Study of the efficiency of stone columns in soft clay considering the effect of clay minerals in soil
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This document explores the efficiency of stone columns in improving soft clay soils, specifically focusing on the effects of different clay mineral concentrations from various sites in Iraq. Laboratory tests were conducted to analyze bearing improvement and settlement reduction ratios, revealing that soils with higher montmorillonite content yielded better performance compared to those with lower levels. The findings indicate that the stone columns technique is particularly effective in enhancing the mechanical properties of weak soils when appropriately designed and applied.
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 9, September (2014), pp. 241-251
© IAEME: www.iaeme.com/Ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
www.jifactor.com
IJCIET
©IAEME
STUDY OF THE EFFICIENCY OF STONE COLUMNS IN SOFT CLAY:
CONSIDERING THE EFFECT OF CLAY MINERALS IN SOIL
Esraa A. Mandhour1, Saad N. Al-Saadi2, Saad F. Ibrahim3
1Assistant Professor, Department of Physics, College of Science, University of Thi-Qar, Iraq
2Professor, Department of Geology, College of Science, University of Baghdad, Iraq
3Professor, Department of Highway and Transportation Engineering, College of Engineering,
University of Mustansiriyah, Iraq
241
ABSTRACT
This paper presents the behaviors of stone columns in soft clay. A laboratory model tests
were conducted on three different soils brought from different sites in Iraq to guarantee the
difference between these soils in amount of clay minerals. The effect of increasing of the number of
stone columns with difference of amount of clay minerals of soil were studied in this research, the
columns were constructed on a triangular pattern at 2D spacing inside steel container of (500mm ×
300mm × 350mm).
From laboratory results, the bearing improvement ratios (BIR) and settlement reduction ratios
(SRR) were determined and on bases of these results the stone columns give more efficiency in soils
which contain high amount of montmorillonite with few amount of kaolin than soils which have low
amount of montmorillonite with high amount of kaolin.
Keywords: Stone Columns, Soft Cay, Clay Minerals.
1. INTRODUCTION
The growing urban expansion and continuous population growth led to the creation of many
projects in locations with poor and incapable soils such as filled ground sites and areas containing
recently deposited alluvium.
Over the years, many techniques have been developed to improve the properties of weak soil
deposits such as stone columns, sand drains, blasting compaction, vibro-compaction, etc. [1]-[2]. The
stone columns technique is considered more efficient and suited among a number of techniques for
improving soft clays, silts and loose silty sand [3]-[4].](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-1-320.jpg)
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
In Iraq, there are many sites have soft cohesive soils especially in the middle and south
242
parts [5].
In this paper, the effect of amount and type of clay minerals on act and efficiency of stone
columns were studied with take into consideration the effect of the number of stone columns.
2. PROPERTIES OF USED MATERIALS
Three soft soil were collected from three sites from different cities in Iraq: Duekhla quarry in
Al – Anbar city (Soil1), Baghdad University at Al – Jadriya area in Baghdad city capital of Iraq
(Soil2) and from Al – Nasiriya city at area lies near birth hospital (Soil3) as shown in Fig.1.
Fig.1: Illustrates locations of the study areas on Iraq map
The physical and chemical properties of the used soils for model are given in Table 1. The
properties of the sand which used as a bottom layer (30mm in thickness) in the base of the container
and the gravel which used as a backfilling materials in all stone columns are given in Table 2.
The particle sizes of gravel for the columns are chosen according to guide lines of Nayak
which suggests that they should be in the range of (1/6 – 1/7) diameter of column [6]. The physical
and chemical properties for these materials were determined according to the American
specifications for testing and material in addition to British standard [7]-[8]-[9].](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-2-320.jpg)
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
Table 1: Physical and chemical properties of the used soils
243
Chemical properties
Physical properties
Soils Unified soil classification system (USCS)
Grain size analysis (%) Properties index (%) Soil symbol
pH 7.5
CH
Clay 82 LL 60
Soil1 Silt 18 PL 29 OM 2.9
Sand 0 PI 31 SO3 0.4
pH 7.7
CL
Clay 69 LL 42
Soil2 Silt 31 PL 21 OM 3.1
Sand 0 PI 21 SO3 0.6
pH 7.7
CL
Clay 59 LL 37
Soil3 Silt 41 PL 18 OM 4.1
Sand 0 PI 19 SO3 0.6
Note: LL: Liquid limit, PL: Plastic limit, PI: Plasticity index, CH: Inorganic clay of high plasticity,
CL: Inorganic clay of low plasticity, pH: Power of hydrogen, OM: Organic matter, SO3: Sulphates.
