Study of Suction Versus Water Content of Soil of Turamdih Area Mixed with Bentonite and Its Implication on the Liner Property of Tailing Dam: A Case Study of East Singhbhum, Jharkhand, Eastern India

  • Brahm Deo Yadav
  • Sunil Kumar Gupta
  • Sahendra Singh
Conference paper
Part of the Water Science and Technology Library book series (WSTL, volume 78)

Abstract

The pressure difference between air and water component in soil void is a key variable in the analysis of hydromechanical behavior of unsaturated soils. Capillary action is directly related to the free energy of the pore water in a soil and can be used to classify the relative swelling potential of expansive soil. Lower hydraulic conductivity requirement of compact clay liner (CCL) is fulfilled through addition of bentonite to the locally available soil material. Thus, the nature of CCL becomes expansive. It is clear from the test data that higher the suction pressure, lower is the hydraulic conductivity and higher is the swelling. The behavior of alternate swelling and shrinking is harmful in other case, but in the area of linear application it is always saturated under wet tailings. So, in between high swelling and low hydraulic conductivity, suction gives positive response towards liner design in uranium ore tailing dams. The relationship between the affinity of soil to retain water and suction can be measured based on the filter paper technique of total section. The obtained value of total suction was thereafter used to estimate the expansiveness of soils. Compacted soils have been widely used as landfill barriers because of many favorable characteristics such as low permeability and high swelling. Compacted clay liner made of different alternatives are normally unsaturated and therefore, suction can be used as a behavior indicator in addition to generally used factor such as water content, dry density, void ratio hydraulic conductivity, etc. This study is mainly focused on investigating suction characteristics of CCL mixtures. Suction was measured using filter paper method for these combinations. The laboratory results were analyzed to provide on understanding of the suction concept. It was found that suction depends primarily on the water content and the bentonite content of the mixture.

Keywords

Suction Compacted clay liner Landfill barrier Hydration Hydraulic conductivity Swelling Filter paper 

Introduction

In landfill applications of compacted clay, one of the criteria commonly used for the performance of landfill liner is the coefficient of permeability of the liner. The presence of clay material is, therefore, important. The addition of bentonite to granular material can change the performance of a highly permeable material and transform it to a material suitable for use as an engineered barrier for landfill. This type of mixture is often referred to as a bentonite enhanced mixture with low percentage of bentonite. On dry mass basis, addition of 01% sodium-type bentonite is sufficient to reduce the permeability of material up to several degree of magnitude (Stewart et al. 1999). A further increase in the percentage of bentonite may not lead to a decrease in the coefficient of permeability of the mixture (Studds et al. 1998). For a less active bentonite such as a calcium type bentonite, a higher percentage of bentonite, with higher field compaction density, is required to achieve the same performance as a sodium-type bentonite–local soil compacted mixtures.

Compacted bentonite soil mixtures are normally unsaturated and, therefore, suction can be used as a behavioral indicator in addition to generally used factors such as water content, dry density, or void ratio. The presence of suction in compacted bentonite soil mixture is often associated with collapse behavior of compacted mixtures. However there is also a correlation between suction, collapse behavior, and the coefficient of permeability of the mixtures. A mixture, which is compacted at moisture content lesser than its optimum value, has a relatively low degree of saturation and high suction and tends to exhibit collapse under specific over burden pressures because of its metastable flocculated structures. Therefore, the mixture can have a relatively high coefficient of permeability. If the same mixture gets compacted close to its optimum water content, maximum dry density with some compaction energy has a higher degree of saturation and lower suction. The mixture undergoes swelling when wetted at the same load and has a lower coefficient of permeability. Strength and stiffness of a compacted bentonite soil mixture generally increases with increase in suction. The objective of this study is to investigate the suction characteristics of bentonite soil mixtures containing different proportions of bentonite.

Assessments of optimum bentonite content in bentonite soil mixtures in relation to the application in landfill are not within the scope of this paper. Although compacted mixtures may undergo changes in suction in the field due to environmentally induced wetting and drying cycles. The initial suction plays an important role in the behavior of the compacted mixtures (Fredlund 1979; Mckeen 1981, 1992; Dineen et al. 1999; Likos and Lu 2003).

