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CHAPTER 3

MATERIALS AND METHODS

3.1 GENERAL This chapter deals with the index properties of three natural soils,

three commercial soils (Bentonites), geosynthetics and admixtures

(Sand, flyash and quarry dust). This chapter also brings out the different

test procedures adopted for the determination of the index properties,

swelling, shrinkage, undrained shear strength and compressibility

characteristics of swollen and unswollen clays, with varying number of

geosynthetics, orientation and end confinement. The details of load test

conducted in a model tank on the swollen sample with and without

geosynthetics are also discussed in this chapter.

3.2 MATERIALS 3.2.1 Natural Soils Both natural soils and commercially available Bentonite clay were

selected for the present study such that they exhibit high plasticity,

swelling and compressibility characteristics. Three natural soils were

collected from Anna Nagar, Taramani and Tiruneermalai in Chennai,

Tamil Nadu at a depth of 2.0 m. These samples were air dried before

33

subjected to laboratory tests. The natural soils are named as soil (1), (2)

and (3) whose liquid limits are 63 %, 70 % and 72 % respectively. The

index properties of the natural soil (1), (2) and (3) are furnished in the

Table 3.1. All the natural soils are classified as clay of very high

swelling nature based on plasticity characteristics and free swell index

values (IS: 2911 (Part III) – 1981).

Table 3.1 Physical Properties of Soils Used

Soil DescriptionNatural

Soil-(1)

Natural

Soil-(2)

Natural

Soil-(3)

Ben-

tonite

(1)

Ben-

tonite

(2)

Ben-

tonite

(3)

Specific gravity (G) 2.73 2.72 2.75 2.77 2.77 2.80 Grain Size Distribution

Sand % 4 0 1 0 3 0 Silt % 42 42 48 27 45 0 Clay % 54 58 51 73 52 100

LL % 63 70 72 430 71 350 PL % 28 27 29 48 41 56 PI % 35 43 43 382 30 294 SL % 9.0 9.10 8.7 7.5 8.5 8.0 FSI % 76 120 140 350 294 320

Standard Proctor Compaction results

d max

kN /m3 16.5 15.9 16 12.8 13.3 12.1

OMC % 23.4 25.5 27.5 35 31.5 33

Swell ClassificationVery High

Very High

Very High

Very High

Very High

Very High

34

3.2.2 Bentonites

Three commercial soils (Bentonites) collected from local market

were used along with natural soils for comparison. The Bentonites (1),

(2) and (3) are having liquid limit of 430 %, 70 %, 350 % respectively.

The index properties of the commercials soil (1),(2) and (3) are shown in

the Table 3.1. All these soils are classified as clay very high swelling

nature. These bentonite clays were chosen because of its pure clay

system where changes in swell-shrink, compressibility etc., would be

significant and considerable, unlike the natural soils whose behaviour is

masked by the presence of non-clay fraction in the form of silt and sand.

3.2.3 Geosynthetics Geosynthetics which include geogrid, geotextile, geomembarane,

and geocomposite were used in layers both horizontal and vertical

orientation to control swell – shrink potential of clay. Geogrid used in

this study is having aperture size of 8 mm x 6 mm and tensile strength of

7.68 kN/m. The geotextile selected is having narrow strip tensile strength

of 10 kN/m. The properties of geogrid, geotextile are shown in Table 3.2

(a) and (b) respectively. The geomembarane used is having thickness of

0.60 mm. Geogrid and geotextile were stitched together to form

geocomposite. Plate 3.1 (a), (b), (c), and (d) show view of geosynthetic

materials used in the present work and they were used in compacted soil

for varying number of layers, orientation, with and without end

confinement, to study their performance in the control of swell-shrink

behaviour of clays.

35

Table 3.2(a) Properties of Geogrid

Description Values

Type Netlon 121

Aperture size (mm) 8x6

Mesh thickness (mm) 3

Weight (g/m2) 736

Tensile strength (kN/m) 7.68

Extension at maximum load (%) 20.2

Load at 10% extension (kN/m) 6.8

Table 3.2(b) Properties of Geotextile

Description Values

Narrow strip tensile strength (kN/m) 10

CBR plunger load (kN) 0.5

Trapezoidal tear load (kN) 0.27

Stiffness (mg-cm) 9342.72

Diameter of the hole (mm) (using cone

drop test)15

3.2.4 Admixtures (Sand , Quarry dust and Flyash)

The admixture include river sand (size ranging from 600 micron to

2.36 mm), Ennore fly ash, Tamil Nadu (G= 2.0 d max =8.9 kN/m3 and

OMC =41%) and quarry dust (G= 2.6, d max = 18 kN/m3, OMC = 22%)

were used in this investigation. These materials were mixed with

expansive clays at different proportions varying from 0, 10, 20, 30, 50,

and 70 % to control the swell and shrink potential of different expansive

36

clays. Quarry dust is a by-product during quarrying and sizing of

aggregate in crushing plant. Flyash is a by-product of combustion of coal

from thermal power plants. Considerable work has been carried out to

utilize these wastes for the beneficial improvement of problematic clays.

