Effect of acid rain on geotechnical properties of composite fine-grained soil

Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 2, 2012 © 2012 by the authors – Licensee IJASER- Under Creative Commons License...
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Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 2, 2012 © 2012 by the authors – Licensee IJASER- Under Creative Commons License 3.0 Research article

www.ijaser.com [email protected] ISSN 2277 – 9442

Effect of acid rain on geotechnical properties of composite fine-grained soil 1*

Grytan Sarkar, 2Md. Rafiqul Islam, 3Muhammed Alamgir, 4Md. Rokonuzzaman 1 Lecturer, Department of Civil Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh 2 Undergraduate student, Department of Civil Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh. 3 Professor, Department of Civil Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh. 4 Associate Professor, Department of Civil Engineering, Khulna University of Engineering & Technology, Khulna-9203, Bangladesh. doi: 10.6088/ijaser.0020101007 Abstract: Generally the atmospheric releasing gaseous pollutants like sulfur dioxide and oxides of nitrogen travels very far away from their sources. These gaseous pollutants combined with moisture in the atmosphere to form sulfuric acid and nitric acid solutions that fall to earth in rain is termed as acid rain. Though there is no significant record of acid rain in Bangladesh but it may be a happen due to the increasing urbanization, heavy industrialization, climate change and global warming. The main objectives in this study is to pridict the probable effect of acid rain on geotechnical properties of soil inorder to increase our understanding and taking proper consideration during construction of substructure. At first, the collected soil samples were treated with two different acid of varying concentration through three setups. After that, the geotechnical properties of original and treated samples were determined. These test result shows that the physico-chemical behaviours, free swell index and consistency of soil were strongly affected by acid treatment due to rapid leaching of cations and the diminution of inter-particle repulsion. Besides that the unconfined compressive strength (UCS) and shear strength parameters decrease with the addition of acid rain and their increasing concentration because of the changing of internal structural of soil and reduction of the electric forces as concentration of exchangeable cations reduced on acid treatment. Key words: Acid rain, Physico-Chemical properties, Consistency, Swelling and strength properties.

1. Introduction Acid deposition into the soil in the form of acid rain is the result of sulfur and nitrogen dioxide being emitted into the air caused by the growth of industrialization. This leads to the creation of acidic compounds that are absorbed by clouds, which in turn makes rain or snow more acidic, traveling and landing in a different place, and changing the acidity of the water or land on which the chemicals fall. As most of the Asian countries are in the process of development, they are not responsible for acid rain. Indeed, while China and India account for 8 per cent and 2 per cent respectively of the cumulative CO2 emissions over the period 1900-2005, the US and the EU are responsible for more than half of these emissions. It not only affects the place where the pollution is emitted but it can be transported over thousands of miles. For example, Japan and Korea are suffering from Chinese pollution through acid rain, while Bangladesh suffers from Indian pollution. For example, in developing countries, people tend to rely on wood, dung or crop residues for domestic energy (www.articleinput.com, 2009). Exposure to this polluted air leads, among other things, to have adverse impacts on forests, freshwaters and soils, killing 68 * Grytan Sarkar (e-mail: grytan_ce04@yahoo .com) Received on Jan., 2012; Accepted on Feb. 16, 2012; Published on Feb. 26, 2012

Effect of acid rain on geotechnical properties of composite fine-grained soil

insect and aquatic life-forms as well as causing damage to buildings and having impacts on human health. Several processes can result in the formation of acid deposition in to the soil. In dry deposition, Nitrogen oxides (NOx) and sulfur dioxide (SO2) released into the atmosphere from a variety of sources fall to the ground and converted into acids when these deposited chemicals meet water. In the case of wet acid deposition, nitrogen oxides (NOx) and sulfur dioxide (SO2) are converted to nitric acid (HNO3) and sulfuric acid (H2SO4) through oxidation and dissolution (Pidwirny, M. 2006). The H+ content of acid rain falling for a small duration is very low yet its influence on the physical, chemical and engineering properties of soil will be alarming in near future as ever growing industrialization/pollution will keep on substantially decreasing its PH. The enhanced rate of leaching of cations and absorption of H+, SO42-, NO3and CO32- alter its physical, chemical and engineering properties (Masashi, K., et al., 1997). It is thus one of the most influential environmental factors which directly affect the properties of soil (Yamaguchi, H, 1993). The present study is carried out on soil, collected from Khanjahan Ali Hall at Khulna University of Engineering & Technology (KUET) in Khulna, Bangladesh to find out physico-chemical and the engineering properties on exposure to acid rains of various simulated strengths.