Theoretical Background of Suction

The powerful molecular and physicochemical forces acting at the boundary between the soil particle and the soil water lying above the water table causes the water to be either drawn up into the empty void spaces or held there without drainage following infiltration from the surface. Thus, the attractive force that the soil exerts on the water is termed as soil suction and it is regarded as tensile hydraulic stress in a saturated piezometer with a porous filter placed in intimate contact with water in the soil. The magnitude of attractive force that the soil above water table exerts on water is governed by the size of void in a manner similar to the capillary dia. The smaller the void, harder is to remove the water. Meniscus formed between adjacent particles of soil by soil suction, creates a normal force between the particles, which bonds them. Thus soil suction can enhance the stability of earth structure. However, soil suction also provides an attractive force for free water, which can result in loss of stability in loosely compacted soil or swelling in densely compacted soil.

Total suction using Kelvin equation, derived from ideal gas law is given as
$$h_{t} = {{R}}T/V\ln \left( {P/P_{o} } \right)$$
R

Universal gas constant

T

Absolute temperature

V

Molecular volume of water

P/Po

Relative humidity

P

Partial pressure of pore water vapor

Po

Saturation pressure of water vapor

At a reference temperature of 25 °C, the following relation exists, ht = 13.7.182 ln (P/Po):
  • The suction is calculated either as log10 (kPa) or pF.

  • The pF is represented by log10 (suction in cm of water).

  • The two systems are approximately related by log (kPa) = pF − 1 (Bulut et al. 2001).

The osmotic suction of electrolyte solutions, which are usually employed in the calibration of filter papers, can be calculated using the relationship between osmotic coefficient and osmotic suction. Osmotic coefficient can be obtained from the following relationship
$$\phi = - \rho_{w} /\left( {vmw} \right)\ln \left( {P/P_{o} } \right)$$
where
ϕ

Osmotic coefficient

v

Number of ions from one molecule of soil

2 for NaCl, Kcl, NH4Cl and

3 for Na2SO4, CaCl2, Na2 S2O3, etc.

m

Molality

w

Molecular mass of water

ρw

density of water

P/Po

Relative humility also known as activity of water (9w) combining with Kelvin equation

ho

vRTm ϕ.

Soil suction is a microscopic property that indicates the intensity of free energy level of water that the soil attracts (Fredlund and Rahardjo 1993; Bulut et al. 2001; Ridley et al. 2003; Rao and Shivananda 2005; Sreedeep and Singh 2006). Soil suction comprises two components—Osmotic and capillary (Matric) suction. The suction due to capillary nature, texture, and adsorptive forces of unsaturated soils and which varies with change in moisture content of the soils is called matric suction. The osmotic suction is a result of the presence of dissolved salts in the pore fluid. The relation between different types and suction (Chen 1988) are:
  • ht = ho + hm

  • ho = Osmotic suction = Ua Uw

  • Ua = Pore air pressure

  • Uw = Pore water pressure

  • Hm = Matric suction

  • Ht = Total suction.

For expansive soil matric suction is dominant, while for nonexpansive soil osmotic suction can be generated by saturating the soil with salt solution.

Hydration forces play an important role in controlling the suction characteristics especially matric component in dry condition, because of unhydrated exchangeable cations near the clay surface. An increase in water content satisfies these forces and increase the interlayer separation distance to about three mono layers of water molecules (about 10 Å), as a result crystalline swelling occurs (Yong 1999). The hydration forces provide an additional driving force for water in a similar manner to capillary forces and osmotic suction. Besides the hydration forces, the other contributing forces arise from van der Waals force fields. Both the hydration and van der Waals forces are operative at a short range from clay particles and are called sorptive forces. These sorptive forces dominate the matric component of suction; the presence of water menisci or capillary action is not necessary for soil to have matric suction (Young 1999).

The increase in moisture content is usually associated with the decrease in suction and vice versa (Sreedeep and Singh 2006). Conversely, soil volume decreases as the soil suction increases and vice versa. An increase in suction will remove the absorbed water from the soils. When the moisture content of the clay soils is reduced the clay shrinks causing downward movement. On the other hand, decrease in suction triggers the entry of water molecules between the clay layers, thus inducing the swelling of soil (Lucian 2009). Ultimately, hydraulic conductivity and swelling characteristics is inverse to the suction.

