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Effect of deep chemical mixing columns on properties of surrounding soft clay.pdf

This study examines an alkaline material for improving soft clay soil. A series of tests, including unconfined compression strength, pH, undrained shear strength, electrical conductivity, and microstructural analysis, were conducted.

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Effect of deep chemical mixing columns
on properties of surrounding soft clay
&
1 Majid Bagherinia PhD
Lecturer, Civil Engineering Department, Engineering Faculty,
Ataturk University, Erzurum, Turkey (corresponding author:
mbagheriniaa@gmail.com)
&
2 Ahmet Şahin Zaimoğlu PhD
Professor, Civil Engineering Department, Engineering Faculty,
Ataturk University, Erzurum, Turkey
1 2
In the study reported in this paper, potassium hydroxide (KOH) was used as a chemical additive to improve some
engineering properties of low-plasticity clay. The experimental study was carried out in two stages. In the first stage,
potassium hydroxide was added to dry clay at different ratios, and samples were prepared for unconfined
compressive strength (UCS) testing. A scanning electron microscopic analysis was performed on some specimens to
monitor the effect of the additive on the clay. The second stage involved using the additive to form deep-mixed
columns in soft clay. Changes in the properties of the surrounding soft clay were measured at certain distances from
the edges of the columns by carrying out undrained shear strength, pH, electrical conductivity (EC) and water content
experiments. According to the test results, the maximum UCS of about 1173 kPa was obtained at a curing time of
28 d and with 15% additive. It was determined that the undrained shear strength, EC and pH values generally
increased in all curing times in the area near the edge of the columns with potassium hydroxide, while the water
content decreased.
Notation
a amount of binder
b binder ratio
C constant, determined by the angle between the
ground and the cone C = 0·8 at 30°C
Cu undrained shear strength
d diameter of column
g ground acceleration
i amount of cone penetration
k hydraulic conductivity
l length of column
m cone weight
p producing method
S specimen
t curing times
W water content
Wopt optimum water content
γdmax maximum dry unit weight
1. Introduction
The deep-mixing method (DMM) is one of the ground
improvement techniques used in the field. In this method, the
binder (cementitious and/or other materials) is injected in the
dry or wet form into the ground and blended together with
the soil particles. The binder is injected into the ground with a
hollow auger and mixed by turning with the cutting tools
located at the ends of the auger (Bruce and Bruce, 2003).
This method was first used by Intrusion-Prepakt Inc. in 1950
(FHW
A, 2000). In the Scandinavian countries, in the
mid-1970s, dry binder, in powder form, began to be applied
into the ground by air pressure in practice (Broms, 1975;
Broms and Boman, 1979). Lime and cement are used as the
most common binder according to the European standard. For
this reason, they have been termed ‘lime–cement columns’ and
the method is known as ‘Scandinavian dry deep mixing’ since
the late 1980s (CEN, 2005).
The effects of lime and cement on the soil properties, the
binder (lime and cement)/water ratio relation, curing times,
durability, strength and stiffness have been investigated by a
number of researchers (Ahnberg, 1996; Bergado and Lorenzo,
2005; Consoli et al., 2017; Consoli et al., 2018a, 2018b; Dias
et al., 2012; Jacobson et al., 2003; Lorenzo and Bergado, 2004,
2006; Porbaha et al., 1998, 2000). In recent years, apart from
traditional binders, research on fly ash, silica dust, sludge and
polymers has also become widespread in relation to the DMM
(Ahnberg, 2006; Ahnberg and Holm, 1996; Ajorloo, 2010;
Arasan et al., 2017; Bagherinia, 2013).
The geotechnical properties of soft clay soils can vary around
the lime–cement columns. It has been stated that the plastic
1
Cite this article
Bagherinia M and Zaimoğlu AŞ
Effect of deep chemical mixing columns on properties of surrounding soft clay.
Proceedings of the Institution of Civil Engineers – Ground Improvement,
https://doi.org/10.1680/jgrim.18.00108
Ground Improvement
Research Article
Paper 1800108
Received 03/11/2018;
Accepted 24/05/2019
ICE Publishing: All rights reserved
Keywords: columns/composite
structures/geotechnical engineering
Proceedings of the Institution of Civil Engineers - Ground Improvement
limit (PL), pH, electrical conductivity (EC), Cu and cation
concentration are increased when the liquidity index and water
content of soft clay around the lime–cement columns are
reduced (Shen et al., 2003a, 2003b, 2008; Zhang and Xu,
1996). Larsson et al. (2009) determined that the surrounding
soft clay Cu value is significantly influenced by the migration
of the calcium (Ca2+
), sodium (Na+
) and potassium (K+
) ions
from deep-mixed lime–cement columns.
In studies by Cristelo et al. (2013) and Sargent et al. (2013),
fly ash and blast furnace slag were activated by sodium
hydroxide as an alkali material for the purpose of stabilising
soft soils. Miao et al. (2017), on improving the swelling
potential of soils, used potassium hydroxide (chemical formula
KOH) and calcium hydroxide (Ca(OH)2) as alkali materials
and also used volcanic ash as binder. According to the results
of the test, the plasticity index (PI) and swelling potential of
the soil, respectively, reduced from 34·8 to 14·2% and 15·7 to
2·3–4·2%.
There is limited literature on the improvement of the engineer-
ing properties of clay with high water content (liquid limit
(LL) consistency) by installing columns using potassium
hydroxide as the binder and the DMM. In this study, potass-
ium hydroxide is used as a chemical additive to improve some
engineering properties of low-plasticity clay (CL).
2. Materials and methods
2.1 Soft clay and binder
The CL used in the experiments was provided by a private
firm (Ankara, Turkey). Properties of the clay are given in
Table 1. The Atterberg limits of the clay (LL, PL), maximum
dry density, optimum moisture content and hydraulic conduc-
tivity measurements are, respectively, according to the ASTM
D 4318-17 (ASTM, 2017), ASTM D 1557-12 (ASTM, 2012)
and ASTM D 5084-00 (ASTM, 2000) standards.
In this study, X-ray diffraction (XRD) was used for a micro-
structure analysis of the CL clay (Figure 1). XRD analysis was
conducted on the powder form of the CL clay with a
Panalytical Empyrean model device. The specimen was
scanned for 2θ values ranging from 5 to 75°, a step length of
0·02°, a scan rate of 2°/min and a slot width of 0·3 mm.
