Journal of Engineering Geology, Vol. 9, No. 2, Summer 2015

The Effect of Wetting-Drying Cycles and
Plasticity Index on California Bearing Ratio of Lime Stabilized Clays
*Naeini S. A., Gholampoor N., NajmosadatyYazdy S. A.,
Department of Civil Engineering, Imam Khomeini
International University,Iran
Received: 6 Oct 2013 Revised: 8 March 2014
Abstract
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

This paper aims to present an experimental and numerical study on the effect of wetting-drying cycles and plasticity index on the California Bearing Ratio (CBR) of lime stabilized clayey soils. The numerical analysis was carried out based on finite element method for comparison between results of experimental and numerical studies. Three clays with different plasticity indices were mixed with various amounts of hydrated lime and compacted at optimum water content. The CBR tests were conducted to the soils and admixtures after specified curing time and various numbers of wetting-drying cycles. The experimental results indicate that addition of lime content up to 4% causes significant increase in the CBR values. Based on the obtained results the CBR decreases during the wetting phase and increases during the drying phase of each cycle. After 3 cycles the CBR values of lime stabilized clayey soils are increased. Also, for stabilized clays by increasing the plasticity index, the CBR values resulted by increase of lime content are decreased. The comparison between numerical and experimental analyses indicates a good agreement between results.
Keywords: Lime stabilized clay, Plasticity Index, Wet-Dry cycle, CBR tests, Numerical analysis.

*Corresponding author [email protected]
Introduction
The reduction in strength of soft clays that causes bearing capacity failure and excessive settlement leads to severe damage to buildings and foundations. The stabilization, especially with lime, is a common applied method among others because of its effectiveness and economic benefits. Almost all fine-grained soils can be modified by lime, but the most dramatic improvement occurs in clayey soils of moderate to high plasticity.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Lime-clay reactions occur via two distinct processes (Clare and Cruchley [1], Eades and Grim [2], Wang et al. [3], Greaves [4], Holt and Fleer-Hewish [5], Rogers and Glendinning [6], Boardman et al. [7]): (i) rapid ion exchange reactions known as soil improvement or modification and (ii) slower soil-lime pozzolanic reactions known as stabilization/solidification. Based on the studies conducted by Thomson [8], Thompson [9], as a result of lime stabilization, clay particles stick to each other and form larger particles. They have found that the plasticity indices are reduced and CBR values are increased.
Akinlabi [10] investigated the stabilization of Lateratic soils in Zarya, Nigeria with hydrated lime, by performing wet CBR tests. His results indicate that by addition of lime, maximum dry density and plasticity index are reduced, but optimum water content and liquid limit are increased. Rahman [11] indicated that for Lateratic soils stabilization, addition of 5% of lime can improve strength properties of Lateratic soils to use in subgrade layers, while Bell [12] found that the optimum addition of lime needed for the stabilization of clays is between 1% to 3% and Kassim and Chern [13] presented 3% to 6% of lime as an optimum additional lime content. Researchers have illustrated that the impact of lime addition on strength of clayey soils depends on soil type, curing time, test method, moisture content, soil unit weight and time elapsed between mixing and compaction
(Mitchell and Hooper [14], Ingles and Metcalf [15], Al-Rawi [16],
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Lees et al. [17], Bell [12], Locat et al. [18], Greaves [4], Rao and Venkataswamy [19]). Kamon and Katsumit [20] investigated engineering properties of soil stabilized with Ferrum lime, and they found that, lime and ferioxid admixture is effective in improvement of durability of stabilized road bases. Guettala et al. [21] evaluated durability of lime stabilized earth blocks by carrying out wettingdrying and freezing-thawing tests on soil samples of Biskra (south east of Algeria), they concluded that, in both wetting-drying and freezingthawing tests to 12 cycles, increasing of compacting stress and lime content improves the compressive strength and reduces weight loss and water absorption. Kavak et al. [22] explained that the use of lime stabilization for road construction reduces the thickness of the upper layers due to high CBR values and makes the overall constructions more economical. They concluded that, permanent deformation in green and brown lime stabilized clays is reduced from 18 mm to 1 mm and 24 mm to 4 mm, respectively. Khattab et al. [23] evaluated the effect of lime and industrial waste lime admixture on strength, durability and hydraulic properties of clays, and found that by increasing in setting time and stabilizer content, confined compressive strength is increased. The studies of Abdel Majid and Muzahim [24] on effect of hydrated lime on engineering behavior of expansive soils indicate that, addition of hydrated lime to this type of soils is so effective on swelling pressure and swelling potential reduction. Manasseh and Olufemi [25] studied the effect of lime on geotechnical properties of Igumale shale, and concluded that, by addition of 14% lime to Igumale shale, liquid limit and plasticity index of soil is reduced and plastic limit is increased. Also, they found that maximum CBR value of 37% is achieved in this amount of lime. Soni and Jain [26] evaluated the effect of wetting-drying and freezing-thawing cycles on tensile strength of Black Cotton soil stabilized with lime and fly ash. It was found that maximum tensile strength arise, when lime/fly ash ratio is between 1:4 and 1:3. Tawfiq and Nalbantoglu [27] investigated swell-shrink behavior of expansive clays. The results indicate that wetting-drying cycles caused an increase in the swell potential of the soils which were subjected to full swell-full shrinkage cycles. Sahoo and Pradhan [28] investigated the effect of lime stabilized soil cushion on strength behavior of expansive soil, by conducting Unconfined Compression and CBR tests. The test results reveal that maximum increase in strength was achieved after 14 days of curing for 8% lime content. Harichane et al. [29] investigated the effect of lime and natural pozzolana admixture on durability of clayey soils by performing a study on two types of clays, red and grey. The results indicate that stabilized samples have more workability and can endure 12 wetting-drying cycles. Akcanca and Aytekin [30] investigated the influence of wetting–drying cycles on swelling pressures of sand–bentonite mixtures before and after lime treatment of the mixtures. Their results indicated that the swelling pressure is decreased when lime is added to the mixtures. In addition, decrements were observed on swelling pressures by wetting–drying cycles.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