2. Materials and methods 2.1 Geotechnical properties of Collected Soil To analyse the effect of acid concentration on soil nearly greyish coloured silty clay was used in this study, collected from backside of Khan Jahan Ali Hall at Khulna University of Engineering & Technology (KUET) in Khulna, Bangladesh. The collected sample was oven dried at about 1050C to remove the moisture content and suppress the microbial activities. Soil samples were screened through 4.75 mm sieve to obtain the geotechnical properties of original sample. The geotechnical property of original soil samples is shown in Table 1. Table 1: Characteristics of original samples Characteristic P

H

Result 6.83

Organic matter (%)

8.57

Liquid Limit (%)

54

Plastic Limit (%)

30

Shrinkage Limit (%)

18

Free Swell Index (%)

20

Specific Gravity

2.78

Unconfined Compressive strength (UCS), qu (MPa)

8.09

Cohesion, C (KPa)

44.4

Angle of Internal Friction, φ (degree)

18.26

According to the AASHTO classifiation systems, the soil is characterized as A-7-6 and acoording to the Unified soil classification sytems, samples are naming as CL (Clay with low plasticity). The particle size distribution of the collected original soil is show in figure 1. The diagram below shows the grain size distribution of the clayey soil collected for this study.

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Effect of acid rain on geotechnical properties of composite fine-grained soil

Figure 1: Particle size distribution of original soil

2.2 Preparation of Tested Sample The oven dried samples were grinding and passing through 4.75 mm sieve. Soil samples which are passing through 4.75 mm sieve were mixed with different concentration of H2SO4 and HNO3 acid and distilled water as shown in Table 2. The proportion of H2SO4 and HNO3 acid were taken as near as to the concentration of these acids in acid rain. These samples were shaken with mechanical shaker for about 8 hours to obtain a homogeneous mixture of soil and acid. After proper shaking of the samples were kept overnight at room temperature. The treated samples were then filtrated for the extraction of water from it and kept it on the ground for sun drying. The drying samples were then grinding and sent to the laboratory for determining the geotechnical properties of that soil. Table 2: Combination scheme of soil samples Samples Description Samples ID

st

1 setup

2nd setup

3rd setup

Strength of Acid

Soil

1N

1N

Distilled

sample(Kg)

H2SO4(ml)

HNO3(ml)

Water(ml)

Original soil

1

--

--

--

--

S-1

1

5

--

995

0.005 N

S-2

1

10

--

990

0.01N

S-3

1

20

980

0.02N

S-4

1

50

--

950

0.05N

N-1

1

--

5

995

0.005 N

N-2

1

--

10

990

0.01N

N-3

1

--

20

980

0.02N

N-4

1

--

50

950

0.05N

SN-1

1

5

5

990

--

SN-2

1

10

10

980

--

SN-3

1

20

20

960

--

SN-4

1

50

50

900

--

2.3 Testing Protocol A series of tests were conducted to determine the effect of acid on the consistency, swelling, shrinkage Grytan Sarkar et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 1, 2012

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Effect of acid rain on geotechnical properties of composite fine-grained soil

and strength characteristics of soil through three test setup. The pH of the soil is a useful variable in determining the solubility of soil minerals and the mobility of ions in the soil. The PH of the original and the acid treated soils were determined by ASTM D4972. To perform these test 10g of air dried samples were mixed with 10mL of distilled water thoroughly and kept it about one hour. After that the value of PH were recorded by PH meter. Consistency of soil is expressed in terms of liquid limits and plastic limits are extensively used to characterize the fine-grained fractions of soils. Factors which significantly affect the consistency of soil depends on the type of soil, electrical charge of exchangeable cations absorbed by soil particles and concentration of cations in soil water( Masashi, K., et al.,1997). Acid rain increases the exchange between H+ and cations like potassium (K), magnesium (Mg) and calcium (Ca) in the soil. These cations are liberated into soil and can be rapidly leached out in soil solution along with sulphate from acid input (Van Breeman et al., 1984). The effect of shrinkage of fine grained soils are of considerable significance to cause serious damage to small building and highway pavements Consistency of the original and treated soil samples were determined by Atterberg limit test(ASTM D-4318-10). Specific gravity is is the indirect measurement of density of soil and used in phase relationship of soil such as void ratio and degree of saturation. Specific gravity of original and ash treated soil samples were determined according to ASTM D854-10. Free swell index of soil samples were determined as per as IS: 2720(Part-40). Ten grams of soil samples were put into two 100ml glass cylinder and the remaining 90ml of the cylinder was filled with distilled water and kerosene respectively. After keeping it overnight the volume of soil in each cylinder was measured and from this volume free swell index of soil was determined from the equation shown in below. Free swell index, %=