According to the analysis results, the CL clay consists of
kaolinite, illite and quartz minerals.
In the experimental study, tap water was used for the prep-
aration of the specimens. Some elements found in the tap
water are mentioned in Table 2. Potassium hydroxide was used
as an additive in the experiments. Potassium hydroxide in the
solid form is odourless and white in colour and it is soluble in
water, alcohol and glycerine. It absorbs moisture in the air and
slowly dissolves, and an exothermic reaction occurs when it is
soluble in water. It is used in agriculture, industrial products,
the cleaning sector, the medical field and many other places.
Some chemical properties of potassium hydroxide obtained
from a private company are given in Table 3.
2.2 Stabilised CL specimen preparation and testing
At the first stage, the solid form of potassium hydroxide at
different ratios (5, 10, 15 and 20% according to the dry weight
of the CL clay) was added to dry CL and mixed by hand until
homogeneous, then the mixture was placed in a mechanical
Table 1. Properties of the untreated CL
CL
EC 0·8–1·0 ms/cm
Cu 0·55 kPa
pH 6–6·5
UCS in 28 d 430 kPa
LL: % 40
PL: % 22
PI: % 18
Wopt: % 16
γd max: kN/m3
18·5
k: cm/s 6·9  10−7
10 20 30 40
Intensity
2θ: degrees
50 60 70
k
I I I
I
Q
Q
Q
Q Q Q
Q
Q
Q Q
k
k
k k kk
k = kaolinite
I = illite
Q = quartz
Raw CL
Figure 1. XRD diffractograms of unstabilised CL
Table 2. Chemical analysis of tap water
mg/l
Fluoride 0·26–0·35
Chloride 12·46–13·13
Nitrate 18·08–23·21
Sulfate 27·14–27·96
Sodium 6·40–6·52
Potassium 3·42–3·44
Magnesium 13·98–14·04
Calcium 50·10–50·59
2
Ground Improvement Effect of deep chemical mixing columns
on properties of surrounding soft clay
Bagherinia and Zaimoğlu
Proceedings of the Institution of Civil Engineers - Ground Improvement
stirrer and the LL water content of CL (w = 40%) was added
to the mixture. The mixture was mixed at a speed of 150 r/min
for 10 min. This mixture was carefully filled in three layers
into cylindrical moulds 38 mm in diameter and 76 mm in
height. To prevent air bubbles at the edge of the mould, it was
lightly vibrated by hand. The inside of the moulds was lubri-
cated with a thin film layer to reduce friction. The prepared
specimens were kept in the curing room for 7, 14, 28, 56 and
112 d under 90% moisture and 20 ± 3°C conditions. The prep-
aration of the specimens and the curing conditions were con-
ducted according to Euro Soil Stab (EC, 2002) and Arasan
et al. (2017).
(a) Unconfined compressive strength (UCS) test. At the end
of the curing times, UCS tests were conducted on the
specimens, in accordance with the ASTM
D2166/D2166M (ASTM, 2016) standard.
(b) Scanning electron microscope (SEM) analysis. SEM was
performed for the maximum value obtained from the
UCS test. For this, the specimen in the powder form was
put on the specimen plate with a carbon band adhered.
As the specimen is not a conductive material, it tends
to be charged when it is scanned, so it is coated with
gold, a conductive material, at a thickness of 5 nm.
Vacuum treatment was carried out for 3 min after the
coating process. Then it was placed in the specimen
holder and analysed using a Zeiss brand Sigma 300
device.
2.3 Deep-mixing specimen preparation and testing
At the second stage, the CL clay was prepared with 40% water
content and then placed in three layers in polyvinyl chloride
(PVC) moulds 100 mm in diameter and 110 mm in height. For
installation of columns by the DMM, a system consisting of
three parts was used: two hollow tubes with 30 and 6 mm dia.,
150 mm height and 0·5 mm wall thickness, and a 5 mm dia.
and 160 mm high filled cylinder rod. For the application of
the column, the rod with a dia. of 5 mm was placed in the
6 mm dia. tube and they were inserted into the ground
together. Once the rod had been removed, the potassium
hydroxide was placed in the tube that remained on the ground
(Kosche, 2004; Larsson et al., 2009). When the tube was
removed, the 30 mm dia. tube was inserted into the ground to
centre the potassium hydroxide placed on it. The potassium
hydroxide remaining in the tube was mixed with soft clay until
it became homogeneous and the tube was then taken out.
A handmade auger was used for the mixing process. Thus, a
column was formed in accordance with the DMM with a
diameter of 30 mm and a height of 110 mm. Table 4 shows the
manufacturing data of the columns. A schematic view of
the experiment is given in Figure 2 and the preparation of the
specimens is shown in Figure 3. The prepared specimens
were wrapped with a plastic cover to prevent the loss of
the water content and were kept under curing conditions with
40% constant moisture and 20 ± 3°C constant temperature
for 28, 56 and 112 d. At the end of the curing period,
Cu (ISO/TS 17892-6: (CEN, 2004); Larsson et al., 2009;
Pham, 2012), pH (ASTM D4972 (ASTM, 2013)), EC
(Rayment and Higginson, 1992) and water content (ASTM
D2216 (ASTM, 2016)) tests were carried out on the surround-
ing columns.
(a) Undrained shear strength (Cu) test: Cu values were
obtained by the fall cone penetration test for the purpose
of determining the improvement in the strength
properties of the soft clay at the edge of the column.
Cu values were determined according to relation 1
(Hansbo, 1957).
1: Cu ¼ Cg
m
i2
(b) pH test: The pH test was carried out at a certain distance
from the edge of the column to determine the change in
the pH value of the soft clay. For this reason, 10 g of
air-dried soil passing sieve number 10 was taken and
placed in a glass container, followed by 10 ml of distilled
water and the mixture stirred every 10 min for the
duration of 1 h. After 1 h, the pH of the mixture was
read using a pH meter.
