Dispersive Clay: Influence of Physical and Chemical Properties on Dispersion Degree Abdelkader Belarbi PhD Student Department of Civil Engineering, Faculty of Technology,, Tlemcen University Algeria;
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Abdeldjalil Zadjaoui Teacher-researcher at Tlemcen University Department of Civil Engineering, Faculty of Technology,, Tlemcen University Algeria;
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Abdelmalek Bekkouche Professor at Tlemcen University Department of Civil Engineering, University Center of Ain Temouchent Algeria
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ABSTRACT Dispersive soils are characterized by an unstable structure, easily flocculated in water, and very erodible (Zorluer et al., 2010). Using dispersive clay soils in hydraulic structures, embankment dams, or other structures such as roadway embankments can cause serious engineering problems if these soils are not identified and used appropriately. This .problem is worldwide, and structural failures attributed to dispersive soils have occurred in many countries. (Knodel, 1991). In our laboratories, only AFNOR tests it’s used to identifying soils in road embankment and small hydraulic structures projects. However, there is simple method to identify the dispersivity of the soils and even more difficult to quantify the dispersivity. Visual classification, Atterberg’s limits and particle size analysis do not provide sufficient basis to differentiate between dispersive clays and ordinary erosion resistant clays (Umesha and al., 2011).Dispersive clay identified by ASTM tests such as: Pinhole test, Crumb test, double hydrometer test and chemical test. But the question is there are relations between AFNOR tests identifying and dispersion parameters? In this paper, we studied the dispersivity with chemical tests and double hydrometer test for different type of soil from the west of Algeria after identification with AFNOR tests, and we used correlations to determine relations between different parameters.
KEYWORDS:
Dispersion; ASTM; AFNOR; correlation; SAR; SP; Ip; Activity.
INTRODUCTION Dispersive soils are a major contributing factor to piping failure of embankments dams, particularly for small dams constructed without filters and often with poor construction supervision (Fell et al., 1992). Foster et al. (2000) conducted a statistical study on 11,192 - 1727 -
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hydraulic structures in the ground; 136 underwent disorders with 6% by landslide, 46% by internal erosion and 48% by overflow (Rosquoët, 2005). The erosion occurs when shearing stress induced by fluid flow on a surface is large enough to cause particle removal from the surface. The resistance to erosion is offered by the submerged weight of the sediment, i.e. gravity forces for non-cohesive soils. But in cohesive soil the structure of the soil and the interaction between pore and eroding fluids at the surface is the phenomenon involved in soil erosion. The amount and type of clay, pH, organic matter, temperature, water content, thixotropy and type and concentration of ions in the pore and erod-ing fluids are the factors that affect the critical shear stress required to initiate erosion (Umesh and al., 2011). In the practice of soil mechanics, correlations between parameters are used as a means of monitoring the results of field and laboratory tests, and as a means of making complementary values of certain parameters depending on others. And to estimate certain soil properties based on the characteristics that were measured (Magnan, 1993).
DISPERSIVE SOILS Dispersive clays are a particular type of soil in with the clay fraction erodes in the presence of water by a process of defloculation (Forrest, 1980). These soils are highly erodible in nature and tend to crumble in the presence of water and erode under low flow rate, which leads to stability problems in earthworks. Erosion due to soil dispersion depends on the mineralogy and chemical composition of clay as well as on the salts dissolved in interstitial water. Dispersive clays are highly erosive because they contain a higher percentage of dissolved sodium cations in their pore water than do ordinary clays. The sodium increases the thickness of the diffused double water layer surrounding the individual clay particles. This causes the repulsive forces to exceed the attractive forces so that the particles readily go into suspension in the presence of water (McElroy, 1987). Sodic clay (high ESP)
In a sodic soil, sodium is adsorbed onto the surface of the clay. It is a large ion with a weak charge. The positive ions bind the negatively charged clay particles together. Non-sodic soil
Sodic clay + water
Aw water is added to a sodic soil, water is attracted to the sodium. The ions hydrate, forcing the plates apart. The ions role in binding the clay platelets is overcome, and the clay swells then disperses with water Non-sodic soil + water
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In a non-sodic soil calcium is adsorbed onto the surface of clay. This is a small sized ion with a strong charge.
