ICCBT2008
Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat Y. Duraisamy*, University Malaysia Pahang, MALAYSIA
ABSTRACT
This paper presents the preliminary design chart of cement columns used for deep soil mixing method. Initially, the effects of the cement column diameter on the compressibility have been investigated in this study. The results indicated that compressibility index C c and C decreased with increasing diameter of the cement column. Various dimensions of cement columns were used to form cement columns in order to study the influence. Specimens with 15 mm, 30 mm, 45 mm, 50 mm, 60 mm, 80 mm and and 100 mm diameter of cement columns were cured for 7, 14 and 28 days, after which they were subjected to Rowe Cell consolidation test. Results are also presented from test conducted on groups of cement columns using four, six, nine and twelve columns of 15 mm diameter each to investigate the influence of number of cement columns on compressibility of peat. Based on the results obtained, preliminary design charts for cement columns were established as a guideline to engineers and academicians.
α α
Keywords: Cement columns, compressibility, deep soil mixing, design chart, fibrous peat soil, organic soil, Rowe Cell consolidation.
*Correspondence Author: Youventharan Duraisamy, University Malaysia +6095492284, Fax: +6095492299. E-mail:
[email protected] E-mail:
[email protected]
ICCBT 2008 - E - (40) – pp495-510
Pahang,
Malaysia.
Tel:
Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat
1.
INTRODUCTION
Peat represents the extreme form of soft soil. It is an organic soil which consists more than 70% of organic matters. Peat deposits are found where conditions are favorable for their formation. In Malaysia, some 3 million hectares of land is covered with peat. While in Indonesia, peat covers about 26 million hectares of the country land area. Two third of the world coverage of tropical peat are in South East Asia. Since the coverage of peat soil is quite extensive, utilization of these marginal soil are required in the recent years. Hence, suitable geotechnical design parameters and construction techniques needed for this type of ground condition. Peat poses serious problems in construction due to its long-term consolidation settlements even when subjected to a moderate load [1]. Hence, peat is considered unsuitable for supporting foundations in its natural state. Various construction techniques have been carried out to support embankments over peat deposits without risking bearing failures but settlement of these embankments remains excessively large and continues for many years. Besides settlement, stability problems during construction such as localized bearing failures and slip failures need to be considered. Deep Soil mixing (DSM) also referred to as Lime Cement Column Method or just Cement Columns, invented by Kjeld Paus 30 years ago. It is a form of soil improvement involving the mechanical mixing of in-situ soft and weak soils with a cementatious compound such as lime, cement or a combination of both in different proportions. Dry DSM method has been used in Sweden and Finland since 1967 for improvement in soft clays and organic soils to increase the stability and to reduce the settlements of embankments. This method seems to work well for soft silty clay though its application for peat is yet to be proven. Thus the author initiated this laboratory based study involving cement columns in peat soils prior to full scale test in order to evaluate the performance.
2.
EXPERIMENTAL DESIGN AND LABORATORY WORK
The main objective of this research was to find out the effects of cement column on compressibility when installed in tropical peat soil. Apart from that researcher was also interested to examine the peculiar engineering behavior of tropical peat with respect to their compressibility characteristics due to variation in fiber content and organic content. Meanwhile the index properties such as natural water content, organic content, liquid limit, specific gravity and density of fibrous peat soils were obtained to establish suitable correlation. Understanding the engineering properties and compressibility characteristics of fibrous peat will be handy for engineers in determining suitable ground improvement method. Thus, proper construction and foundation design guide for fibrous peat soils could be outlined for future developments in peat ground. 2.1 Sample Preparation
Undisturbed samples of fibrous peat soils were taken from three different locations in Banting (located on the West coast of Peninsular Malaysia) by using a sampling tube. A suitable auger was designed and fabricated to collect undisturbed fibrous peat samples as shown in Figure 1. The handle was formed of a 60 cm cross bar and the stem of 100 cm height. The cylindrical tube is 150 mm (internal) in diameter. The upper part of the cylindrical hollow body is fitted with a cover plate. Meanwhile the lower part of the cylindrical tube was sharpened to cut roots as the auger is slowly rotated into the peat ground during sampling. The thin tube was 496