  • Expansive potential using suction values

Using matric suction values, PI, and estimated over burden pressure relation was employed to estimate the expansiveness (Brackley 1980)
$${\text{Swell}}\;(\% ) = {\text{PI}} - 10\;\log _{{10}} ({\text{S}}/{\text{P}})$$
where
S

Soil suction at the center of layer

P

Overburden plus foundation stress at that depta.

Methods Used

There are four different methods for determining soil suction namely,
  • Filter paper (FP) Technique

  • Psychrometer (PSY) Technique

  • Dew point sensor (DP) Technique

  • Chilled mirror hygrometer (CMH) Technique.

Out of the four methods, the simple and cheap favorable method to conduct the suction test over a wide range of suction is by the use of filter paper in accordance with ASTM D 5298. Only the FP technique is used to measure total and matric suction in both field and in laboratory. The other three techniques only measures total suction. In the FP method, the soil specimen and filter paper are brought to equilibrium either in contact (for matric suction measurement), or in a noncontact (for total suction measurement) method in a constant temperature environment. This view is explained in Fig. 1. After equilibrium is established between the filter paper and soil, the water content of the filter paper disc is measured. Then, by using a filter paper calibration curve of water content versus suction, the corresponding suction value is found from the curve. The filter paper method is an indirect method of measuring soil suction. Therefore, a calibration curve should be constructed using pressure plate apparatus for suction less than 1500 kPa or be adopted. In this study, calibration curve for whatman No 42 filter paper disks in ASTM D 5298-94 are adopted.
Fig. 1

Contact and noncontact filter paper methods for measuring total matric suction

  • Apparatus required for soil suction measurements:

Filter papers; the ash-free quantitative Schleicher & Shuell No. 589 Whatman No. 42-type filter papers.
  1. (i)

    Sealed containers; glass jar with lids.

     
  2. (ii)

    Small aluminum cans; the cans with lids are used as carriers for filter papers during moisture content determination.

     
  3. (iii)

    A balance with accuracy to the nearest 0.0001 gm is used for moisture content determination.

     
  4. (iv)

    An oven; for determining moisture contents of the filter papers by leaving them in it for 24 h at 105 ± 5 °C temperature in the aluminum moisture cans (standard test method for water content determination of soils).

     
  5. (v)

    A temperature room; a controlled temperature room in which the temperature fluctuations are kept below ±1 °C (used for equilibrium period).

     
  6. (vi)

    An aluminum block; the block is used as heat sink to cool the aluminum cans for about 20 s after removing them from the oven.

     

In addition, latex gloves, tweezers, plastic tapes, plastic bags, ice-chests, PVC Ring, scissors, and a knife are used to setup the test.

Soil Total Suction Measurement

Glass jar that are between 250 and 500 ml volume size are readily available in the market can be easily adopted for suction measurement. Glass Jars, especially, 3.5–4 inch diameter can contain the 3 inch diameter Shelby tube samples very nicely.

Experimental Procedure

  1. 1.

    At least 75% by volume of a glass jar is filled up with the soil; the smaller the empty space remaining in the glass jar, the smaller the time period that the filter paper and the soil system requires to come to equilibrium.

     
  2. 2.

    A ring-type support, which has diameter smaller than filter paper diameter and about 1–2 cm in height, is put on top of the soil to provide a noncontact system between the filter paper and the soil. Care must be taken when selecting the support material; materials that can corrode should be avoided, plastic or glass-type materials are much better for this job.

     
  3. 3.

    Two filter papers one on top of the other are inserted on the ring using tweezers. The filter papers should not touch the soil, the inside wall of the jar, and underneath the lid in any way.

     
  4. 4.

    Then, the glass jar lid is sealed very tightly with plastic tape.

     
  5. 5.

    Steps 1–4 are repeated for every soil sample.

     
  6. 6.

    After that, the glass jar is put into the ice-chests in a controlled temperature room for equilibrium.