Table 2: Some physical properties of the sand and gravel used in test model
properties
Note: Gs: Specific gravity, D10: Diameter for 10% finer by weight of the sample, D30: Diameter for
30% finer by weight of the sample, D60: Diameter for 60% finer by weight of the sample, Cu:
Coefficient of uniformity, Cv: Coefficient of curvature, SP: poorly - graded sand, GP: poorly - graded
gravel.
3. CLAY MINERALS IN THE USED SOIL
Clay minerals are very small crystalline substances (less than 2μm in diameter) which
composed in general of alumina, silica and water with lesser quantities of iron, magnesium, sodium
and potassium [10]-[11]-[12].
The basic structure of clay minerals consist of two crystal sheets: the tetrahedral (silica)
sheets and the octahedral (alumina) sheets as shown in Fig.2.
These sheets are stacked together with different bonding and different metallic ions in the
crystal lattice to form the different clay minerals [10]-[12].
Materials
Sand Gravel
Gs 2.6 2.6
uniformity
Diameters of particles (mm)
D10 0.28 5.8
D30 0.40 7.0
D60 0.59 7.1
Cu 2.1 1.3
Cv 0.96 1.05
Unified soil classification system (USCS) SP GP](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-3-320.jpg)
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp.
(a)
(c)
Fig. 2 Diagrammatic
241-251 © IAEME
(b)
(d)
sketch showing. (a) Single silica tetrahedron,
(b) The sheet structure of silica tetrahedron arranged in a hexagonal network
(c) Single octahedral unit. (d) The sheet structure of the octahedral units [10].
There are three main groups of clay minerals:
3.1 Kaolinite
Kaolinite is a common phylosilicate minerals composed of one tetrahedral sheet and one
octahedral sheet. In layer of kaolinite the tetrahedral and octahedral sheets are held together tightly
by oxygen atoms and these layers are held to
kaolinite is no expansion when the clay is wetted. Therefore, the water do not enter between the
structure layers of kaolinite.
3.2 Montmorillonite
together by hydrogen bonding. In turn, the structure of
Montmorillonite is composed of two sheets of te
linked by shared oxygen atoms. The structure of montmorillonite is expansion and swelling when
wetted. Therefore, the water enters the interlayer space and force the layers apart and this is due to
the little attraction between oxygen atoms in the bottom tetrahedral sheet with those in the top of
another of tetrahedral sheet.
3.3 Illite
Illite has a structure similar to montmorillonite therefore it is composed of two tetrahedral
sheets with central octahedral sheet but the interlayer are bonded together with potassium atoms. The
degree of swelling is considerable less for montmorillonite and more than kaolinite.
Table 3 illustrates the percentage of the dominant clay minerals for used soils
tested by X – Ray diffraction. Soil1 contains high percentage of kaolinite with little montmorillonite
and illite while soil2 and 3 have lower percentage of kaolinite and with higher amounts of
montmorillonite and illite. Clay samples were test
244
tetrahedral and one sheet of octahedral sheet
raction tested according to [13]-[14].
– 6308 (Print),
network,
gether trahedral which were](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-4-320.jpg)
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
300mm
Soil
Soil
75mm
(a) (b)
300mm
Soil
75mm
(c) (d)
Fig. 5: Overview of arrangement of stone columns. (a) Untreated soil.
(b) Treated soil with single stone column. (c) Treated soil with two stone columns.