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fitted with a valve, which is left open during sampling to release both air and water pressure. The valve is then closed prior to withdrawal of the tube with the peat sample enclosed, thus providing a vacuum effect to help the sample in place. Soon after the sampler is withdrawn, the cylindrical tube was sealed with paraffin wax. Once in the laboratory, the top cover on the cylindrical tube was opened to extract the sample into the Rowe Cell. This sampler is suitable for sampling peat soil up to depth of about 1 m only. The auger enables the extraction of peat core sample of 150 mm diameter by 230 mm length. The top and bottom of the specimen was trimmed. Fibrous soil such as peat is easily disturbed therefore the trimming process was carried out carefully. Furthermore, the trimming process was carried out quickly to minimize changes in the water content of the soil sample. Sample was then tested using Rowe Cell consolidation to overcome most of the disadvantages of the conventional oedometer apparatus when performing consolidation tests on low permeability soils, including non-uniform deposits. The most important features are the ability to control drainage and to measure pore water pressure during the course of consolidation tests. Figure 2 shows the experimental set up of using Rowe Cell. This system is based on Rowe Cell consolidation cell and GDS® pressure/volume controllers. Size of the cell used in this research was 150 mm in diameter and 50 mm in height. The hydraulic pressure system and vertical load can be applied to the sample surface either via a flexible diaphragm to give a uniformly distributed pressure (free strain) or via a rigid plate to give uniform settlement (equal strain). Rigid plate was used in the research as shown in Figure 3. Back pressure of 200 kN/m2 was applied to the top drain of the cell so that the field hydraulic gradients can be modeled. The bottom drain was provided with a tapping to a pressure transducer.
Figure 1. In-house peat sampler.
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Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat
Data Logger
Displacement Transducer
Computer Rowe Cell
GDS Back Pressure Controller
Figure 2. The experimental set up of Rowe Cell consolidation
Figure 3. Rigid plate to give equal strain.
To investigate the influence of diameter of columns, a single cement column was placed at the center of the cell containing peat sample. A portion of the peat soil was taken out from the cell using a PVC tube and replaced with dry cement powder to form the cement column as shown in Figure 4. The diameters of the cement column were 15 mm, 30 mm, 45 mm, 50 mm, 60 mm and 80 mm. The samples were cured for 7, 14 and 28 days in a soaking basin as shown in Figure 5. After the curing days, Rowe Cell consolidation test was carried out on the samples consecutively. Meanwhile group cement columns of four, six, nine and twelve columns were formed using 15 mm diameter PVC tube at the spacing of 2d (2 times the value of column diameter) to investigate the influence of group cement columns in reducing compressibility of peat soil. Based on past researcher’s recommendations and historical data, the author chose typical dosage rate commonly used for peat soil 100 kg/m3, which corresponds to nine percent by weight of dry soil to form cement columns.
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Figure 4. Method used to form cement column
Figure 5. Method used to cure peat-cement column sample.
Load increment was applied at 20, 40, 80, 160, and 320kN/m 2. Additional load was placed on the soil specimen to determine the soil behavior at higher pressure. Each load increment was maintained for 24 hours. The test started with a vertical load of 20 kN/m 2 and deformation transducer readings with corresponding time observations were recorded using data logger, which was connected to computer. The load was maintained for 24 hours. After 24 hours, the same procedure was repeated with different applied load. Time-deformation graphs were plotted and settlements were determined using GDSLAB® control and acquisition software. 2.2 Testing programs
Index properties of peat soil used in the classification system of peat namely the water content, organic content, specific gravity, fiber content, degree of humification and Atterberg limits were determined based on test procedures according to the British Standard BS1377: 1990, ‘Methods of test for soils for civil engineering purposes’. Apart from the classifying tests, compressibility behavior of the peat soil was determined by Rowe Cell consolidation test for both the natural (untreated) and cement column installed peat samples. Due to the large number of specimens, the testing procedures were separated into phases and sample identification system was developed to assign each specimen with identifying labels. Table 1 illustrates the sample identification system used, type of column, dimensions of cement column¸ interface area and the area ratio.
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Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat
Column SC1 SC2 SC3 SC4 SC5 GC1 GC2 GC3 GC2
3.