     
The suggested equilibrium period is at least one week (ASTM D 5298). After the equilibrium time, the procedure for the filter paper water content measurement can be as follows:
  1. 1.

    Before removing the glass jar containers from the temperature room, all aluminum cans that are used for moisture content measurements are weighed to the nearest 0.0001 gm accuracy and recorded.

     
  2. 2.

    After that, all measurements are carried out by two persons. While one person is opening the sealed glass jar, the other is putting the filter paper into the aluminum can very quickly in a few seconds using tweezers.

     
  3. 3.

    Then, the weights of each can with wet filter paper inside are taken very quickly.

     
  4. 4.

    Steps 2 and 3 are fallowed for every glass jar. Then, all cans are put into the oven with the lids half-open to allow evaporation. All filter papers are kept at 105 ± 5 °C temperature inside the oven for at least 10 h.

     
  5. 5.

    Before taking measurements on the dried filter papers, the cans are closed with their lids and allowed to equilibrate for about 5 min. Then, a can is removed from the oven and put on an aluminum block (heat sink) for about 20 s to cool down; the aluminum block functions as a heat sink and expedites the cooling of the can. After that, the can with the dry filter paper inside is weighed very quickly. The dry filter paper is taken from the can and the cooled can is weighed again in a few seconds.

     
  6. 6.

    Step 5 is repeated for every can.

     

After obtaining all of the filter paper water contents an appropriate calibration curve is employed to get total suction values of the soil sample.

Soil Matric Suction Measurements

It is similar to the total suction measurements but a good intimate contact should be provided between the filter paper and the soil for matric suction measurements. Both matric and total suction measurements can be performed on the same soil sample in a glass jar as shown in Fig. 1.

Experimental Procedure

  1. 1.

    A filter paper is sandwiched between two larger size protective filter papers, so either a filter paper is cut to a smaller diameter and sandwiched between two 5.5 cm papers or bigger diameter filter papers are used as protective.

     
  2. 2.

    Then, these sandwiched filter papers are inserted into the soil sample in a very good contact manner. An intimate contact between the filter paper and the soil is very important.

     
  3. 3.

    After that, the soil sample with embedded filter papers is put into the glass jar container. The glass container is sealed up very tightly with plastic tape.

     
  4. 4.

    Step 1–3 are repeated for every soil sample.

     
  5. 5.

    The prepared containers are put into ice-chests in a controlled temperature room for equilibrium.

     
The suggested equilibrium period is 3–5 days (ASTM D 5298). However, if both matric and total suction measurements are performed on the same sample in the glass jar, then the final equilibrating time will be at least 7 days of total suction equilibrating period (Figs. 2 and 3).
Fig. 2

Calibration curve for suction pressure measurement

Fig. 3

Filter paper calibration relationship

The procedure for the filter paper water content measurements at the end of the equilibration is exactly same as that of outlined for the total suction water content measurements. After obtaining all the filter paper water contents, the appropriate calibration curve may be employed to get the matric suction values of the soil sample.

Filter Paper

log10\(\left| {{\text{suction}}\;{\text{in}}\;{\text{kPa}}} \right|\)

pF = log10\(\left| {{\text{suction}}\;{\text{in}}\;{\text{cm}}\;{\text{of}}\;{\text{water}}} \right|\)

Schneider & Schuell No.—589—WH

\(\left| h \right|\) = 5.4246–8.247 \(\omega\)

R2 = 0.9969

1.5 < \(\left| h \right|\) < 4.15

\(\left| h \right|\) = 6.3662–8.2414 \(\omega\)

R2 = 0.9899

\(\left| h \right|\) > 2.5 pF

Test Materials

Tests were performed on local soil of Turamdih tailings dam site of UCIL, Jaduguda which has been used as liner construction for Uranium tailings dam. Its grain size distribution is indicated in Fig. 4. Basic properties of local soil is given in Table 1.
Fig. 4

Grain size distribution curve of UCIL soil

Table 1

Basic properties of local soil

LL (%)

28.86

PL (%)

20.32

SL (%)

16.19

PI (%)

8.54

Specific gravity

2.47

OMC (standard Proctor) (%)

Dry density (kN/m3)

15.25

18.75

OMC (modified Proctor) (%)