(d) Treated soil with four stone columns
246
4.3 Columns Installation
The tests were carried out on single columns and groups of two and four columns. The
columns were installed with diameter (D) about 25mm and length (L) of 100mm placed at spacing
2D center to center with depth factor (L/D) equal to 4.
Steel bearing plate of size (292mm x 75mm) as shown in Fig.3 was placed over the columns
and these columns supported plates were loaded during the load test. The arrangement of stone
columns is illustrated in Fig.5.
300mm
Soil
500mm
212.5mm
212.5mm
Footing
area
292mm
500mm
212.5mm
75mm
212.5mm
292mm
500mm
212.5mm
212.5mm
300mm
292mm
500mm
212.5mm
75mm
212.5mm
Soil
292mm
5. ROLE OF CLAY MINERALS IN IMPROVED SOIL WITH STONE COLUMN
Stone columns have been used as drain wells to speed up the consolidation of compressible
soils which subjected to new load and the compressive stresses cause a lowering of pore space and
expel excess water in the case of saturated soils.
The stone columns which confined by surrounding soil and this allows the column to develop
high bearing pressure relative to the surrounding soil. In turn, the stone columns and the surrounding
soil behave as an integrated system with low compressibility and improved sustainability.
At the beginning, the new compressive stress is carried by the water and as the excess water
drains the compressive stresses are transferred to grains of soil and cause an increase in the inter
granular pressure. Increasing loads on foundation soils will create shearing stresses and this means
increasing shear strength with reduction in soil pore water [15].
In case of saturated or oversaturated soils subjected to applied stress, the water may migrate.
The properties of clays are effected with water content and in case of loaded clays, water is squeezed
out at a rate which depends upon the permeability [16].
Permeability of clays is very small because the size of the pores between the granular too
small. The montmorillonite has the lowest permeability compared with the other clay minerals while
the permeability of kaolinite is decreasing more gradual than montmorillonite with increasing
load [10].](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-6-320.jpg)
![International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
S/B%
Fig. 6: Variation of (q/cu) with (S/B%) for different untreated soils
247
6. RESULTS AND DISCUSSION
The model tests were carried out to investigate the behavior of single and groups of stone
columns under incremental vertical stress in comparison with model tests of untreated soil with stone
columns.
Four terms were used to analysis of results for each model test: the first term is bearing ratio
(q/cu) where q/cu represents the ratio of applied stress (q) to the un-drained shear strength of
soil(cu), whereas the second term is deformation ratio (S/B%) where S/B% represents the percentage
of settlement (S) to footing width (B). While third term is bearing improvement ratio
(BIR) = (qtreated/ quntreated), where qtreated (qt) represents the ratio of applied stress (q) to the un-drained
shear strength (cut) of treated soil while quntreated (qunt) represents the ratio of applied stress (q) to the
un-drained shear strength (cuunt) of untreated soil. The last term is settlement reduction ratio
(SRR) = (Streated/Suntreated), where Streated (St) represents settlement of treated soil while Suntreated (sunt)
represents settlement of untreated soil.
First of all, the model tests were performed on untreated soft soils samples of. Figure 6
represents the bearing ratio plotted against deformation ratio. In general, it can be seen that all soils
give the same pattern that means increase the deformation ratio with increasing of bearing ratio.
q/cu
In spite of the fact that all types of soils when treated with stone columns they give a similar
behavior of increase of bearing ratio at all deformation ratios. There is difference in response of these
soils to this treatment. Figure 7 shows that the bearing ratio in soil2 is more pronounced than soil1
and soil3.
From results of X-Ray diffraction, we can be seen that the construction of stone columns in
soil characterized by the presence or increase in the percentage of the montmorillonite mineral will
increase the q/cu for soil with loading depend on the mineralogical structure for these minerals as
montmorillonite has a very strong attraction for water and soils containing montmorillonite are very
susceptible to swelling as they change (increase) water content [17].