Type Single Single Single Single Single Group (2 x 2) Group (2 x 3) Group (3 x 3) Group (3 x 4)
Table 1. Sample identification system Diameter Length Area (m2) (mm) (mm) 30 50 0.0061 45 50 0.0102 50 50 0.0118 60 50 0.0122 80 50 0.0226 15 50 0.0108 15 50 0.0162 15 50 0.0244 15 50 0.0325
l/d ratio
1.67 1.11 1.00 0.83 0.62 3.33 3.33 3.33 3.33
Area Ratio 0.04 0.09 0.11 0.16 0.28 0.04 0.06 0.09 0.12
RESULTS AND DISCUSSIONS
One of the objectives of this study was to find the relationship between the basic geotechnical properties of fibrous peat soil with index parameters such as natural water content, organic content and liquid limit. It must also be appreciated that compared with soils of mineral origin, the peat soils, in particular those of the tropical genesis, have only recently been given attention. As such even determination methods of some of the basic properties are still being researched. In some cases no consensus has been reached, either with respects to the methods, nor details of any given methods. However, for ease of comparison, the most commonly used methods of determination of soil basic properties were used in this study. 3.1 Soil Description
Fibrous peat sample was obtained from marine and continental deposits on the West Coast of Peninsular Malaysia. It consists primarily of low plasticity fines; some fine to medium sands and it is dark brown in color. Characterization tests were performed according to the USDA classification system and Von Post Scale. Soil classification tests were carried out on each soil sample in accordance with accepted BS 1377: 1990 and ASTM ranges. The results of the characterization tests are in Table 2. The Atterberg limits were determined on the soil particles passing the 475 μm sieve. As seen in Table 2, a fairly significant increase in liquid limit with the increase in natural water content. Huat [2] stated that the natural water content of peat in West Malaysia ranges from 200 % to 700 % and with organic content in the range of 50 % to 95 %. The recorded values in Table 2 fulfill this statement. Further more the liquid limit was in the range of 200 % to 500 % as reported by Huat [2]. Engineering properties such as specific gravity and bulk density of the samples were within the range as reported by Huat [2].
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3.2 Correlations of Index Properties
As mentioned before, one of the objectives of this paper was to study the relationship of the basic geotechnical properties of tropical peat soils with some of the easily determined parameters such as natural water content, organic content or liquid limit. Comparison was made with the published correlations of the more established organic soils of the temperate genesis.
Figure 6 shows the empirical relationships between organic content (OC ) and liquid limit ( LL) which has been proposed by Skempton and Petley [3] for temperate peat. However equation (1) does not seem to fit well in the case of tropical peat. For the case of tropical peat studied in Malaysia, the best fit line of the samples is given in equation (2) ( LL and OC in percent). Liquid limit of the tropical peat soils found to range from 150 - 400%. In general, the liquid limit of peat increases with increase in organic content. Using statistical analysis the correlation between liquid limit and organic content of Banting peat was 0.6178. LL = 0.5 + 5.0OC LL = 0.3 + 3.0OC
(1) (2)
600 S ke mp t on & Pe tl ey (1 97 0)
P re se nt St u dy
500
400 % , t i m i L300 d i u q i L
200
100
0 0
20
40
60 Organic Content, %
80
100
120
Figure 6. Liquid limit versus organic content.
Figure 7 shows the relationship of dry density ( ρ d) and natural water content (w). For temperate peat soils in the district of central Netherlands, the best fit line is given by equation (3), proposed by Den Haan [4]. Data collected from the tropical peat sample was plotted on the same figure and both the sample fit close to each other. However for identification of tropical peat, a special equation was formed as equation (4). Using statistical analysis, the correlation coefficient between dry density and natural water content of Banting peat was 0.7828.
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Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat 0.856
ρ d
=
35.075( w)
−
ρ d
=
22.422( w)
−
0.804
(3)
(4)
1,600 Present Study
Den Haan (1997)
1,400
1,200
3
1,000
m / g M , y t i 0,800 s n e D y r 0,600 D
0,400
0,200
0,000 0
100
200
300
400 500 Natural Water Content, %
600
700
800
900
Figure 7. Dry density versus natural water content
Specific gravity in peat soils are affected by the organic constituents, and cannot therefore simply be set to somewhere near 2.65 – 2.75 as for in mineral soils. Den Haan [4] for example quoted cellulose and lignin to have specific gravity of approximately 1.58 and 1.40 respectively. These low values would as expected reduces the compounded specific gravity of organic soils. Figure 8 shows the variation of specific gravity with organic content using correlation proposed by Kaniraj and Joseph [5], Huat [2], Skempton and Petley [3] and Den Haan [4]. Experimental results plotted for specific gravity of tropical peat, fit closely with equation 8 proposed by Den Haan [4]. Thus an equation was formed to establish the identification process of tropical peat soil. Using statistical analysis, the correlation coefficient between specific gravity and organic content of Banting peat was 0.9956.