Dry density (kN/m3)

14.85

20.35

USCS classification

SW-SM

Clay (%)

1.61

Gravel (%)

2.82

Silt (%)

2.11

Sand (%)

93.46

Coefficient of uniformity (Cu)

9.357

Coefficient of contraction (CC)

0.211

Cohesion (C) in kN/m2

43.921 kN/m2

Angle of Internal Friction (ϕ)

23°7′

The local soil as per need was amended with different proportions of fly ash and bentonite. The alternatives taken as follows:
  1. (i)

    Local soil alone (A)

     
  2. (ii)

    Local soil + 10% Flyash (B)

     
  3. (iii)

    Local soil + 20% Flyash (C)

     
  4. (iv)

    Local soil + 10% Bentonite (D)

     
  5. (v)

    Local soil + 20% Bentonite (E)

     
  6. (vi)

    Local soil + 10% Flyash + 10% Bentonite (F)

     
  7. (vii)

    Local soil + 20% Flyash + 10% Bentonite (G)

     
  8. (viii)

    Local soil + 20% Flyash + 20% Bentonite (H)

     

The soil materials were sieved to avoid the presence of coarse grains (max size 4.75 mm) then mixed at initial water content, and an adequate amount of water was subsequently added using a water sprayer to reach the target water content. The composition of bentonite/and or flyash in the mixture was prepared to obtain different materials with different degree of plasticity, and in which suction is expected to differ. The mixture were subsequently cured in two layered plastic bags for 2 weeks to allow the hydric equilibrium to establish. The different compaction curves were obtained by dynamically compacting the mixture using the standard proctor method following the ASTM D 698-91. The total suction measurement using the FP technique was performed on standard proctor sample having 102 mm in diameter and height. The Whatman 42 filter paper was used in all 23.35 mm tests.

Result and Discussion

  1. (i)

    The total suction of different alternatives of soil, flyash, and bentonite mixture is primarily a function of water content and bentonite content. There is a lesser dependency on fly ash.

     
  2. (ii)

    Pore geometry or fabric ultimately void ratio have no apparent effect on total suction, and thus an insignificant contribution of the capillary component of suction.

     
  3. (iii)

    Redistribution of water occurs after compaction because of a difference in total suction in the different levels of the pores, so total suction of specimen in the compacted state does not represent the true suction at equilibrium.

     
  4. (iv)

    The in contact filter paper technique appears to measure the capillary matric suction component. The component due to the action of sorptive forces is not measured using this technique. This technique should only be used to measure a capillary suction component of less than 1500 kPa.

     
  5. (v)

    The noncontact filter paper technique measures total suction but due to its long equilibration time, it is very difficult for measuring as compacted total suction of different samples.

     
  6. (vi)

    The results of total suction for different sample at their OMC, shows that as the suction increases, hydraulic conductivity decreases and volumetric swell decreases. This is one of the greatest finding for use as liner material. There is no problem for alternate swelling and shrinkage for liner as it is always placed under wet tailings.

     
  7. (vii)

    The age of specimens used for the measurements varied significantly in different methods and it is 5 weeks for FP techniques.

     
  8. (viii)

    The measurement of total suction in compacted specimens provides values corresponding to a transient state. Redistribution of water is believed to occur as time elapses.

     
  9. (ix)

    The results obtained from the FP technique show that the compaction technique plays no significant role in the magnitude of total suction for the compacted soil–bentonite mixture.

     
  10. (x)

    Values of total suction for all the eight combinations show that suction characteristics for combination E (local soil + 20% bentonite) is very much improved. This fact justifies the high % of bentonite. Values for combination H (local soil + 20% fly ash + 20% bentonite) closely follows the values for combination E. 10 keeping in views of suction properties and economic combination H is most suitable for liner application.

     

References

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Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  • Brahm Deo Yadav
    • 1
  • Sunil Kumar Gupta
    • 1
  • Sahendra Singh
    • 2
  1. 1.Department of Environmental Science and EngineeringIndian Institute of Technology (Indian School of Mines)DhanbadIndia
  2. 2.Department of Applied GeologyIndian Institute of Technology (Indian School of Mines)DhanbadIndia

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