Therefore the presence of water in the interlayer molecular spaces of montmorillonite
squeeze out toward the stone columns with applied stress and the moisture movement cause increase
in shearing stress with reduction of the soil water.
This process takes place in kaolin but in low degree depend on it is crystal structure.
Therefore, the bearing ratio increases in soil2 and soil3 more than soil1.](https://image.slidesharecdn.com/studyoftheefficiencyofstonecolumnsinsoftclayconsideringtheeffectofclaymineralsinsoil-141110081249-conversion-gate02/85/Study-of-the-efficiency-of-stone-columns-in-soft-clay-considering-the-effect-of-clay-minerals-in-soil-7-320.jpg)
Study of the efficiency of stone columns in soft clay considering the effect of clay minerals in soil
- 1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND TECHNOLOGY (IJCIET) ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online) Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME: www.iaeme.com/Ijciet.asp Journal Impact Factor (2014): 7.9290 (Calculated by GISI) www.jifactor.com IJCIET ©IAEME STUDY OF THE EFFICIENCY OF STONE COLUMNS IN SOFT CLAY: CONSIDERING THE EFFECT OF CLAY MINERALS IN SOIL Esraa A. Mandhour1, Saad N. Al-Saadi2, Saad F. Ibrahim3 1Assistant Professor, Department of Physics, College of Science, University of Thi-Qar, Iraq 2Professor, Department of Geology, College of Science, University of Baghdad, Iraq 3Professor, Department of Highway and Transportation Engineering, College of Engineering, University of Mustansiriyah, Iraq 241 ABSTRACT This paper presents the behaviors of stone columns in soft clay. A laboratory model tests were conducted on three different soils brought from different sites in Iraq to guarantee the difference between these soils in amount of clay minerals. The effect of increasing of the number of stone columns with difference of amount of clay minerals of soil were studied in this research, the columns were constructed on a triangular pattern at 2D spacing inside steel container of (500mm × 300mm × 350mm). From laboratory results, the bearing improvement ratios (BIR) and settlement reduction ratios (SRR) were determined and on bases of these results the stone columns give more efficiency in soils which contain high amount of montmorillonite with few amount of kaolin than soils which have low amount of montmorillonite with high amount of kaolin. Keywords: Stone Columns, Soft Cay, Clay Minerals. 1. INTRODUCTION The growing urban expansion and continuous population growth led to the creation of many projects in locations with poor and incapable soils such as filled ground sites and areas containing recently deposited alluvium. Over the years, many techniques have been developed to improve the properties of weak soil deposits such as stone columns, sand drains, blasting compaction, vibro-compaction, etc. [1]-[2]. The stone columns technique is considered more efficient and suited among a number of techniques for improving soft clays, silts and loose silty sand [3]-[4].
- 2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME In Iraq, there are many sites have soft cohesive soils especially in the middle and south 242 parts [5]. In this paper, the effect of amount and type of clay minerals on act and efficiency of stone columns were studied with take into consideration the effect of the number of stone columns. 2. PROPERTIES OF USED MATERIALS Three soft soil were collected from three sites from different cities in Iraq: Duekhla quarry in Al – Anbar city (Soil1), Baghdad University at Al – Jadriya area in Baghdad city capital of Iraq (Soil2) and from Al – Nasiriya city at area lies near birth hospital (Soil3) as shown in Fig.1. Fig.1: Illustrates locations of the study areas on Iraq map The physical and chemical properties of the used soils for model are given in Table 1. The properties of the sand which used as a bottom layer (30mm in thickness) in the base of the container and the gravel which used as a backfilling materials in all stone columns are given in Table 2. The particle sizes of gravel for the columns are chosen according to guide lines of Nayak which suggests that they should be in the range of (1/6 – 1/7) diameter of column [6]. The physical and chemical properties for these materials were determined according to the American specifications for testing and material in addition to British standard [7]-[8]-[9].