The lime stabilized clayey soils used for highway construction, airports and building foundations are usually exposed to different environmental conditions. One of most common condition is wet-dry process. Due to the importance of this issue and a few experimental works about the effect of wetting-drying conditions on clayey soil’s strength and no performance of CBR tests in this issue, and also using a finite element method has not been extensively analyzed and developed about this thus, the purpose of this study is to present an experimental and numerical analysis of the effect of plasticity index and wet-dry cycles on the CBR value of clayey soils stabilized with hydrated lime.
Experimental Study
1. Materials used
Three clayey soils used in the present experimental test were obtained from the clay deposits of Abyek, Iran. They are defined as soil (I) and soil (II) with low plasticity soils (CL) and soil (III) defined as high plasticity soils (CH) according to the unified soil classification system ASTM D422-63 [31]. Due to results of XRD test, these clayey soils consist of montmerillonite, nontronite, halloysite, palygorskite and hydrobiotite. The ASTM D4318-00 [32] test was used for the determination of liquid and plastic limits of the soils. The grain size distribution of the selected reference soils are shown in Figure 1. Also, physical and mechanical properties of the selected reference soils and mixture of them with optimum lime content are presented in Tables 1 and 2, respectively.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

The material used for stabilization of the considered clays in this study, is hydrated lime supplied by the Hamadan Lime Company. This type of lime has been selected because its usage is safer and more common in industry. It is very fine and passes through an 80 μm sieve opening and contain 85-90 percent Ca (OH) 2. The standard chemical and physical properties of the lime used are given in Table 3
208534-83921

.