Volume of in distilled water − Volume of in distilled ker osene x100 Volume of in distilled ker osene

All the test specimens were prepared at the optimum moisture content before performed the remaining selected properties. After adding water the test specimens were prepared with the standard Proctor compaction test (ASTM D 698). The specimens were demolded after completion of compaction and samples of different size were prepared as per requirement for performing the selected test in uncured condition. The uncured unconfined compressive strength of the specimens was determined according to ASTM D-2166-98 and cylindrical specimens of 36-mm-diameter and 71-mm-lengthwere used for this test. Drained shear strength parameters(c & φ) were determined by direct shear test (ASTM D3080-3) of the compacted uncured soil specimens. To perform these tests, three samples of 60mm diameter and 25 mm height were prepared from the compacted samples

3. Results and discussion 3.1 Physico-Chemical Properties The variations of PH of original and treated soils are illustrated in Figure 2. The value of PH decreases as the concentration of acid increases in all the three cases. This Figure shows that the value of PH decreases more rapidly in case of 1st setup containing H2SO4 acid treated soil than 2nd setup containing HNO3 treated soil for the same acid concentration. In case of 3rd setup where both H2SO4 and HNO3 were using for treating the soil is much more susceptible to decrease the value of PH than the 1st and 2nd setup. The decrease in soil PH is attributed to increases in the exchange between H+ in acid rain and cations like magnesium (Mg) and calcium (Ca) in the soil.

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Effect of acid rain on geotechnical properties of composite fine-grained soil

Figure 2: The effect of various acids with different concentrations on PH of soil The percentage of organic matter present in the soil is decreased for all the three setup and with the increase of acid concentration as shown in Figure 3. This Figure shows that the percentage of organic matter decreases more rapidly in case of 1st setup than 2nd setup for the same acid concentration. In case of 3rd setup, the decrease in percentage of organic matter is much more susceptible than the 1st and 2nd setup. These reductions in organic matter of soil depicts that it’s digested as the concentration of acid increases and is more susceptible for HNO3 than H2SO4.

Figure 3: The effect of various acids with different concentrations on organic content of soil

3.2 Consistency Characteristics Generally consistency of soil is expressed in terms of liquid limit, plastic limit and shrinkage limit. The change in liquid limit of soil for the various acid of different concentration is shown in Figure 4. This Grytan Sarkar et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 1, 2012

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Effect of acid rain on geotechnical properties of composite fine-grained soil

figure illustrated that the value of liquid limit decreased for the increase of acid concentration. The results indicate that using acid solutions as pore fluids decreases the liquid limit of the mixtures. The effect of H2SO4 acid on the liquid limit is more than HNO3. In case of 3rd setup, the liquid limit is much more susceptible on acid than the 1st and 2nd setup. The similar trend were found in case of plastic limit is shown in Figure 5. This reduction in liquid limit and plastic limit of soil is the result of rapid leaching of cations and the diminution of inter-particle repulsion due to the addition of acid. Besides that, as the concentration of acid increases, the tendency of cation exchange increase which results a rapid movement of soil particles in a lower water content and thus the liquid and plastic limit of soil decreases.

Figure 4: The effect of various acids with different concentrations on liquid limit of soil

Figure 5: The effect of various acids with different concentrations on plastic limit of soil

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Effect of acid rain on geotechnical properties of composite fine-grained soil

On the other hand the shrinkage limit shows a different trend from the liquid limit and plastic as shown in Figure 6. In this illustration, the value of shrinkage limit increases with the increases of acid concentration. This increase in shrinkage limit is attributed to increase in inter particulate distances due to reduction in the forces between soil particles.

Figure 6: The effect of various acids with different concentrations on shrinkage limit of soil

3.3 Free Swell Index The variation of free swell index with various acid of different concentration is illustrated in Figure 7. This figure depicts that the value of free swell index decreases with the addition of acid and increasing of acid concentration. The H+ in the acid increases the rate of cation exchange which results a rise of free energy for forcing water to leave out from the inter-particle region and leads to a decrease in swelling volume. As the concentration of acid increases the free energy for removing water into the inter-particle region also increases as well as the swelling volume of soil decreases.

