravelly sand. Although
similar to natural aggregate, bottom ash is
lighter and more brittle and has a greater
resemble to cement clicker [1].
The initial design of foundation introduced as a
geotextile encased columns (GECs) which has
been successfully adopted and is well
established in engineering properties [2]. Similar

2. © FKASA PROCEDIA CIVIL ENGINEERING | 2014
concepts have been recently been introduced
and investigate in order to demonstrate the
effectiveness of geosynthetic encasement and
to improve the design methods [3].
This paper aimed to determining the
improvement made by the installation of
encapsulated BACs to the soft soil in small scale
modelling. A series of laboratory tests were
carried out to investigate whether the bottom
ash is suitable to be used in columns for ground
improvement technique.
The replacement of sand with bottom ash waste
reduces the usage on NRNMs while avoids the
future bottom ash landfill area. Bottom Ash also
classified under Scheduled Waste SW 104
(Environmental Quality Act) and by using this
material, it is more environmentally friendly and
sustainable thus avoids the use of natural
resources such as sand and gravel [4].
The study carried out had the objective as
follows:
i) To determine physical characteristics of
kaolin clay and bottom ash.
ii) To determine undrained shear strength
parameter of kaolin clay and the kaolin
clay reinforced with various dimensions
of single encapsulated bottom ash
columns.
iii) To correlate properties of soft clay
reinforced with single encapsulated
bottom ash columns.
METHODOLOGY
This paper includes the works and activities that
conducted in order to fulfil the objectives of the
project. The study starts with the identification of
the problem related to the bottom ash which had
causes an environmental issue when the large
amount of disposed bottom ash produced by the
power plant.
The soft clay was prepared using customised
compaction method and the BAC had been
installed in the soft clay using the replacement
method. The kaolin was air dried and then mixed
with 18.2 % of water which is the optimum
moisture content of the kaolin obtained from
standard compaction test. After uniformly mixing
the soil, it was poured into the customized steel
mould of 180 mm height and 50 mm internal
diameter and compacted in three layers. Each
layer had been compacted with five free fall
blows of a steel hammer. The kaolin was poured
into the customized mould in 3 layers. Every
layer was compacted with 5 free fall blows by
customized steel extruder. The customized
mould was designed so that the amount of clay
using inside it will be compressed into a 50mm
diameter and 100 mm high specimen. By using
this procedure, the uniformity of each specimen
could be maintained since the mass of the soil
and the volume of the mould are almost the
same.
One batch of kaolin specimen had twelve (12)
samples with 50 mm in diameter and 100 mm in
height. Each batch of kaolin specimen contains
the same penetration ratio, which is 0, 0.6, 0.8
and 1.0, but different diameter of columns and
area replacement ratio. Another batch of kaolin
specimen been encapsulated but have the same
penetration ratio with different diameter and
height. Unconfined compression test was
conducted to test every same penetration ratio
for four (4) times to obtain an average value.
The sample without any reinforcement of bottom
ash, which is of 0 penetration ratio, was
considered as the ‘controlled sample’ to
determine the shear strength of unreinforced
sample.
Figure 1 | Detailed column(s) arrangement for
diameter 10mm and 16mm