The chemical properties of quarry dust and flyash are shown in

Table 3.3. Both are having CaO content ranging from 2.72 % to 4.68 %.

Table 3.3 Properties of Solid Waste

Description Quarry Dust Flyash

Loss of ignition, % 0.47 1.46

Silica as SiO2 63.63 58.05

Iron as Fe2 O3 % 13.71 7.24

Titanium as TiO2 % 0.38 1.33

Calcium as CaO % 4.68 2.72

Magnesium as MgO, % - -

Sodium as Na2O,% 2.87 -

Potassium as K2O,% 1.35 -

Sulphur,SO3 - 0.99

3.3 METHODS 3.3.1 Test Programme Swelling, shrinkage, consolidation, unconfined compression

strength and load carrying capacity tests were conducted on six different

expansive clays with and without the addition of geosynthetics, sand and

solid waste (Quarry Dust and Flyash).

37

Basically three phases of experiments were conducted in this

investigation. Test details in each phases are shown in Table 3.4, 3.5 and

3.6 respectively for phase I, II, and III. In phase I, swelling and

shrinkage tests were conducted on two natural soils (soil 1 & 3) and a

Bentonite (Bentonite (3)) for varying initial density and initial moisture

content (IMC) ( Table 3.4) using conventional odeometer swell

apparatus. In phase II, unconfined compressive strength and

consolidation tests were conducted on both the swollen and unswollen

natural soil samples (soil (1), (2) and (3) ), for varying initial densities

and moisture content (Table 3.5) in two series. In series (1) keeping

initial density constant, IMC was varied and series (2), the IMC was kept

constant and initial density varied. In phase III swelling, shrinkage and

load tests were conducted on soil (2) with geosynthetics (geogrid,

geotextile, geomembarane and geocomposite) for varying number of

layers, orientation and end-confinement (Table 3.6) in the model tank. In

addition, the swell and shrink tests were also conducted on clays (soil

(2), Bentonite (1) and (2)) with increase of % of sand, fly ash and quarry

dust in phase III. The details of IMC and density selected for swelling,

shrinkage, consolidation and UCC strength in phase I and phase II are

shown in Table 3.4 & 3.5. In phase III , swelling tests with and without

geosynthetics, varying orientation, number and type of geosynthetics

were conducted on the soil at a constant initial density of 16.5 kN/m3 and

IMC of 8 %.

38

Table 3.4 Details of Test Programme in Phase I: (Swell – Shrink Test

for Varying Dry Density and IMC)

Description

Swell Test Shrinkage Test

Dry

Density

(kN /m3)

IMC % IMC %

Soil (1)

13.75,

14.6

16.5

0,8,30

0,8,15,25,30

0,15,30

21,31,43,50,

62,73,78,87

Soil (3)

14

15

16

0,15,30

0,8,15,25,30

0,15,30

14,27,41,46,

54,62,69,77

Bentonite (3)

12.1

10.7

15.1

0,8,15,25,30,50

0,15,30

0,15,30

75,224,350,430

39

Table 3.5 (a) Details of Test Programme in Phase II: (UCC and

Consolidation Test on Unswollen Clay for Varying Dry Density and

IMC)

Description

UCC Strength Tests Consolidation Tests

Initial Dry di

(kN / m3)

Initial Water

Content Wi (%)

Initial Dry di

(kN / m3)

Initial Water

ContentWi (%)

Soil (1)

Series (1)

16.516.516.516.5

23.3615.0 10.0 5.0

16.5 - -

16.5

23.36 - -

5.0

Series (2)

16.514.013.012.0

5.0 5.0 5.0 5.0

16.5 - -

12.0

5.0 - -

5.0

Soil (2)

Series (1)

15.915.915.915.9

25.5015.0 10.0 5.0

15.9 - -

15.9

25.5 - -

5.0

Series (2)

15.914.013.012.0

5.0 5.0 5.0 5.0

15.9 - -

12.0

5.0 - -

5.0

Soil (3)