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Water can enter between the platelets in a nonsodic soil, which leads to swelling. However, the binding forces between the particles by calcium ions are never completely overcome. The soil does not disperse.
Figure 1: Behavior of non sodic and sodic soils in water (Anon, 1999).
LABORATORY TESTS TO IDENTIFICATION OF DISPERSIVE CLAYS Many investigations have been performed to refine procedures for identifying dispersive clays, because they cannot be identified by the conventional laboratory index tests such as visual classification, gradation, specific gravity, or Atterberg limits. Observations show there can be great differences in erodeability in materials with identical visual appearance and index properties when the samples are taken from locations only a few feet apart (Vyas and al., 2011). The four laboratory tests most generally performed to identify dispersive clays are the crumb test, the double hydrometer test, the pinhole test and the test of dissolved salts in the pore water. The crumb test and the pinhole test are qualitative test, so they are not useful in correlation study. We use double hydrometer tests in this paper.
Double hydrometer test The particle size distribution is first determined using the standard hydrometer test in which the soil specimen is dispersed in distilled water with strong mechanical agitation and a chemical dispersant. A parallel hydrometer test is then made on a duplicate soil specimen, but without mechanical agitation and without a chemical dispersant. The "percent dispersion" is calculated by dividing the percent passing the 5-μm size using this test method by the percent passing the 5-μm size obtained using Test Method D 422 and by multiplying the result by 100.
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Figure 2: Double hydrometer test for the determination of percentage of dispersivity. a: grain size curve determined with chemical dispersant; b: grain size curve determined without chemical dispersant but with strong mechanical agitation (Vanicek, 2008).
D=
%pas sin g5µm( withoutdispersantagent ) B *100 = *100 %pas sin g5µm(s tan dard) A
(1)
Criteria for evaluating degree of dispersion using results from the double hydrometer test are: Table 1: Area of the dispersion according to the percent dispersion Authors ASTM D-4221 Decker et Dunnigan (1977)
Knodel (1991)
Percent dispersion (%) Near 100 Near 0 < 35 35 - 50 > 50 < 30 30 - 50 > 50
Dispersion property Completely dispersive Soil no dispersive no dispersivity problem probable dispersivity problem of dispersivity No dispersive Intermediate Dispersive
Total Dissolved Salts Test Soil is mixed with distilled water to a consistency near the liquid limit. A pore-water sample (“saturated extract”) is sucked out by a vacuum using a filter and finally the extract is tested to determine the quantities of the four main metallic cations in solution (calcium, magnesium, sodium, and potassium) in miliequivalents per liter. Sodium adsorption ratio (SAR) is used as a criterion of proportion of sodium to other cations (with neglecting potassium):
SAR =
Na + 1 (Ca + + + Mg + + ) 2
1/ 2
(2)
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Or with the help of a percentage of sodium – Na% (SP):
SP =
Na + × 100 TDS
(3)
where TDS is total dissolved salts total amount of dissolved cations in pore water ( TDS= Na + + K + + Ca + + + Mg + + ).
Figure 3: Relationship between dispersion and soil pore water chemistry based on pinhole erosion tests and experience with erosion in nature (Sherard et al., 1977).
Sites Location and identification of the studied soils The experimental study was performed on reworked soils which come from the west of Algeria (figure 4). Mechanical and physico-chemical identification tests were performed in the Geotechnical Laboratory of the Faculty of Technology, University of Tlemcen and in the Laboratory of Public Works of West (LTPO). The results are summarized in Table 2.