Table 3. Chemical properties of potassium hydroxide
Chemical formula KOH
Molar mass 56·1056 g/mol
Melting point 406°C
Boiling point 1327°C
pH 14
Density 2·044 g/cm3
Soluble in Water, alcohol, glycerol
Table 4. Column installation data
Number d: mm l: mm b: % a: kg/m3
Method of production t: d
1 30 110 5 63·7 Dry 28, 56, 112
2 30 110 10 127·4 Dry 28, 56, 112
3 30 110 15 191·1 Dry 28, 56, 112
4 30 110 20 254·8 Dry 28, 56, 112
d, diameter of column; l, length of column; b, binder ratio; a, amount of binder; t, curing days
3
Ground Improvement Effect of deep chemical mixing columns
on properties of surrounding soft clay
Bagherinia and Zaimoğlu
Proceedings of the Institution of Civil Engineers - Ground Improvement
(c) Electrical conductivity test. The EC test was carried out
at a certain distance from the edge of the column to
determine the change in the EC value of the soft clay.
In determining the EC for the soft clay, a test was carried
out as described in list point (b), but the clay:distilled
water ratio was 1 : 2·5 (Rayment and Higginson, 1992).
1 2 3
4 5 6
Soft clay
Template
5 mm rod
6 mm tube
Guide tube
Dry potassium
hydroxide
6 mm tube
Pull out
30 mm tube
Guide tube
Handmade
auger
Manufactured column 30 mm dia. column
Soft clay
Transition zone
Figure 2. Schematic view of chemical column installation
(a) (b) (c)
Figure 3. Preparation of specimens: (a) CL at 40% water content into the moulds; (b) column installation with DMM; (c) covering the
specimens with plastic cover and waiting in the curing room
4
Ground Improvement Effect of deep chemical mixing columns
on properties of surrounding soft clay
Bagherinia and Zaimoğlu
Proceedings of the Institution of Civil Engineers - Ground Improvement
(d) Water content test (w). The water content test was
carried out at a certain distance from the edge of the
column to determine the change in the value of w of
the soft clay.
3. Results and discussion
3.1 UCS test results
According to the UCS test, the potassium hydroxide
ratio–UCS–curing time correlations are shown in Figures 4(a)
and 4(b). However, the average values of the UCS test are
given in Table 5. It can be seen that the UCS values generally
increase until 28 d of curing, but after this time, the UCS
values decrease. The reason for this is that the hydroxyl group
and potassium react with water in the body of the soft clay
and blend the soil particles together with reducing the water
content. This process caused the UCS to increase up to 28 d.
However, by increasing the curing time, the potassium and
hydroxyl group tended to migrate. They slowly absorbed the
moisture in the curing room as a result of the accumulation on
the surface of the specimen, resulting in the deposition of
water on the outer surface of the specimen and a partial
reduction of the UCS value. Figures 4(a) and 4(b) show that
the UCS value decreases on increasing the potassium hydrox-
ide ratio (especially after 15% potassium hydroxide). This is
due to the increase in porosity of the specimen due to the
increment of the additive ratio.
It was determined that the maximum UCS value was about
1173 kPa, obtained from 28 d curing of the specimen prepared
with 15% potassium hydroxide. With respect to the literature,
it is stated that the UCS value of the soil improved by
deep mixing is about 0·2–5·0 MPa (200–5000 kPa). For the
UCS of cohesive soils with 28 d of curing, values of
0·2–2·0 MPa (200–2000 kPa) were obtained (Bruce and Bruce,
2003).
7
14
28
56
112
0
100
200
300
400
500
600
5
10
267
179
435
385
440
537 450
472
350
399·5
UCS:
kPa
7
14
28
56
112
0
200
400
600
800
1000
1200
15
20
170
91
362
323
1173
678
1046
540
903
459
UCS:
kPa
Curing time: d
Curing time: d
P
o
t
a
s
s
i
u
m
h
y
d
r
o
x
i
d
e
r
a
t
i
o
:
%
P
o
t
a
s
s
i
u
m
h
y
d
r
o
x
i
d
e
r
a
t
i
o
:
%
(a)
(b)
Figure 4. Binder ratio–UCS−curing time correlations test result: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium
hydroxide ratio
5
Ground Improvement Effect of deep chemical mixing columns
on properties of surrounding soft clay
Bagherinia and Zaimoğlu
Proceedings of the Institution of Civil Engineers - Ground Improvement
3.2 SEM test results
Figure 5(a) shows the SEM image of raw CL. The internal
structure of the CL appears to be porous, the plates are distant
from each other, and there are microvoids between them. In
Figure 5(b), it is seen that the structure of raw potassium
hydroxide has a flat, square, non-porous (filled) structure. With
the powder form of potassium hydroxide, it was not possible to
obtain images from closer distances as it starts to melt by
sucking up moisture in the air (starting to burn) and may
damage the device. In Figure 5(c), the image of the CL + 15%
potassium hydroxide specimen (28 d curing) is shown. It is seen
that lumps form and agglomerated structures are obtained. As
can be seen from the figure, by adding 15% potassium hydrox-
ide to CL, the volume of the voids decreases greatly, the clay
minerals stick together and a homogeneous structure is
obtained.
3.3 Cu test results
Figure 6 shows the distance–Cu relation at different curing
times. By examining Figures 6(a) and 6(b) together, it can be
seen that the Cu value is increased near the edge of the column,
but at a distance from the edge of the column, the Cu value is
decreased. This is thought to be because, with greater distance
from the edge of the column, the interaction between the pot-
assium hydroxide and the CL clay is decreased. In other words,
near the edge of the column periphery, the hydroxyl group and
potassium migrated with ease and caused the increase of the Cu
value of the clay. However, these migration waves start to
decrease in parts away from the column edge and this caused
the decrease in the Cu value. The physical, mechanical and
chemical properties of the clay in the effective area or transition
zone surrounding the deep-mixing columns vary depending on
the curing time. In the transition zone, especially at distances
close to the column, undrained shear strength (Cu) increases
with increasing curing time (Larsson et al., 2009; Shen et al.,
2003a, 2003b). In Figures 6(a) and 6(b), it is also seen that the
increase of the curing time leads to the increase of the Cu value
near the edge of the column.