Figure 7: The effect of various acids with different concentrations on liquid limit of soil Grytan Sarkar et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 1, 2012

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Effect of acid rain on geotechnical properties of composite fine-grained soil

3.4 Specific gravity The change in specific gravity for the addition of various acid of different concentration is illustrated in Figure 8. There is no significance change in specific gravity of soil for acid of low concentration. The specific gravity of soil decreases with the increases of acid concentration.

Figure 8: The effect of various acids with different concentrations on specific gravity of soil

3.5 Strength characteristics The UCS of original soil and acid treated soil are illustrated in Figure 9. This figure depicts that there is a little effect of acid on the compressive strength of soil. The effect of H2SO4 acid on the UCS is more than HNO3. In case of 3rd setup, the UCS is much more susceptible on acid than the 1st and 2nd setup. The similar trend were found in case of plastic limit is shown in Figure 5. The compressive strength of soil decreases as the addition of acid and for their increasing amount of acid concentration. When acid were mixed with soil, the inter-particle attraction of soil decreased. The particle of soil moves more rapidly and changes their internal structure through cations exchange with H+.

Figure 9: The effect of various acids with different concentrations on UCS of soil Grytan Sarkar et al., Int. Journal of Applied Sciences and Engineering Research, Vol. 1, No. 1, 2012

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Effect of acid rain on geotechnical properties of composite fine-grained soil

The change in cohesion of soil due to the acid treatment of varying concentration is shown in Figure 10. This figure illustrate that the value of cohesion decreases with the addition of acid and to the increases of acid concentration.

Figure 10: The effect of various acids with different concentrations on cohesion of soil

Figure 11: The effect of various acids with different concentrations on liquid limit of soil

4. Conclusions A study has been conducted to investigate the probable effect of acid rain on the geotechnical properties of soil. Though there is no record of significance acid rain in Bangladesh but in the recent time Bangladesh is hardly affected by the climate change. Generally two acids are formed after acid rains (H2SO4 and HNO3) which are responsible for the changing of geotechnical properties of soil. In this study three setups were conducted to observe the effect of acid on some geotechnical properties of soil. The following conclusions, based on the test results in this study, are drawn.

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Effect of acid rain on geotechnical properties of composite fine-grained soil

1. Acid rain results in changes in physico-chemical characteristics of soil due to cations exchange between H+ and cations present in soil. PH of the soil decreases as the addition of acid and with their increasing concentration. 2. Using acid solutions as pore fluids decreases the liquid limit and plastic limit of the mixtures. Higher cation valance and acid concentration cause higher decrease in liquid limit and plastic limit. On the other hand the shrinkage limit of soil shows opposite trend due to reduction in the forces between soil particles. 3. The swelling volume of soil decreases with the addition of acid and their increasing concentration by removing the water into the inter-particle region. 4. The value of UCS and shear strength parameters decreases with the addition of acid and their increasing concentration due to the changing of internal structural of soil and reduction of the electric forces as concentration of exchangeable cations reduced on acid treatment.

5. References 1. ASTM D 4972, D 4318-10, D 854-10, D 698, D 2166-98, D 3080-3,( March 2005), Soil and Rock (I), 4(8). 2. IS 2720 part 40,1997. Methods for Testing of Soils. 3. Masashi, K., Changyun, Y. and Takeshi, K.,1997. Effect of Acid Rain on Physico-Chemical and Engineering Properties of Soils, Japanese Geotechnical Society, 37 (4), 23-32. 4. Pidwirny, M. 2006. Acid Precipitation". Fundamentals of Physical Geography, 2nd Edition, date Viewed. 5. Sharma, P., Vyas, S.,mahure, N.V., Kachhal, P.I. Sivakumar, N. and Ratnam, M. (2011), Effect of acid rain on geotechnical properties of soils of high and low plasticity, International Journal of Earth Sciences and Engineering, 04, 158-160. 6. Van Breeman, N., C.T. Driscoll and Mulder, J., 1984, Acidification and Internal Proton Sources in Acidification of Soil and Water. Nature,” London, 307, 599-604. 7. Yamaguchi, H., Ui, M., Fukuda, M. and Kuroshima, I.,1993. Change in Environmental Properties of Soils taking Acid Rain into Consideration, Tsuchi-to-Kiso, 41(6), 47-52. 8. Environmental situation of the asian countries, available at http://www.articleinput.com/e/a/title/ The-environmental-situation-of-the-Asian-countries/, accessed during January, 2012.

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