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Figure 4: Location of sampling sites. Table 2: Physico-chemical characteristics of soils. Soil N° 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Finer (%) 91,60 97 96,50 96 98,80 95,96 98 95,10 77 71 92,50 56 81 48 57 62 50 52 71 68 97 88
Clay (%) 62 57 61 53 56 61 63 66,5 43 38 57 31 33 20 27 41 15 18 41 39 68 38
Wl (%) 51,83 71 65,12 61 66,20 65,12 58,00 68,45 46 44 69,8 43 35 29 29 35 29 23 39 40 103,4 31
Wp (%) 27,10 26 33,85 23 30, 30,85 25,00 26,41 22 22 26,46 22 17 16 14 20 24 13 18 19 48,06 18
Ip (%) 24,73 35 31,27 28 36,20 35,55 33,00 42,04 24 22 43,34 21 18 13 15 19 5 10 21 21 55,34 13
Activity 0,399 0,614 0,513 0,528 0,646 0,583 0,524 0,632 0,558 0,579 0,760 0,677 0,545 0,650 0,556 0,463 0,333 0,556 0,512 0.538 0,814 0,342
Vbs (cm3) 7,60 7,20 9,70 6,50 9,00 9,40 7,90 8,00 5,30 6,50 11,40 4,80 4,40 4,50 3,80 10,6 4,00 4,20 10,2 9,5 26,5 4,50
S.S.T (m2/g) 159,60 151,20 203,70 136,50 189,00 197,40 165,90 168,00 111,30 136,50 239,40 100,80 92,40 94,50 79,80 222,60 84,00 88,20 214,20 199,50 556,5 94,50
CaCo3 (%) 2,04 13 13,40 34 16,45 13,84 17,00 2,47 20 20 3,18 6 31 14 15 24 9 7
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Dispersion characterization of samples Double hydrometer test Table 3: Percent dispersion of soils studied. Soil N° 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
< 5 µm (standard test) (%) 83,39 73,32 83,67 9 71,76 79,22 80,98 80,28 70,52 62,49 61,98 81,79 52,28 54,65 36,40 39,72 54,83 22,55 20,89 38,21 39,13 84,55 45,08
< 5µm (without dispensing) (%) 17,92 23,71 31,25 21,76 33,79 32,67 36,50 18,47 17,02 14,66 54,83 21,27 14,66 11,76 9,98 15,47 3,35 11,36 12,68 12,22 55,00 9,79
Percent dispersion (%) 21,49 32,33 37,35 30,32 42,66 40,35 45,47 26,20 27,24 23,65 67,04 40,67 26,82 32,30 25,12 28,21 14,83 54,38 33,19 31,24 62,69 21,73
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Chemical test Table 4: Total Dissolved Salts of soils studied. Soil N°
TDS (mEq)
SAR
SP (%)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
3,94 4,29 6,28 4,35 9,98 6,93 3,79 19,20 3,82 3,09 17,86 4,56 3,61 3,39 3,18 5,41 3,58 3,39 5,19 4,88 9,29 5,33
1,57 1,41 3,75 1,41 8,32 4,17 2,35 4,11 1,87 2,14 32,55 1,73 1,22 1,39 1,21 4,85 1,01 1,04 4,58 4,02 48,78 1,53
38,48 37,65 63,26 37,30 80,74 64,54 55,04 47,10 47,71 55,70 96,37 41,87 35,78 40,38 37,49 73,16 30,85 37,29 72,05 69,48 98,33 36,19
Simple Correlation Relationship between the percent dispersion and soil activity Figure 5 shows the relationship between the dispersion index and the activity of the soils studied, the obtained regression line on these data correspond to an average value of correlation coefficient (0.54). But we see that dispersive soils (higher percent dispersion) are more active.
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Figure 5: Correlation between the percent dispersion and soil activity.
Relationship between SAR and Surface Specific Figure 6 shows the relationship between the Sodium Adsorption Ratio and Surface Specific for studied soils, in this event, the correlation coefficient is higher (0.76), soil with high SAR have a high specific surface.
Figure 6: Correlation between SAR and Specific Surface.
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Relationship between SAR and Plastic index Figure 6 shows the relationship between the Sodium Adsorption Ratio and the plastic index for studied soils, the correlation coefficient is low (0.43). ), points are somewhat scattered. Also, we see that there is some soil have almost the same plastic index but with big different on SAR.
Figure 7: Correlation between SAR and Plastic Index.