3.4 pH test results
The pH values of the CL clay taken from the edge of the
column are illustrated in Figures 7(a) and 7(b). In both figures,
as the potassium hydroxide ratio increases, the pH value of the
CL clay increases, especially near the column. In the same way,
the pH value of the CL clay increases with the increase of the
curing time. These increases are clearly visible near the column.
A low pH value indicates flocculation and loosening on the
ground, while a high pH value indicates dispersion and firm
ground (Vural, 2012). According to the pH test results and the
Vural (2012) definition, increasing the pH value of the soft clay
at the edge of the column means improvement of the clay prop-
erties. This is also confirmed by some other researchers (Larsson
et al., 2009; Shen et al., 2003a, 2003b; Tonoz et al., 2003).
3.5 EC test results
In this study, EC was also investigated on the CL clay surround-
ing the deep-mixing columns. The results of the distance–EC
relation are shown in Figures 8(a) and 8(b). In both figures, it is
Table 5. Average values of the UCS test
Number
Potassium
hydroxide
ratio: %
UCS: kPa UCS: kPa UCS: kPa UCS: kPa UCS: kPa
7 d 14 d 28 d 56 d 112 d
S1a
5 253·6 422 451·3 438 352
S2 5 269 438 442·8 459 346
S3 5 278 445 426 453 352
Average values
266·87 ≈ 267 435 440·03 ≈ 440 450 350
S1 10 187 368 536 445 411
S2 10 173 394·6 540 483 372
S3 10 176 391 535 488 415·5
Average values
178·67 ≈ 179 384·53 ≈ 385 537 472 399·5
S1 15 159·8 360 1150·4 1025·2 905
S2 15 181 357·5 1190 1038 891
S3 15 168 368·3 1178 1074 913
Average values
169·6 ≈ 170 361·93 ≈ 362 1172·8 ≈ 1173 1045·7 ≈ 1046 903
S1 20 83 330 683 573 458
S2 20 104 314 671·3 549 463
S3 20 85·5 324·4 679 498 456
Average values
90·83 ≈ 91 322·8 ≈ 323 677·77 ≈ 678 540 459
a
S = specimen
6
Ground Improvement Effect of deep chemical mixing columns
on properties of surrounding soft clay
Bagherinia and Zaimoğlu
Proceedings of the Institution of Civil Engineers - Ground Improvement
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Effect of deep chemical mixing columns on properties of surrounding soft clay.pdf

  • 1. Effect of deep chemical mixing columns on properties of surrounding soft clay & 1 Majid Bagherinia PhD Lecturer, Civil Engineering Department, Engineering Faculty, Ataturk University, Erzurum, Turkey (corresponding author: mbagheriniaa@gmail.com) & 2 Ahmet Şahin Zaimoğlu PhD Professor, Civil Engineering Department, Engineering Faculty, Ataturk University, Erzurum, Turkey 1 2 In the study reported in this paper, potassium hydroxide (KOH) was used as a chemical additive to improve some engineering properties of low-plasticity clay. The experimental study was carried out in two stages. In the first stage, potassium hydroxide was added to dry clay at different ratios, and samples were prepared for unconfined compressive strength (UCS) testing. A scanning electron microscopic analysis was performed on some specimens to monitor the effect of the additive on the clay. The second stage involved using the additive to form deep-mixed columns in soft clay. Changes in the properties of the surrounding soft clay were measured at certain distances from the edges of the columns by carrying out undrained shear strength, pH, electrical conductivity (EC) and water content experiments. According to the test results, the maximum UCS of about 1173 kPa was obtained at a curing time of 28 d and with 15% additive. It was determined that the undrained shear strength, EC and pH values generally increased in all curing times in the area near the edge of the columns with potassium hydroxide, while the water content decreased. Notation a amount of binder b binder ratio C constant, determined by the angle between the ground and the cone C = 0·8 at 30°C Cu undrained shear strength d diameter of column g ground acceleration i amount of cone penetration k hydraulic conductivity l length of column m cone weight p producing method S specimen t curing times W water content Wopt optimum water content γdmax maximum dry unit weight 1. Introduction The deep-mixing method (DMM) is one of the ground improvement techniques used in the field. In this method, the binder (cementitious and/or other materials) is injected in the dry or wet form into the ground and blended together with the soil particles. The binder is injected into the ground with a hollow auger and mixed by turning with the cutting tools located at the ends of the auger (Bruce and Bruce, 2003). This method was first used by Intrusion-Prepakt Inc. in 1950 (FHW A, 2000). In the Scandinavian countries, in the mid-1970s, dry binder, in powder form, began to be applied into the ground by air pressure in practice (Broms, 1975; Broms and Boman, 1979). Lime and cement are used as the most common binder according to the European standard. For this reason, they have been termed ‘lime–cement columns’ and the method is known as ‘Scandinavian dry deep mixing’ since the late 1980s (CEN, 2005). The effects of lime and cement on the soil properties, the binder (lime and cement)/water ratio relation, curing times, durability, strength and stiffness have been investigated by a number of researchers (Ahnberg, 1996; Bergado and Lorenzo, 2005; Consoli et al., 2017; Consoli et al., 2018a, 2018b; Dias et al., 2012; Jacobson et al., 2003; Lorenzo and Bergado, 2004, 2006; Porbaha et al., 1998, 2000). In recent years, apart from traditional binders, research on fly ash, silica dust, sludge and polymers has also become widespread in relation to the DMM (Ahnberg, 2006; Ahnberg and Holm, 1996; Ajorloo, 2010; Arasan et al., 2017; Bagherinia, 2013). The geotechnical properties of soft clay soils can vary around the lime–cement columns. It has been stated that the plastic 1 Cite this article Bagherinia M and Zaimoğlu AŞ Effect of deep chemical mixing columns on properties of surrounding soft clay. Proceedings of the Institution of Civil Engineers – Ground Improvement, https://doi.org/10.1680/jgrim.18.00108 Ground Improvement Research Article Paper 1800108 Received 03/11/2018; Accepted 24/05/2019 ICE Publishing: All rights reserved Keywords: columns/composite structures/geotechnical engineering Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 2. limit (PL), pH, electrical conductivity (EC), Cu and cation concentration are increased when the liquidity index and water content of soft clay around the lime–cement columns are reduced (Shen et al., 2003a, 