- 3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME Table 1: Physical and chemical properties of the used soils 243 Chemical properties Physical properties Soils Unified soil classification system (USCS) Grain size analysis (%) Properties index (%) Soil symbol pH 7.5 CH Clay 82 LL 60 Soil1 Silt 18 PL 29 OM 2.9 Sand 0 PI 31 SO3 0.4 pH 7.7 CL Clay 69 LL 42 Soil2 Silt 31 PL 21 OM 3.1 Sand 0 PI 21 SO3 0.6 pH 7.7 CL Clay 59 LL 37 Soil3 Silt 41 PL 18 OM 4.1 Sand 0 PI 19 SO3 0.6 Note: LL: Liquid limit, PL: Plastic limit, PI: Plasticity index, CH: Inorganic clay of high plasticity, CL: Inorganic clay of low plasticity, pH: Power of hydrogen, OM: Organic matter, SO3: Sulphates. Table 2: Some physical properties of the sand and gravel used in test model properties Note: Gs: Specific gravity, D10: Diameter for 10% finer by weight of the sample, D30: Diameter for 30% finer by weight of the sample, D60: Diameter for 60% finer by weight of the sample, Cu: Coefficient of uniformity, Cv: Coefficient of curvature, SP: poorly - graded sand, GP: poorly - graded gravel. 3. CLAY MINERALS IN THE USED SOIL Clay minerals are very small crystalline substances (less than 2μm in diameter) which composed in general of alumina, silica and water with lesser quantities of iron, magnesium, sodium and potassium [10]-[11]-[12]. The basic structure of clay minerals consist of two crystal sheets: the tetrahedral (silica) sheets and the octahedral (alumina) sheets as shown in Fig.2. These sheets are stacked together with different bonding and different metallic ions in the crystal lattice to form the different clay minerals [10]-[12]. Materials Sand Gravel Gs 2.6 2.6 uniformity Diameters of particles (mm) D10 0.28 5.8 D30 0.40 7.0 D60 0.59 7.1 Cu 2.1 1.3 Cv 0.96 1.05 Unified soil classification system (USCS) SP GP
- 4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. (a) (c) Fig. 2 Diagrammatic 241-251 © IAEME (b) (d) sketch showing. (a) Single silica tetrahedron, (b) The sheet structure of silica tetrahedron arranged in a hexagonal network (c) Single octahedral unit. (d) The sheet structure of the octahedral units [10]. There are three main groups of clay minerals: 3.1 Kaolinite Kaolinite is a common phylosilicate minerals composed of one tetrahedral sheet and one octahedral sheet. In layer of kaolinite the tetrahedral and octahedral sheets are held together tightly by oxygen atoms and these layers are held to kaolinite is no expansion when the clay is wetted. Therefore, the water do not enter between the structure layers of kaolinite. 3.2 Montmorillonite together by hydrogen bonding. In turn, the structure of Montmorillonite is composed of two sheets of te linked by shared oxygen atoms. The structure of montmorillonite is expansion and swelling when wetted. Therefore, the water enters the interlayer space and force the layers apart and this is due to the little attraction between oxygen atoms in the bottom tetrahedral sheet with those in the top of another of tetrahedral sheet. 3.3 Illite Illite has a structure similar to montmorillonite therefore it is composed of two tetrahedral sheets with central octahedral sheet but the interlayer are bonded together with potassium atoms. The degree of swelling is considerable less for montmorillonite and more than kaolinite. Table 3 illustrates the percentage of the dominant clay minerals for used soils tested by X – Ray diffraction. Soil1 contains high percentage of kaolinite with little montmorillonite and illite while soil2 and 3 have lower percentage of kaolinite and with higher amounts of montmorillonite and illite. Clay samples were test 244 tetrahedral and one sheet of octahedral sheet raction tested according to [13]-[14]. – 6308 (Print), network, gether trahedral which were