Relationship between Sodium Percent and Surface Specific Figure 3 shows the regression between the percentage of sodium and specific surface area of the soils studied, in this event, the correlation coefficient is higher (0.65), generally soil have a high percent on sodium have a big specific surface.
Figure 8: Correlation between SP and SS.
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Relationship between Sodium Percent and Plastic index Figure 6 shows the relationship between the Sodium Adsorption Ratio and the plastic index for studied soils, points are somewhat scattered, and the relationship may be considered quasireliable.
Figure 7: Correlation between SP and Ip.
Other relations have a low correlation coefficient (less than 0.20), so we didn’t present its.
CONCLUSION In this study we see that there are some relations between AFNOR identifying tests and ASTM dispersion parameters: 1. Dispersive soils with higher percent dispersion determined by the double hydrometer test are more active; 2. Dispersive soils with high sodium percent have a big specific surface. Also, correlations show that some soils have same characteristics (plastic index, specific surface), but have different degree of dispersion. Finally, ASTM dispersion tests rest an obligation to prevent erosion phenomena thought embankment.
REFERENCES 1. AFNOR, Géotechnique (1998) “Essais de reconnaissance des sols, Tome 1,” Edition AFNOR, 2ième Edition, Paris, France. 2. ASTM D 422 - 63 (2002) “Standard Test Method for Particle-Size Analysis of Soils” Annual Book of ASTM Standards, vol. 04.08.
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3. ASTM D 4221 (1999) “Standard Test Method for Dispersive Characteristics of Clay Soil by Double Hydrometer” Annual Book of ASTM Standards, vol. 04.08. 4. Anon (1999) “Effects of sodicity and salinity on soil structure” SOILpak for dryland farmers on the red soil of Central Western NSW, NSW Dept. Primary Industry. 5. Decker, R. S. and Dunnigan, L. P. (1977) “Development and Use of the SCS Dispersion,Test” Dispersive Clays, Related Piping, and Erosion in Geotechnical Engineering Projects, ASTM Special Technical Publication No. 623, American Society for Testing and Materials, pp 94-109. 6. Fell, R. Macgregeor, P. and Stapledon, D. (1992) “Geotechnical engineering of embankment dams” A.A. Balkema, Rotterdam. 7. Forrest, T. G. (1980) “Engineering and design - Laboratory soils testing, Appendix XIII: Pinhole erosion test for identification of dispersive clays” Department of tee army, Washington, U.S.A. 8. Knodel, P. C. (1991) “Characteristics and problems of dispersive clay soils” United States Departement of the Interior, Colorado. 9. Magnan, J.P. (1993) “Corrélations entre les propriétés des sols” Série Techniques de l’Ingénieur, C219. 10. McElroy, C. H. (1987) “Using Hydrated Lime to Control Erosion of Dispersive Clays” Lime for Environmental Uses. Gutschich K G. ASTM STP, 931, pp 100-114. 11. Rosquoët, F. Bendahmane, F. Marot, D. and Alexis, A. (2005) “Experimental Characterization of internal erosion on sandy clay samples” 23rd academic symposium of civil engineering. 12. Sherard, J. L. and Decker, R. S. (1977) “Dispersive clays, related piping, and erosion in geotechnical projects” American society for testing and materials. 13. Umesha, T. S. Dinesh, S. V. and Sivapullaiah, P. V. (2011) “Characterization of Dispersive Soils” Materials Sciences and Applications 2, pp 629-633 14. Vanicek, I. and Vanicek, M. (2008) “Earth structures, in transport, water and environmental engineering” Springer. 15. Vyas, S. Phougat, N. Sharma, P. and Ratnam, M. (2011) “Stabilization of Dispersive Soil by Blending Polymers” International Journal of Earth Sciences and Engineering. ISSN 0974-5904, Volume 04, No 06 SPL, pp 52-54 16. Zorluer, I. Icaga, Y. Yurtcu, S. and Tosun, H. (2010) “Application of a fuzzy rulebased method for the determination of clay dispersibility” Geoderma journal 160, pp 189–196.
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