2003b, 2008; Zhang and Xu, 1996). Larsson et al. (2009) determined that the surrounding soft clay Cu value is significantly influenced by the migration of the calcium (Ca2+ ), sodium (Na+ ) and potassium (K+ ) ions from deep-mixed lime–cement columns. In studies by Cristelo et al. (2013) and Sargent et al. (2013), fly ash and blast furnace slag were activated by sodium hydroxide as an alkali material for the purpose of stabilising soft soils. Miao et al. (2017), on improving the swelling potential of soils, used potassium hydroxide (chemical formula KOH) and calcium hydroxide (Ca(OH)2) as alkali materials and also used volcanic ash as binder. According to the results of the test, the plasticity index (PI) and swelling potential of the soil, respectively, reduced from 34·8 to 14·2% and 15·7 to 2·3–4·2%. There is limited literature on the improvement of the engineer- ing properties of clay with high water content (liquid limit (LL) consistency) by installing columns using potassium hydroxide as the binder and the DMM. In this study, potass- ium hydroxide is used as a chemical additive to improve some engineering properties of low-plasticity clay (CL). 2. Materials and methods 2.1 Soft clay and binder The CL used in the experiments was provided by a private firm (Ankara, Turkey). Properties of the clay are given in Table 1. The Atterberg limits of the clay (LL, PL), maximum dry density, optimum moisture content and hydraulic conduc- tivity measurements are, respectively, according to the ASTM D 4318-17 (ASTM, 2017), ASTM D 1557-12 (ASTM, 2012) and ASTM D 5084-00 (ASTM, 2000) standards. In this study, X-ray diffraction (XRD) was used for a micro- structure analysis of the CL clay (Figure 1). XRD analysis was conducted on the powder form of the CL clay with a Panalytical Empyrean model device. The specimen was scanned for 2θ values ranging from 5 to 75°, a step length of 0·02°, a scan rate of 2°/min and a slot width of 0·3 mm. According to the analysis results, the CL clay consists of kaolinite, illite and quartz minerals. In the experimental study, tap water was used for the prep- aration of the specimens. Some elements found in the tap water are mentioned in Table 2. Potassium hydroxide was used as an additive in the experiments. Potassium hydroxide in the solid form is odourless and white in colour and it is soluble in water, alcohol and glycerine. It absorbs moisture in the air and slowly dissolves, and an exothermic reaction occurs when it is soluble in water. It is used in agriculture, industrial products, the cleaning sector, the medical field and many other places. Some chemical properties of potassium hydroxide obtained from a private company are given in Table 3. 2.2 Stabilised CL specimen preparation and testing At the first stage, the solid form of potassium hydroxide at different ratios (5, 10, 15 and 20% according to the dry weight of the CL clay) was added to dry CL and mixed by hand until homogeneous, then the mixture was placed in a mechanical Table 1. Properties of the untreated CL CL EC 0·8–1·0 ms/cm Cu 0·55 kPa pH 6–6·5 UCS in 28 d 430 kPa LL: % 40 PL: % 22 PI: % 18 Wopt: % 16 γd max: kN/m3 18·5 k: cm/s 6·9 10−7 10 20 30 40 Intensity 2θ: degrees 50 60 70 k I I I I Q Q Q Q Q Q Q Q Q Q k k k k kk k = kaolinite I = illite Q = quartz Raw CL Figure 1. XRD diffractograms of unstabilised CL Table 2. Chemical analysis of tap water mg/l Fluoride 0·26–0·35 Chloride 12·46–13·13 Nitrate 18·08–23·21 Sulfate 27·14–27·96 Sodium 6·40–6·52 Potassium 3·42–3·44 Magnesium 13·98–14·04 Calcium 50·10–50·59 2 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 3. stirrer and the LL water content of CL (w = 40%) was added to the mixture. The mixture was mixed at a speed of 150 r/min for 10 min. This mixture was carefully filled in three layers into cylindrical moulds 38 mm in diameter and 76 mm in height. To prevent air bubbles at the edge of the mould, it was lightly vibrated by hand. The inside of the moulds was lubri- cated with a thin film layer to reduce friction. The prepared specimens were kept in the curing room for 7, 14, 28, 56 and 112 d under 90% moisture and 20 ± 3°C conditions. The prep- aration of the specimens and the curing conditions were con- ducted according to Euro Soil Stab (EC, 2002) and Arasan et al. (2017). (a) Unconfined compressive strength (UCS) test. At the end of the curing times, UCS tests were conducted on the specimens, in accordance with the ASTM D2166/D2166M (ASTM, 2016) standard. (b) Scanning electron microscope (SEM) analysis. SEM was performed for the maximum value obtained from the UCS test. For this, the specimen in the powder form was put on the specimen plate with a carbon band adhered. As the specimen is not a conductive material, it tends to be charged when it is scanned, so it is coated with gold, a conductive material, at a thickness of 5 nm. Vacuum treatment was carried out for 3 min after the coating process. Then it was placed in the specimen holder and analysed using a Zeiss brand Sigma 300 device. 2.3 Deep-mixing specimen preparation and testing At the second stage, the CL clay was prepared with 40% water content and then placed in three layers in polyvinyl chloride (PVC) moulds 100 mm in diameter and 110 mm in height. For installation of columns by the DMM, a system consisting of three parts was used: two hollow tubes with 30 and 6 mm dia., 150 mm height and 0·5 mm wall thickness, and a 5 mm dia. and 160 mm high filled cylinder rod. For the application of the column, the rod with a dia. of 5 mm was placed in the 6 mm dia. tube and they were inserted into the ground together. Once the rod had been removed, the potassium hydroxide was placed in the tube that remained on the ground (Kosche, 2004; Larsson et al., 2009). When the tube was removed, the 30 mm dia. tube was inserted into the ground to centre the potassium hydroxide placed on it. The potassium hydroxide remaining in the tube was mixed with soft clay until it became homogeneous and the tube was then taken out. A handmade auger was used for the mixing process. Thus, a column was formed in accordance with the DMM with a diameter of 30 mm and a height of 110 mm. Table 4 shows the manufacturing data of the columns. A schematic view of the experiment is given in Figure 2 and the preparation of the specimens is shown in Figure 3. The prepared specimens were wrapped with a plastic cover to prevent the loss of the water content and were kept under curing conditions with 40% constant moisture and 20 ± 3°C constant temperature for 28, 56 and 112 d. At the end of the curing period, Cu (ISO/TS 17892-6: (CEN, 2004); Larsson et al., 2009; Pham, 2012), pH (ASTM D4972 (ASTM, 2013)), EC (Rayment and Higginson, 1992) and water content (ASTM D2216 (ASTM, 2016)) tests were carried out on the surround- ing columns. (a) Undrained shear strength (Cu) test: Cu values were obtained by the fall cone penetration test for the purpose of determining the improvement in the strength properties of the soft clay at the edge of the column. Cu values were determined according to relation 1 (Hansbo, 1957). 