- 5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME Table 3: The percentage of clay minerals of the used soils Percentage of valid clay minerals (a) (b) Fig. 3: Experimental setup. (a) Testing apparatus. (b) Overview of testing apparatus 245 Soils Kaolinite Montmorillonite Illite Soil1 90 - - Soil2 37 42.5 20.5 Soil3 23.2 45.7 31.3 4. PROGRAM OF TESTS 4.1 Testing Equipment Steel container of size 500mm x 300mm x 350mm was used to carry out the model tests. Figure 3 illustrates the testing apparatus and the steel loading frame which was designed and used in this study. 4.2 Preparation of the Test Bed of Soils The tests were carried out on specimens of dry soils which mixed with enough water at moisture content equal to 0.35 to get the desired shear strength 8.0kPa, 7.8kPa and 7.5kPa for soil1, soil2 and soil3 respectively. The soils were packed in layers inside the steel container to get the final thickness about 220mm. a layer of poorly graded sand was placed at the bottom of the container below layers of soil with final thickness about a 30mm and unit weight 16kN/m3 as shown in Fig.4. 220mm 30mm 250mm Soil Sand Fig. 4: Beds of soil inside a container
- 6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME 300mm Soil Soil 75mm (a) (b) 300mm Soil 75mm (c) (d) Fig. 5: Overview of arrangement of stone columns. (a) Untreated soil. (b) Treated soil with single stone column. (c) Treated soil with two stone columns. (d) Treated soil with four stone columns 246 4.3 Columns Installation The tests were carried out on single columns and groups of two and four columns. The columns were installed with diameter (D) about 25mm and length (L) of 100mm placed at spacing 2D center to center with depth factor (L/D) equal to 4. Steel bearing plate of size (292mm x 75mm) as shown in Fig.3 was placed over the columns and these columns supported plates were loaded during the load test. The arrangement of stone columns is illustrated in Fig.5. 300mm Soil 500mm 212.5mm 212.5mm Footing area 292mm 500mm 212.5mm 75mm 212.5mm 292mm 500mm 212.5mm 212.5mm 300mm 292mm 500mm 212.5mm 75mm 212.5mm Soil 292mm 5. ROLE OF CLAY MINERALS IN IMPROVED SOIL WITH STONE COLUMN Stone columns have been used as drain wells to speed up the consolidation of compressible soils which subjected to new load and the compressive stresses cause a lowering of pore space and expel excess water in the case of saturated soils. The stone columns which confined by surrounding soil and this allows the column to develop high bearing pressure relative to the surrounding soil. In turn, the stone columns and the surrounding soil behave as an integrated system with low compressibility and improved sustainability. At the beginning, the new compressive stress is carried by the water and as the excess water drains the compressive stresses are transferred to grains of soil and cause an increase in the inter granular pressure. Increasing loads on foundation soils will create shearing stresses and this means increasing shear strength with reduction in soil pore water [15]. In case of saturated or oversaturated soils subjected to applied stress, the water may migrate. The properties of clays are effected with water content and in case of loaded clays, water is squeezed out at a rate which depends upon the permeability [16]. Permeability of clays is very small because the size of the pores between the granular too small. The montmorillonite has the lowest permeability compared with the other clay minerals while the permeability of kaolinite is decreasing more gradual than montmorillonite with increasing load [10].