Series (1)

16.016.016.016.0

27.5015.0 10.0 5.0

- - - -

- - - -

Series (2)

16.014.013.012.0

5.0 5.0 5.0 5.0

- - - -

- - - -

40

Table 3.5 (b) Details of Test Programme in Phase II: (UCC and

Consolidation Test on Swollen Clay for Varying Dry Density and

IMC)

Description

UCC strength Tests Consolidation tests Swollen

Dry Density

df

(kN/m3)

Swollen Water

ContentWSW (%)

Swollen Dry

Density df

(kN/m3)

Swollen Water

ContentWSW (%)

Soil (1)

Series (1)

15.67 15.72 15.67 15.69

33.33 34.40 36.85 37.39

- 15.72

- 15.69

- 34.40

- 37.39

Series (2)

15.69 13.39 12.18 11.45

37.39 46.00 42.51 44.73

15.69 13.39 12.18 11.45

37.39 4.60

42.51 44.73

Soil (2)

Series (1)

14.83 15.16 15.27 15.41

33.64 34.05 36.09 37.38

- 15.16

- 1.541

- 34.05

- 37.38

Series (2)

15.41 13.53 12.28 17.17

37.38 40.35 42.87 44.93

15.41 13.53 12.28 17.17

37.38 40.35 42.87 44.93

Soil (3)

Series (1)

14.73 14.76 14.78 14.93

41.27 42.35 43.64 44.92

- - - -

- - - -

Series (2)

14.93 13.30 11.74

44.92 49.50 52.94

- - -

- - -

41

42

43

3.3.2 Basic Tests Liquid and plastic limit of the soils were determined by using

Casagrande apparatus as per IS: 2720 (Part5)-1985. The liquid limit

values are reported an average of two determinations and the plastic limit

values reported are an average of three determinations. Grain size

distribution analysis was performed by hydrometer method (IS:

2720(part4)-185). Free swell test was done as per (IS: 2720(part 40)-

1977). Standard Proctor Compaction tests were conducted as per IS:

2720 (part VII) -1980.

3.3.3 Swelling Test 3.3.3.1 In Odeometer Apparatus Conventional odeometer apparatus was used for the determination

of swelling behaviour of natural soil (1), (2) and bentonite (3) for

phase I. The soil samples were statically compacted in the mould to a

required density at specified water content and inundated with distilled

water and then allowed to swell until it reached equilibrium values of

swelling. The % swell and swell pressure were determined by expanding

volume method as per IS 2720 (part 41) - 1977.

3.3.3.2 In Model Tank

In connection with the experiments in phase III, swelling test was

conducted in a mould of diameter 100 mm and height of 36 mm, the soil

sample was statically compacted in layers to a height of 12 mm at 8 %

moisture content. The geosynthetic materials were cut into a size equal

44

to the inner diameter of the swelling mould and placed at 1/2 and 2/3 of

the sample height respectively for one and two layer of geosynthetics.

The samples were then submerged in water with a surcharge pressure of

5 kN/m2. Dial gauges were fixed and the time-swelling observations

were taken until equilibrium values reached. The schematic view of

swelling test set up for soil alone, soil with one layer of horizontally

placed geosynthetics, soil with two layers horizontally placed

geosynthetic and soil with one layer vertically placed geosynthetics

respectively are shown in Figure 3.1 (a), to (d). Plate 3.2 shows the view

of fabricated mould used for swelling test without end confinement of

geosynthetics under submerged condition.

3.3.3.3 In Model Tank with a Provision of End Confinement In order to conduct the swelling test with end-confined

geosynthetic material (in horizontal direction), swelling mould has been

specially fabricated in such a way that the geosynthetic material can be

clamped at the edges of the mould (Figure 3.2). This could be possible

by making two half moulds (annular ring) of height each 50 mm and

inner diameter 100 mm and outer diameter of 170 mm. The parts of the

mould can be connected by grooving arrangement. The lower part of the

mould is filled with soil and it is statically compacted. After that,

geosynthetics were placed at the top of the soil and another mould is

placed above it such that geosynthetics could be clamped in between the

mould using the grooving arrangement. Then the upper part of the mould

is filled with the soil and it is statically compacted. Entire setup is

submerged in water and allowed to swell under the surcharge pressure of

5 kN/m2. Dial gauges were fixed and the time – swell observation were

45

taken until the equilibrium values were reached. Plate 3.3 (a) and (b)