1: Cu ¼ Cg m i2 (b) pH test: The pH test was carried out at a certain distance from the edge of the column to determine the change in the pH value of the soft clay. For this reason, 10 g of air-dried soil passing sieve number 10 was taken and placed in a glass container, followed by 10 ml of distilled water and the mixture stirred every 10 min for the duration of 1 h. After 1 h, the pH of the mixture was read using a pH meter. Table 3. Chemical properties of potassium hydroxide Chemical formula KOH Molar mass 56·1056 g/mol Melting point 406°C Boiling point 1327°C pH 14 Density 2·044 g/cm3 Soluble in Water, alcohol, glycerol Table 4. Column installation data Number d: mm l: mm b: % a: kg/m3 Method of production t: d 1 30 110 5 63·7 Dry 28, 56, 112 2 30 110 10 127·4 Dry 28, 56, 112 3 30 110 15 191·1 Dry 28, 56, 112 4 30 110 20 254·8 Dry 28, 56, 112 d, diameter of column; l, length of column; b, binder ratio; a, amount of binder; t, curing days 3 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 4. (c) Electrical conductivity test. The EC test was carried out at a certain distance from the edge of the column to determine the change in the EC value of the soft clay. In determining the EC for the soft clay, a test was carried out as described in list point (b), but the clay:distilled water ratio was 1 : 2·5 (Rayment and Higginson, 1992). 1 2 3 4 5 6 Soft clay Template 5 mm rod 6 mm tube Guide tube Dry potassium hydroxide 6 mm tube Pull out 30 mm tube Guide tube Handmade auger Manufactured column 30 mm dia. column Soft clay Transition zone Figure 2. Schematic view of chemical column installation (a) (b) (c) Figure 3. Preparation of specimens: (a) CL at 40% water content into the moulds; (b) column installation with DMM; (c) covering the specimens with plastic cover and waiting in the curing room 4 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 5. (d) Water content test (w). The water content test was carried out at a certain distance from the edge of the column to determine the change in the value of w of the soft clay. 3. Results and discussion 3.1 UCS test results According to the UCS test, the potassium hydroxide ratio–UCS–curing time correlations are shown in Figures 4(a) and 4(b). However, the average values of the UCS test are given in Table 5. It can be seen that the UCS values generally increase until 28 d of curing, but after this time, the UCS values decrease. The reason for this is that the hydroxyl group and potassium react with water in the body of the soft clay and blend the soil particles together with reducing the water content. This process caused the UCS to increase up to 28 d. However, by increasing the curing time, the potassium and hydroxyl group tended to migrate. They slowly absorbed the moisture in the curing room as a result of the accumulation on the surface of the specimen, resulting in the deposition of water on the outer surface of the specimen and a partial reduction of the UCS value. Figures 4(a) and 4(b) show that the UCS value decreases on increasing the potassium hydrox- ide ratio (especially after 15% potassium hydroxide). This is due to the increase in porosity of the specimen due to the increment of the additive ratio. It was determined that the maximum UCS value was about 1173 kPa, obtained from 28 d curing of the specimen prepared with 15% potassium hydroxide. With respect to the literature, it is stated that the UCS value of the soil improved by deep mixing is about 0·2–5·0 MPa (200–5000 kPa). For the UCS of cohesive soils with 28 d of curing, values of 0·2–2·0 MPa (200–2000 kPa) were obtained (Bruce and Bruce, 2003). 7 14 28 56 112 0 100 200 300 400 500 600 5 10 267 179 435 385 440 537 450 472 350 399·5 UCS: kPa 7 14 28 56 112 0 200 400 600 800 1000 1200 15 20 170 91 362 323 1173 678 1046 540 903 459 UCS: kPa Curing time: d Curing time: d P o t a s s i u m h y d r o x i d e r a t i o : % P o t a s s i u m h y d r o x i d e r a t i o : % (a) (b) Figure 4. Binder ratio–UCS−curing time correlations test result: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium hydroxide ratio 5 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 6. 3.2 SEM test results Figure 5(a) shows the SEM image of raw CL. The internal structure of the CL appears to be porous, the plates are distant from each other, and there are microvoids between them. In Figure 5(b), it is seen that the structure of raw potassium hydroxide has a flat, square, non-porous (filled) structure. With the powder form of potassium hydroxide, it was not possible to obtain images from closer distances as it starts to melt by sucking up moisture in the air (starting to burn) and may damage the device. In Figure 5(c), the image of the CL + 15% potassium hydroxide specimen (28 d curing) is shown. It is seen that lumps form and agglomerated structures are obtained. As can be seen from the figure, by adding 15% potassium hydrox- ide to CL, the volume of the voids decreases greatly, the clay minerals stick together and a homogeneous structure is obtained. 3.3 Cu test results Figure 6 shows the distance–Cu relation at different curing times. By examining Figures 6(a) and 6(b) together, it can be seen that the Cu value is increased near the edge of the column, but at a distance from the edge of the column, the Cu value is decreased. This is thought to be because, with greater distance from the edge of the column, the interaction between the pot- assium hydroxide and the CL clay is decreased. In other words, near the edge of the column periphery, the hydroxyl group and potassium migrated with ease and caused the increase of the Cu value of the clay. However, these migration waves start to decrease in parts away from the column edge and this caused the decrease in the Cu value. The physical, mechanical and chemical properties of the clay in the effective area or transition zone surrounding the deep-mixing columns vary depending on the curing time. In the transition zone, especially at distances close to the column, undrained shear strength (Cu) increases with increasing curing time (Larsson et al., 2009; Shen et al., 2003a, 2003b). In Figures 6(a) and 6(b), it is also seen that the increase of the curing time leads to the increase of the Cu value near the edge of the column. 