- 7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME S/B% Fig. 6: Variation of (q/cu) with (S/B%) for different untreated soils 247 6. RESULTS AND DISCUSSION The model tests were carried out to investigate the behavior of single and groups of stone columns under incremental vertical stress in comparison with model tests of untreated soil with stone columns. Four terms were used to analysis of results for each model test: the first term is bearing ratio (q/cu) where q/cu represents the ratio of applied stress (q) to the un-drained shear strength of soil(cu), whereas the second term is deformation ratio (S/B%) where S/B% represents the percentage of settlement (S) to footing width (B). While third term is bearing improvement ratio (BIR) = (qtreated/ quntreated), where qtreated (qt) represents the ratio of applied stress (q) to the un-drained shear strength (cut) of treated soil while quntreated (qunt) represents the ratio of applied stress (q) to the un-drained shear strength (cuunt) of untreated soil. The last term is settlement reduction ratio (SRR) = (Streated/Suntreated), where Streated (St) represents settlement of treated soil while Suntreated (sunt) represents settlement of untreated soil. First of all, the model tests were performed on untreated soft soils samples of. Figure 6 represents the bearing ratio plotted against deformation ratio. In general, it can be seen that all soils give the same pattern that means increase the deformation ratio with increasing of bearing ratio. q/cu In spite of the fact that all types of soils when treated with stone columns they give a similar behavior of increase of bearing ratio at all deformation ratios. There is difference in response of these soils to this treatment. Figure 7 shows that the bearing ratio in soil2 is more pronounced than soil1 and soil3. From results of X-Ray diffraction, we can be seen that the construction of stone columns in soil characterized by the presence or increase in the percentage of the montmorillonite mineral will increase the q/cu for soil with loading depend on the mineralogical structure for these minerals as montmorillonite has a very strong attraction for water and soils containing montmorillonite are very susceptible to swelling as they change (increase) water content [17]. Therefore the presence of water in the interlayer molecular spaces of montmorillonite squeeze out toward the stone columns with applied stress and the moisture movement cause increase in shearing stress with reduction of the soil water. This process takes place in kaolin but in low degree depend on it is crystal structure. Therefore, the bearing ratio increases in soil2 and soil3 more than soil1.
- 8. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME
- 9. In Fig.8, The values of the bearing improvement ratios (qt/qunt) indicate that the soil2 and soil3 give large improvement in comparison with soil1 and the maximum values of bearing improvement ratios are obtained at deformation ratio (S/B%) about (1-2%) then gradual decrease is observed. This is probably due to the difference in shear strength and mineralogy between the soils. The high increase in the bearing capacity in soil2 and soil3 in the early stages of load application may be explained by the fact that these soils (2 and 3) have high percentage of montmorillonite, while the low increase in bearing capacity in soil1 may be explained by the absence of montmorillonite in this soil and the presence of high percentage of kaolinite in it. 248 q/cu q/cu q/cu S/B% (a) S/B% (b) S/B% (c) Fig. 7: Variation of (q/cu) with (S/ B %) for different soil, (a) Soil1, (b) Soil2, (c) Soil3
- 10. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME Figure 9 shows that the maximum value of settlement reduction ratios (SRR) for soil3 are lower than those detected from soil2 and soil3 respectively in early stage of loading, where with the progress of stages of loading there is an increase in the settlement reduction ratio for all soils till it value becomes semi leveled. The increase in the number of stone columns act to decrease the settlement of soil and for soils with any number of stone columns there are more reduction in the settlements in the soils that contain high percentage of montmorillonite in the early stages of loading rather than the soils which contain high percentage of kaolinite. Therefore, the model tests for stone columns on three different types of soils revealed that the stone columns give most efficiency in soils contain high amount of montmorillonite and few amount of kaolin than those have low amount of montmorillonite and high amount of kaolin. 249 qt/qunt qt/qunt S/B% (a) S/B% (b) S/B% (c) qt/qunt Fig. 8: Variation of (qt/qunt) with (S/B %) for different soil, (a) Soil1, (b) Soil2, (c) Soil3
- 11. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME q/cu (a) q/cu (b) q/cu (c) Fig. 9: Variation of (St/Sunt%) with (S/B %) for different soil, (a) Soil1, (b) Soil2, (c) Soil3 250 7. CONCLUSION St/Sunt% St/Sunt% St /Sunt% For all types of soils and with increasing of stone columns, there are increase in bearing ratio and bearing improvement ratio in addition to decrease in the settlement reduction ratio. The construction of stone columns in soils that contain high amount of montmorillonite leads to increase the bearing ratio and bearing improvement ratio relative to soils that contain high amount of kaolinite. While the settlement reduction ratios decrease in soils contain high amount of montmorillonite relative to soils that contain high amount of kaolinite. 8. ACKNOWLEDGEMENTS The authors wish to thank and gratitude the Department of Civil Engineering in the University of Baghdad especially laboratory of soil mechanic for technical and scientific support in order to complete requirements of this research.