502
G s
= −
1.6281OC + 2.6859
(5)
G s
= −
1.2OC + 2.7
(6)
G s
=
1/ (0.358OC + 0.357)
(7)
G s
=
1/ (0.362OC + 0.371)
(8)
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2 1,9 1,8 1,7 s G , 1,6 y t i v a r G1,5 c i f i c e p 1,4 S
1,3 1,2 1,1 Eq.5
Eq .6
Eq .7
Eq.8
Pr es ent Stud y
1 65
70
75
80 85 Organic Content, %
90
95
100
Figure 8. Specific gravity versus organic content
3.3 Compression index, C c
According to Li and Lee [6], compressibility parameters of soil are to some extent stress dependent. Since developing peat ground often involves massive changes in the state of stress, as well as pressure and saturation changes, it is important to understand the stress dependent behavior of compressibility parameters and incorporate it in the peat soil stabilization plan. Based on Figure 9, the compression index (C c ) values from Rowe Cell consolidation test for the natural fibrous peat were within the range of 1.878 to 3.627 for consolidation pressure of 40 kPa to 320 kPa. These values were from Rowe Cell consolidation test and measured higher than the values from conventional oedometer test results. Results from conventional oedometer test were far less reliable because back pressure was not induced and pore water pressure was not measured during the course of the test. The compression index (C c ) values from oedometer test for fibrous peat was 1.453 to 3.211. However, these values were far smaller than what has been reported for peat as 5 to 10 compared with that of clay of only 0.2 to 0.8 in the literature.
BH
1 2 3 4 5 6 7 8
Water Content (%) 266 330 350 181 241 140 286 300
Table 2: Index properties of fibrous peat samples. Liquid Organic Von Fiber Specific Void Limit Content Post Content Gravity, ratio, (%) (%) Scale (%) Gs e 285 76 H5 65 1.52 7.541 350 84 H4 75 1.45 9.535 398 88 H4 77 1.42 10.48 250 73 H7 55 1.55 5.522 275 75 H6 58 1.53 6.536 240 70 H8 32 1.56 4.125 310 77 H5 68 1.51 7.895 330 80 H8 31 1.49 4.824
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Bulk Density, (Mg/m3) 0.922 0.834 0.811 1.008 0.856 1.019 0.956 0.996 503
Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat
3.4 Coefficient of secondary compression, C
α
Based on Figure 10, the coefficient of secondary compression (C ) values from Rowe Cell consolidation test for the natural (untreated) fibrous peat was within the range of 0.0608 to 0.0985 for consolidation pressure of 40 kPa to 320 kPa. These values were from Rowe Cell consolidation test and measured higher than the values from conventional oedometer test results. The coefficient of secondary compression (C ) value from oedometer test for fibrous peat was 0.0374 to 0.0901. These values are considerably higher than the limiting values of between 0.02 and 0.04 for highly organic soils as suggested by Hobbs [7]. α
α
According to Mesri [8], soil with C values of more than 0.064 is categorized as soil with extremely high secondary compressibility. The coefficient of secondary compression C α (=Δe/ Δlog t) was determined from the slope of the e-log t curves during the period of 4 to 24 hours after load increment, assuming that the secondary compression would have started 4 hours after loading. The variation of C α with applied consolidation pressure can be seen in Figure 10. The C increases as the consolidation pressure is increased. Similar trend was observed with samples tested using oedometer. Thus, fibrous peat samples used in this research will cause high secondary settlements with the increase in loading over the time. [8] α
α
3.5 Law of compressibility
Mesri and Castro [9] reported that the value of C /C c law for peat and muskeg lies in the range of 0.05 to 0.07. Based on Table 4, value of C /C c law for tropical peat determined from conventional oedometer test was about 0.027. Whereas samples tested using Rowe Cell consolidation was recorded 0.02. These values are generally not in agreement with the values reported in literature. Since the value of C /C c law for tropical peat is lower than the value of C /C c law reported in the literature, less creep settlement develops when the fibrous peat soil is loaded. However, this need to be verified with further research works involving field study. Again according to Mesri et al. [10], reliable data suggests that C /C c for peat lies within the range 0.06 ± 0.01. However studies carried out by Paikowsky et al. [11] on Cranberry bog peat, Massachusetts showed that C /C c is not constant but varies. α