3.4 pH test results The pH values of the CL clay taken from the edge of the column are illustrated in Figures 7(a) and 7(b). In both figures, as the potassium hydroxide ratio increases, the pH value of the CL clay increases, especially near the column. In the same way, the pH value of the CL clay increases with the increase of the curing time. These increases are clearly visible near the column. A low pH value indicates flocculation and loosening on the ground, while a high pH value indicates dispersion and firm ground (Vural, 2012). According to the pH test results and the Vural (2012) definition, increasing the pH value of the soft clay at the edge of the column means improvement of the clay prop- erties. This is also confirmed by some other researchers (Larsson et al., 2009; Shen et al., 2003a, 2003b; Tonoz et al., 2003). 3.5 EC test results In this study, EC was also investigated on the CL clay surround- ing the deep-mixing columns. The results of the distance–EC relation are shown in Figures 8(a) and 8(b). In both figures, it is Table 5. Average values of the UCS test Number Potassium hydroxide ratio: % UCS: kPa UCS: kPa UCS: kPa UCS: kPa UCS: kPa 7 d 14 d 28 d 56 d 112 d S1a 5 253·6 422 451·3 438 352 S2 5 269 438 442·8 459 346 S3 5 278 445 426 453 352 Average values 266·87 ≈ 267 435 440·03 ≈ 440 450 350 S1 10 187 368 536 445 411 S2 10 173 394·6 540 483 372 S3 10 176 391 535 488 415·5 Average values 178·67 ≈ 179 384·53 ≈ 385 537 472 399·5 S1 15 159·8 360 1150·4 1025·2 905 S2 15 181 357·5 1190 1038 891 S3 15 168 368·3 1178 1074 913 Average values 169·6 ≈ 170 361·93 ≈ 362 1172·8 ≈ 1173 1045·7 ≈ 1046 903 S1 20 83 330 683 573 458 S2 20 104 314 671·3 549 463 S3 20 85·5 324·4 679 498 456 Average values 90·83 ≈ 91 322·8 ≈ 323 677·77 ≈ 678 540 459 a S = specimen 6 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 7. clearly seen that the EC value of the CL clay is larger near the edge of the column. This is because the interaction between the potassium hydroxide and CL clay near the edge of the column is larger than far from the edge of the column. This is explained in the study by Vural (2012), in which the EC of the clay–water system is related to the type and number of ions in the mixture; when ions at the clay surface are mixed into the solution, the conductivity of cation ions under an electrical field and the motion of the colloidal particles increases the conductivity of the solution. In Figures 8(a) and 8(b) it is also seen that the increase of the curing times caused the increase of the EC value near the edge of the column. If Figure 8(b) is compared with Figure 8(a), it can be clearly seen that the EC value increases on increasing the potassium hydroxide ratio. These increases were more in the vicinity of the column. 3.6 Water content test results Figures 9(a) and 9(b) show the changes in the water content of the CL clay around the deep-mixing columns. As shown in the figures, the water content of the CL clay is decreased near the column and the water content of the CL clay increases further away from the edge of the column. It is known that the water content of the CL clay around the column is decreased by increasing the ratio of potassium hydroxide and the curing times (Figure 9(b)). This effect is even more pronounced near the column. The reduction of the water content of the CL clay at the edge of the column is thought to be attributable to the migration of the hydroxyl group and potassium. 4. Conclusions In this study, potassium hydroxide was used for the improve- ment of CL, and UCS tests and SEM analysis were performed on the specimens to investigate its effect. In the second stage of the experiments, DMM columns manufactured in soft clay and the effect of these columns on the surrounding soil were inves- tigated. In this study, the following conclusions are based on the experimental results and discussion. The maximum UCS value was about 1173 kPa, obtained from 15% potassium hydroxide and 28 d of curing time. In the UCS test, after 15% potassium hydroxide, the strength of the specimens is reduced. This is due to the Agglomerated structure (c) (a) (b) Figure 5. View through a SEM: (a) raw CL; (b) raw potassium hydroxide; (c) CL + 15% potassium hydroxide 7 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 8. porosity of the specimens, which increases by increasing the additive ratio. It is also seen that after 15% potassium hydroxide (the maximum value of UCS) and by increasing the curing time (56 and 112 d) the UCS value partially decreased. This is due to the hydroxyl group and the potassium ion accommodation in the outer layer of specimens leading to absorption of the moisture in the air and causing a reduction in the strength of the specimen. According to the SEM analysis, it is possible to obtain a hardness and agglomeration structure of CL clay at 15% potassium hydroxide ratio. In this study, columns with a diameter of 30 mm were manufactured in accordance with the deep-mixing method and the effect of these columns on the surrounding soft clay was investigated. According to the results of the experiment, the Cu, pH and EC values of the soft clay on the edge of the column increased with the increase of the potassium hydroxide ratio and curing times. It was determined that these values decreased farther away from the edge of the column. The water content of the CL clay decreased at the edge of the column and increased farther away from the column. The maximum effective area from the side of the column was about 25 mm at 20% potassium hydroxide in the specimen with 112 d of curing. In contrast to the UCS results, around the deep-mixing columns by increasing the potassium hydroxide ratio, Cu, pH and EC are increased where w is decreased. The significant reason for this is the diffusion of the hydroxyl group and potassium ion from the potassium hydroxide column to the surrounding soft clay. The hydroxyl group produces heat when dissolved in water. By utilising this feature, when the potassium hydroxide is added to the soft clay (with 40% water content), it begins to react with water in the structure of clay and causes part of the water to evaporate, as well as blending the soil particles together. This process helps to increase the strength of the soft clay. Another advantage of potassium hydroxide is that it can migrate to the surrounding soft clay and improve the properties of clay. Other materials (fly ash, sludge ash) cannot produce heat alone and the migration of these materials has not been reported. From the test results, it is suggested that potassium hydroxide may be used as a binder for the deep improvement of soft clay soils. However, a particular issue should be taken into consideration in field applications in that potassium hydroxide is not hardened at an early stage (7 and 14 d) and is expected to take up to 28 d to harden. 