- 12. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print), ISSN 0976 – 6316(Online), Volume 5, Issue 9, September (2014), pp. 241-251 © IAEME 251 REFERENCES [1] S.R. Gandhi, A.K. Dey and S. Selvam, Densification of pond ash by blasting, Journal of geotechnical and geo-environmental engineering, ASCE, 125(10), 1999, 889-899. [2] V. Sivakumar, D. Mckelvey, J. Graham and D. Hughes, Triaxial tests on model sand columns in clay, Canadian Geotechnical Journal, 41(2), 2004, 299-312. [3] J.K. Mitchell, Stabilization of soils for foundations structures, Crops of engineering manual for foundation design, 1978. [4] J.K. Mitchell and R.K. Katti, Soil improvement state of art-report, 10th international conference on soil mechanics and foundation engineering, Stockholm, 1981, 261-313. [5] M.J. Al-Mosawe, A.J. Abbas and A.H. Majieed, Prediction of ultimate capacity of a single and groups of stone columns, Iraqi Conference on Engineering, Vol.1, Baghdad, 1985, 61-68. [6] N.V. Nayak, Recent advances in ground improvements by stone column, Proceeding of Indian geotechnical Society Conference, Madras, 1983. [7] ASTM (1973), Manual book of ASTM standard by the American society for testing and material, 1973. [8] ASTM (1984), Manual book of ASTM standard by the American society for testing and material, Vol. 04-08, 1984. [9] British standard -1377, Methods of testing soils for civil engineering purposes, 1975. [10] R.E. Grim, Applied clay mineralogy, McGraw-Hill Book Co. Inc, 1962, p.422. [11] D. Carroll, Clay minerals: A guide to their X-ray identification, Geol. Soc. of America, Special paper 126, 1970, p.80. [12] K.M. Banat, Principles of clay mineralogy, Minisry of Higher Education and Scientific Research, University of Baghdad, 1980, p.138. [13] J. Thorez, Practical identification of minerals, G. Lillotte. ed. Dison, Belgium, 1976, p.89. [14] R.E. Grim, Clay mineralogy, 2nd ed., McGraw-Hill Book Co. Inc., 1968, p. 596. [15] R.A. Barron, Consolidation of fine – grained soils by drain wells, Transactions, American Society of Civil Engineers, 1984, 718-743. [16] J.E. Gillott, Clay in engineering geology, Elsevier Pub. Co., Amsterdam, 1968, p.296. [17] R.D. Holtz and W.D. Kovacs, An introduction to geotechnical engineering, Prentice- Hall Civil Engineering and Engineering Mechanics Series, 1981, p.719. ch.4. [18] S. Ramesh Kumar and Dr. K.V.Krishna Reddy, “An Experimental Investigation on Stabilization of Medium Plastic Clay Soil with Bituminous Emulsion”, International Journal of Civil Engineering Technology (IJCIET), Volume 5, Issue 1, 2014, pp. 61 - 65, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [19] Ahmed Neamah Naji, Dr. V. C. Agarwal, Prabhat Kumar Sinha and Mohammed Fadhil Obaid, “Influence of Crude Oil Fouling on Geotechnical Properties of Clayey and Sandy Soils”, International Journal of Civil Engineering Technology (IJCIET), Volume 5, Issue 3, 2014, pp. 60 - 70, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [20] Mohammed Fadhil Obaid, Dr. V. C. Agarwal, Prabhat Kumar Sinha and Ahmed Neamah Naji, “Influence of Crude Oil Fouling on Geotechnical Properties of Clayey and Sandy Soils”, International Journal of Civil Engineering Technology (IJCIET), Volume 5, Issue 3, 2014, pp. 83 - 91, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316. [21] Thulaseedharan V and Narayanan S.P, “The Effect of Soil Improvement on Foundation Super Structure Design”, International Journal of Civil Engineering Technology (IJCIET), Volume 4, Issue 2, 2013, pp. 258 - 269, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.