Figure1. Grain size distribution curve of selected soils

Table1. Physical property of tested soils

-71881-773696

2418334-721880

2926334-721880

CL
II

CH
III
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Table3. Physical and Chemical properties of lime
property Value
Bulk density (Kg/m3) Max: 480
Physical appearance white powder
Specific gravity 1.25-1.5
Over 80 μm (%) 0
Over 90 μm (%) 2-4
Ca (OH) 2 (%) 85-90
Active CaO (%) 59.5-65.2
H2O (%) 1-2
Fe203 (%) 1.5-2
AL203 (%) 2-3
MnO (%) 2-3
MgO (%) 1-2
2. Preparation and Test procedure
For preparation of samples, lime was added to each reference soil at the room temperature (

) in the order of 4%, 6% and 8% by weight. The lime was thoroughly mixed by hand until homogeneity was reached, and the mixture was quickly stored in a large plastic bag to prevent losing of moisture content. All lime treated soil specimens were tested after curing time of 7 days. The optimum water content of the samples and the maximum dry unit weights were analyzed by the Standard Proctor Tests in accordance with ASTM-698-00 [33]. The Proctor Tests were performed for three clays.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

In the CBR experiments performed, the reference clays and clays mixed with 4%, 6% and 8% lime were prepared at their optimum water content and were compacted. The prepared samples were rested for 7 days cure time at room temperatures. The CBR tests were performed in accordance with ASTM D 1883 [34] on wet and dry samples, before and after stabilization. The bearing ratio mould is a rigid metallic cylinder with an inside diameter of 152 mm and a height of 178 mm. A mechanical loading machine equipped with a movable base that moves at a uniform rate of 1.27 mm/min and a calibrated proving ring is attached with a piston, which penetrates into the compacted specimen. The diameter of the piston is 49.6 mm. The loads are carefully recorded as a function of penetration up to 24 mm.
In order to determine the shear strength parameters of unstabilized and lime stabilized samples, a series of direct shear box tests was carried out in accordance with ASTM D 3080-03 [35]. For these tests, samples were placed in the standard shear box of 60 mm× 60 mm in plane and 25 mm in depth. The shear strength parameters such as cohesion and internal friction angle were obtained by performing direct shear tests at the vertical normal stress of 50, 100 and 200 kPa. The strain rate was 0.1 mm/min in all tests.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

The wet–dry cycle tests were performed to investigate the effect of wet-dry conditions on CBR values of lime stabilized clays. After preparing the samples at curing time of 7 days, the wet-dry cycle test was undertaken on samples. This process has some steps for each type of clays and admixtures as follow: (i) six samples of three clays with different plasticity index stabilized with lime were submerged in tap water to absorb water over 24 h. (ii) After 24 h, one of the wetted sample was tested by CBR test and five of the samples were then allowed to air-dry at room temperature of

. The drying of samples required 24 h. (iii) After 24 h, one of the samples that were subjected to 1 wet-dry cycle is tested by CBR test and the others are submerged in water and then, step (ii) was repeated again. This process was continued until CBR test was performed on the last sample that is subjected to 3 wet-dry cycles.

Numerical Study
Finite element analyses
The finite element method has been widely used in analyzing mechanical behavior of soil based materials and structures that deals with soil in recent years. Most of the analyses were used to study stress-strain behavior of soil underlying foundations, earth dams, retaining walls and etc. In this paper, due to experimental study performed in previous sections, in order to investigate the correspondence of results of numerical and experimental analysis, a series of numerical analyses based on Finite Element Method by using ABAQUS 6.9 software were conducted on simulated model of the considered soil. In fact, in this section CBR test is simulated.
126873825500

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Downloaded from jeg.khu.ac.ir at 11:31 IRST on Saturday October 28th 2017 [ DOI: 10.18869/acadpub.jeg.9.2.2817 ]

Due to geometry of soil sample and dimension of mould in CBR test, axisymmetric stress method was used for static analyses. In this model, mechanical properties of test such as, penetration rate and dimension of penetration piston, applied load from annular metal weights and also the interactions between soil and inside wall of mould



قیمت: تومان

دسته بندی : زمین شناسی

دیدگاهتان را بنویسید