α
α
α
α
α
4
3,5
3 c C , 2,5 x e d n I n o 2 i s s e r p m1,5 o C
Fibric Peat (Rowe Cell) Hemic Peat (Rowe Cell) Sapric Peat (Rowe Cell) Fibric Peat (Oedometer)
1
Hemic Peat (Oedometer) Sapric Peat (Oedometer)
0,5
0 0
50
100
150 200 Consolidatio n Pressure, (kPa)
250
300
350
Figure 9: Compression index versus consolidation pressure. 504
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0,1 0,09 0,08 C , n o i s 0,07 s e r p m0,06 o C y r a0,05 d n o c e S0,04 f o t n e0,03 i c i f f e o C0,02
Fibric Peat (Rowe Cell) Hemic Peat (Rowe Cell) Sapric Peat (Rowe Cell) Fibric Peat (Oedometer) Sapric Peat (Oedometer) Hemic Peat (Oedometer)
0,01 0 0
50
100
150
200
250
300
350
Consolidatio n Pressure, (kPa)
Figure 10: Coefficient of secondary compression versus consolidation pressure
3.6 Effect of a single cement column
As for the main objective of this research, cement columns of two dimensions were prepared and installed in peat soils. Cement column with (45 mm diameter x 50 mm length) and (60 mm x 50 mm length) were formed. They were cured for 7, 14 and 28 days to find out the factors influencing the performance of cement columns. Just as expected the cement columns cured for 28 days were proven more effective in reducing the compressibility parameters C c and C when tested using Rowe Cell Consolidation test. A single cement column with 60 mm diameter (area ratio = 0.16) recorded the smallest values of C c and C a compared to 45 mm diameter (area ratio = 0.09) of cement column (see Figure 11). α
2
1,8
1,6
1,4 c C , x 1,2 e d n I n o 1 i s s e r p 0,8 m o C
0,6 SC2 0,4
SC1 SC4 SC3
0,2
0 0
5
10
15
20
25
30
Curing Time, days
Figure 11. Compression Index versus Curing Time for Fibrous Peat Using Single Column
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Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat
3.7 Effect of a group of cement columns
A group of cement columns of diameter 15 mm each with a spacing of 2d were used. Based on Figure 12 when nine cement columns in the form of a 3 x 3 group tested, compressibility parameters were reduced more effectively than only four cement columns (2 x 2) used at the same spacing. This means that compressibility parameters decreased with an increasing number of cement columns in a group. Technically group of nine cement columns have larger area ratio of 0.09 compared to group of four cement columns with area ratio of 0.04, which influence the compressibility. Again the 28 days of curing time has significant impact on the final compressibility parameters values recorded. 1,8
1,6
1,4
1,2
c C , x e d 1 n I n o i s s e 0,8 r p m o C
0,6 SC2 SC4
0,4
GC1 GC2 0,2
0 0
5
10
15
20
25
30
Curing Time, days
Figure 12. Compression Index versus Curing Time for Fibrous Peat Using Group Column
4.
PARAMETRIC STUDY
A parametric study was conducted assuming a normally consolidated 5m-depth peat ground with embankment (see Figure 13). Assumptions and data used in the calculation were presented in Table 3. Using one dimensional consolidation theory and Anglo Saxon method, ultimate consolidation settlements were obtained using equation (9) and (10). p ⎛ H ⎞ ⎟ log p ⎝ 1 + eo ⎠
S p = Cc⎜
(9)
o
Note: S p = primary settlement of the soil layer (m), H = initial thickness of the soil layer (m), Cc, = compression index, eo = initial void ratio, p = total pressure acting at the middle of soil layer (kPa), po = effective overburden pressure acting at the middle of soil layer (kPa) S s = C H log
t s
α
506
t p
(10)
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Note: S s = secondary settlement of the soil layer (m), H = initial thickness of the soil layer (m), C = coefficient of secondary compression, t s = duration of load (days), t p = duration of primary consolidation (days) α
Figure 13. Illustration of Case Study Used for Parametric Study
The following data in Table 3 are based on the data obtained from experimental work carried out in the laboratory and mentioned earlier in this paper. However, the unit weight of fill material was assumed. Table 3. Typical parameters used in settlement calculations Parameter Value Specific Gravity, Gs 1.4 Initial Void Ratio, e o 10 Natural Moisture Content, wo 300% 18 kN/m3 Unit Weight Fill, γd
5.