3. © FKASA PROCEDIA CIVIL ENGINEERING | 2014
RESULTS AND DISCUSSIONS
The laboratory tests carried out to identify
engineering properties of kaolin included
atterberg Limit test, specific gravity test, particle
size distribution test, compaction test, and
permeability test. Meanwhile, for the bottom ash,
the laboratory test performed included specific
gravity test, particle size distribution test, relative
density test, compaction test, permeability test
and direct shear test. Apart from the discussion
of the engineering properties of the materials
used in this project, the unconfined compression
test done on the 4 batches of soft kaolin clay
reinforced with single encapsulated bottom ash
with different diameters and penetration ratio to
determine the increment of shear strength are
discussed in this chapter as well.
Basic Properties
Basic properties tests has been conducted on
Kaolin Clay (S300) and Tanjung Bin Bottom
Ash. All the results related to the basic
properties were tabulated on Table 1 and Table
2.
Table 1 | Properties of Kaolin Clay (S300)
Table 2. Properties of Tanjung Bin Bottom Ash
Soft Clay Reinforced with Single
Encapsulated bottom Ash Column
Shear strength of soft clay reinforced with
bottom ash column was measured by
conducting the Unconfined Compression Test
(UCT). Besides that, the same test was
conducted on another batch of the bottom ash
column and was encapsulated with polyester
non-woven geotextile by FirbroTex. Various
results from the UCT has been tabulated for
’controlled sample’, samples reinforced with
various diameters for singular bottom ash at
different column penetration ratio and the
samples of encased bottom ash column.
Table 4 | Peak deviator stress and axial strain
from UCT for encased bottom ash columns
Area
Ratio,
Ac/As
(%)
Column
Height
Penetratin
g Ratio,
Hc/Hs
Shear
Strengt
h,Su
(kPa)
Average
Axial
Strain
(%)
0 0 8.93 2.69
4 0.6 11.78 1.97
0.8 14.75 2.29
1 12.65 1.84
10.24 0.6 11.29 1.96
0.8 14.48 2.42
1 13.27 1.87
Table 5 | Peak deviator stress and axial strain
from UCT for non-encased bottom ash columns
Area
Ratio,
Ac/As
(%)
Column
Height
Penetrating
Ratio, Hc/Hs
Shear
Strengt
h,Su
(kPa)
Average
Axial
Strain
(%)
0 0 8.93 2.69
4 0.6 10.63 2.09
0.8 12.61 2.16
1 11.67 2.29
10.24 0.6 10.30 2.09
0.8 11.75 2.33
1 11.30 2.27
Properties Results
Liquid Limit 36.47 %
Plastic Limit 27.70 %
Plastic Index 8.30 %
Specific Gravity 2.68
Maximum Dry Density 1.65mg/m3
Optimum moisture content 18.20%
Soil Classification (ASSHTO) A-4
Soil Classification (USCS) ML
Falling Head Permeability 8.89 x 10-12 m/sec
Properties Results
Soil Classification (ASSHTO) A-1-a
Specific Gravity 2.27
Maximum Dry Density 1.53mg/m3
Peak Friction Angle 38.83 º
Peak Cohesion 7.28 kPa
Constant Head Permeability 1.59 x 10-3 m/sec

4. © FKASA PROCEDIA CIVIL ENGINEERING | 2014
Figure 2 | Shear Strength versus height of
penetration ratio between non-encased and
encased bottom ash columns
From the graph, it shows the shear strength of
partially penetrating column for BAC is 10.63
kPa for height penetration ratio of 0.6 while for
the height of penetration of 0.8 is 12.61 kPa and
for the height of penetration of 1.0 is 11.67 kPa.
The same trend occur for the encasement of
BAC which showed some increase of shear
strength for all the height penetration compared
with the non-encased BAC.
Figure 3 | Shear Strength versus area
penetration ratio between non-encased and
encased bottom ash columns
Figure 4 | Improvement Shear strength
versus height over diameter of column
As shown in Figure 3, sample with fully
penetrating columns for area ratio of 4.00% and
10.24% the highest shear strength is 13.27
(10mm diameter group column) and 11.67 kPa
for the encapsulated bottom ash column.
To further study the possible influence of height
over diameter of column ratio to undrained shear
strength, the improvement of undrained shear
strength was plotted versus the height over
diameter of column ratio in Figure 4. Data by [5]
and [6] was plotted on the same figure in order
to compare with the current study. As proposed
by past researcher, “the critical column length”
which is indeed between 4 to 8 times the
diameters of column (Dc) was marked as the
blue area in the Figure 4.
CONCLUSION
From the study it has been shown that the
usage of bottom ash column to improve the
condition of soft soil has been fulfilled based on
the objective of the study. The performance of
smaller diameter bottom ash column is superior
to that of bigger diameter sand column. It is due
to the development of larger additional confining
stresses in smaller diameter reinforced columns.
The encasement of the bottom ash columns
significant improved the shear strength of the
kaolin clay.
REFERENCES
[1] Rogbeck, and Knutz. (1996). Coal bottom ash as
light fill material in construction. Waste
Management, 16(1-3) : 125-8.
[2] Raithel, M., Kampfert, H.G., Kirchner, and A.
(2002). Geotextile-encased columns (GEC) for
foundation of a dike on very soft soil. In
Proceedings of the Seventh International
Conference on Geosynthetics, Nice, France,
1025-1028.
[3] Sivakumar, V. M. (2004). Triaxial test on model
sand column in clay. Can. Geotech. J., 41, 299-31
[4] Ibrahim, M. H. (2012). Waste Management of Coal
Fired Power Plant Potential Utilization of Bottom
Ash, Malakoff. 10th Annual Waste Management
Conference & Exhibition.
[5] Hasan, M. (2013). Strength and Compressibility of
Soft Soil Reinforced with Bottom Ash Columns.
PhD. Thesis, Universiti Teknologi Malaysia
[6] Maakaroun, T., Najjar, S. S., & Sadek, S. (2009).
Effect of Sand Columns on the Undrained Load
Response of Soft Clays. Journal of Geotechnical
and Geoenviromental Engineering @ ASCE.