shows the view of fabricated mould used for swelling test with end

confinement of geosynthetics

Figure 3.1(a) Swelling Test Setup for Soil Alone

Figure 3.1(b) Swelling Test Setup for Soil+ One Layer Geosynthetics

in Horizontal Orientation

46

Figure 3.1(c) Swelling Test Setup for Soil + Two Layer

Geosynthetics in Horizontal Orientation

Figure 3.1(d) Swelling Test Setup for Soil + One Layer

Geosynthetics in Vertical Orientation

47

Figure 3.2 View of Swelling Test Setup with a Provision for

Confining Geosynthetics

3.3.4 Shrinkage Test on Fabricated Mould In connection with the experiments in phase III , shrinkage

studies of soils were conducted on specially fabricated shrinkage cups

without base whose dimensions are 70 mm diameter and 30 mm

height(Figure 3.3 a and b). The shrinkage ring was placed on a perplex

sheet with filter paper at the bottom. Then the ring was filled with

remoulded soil at liquid limit consistency, with and without

geosynthetics, sand, flyash and quarry dust and was allowed to dry at

room temperature. The changes in vertical and horizontal shrinkage of

the soil samples were measured regularly at time intervals of 0, 2 hr,

4 hr, 8 hr, 11 hr, 24 hr, 48 hr, 72 hours etc. until shrinkage completes.

Plate 3.4 shows the photo of fabricated mould used for shrinkage test.

Figure 3.3 (a) and (b) show the experimental set up for shrinkage test for

soil alone and soil with one layer of geosynthetics respectively.

Surcharge of 5 kN/m2

48

Figure 3.3(a) Experimental Setup for Determining Shrinkage

Figure 3.3(b) Experimental Setup for Shrinkage Test with

Geosynthetics

3.3.5 Unconfined Compressive Strength Test After the soil sample has completely swollen in the swelling

apparatus (section 3.3.3), the final swollen water content and swollen dry

density were determined. At these swollen water content and

49

corresponding swollen density, UCC specimens were prepared by static

compaction and the same were used for conducting UCC test. From the

stress-strain graph, unconfined compressive strength values were

calculated and reported.

3.3.6 One Dimensional Consolidation Test

The statically compacted swollen and unswollen samples were

tested in standard fixed ring consolidometer using stainless steel rings of

60 mm diameter and 20 mm height (IS 2720 Part 15-1986). The inner

surfaces of the rings were lubricated with silicon grease to minimize the

side friction between the rings and soil specimen. The lubricated

consolidation ring with entire assembly was mounted in the

consolidation cell and positioned with the loading frame. After

equilibrium has attained for each pressure as indicated by nearly constant

readings in the vertical dial, a pressure increment ratio of unity will be

adopted. Each pressure was maintained normally about 24 hours for all

pressure increments after ensuring the equilibrium void ratio of each

pressure. The pressure Vs Void ratio curves were plotted for the

determination of compression index.

3.3.7 Load Test on Swollen Clay in Model Tank

Load test on swollen clays were conducted in phase III for

soil (2) with geosynthetics, sand, quarry dust and flyash. The soil sample

of height 120 mm was compacted in layers in a mould of diameter

150 mm and height of 180 mm at an initial moisture content of 8 %

50

(Figure 3.4). The required initial dry density of 16.5 kN/m2 was achieved

by static compaction. Geosynthetics were then placed in the sample at

the respective locations as required. The samples were then submerged

in water with a surcharge pressure of 5 kN/ m2 on a 150 mm diameter

circular bearing plate. After the soil sample was allowed to freely swell,

the load was applied over the circular steel plate of 50 mm diameter on

completely swollen sample. Settlement values were observed in dial

gauge for each increment of load after an interval of 1, 2, 5, 10, 20, 40,

60 minutes and thereafter at hourly intervals until the rate of settlement

becomes less than 0.02 mm/hour.

Figure 3.4 Load Test Setup on Swollen Clay Specimen with Two

Layers of Geosynthetics

Steel plate of dia 50 mm, thickness 5 mm

Swollen sample

Sand layer

Sand layer with Filter paper

150 mm

Pressure

Geosynthetics-2 layers120 mm

51

Plate 3.1(a) View of Geogrid Plate.3.1(b) View of Geotextile

Plate 3.1(c) View of Geomembrane Plate.3.1(d) View of Geocomposite

(Geotextile + Geogrid)

52

Plate 3.2 View of Swelling Setup

Plate 3.3 (a) View of Two Layer Geogrid with End Confinement

53

Plate 3.3 (b) View of Two Layer Geotextile with End Confinement

Plate 3.4 View of Shrinkage Setup