DESIGN CHART DEVELOPMENT
With the establishment of geotechnical database on index properties of peat, primary and secondary x-axis for the following chart in figure 14 was constructed for fibrous type of peat soil. Data comprise of C c and C values from fibrous peat sample with corresponding organic content were then plotted in this chart. This chart is suitable as a design guide for engineers to predict settlements using two compressibility parameters Cc and C while the organic content or liquid limit of sample is determined from simple laboratory test. This chart is only applicable for fibrous type of peat with organic content more than 70 % and fiber content more than 66 %. α
α
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Preliminary Design Chart of Cement Columns for Deep Soil Mixing Method in Tropical Peat Liquid Limit, % 249
255
294
4
0,12
3,5
Cα
Cc
0,1 C , n o i s s 0,08 e r p m o C y r a 0,06 d n o c e S f o 0,04 t n e i c i f f e o C
3 c C , x 2,5 e d n I n o 2 i s s e r p m1,5 o C
1
0,02 0,5
0
0 73
75 Organic Content, %
88
Figure 14. Organic content (and liquid limit) versus compression index and coefficient of secondary compression.
Maximum reduction in C c value with the corresponding value of length to diameter ratio (l/d) of each cement column is then plotted in Figure 15. Based on this figure it shows that small l/d ratio of cement column is effective in decreasing compression ratio value. This chart could be used as a design guide to select the effective dimension of cement column for deep soil mixing method in tropical peat soil. Effective l/d ratio can be determined either by using the chart or from the given formula. For example for fibrous soil with 75 % organic content, based on Figure 14, C c value of 1.6 is predicted. Using 60 % of reduction in C c value will give an improved value of 0.96 using cement column is predicted. Referring to Figure 15 for desired C c of 0.96, the effective l/d ratio of 0.8 is needed.
2,5
2
Cc = 0.721Ln(l / d) + 1.1436
c C , x1,5 e d n I n o i s s e r p 1 m o C
0,5 Tropical Fibric Peat
0 0
0,5
1
1,5
2
2,5
3
3,5
(l / d) ratio
Figure 15. Compression index versus l/d ratio.
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CONCLUSIONS
New and novel preliminary design chart has been established based on laboratory experimental data on fibrous peat soil reinforced with cement columns and validated using software. A significant reduction in compressibility was observed by increasing the diameter of the cement columns, increasing the number of cement columns and increasing the amount of cement in cement columns. REFERENCES
[1]. Jarret, P. M. Geoguide 6, Site Investigation for Organics Soils and Peat. JKR Document 207090341-95. Institut Kerja Raya Malaysia 1995. [2]. Huat, B. K. Organic and Peat Soils Engineering. Universiti Putra Malaysia Press , Serdang 2004. [3]. Skempton, A. W. and Petley, D.J. Ignition loss and other properties of peats and clays from Avonmouth, King’s Lynn & Cranberry Moss. Geotechniques. 1970 Vol 20, no. 4, pp. 343-356. [4]. De Haan, E. J. An overview of the mechanical behavior of peat and organic soils and some appropriate construction techniques. In Proceedings of Conference on Recent Advances in Soft Soil Engineering, Kuching , Sarawak, 1997 pp. 17-45. [5]. Kaniraj, S. R. and Joseph, R. R. Geotechnical behavior of organic soils of North Sarawak. Paper presented in 4th International Conference on Soft Soil Engineering, Voncouver Canada, October 46, 2006. [6]. Li, Q. and Lee, S. Stress Dependent Reservoir Properties. Paper presented in GEO Asia 2006 Petroleum Geology Conference. Kuala Lumpur Convention Center, Malays ia, June 4, 2006. [7]. Hobbs, N.B. Morphology and the properties and behavior of some British and foreign peats. Quaterly Journal of Engineering Geology 1986 19:7-80. London. [8]. Mesri, G. Coefficient of secondary compression, J. Soil Mech. Found. Div, ASCE. 1973 Vol. 99, no. SMI. [9]. Mesri, G. and Castro, A. C /Cc concept and K o during secondary compression. Journal of Geotechnical Engineering 1987 Vol. 123. pp. 230-247. α
,
[10].Mesri, G., Statark, T.D., Ajlouni, M.A. & Chen, C.S. Secondary compression of peat with or without surcharging. Journal of Geotechnical & Geoenvironmental Engineering., 1997 123(5), pp.441-421. [11].Paikowsky, S., Elsayed, A & Kurup, P.U. Engineering properties of Cranberry bog peat. In Proceedings of 2nd International Conference on Advances in Soft Soil Engineering and Technology, Putrajaya, Malaysia. 2003 pp. 153-171.
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