0 1 2 3 4 5 6 C u : kPa 5 10 15 20 25 Distance from column periphery: mm 5% – 28 d 10% – 28 d 5% – 56 d 10% – 56 d 5% – 112 d 10% – 112 d 0 2 4 6 8 10 12 14 16 18 5 10 15 20 25 C u : kPa Distance from column periphery: mm (a) (b) 15% – 28 d 20% – 28 d 15% – 56 d 20% – 56 d 15% – 112 d 20% – 112 d Figure 6. Distance–Cu relationship from the column edge applied with DMM: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium hydroxide ratio 7 8 9 10 11 12 0 5 10 15 20 25 30 pH Distance from column periphery: mm 5% – 28 d 10% – 28 d 5% – 56 d 10% – 56 d 5% – 112 d 10% – 112 d 7 8 9 10 11 12 0 5 10 15 20 25 30 pH Distance from column periphery: mm (a) (b) 15% – 28 d 20% – 28 d 15% – 56 d 20% – 56 d 15% – 112 d 20% – 112 d Figure 7. Distance–pH relationship from the column edge applied with DMM: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium hydroxide ratio 8 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
  • 9. To follow up the findings of this study, further large-scale model experiments and field study are recommended to verify the results of the experiments. Also, the cost of using potass- ium hydroxide as a binder in deep mixing should be calculated and compared with other binders. Acknowledgement This study was supported by Scientific Research Projects (BAP) at Ataturk University (Turkey – Erzurum), project number: FDK-2018-6280. REFERENCES Ahnberg H (1996) Stress dependent parameters of cement and lime stabilised soils. Proceedings of the International Conference on Ground Improvement Geosystems, Grouting and Deep Mixing, Tokyo, Japan (Yonekura R, Terashi M and Shibazaki M (eds)). pp. 387–392. Ahnberg H (2006) Strength of Stabilised Soils − A Laboratory Study on Clays and Organic Soils Stabilised with Different Types of Binder. Doctoral thesis, Lund University, Linköping, Sweden. Ahnberg H and Holm G (1996) Stabilisation of some Swedish organic soils with different types of binder. Proceedings of the International Conference on Dry Mix Methods for Deep Soil Stabilisation (Brendenberg H, Broms BB and Holm G (eds)). Balkema, Rotterdam, Netherlands, pp. 101–108. Ajorloo AM (2010) Characterization of the Mechanical Behavior of Improved Loose Sand for Application in Soil-Cement Deep Mixing. Doctoral thesis, University of Lille, Lille, France. Arasan S, Bagherinia M, Akbulut RK and Zaimoglu AS (2017) Utilisation of polymers to improve soft clayey soils using the deep mixing method. Environmental and Engineering Geoscience 23(1): 1–12. https://doi.org/10.2113/gseegeosci.23.1.1. ASTM (American Society for Testing and Materials) (2000) ASTM D5084: Standard test method for measurement of hydraulic conductivity of saturated porous materials using a flexible-wall permeameter. ASTM International, West Conshohocken, PA, USA. ASTM (2012) ASTM D1557: Standard test method for laboratory compaction characteristics of soil using modified effort. ASTM International, West Conshohocken, PA, USA. ASTM (2013) ASTM D4972: Standard test method for pH of soils. ASTM International, West Conshohocken, PA, USA. ASTM (2016) ASTM D2166/D2166M: Standard test method for unconfined compressive strength of cohesive soil. ASTM International, West Conshohocken, PA, USA. ASTM (2017) ASTM D4318: Standard test method for liquid limit, plastic limit and plasticity index of soils. ASTM International, West Conshohocken, PA, USA. Bagherinia M (2013) Utilisation of Unsaturated Polyester in Improvement of Clays with Deep Mixing Method. Master’s thesis, Ataturk University, Erzurum, Turkey (in Turkish with an English summary). Bergado DT and Lorenzo GA (2005) Economical mixing method for cement deep mixing. Proceedings of a Conference on the Innovations in Grouting and Soil Improvement (Geo-Frontiers Congress 2005), Austin, TX, USA (Schaefer VR, Bruce DA and Byle MJ (eds)). American Society of Civil Engineers, Reston, V A, USA, pp. 1–10, https://doi.org/10.1061/40783(162)12. Broms BB (1975) Lime stabilised columns. Proceedings of the 5th Asian Regional Conference on Soil Mechanics and Foundation Engineering, Bangalore, India. Indian Institute of Science, vol. 1, pp. 227–234. Broms BB and Boman P (1979) Lime columns – a new foundation method. Journal of Geotechnical and Geoenvironmental Engineering 105(GT4): 539–556. 0·5 1·0 1·5 2·0 2·5 3·0 3·5 4·0 4·5 0 5 10 15 20 25 30 EC: mS/cm Distance from column periphery: mm 5% – 28 d 10% – 28 d 5% – 56 d 10% – 56 d 5% – 112 d 10% – 112 d 0·5 1·0 1·5 2·0 2·5 3·0 3·5 4·0 4·5 0 5 10 15 20 25 30 EC: mS/cm Distance from column periphery: mm (a) (b) 15% – 28 d 20% – 28 d 15% – 56 d 20% – 56 d 15% – 112 d 20% – 112 d Figure 8. Distance–EC relationship from the column edge applied with DMM: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium hydroxide ratio 38·0 38·5 39·0 39·5 40·0 40·5 41·0 0 5 10 15 20 25 30 Water content: % Distance from column periphery: mm 5% – 28 d 10% – 28 d 5% – 56 d 10% – 56 d 5% – 112 d 10% – 112 d 38·0 38·5 39·0 39·5 40·0 40·5 41·0 0 5 10 15 20 25 30 Water content: % Distance from column periphery: mm (a) (b) 15% – 28 d 20% – 28 d 15% – 56 d 20% – 56 d 15% – 112 d 20% – 112 d Figure 9. Distance–w relationship from the column edge applied with DMM: (a) 5 and 10% potassium hydroxide ratio; (b) 15 and 20% potassium hydroxide ratio 9 Ground Improvement Effect of deep chemical mixing columns on properties of surrounding soft clay Bagherinia and Zaimoğlu Proceedings of the Institution of Civil Engineers - Ground Improvement
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