4.0: Experimental Methodology

4.1 INTRODUCTION

This chapter presents the various materials used for the study, their basic properties,

test procedures adopted for evaluating engineering properties on soil with different

additives.

4.2. MATERIALS USED: In the present study following materials are used.

1. Black cotton soil.

2. Coir fibre.

3. Cement.

4. Polypropylene fibre.

5. RBI-81 chemical.

6. Lime.

7. GGBS.

4.2.1 Black cotton soil

The performance of the pavement is affected by the characteristics of the Subgrade.

Soil is a highly variable material. Under the site conditions, the workability with the clayey

soil is the biggest problem, the primary problem that arises with regard to clayey soil is

excessive volume changing behaviour causing the deformation usually in an uneven pattern

and of such a magnitude as to cause extensive damage to the pavement resting on them

Hence an attempt is made to find the probable solution by the addition of above listed

material available in market to enhance the properties,

For the present investigation Black cotton soil was obtained from Davanagere, about

250 km from Bangalore, Karnataka state, India. This is a residual soil and was collected from

an open excavation, at a depth of one meter below the natural ground surface. The black

cotton soil was air dried and pulverised after separating the pebbles. This pulverised soil

passed through 425micron sieve has been used for the investigation. The physical properties

of oven dried Black cotton soil was analysed as per the standard methods and has been shown

in table3.1. Figure 3.1 gives the grain size distribution curve for black cotton soil.

Table 4.1: Physical Properties of Black Cotton Soil.

Colour Black

Grain size distribution :

Gravel, %

Sand, %

Silt and Clay, %

2.00

38.20

59.80

Atterberg’s limits:

Liquid limit, %

Plastic limit, %

Plasticity index, %

45.7

22.14

23.56

Compaction characteristics:

Maximum dry density (g/cc)

Optimum moisture content, %

1.67

20.08

CBR,% 3.00

Unconfined compressive strength (Pa) 104.06

Table 4.2: Sieve Analysis for BC Soil

Fig 4.1: Particles Size Distribution Curve of BC Soil

4.2.2 Polypropylene Fibre

Sieve Size (mm) % passing

4.750 98.00

2.360 94.80

1.700 89.80

1.000 87.00

0.600 81.50

0.300 73.60

0.150 66.80

0.075 59.80

Polypropylene fibre having 12mm length and aspect ratio 300 was used. Its colour is

white, specific gravity is 0.91 and melting point is 1650C.

Table 4.3 Properties of Polypropylene Fiber

Property Value

Fibre Type Single Fibre

Unit weight 0.92gm/cc

Average Length 12mm

Melting point 1650C

Acid resistance High

Absorption Nil

Elongation 12-15%

Breaking Tensile strength 350Mpa

Electrical conductivity low

4.2.3: RBI-81 Grade Chemical Stabilization

. RBI Grade-81 is a unique and innovative product that was developed for the

stabilization of wide spectrum of soils in an efficient, least-cost manner. RBI Grade-81 is an

environment friendly, inorganic, hydration activated powder-based stabilizer that reacts with

soil particles to create layers that are interconnected through a complex inter-particle

framework. RBI-81 is a unique and highly effective natural inorganic soil stabilizer for

Infrastructure development and repair.

RBI Grade-81 was originally developed by RBI for South African Army Road

Building International for the in the beginning of 1990’s for pavement engineering

applications. RBI-81 is a natural inorganic soil-stabilizer which re-engineers and modifies

the properties of the soil strength it for roads, paving and roads and pavement. Alchemist

Technology is the exclusive manufacturer and distributor of RBI Grade-81 in India.

Table 4.4 Physical Properties of RBI-81 Stabilizer

Chemical Composition of RBI-81 Stabilizer

The chemical composition of the stabilizer as per manufacture is as describedbelow.

Residue (105 °C): 99.2%

Residue (600 °C): 95.8%

Ca 25-45% S 5-15%

Si 5-20% K 0-5%

Mg 0-10% Al 0-5%

Fe 0-5% Zn 0-2%

Property Results

Odour Odourless

pH 12.5

Specific Gravity 2.5

Solubility In water 0.2 Pts/100 Pts

Bulk Density 700 Kg/m3

Freezing Point None, Solid

4.2.4 Coir Fibre (From Tree top to Fibre)

Coir is a versatile vegetable fibre extracted from the fibrous husk that surrounds the coconut.

The fibres are tough, strong and extremely resistant to fungal and bacterial decomposition.

Fibre length varies from 0.3 mm to 250mm; but to an average ranges from100 mm to

200mm. Coir cross sections are highly elliptical and non uniform with average diameter 0.25

mm. It has high degree of crystallinity; spiral angle of the micro fibres ranging between 30°

and 40 ° which imparts greater extensibility compared to other natural fibres. In spite of low

cellulose content, coir fibre has a very close fibre structure which account for its better

durability compared to other natural fibres.

For present study the selected fibres are having aspect ratio 100 with average length

of 30mm and diameter 0.3 mm and specific gravity 0.7 was selected for soil stabilization

studies.

Table 4.5 Engineering Properties of Coir Fibre*

Property Value

Length(mm) 15-280

Density(g/cc) 1.15-1.4

Tenacity(g/tex) 10.0

Breaking Elongation(%) 30.0

Diameter(mm) 0.1-1.5

Swelling in Water(diameter in%) 5.0

Rigidity modulus(dynes/cm2) 1.8924

Specific Gravity 0.7

Young’s Moudulus(GN/m2) 4.5

(*Ayyar et al., 2002)

Table 4.6 Chemical Composition of Coir*

(*Sarma, 1997)

Content Percentage

Lignin 45.84

Cellulose 43.44

Pectin and related compounds 3.00

Ash 2.22

Water Soluble 5.25

4.2.5 Cement

Any cement can be used for stabilization, but Ordinary Portland cement is the most

widely used throughout the world.

The addition of cement to a material, in the presence of moisture, produces hydrated

calcium aluminate and silicate gels, which crystallise and bond the material particles together.

Most of the strength of a cement-stabilized material comes from the physical strength of the

matrix of hydrated cement. A chemical reaction also takes place between the material and

lime, which is released as the cement hydrates, leading to a further increase in strength.

Portland cement is a multi-mineralic compound made up of oxides of calcium, silica,

alumina and iron. When cement is mixed with water, cementing compounds of calcium

silicate-hydrate (C-S-H) and calcium-aluminate-hydrate (C-A-H) are formed and excess

calcium hydroxide is released. Some calcium is therefore available to modify the clay particle

early in the modification process when the water is added, and additional calcium becomes

available later as it is formed as a result of cement hydration. The hydrates help to stabilize

flocculated clay particles through cementation. The hydration reactions and strength increases

occur for the most part between 24 hours and 28 days, although the cement will continue to

hydrate at decreasing rates as long as free moisture is present.

4.2.6 Lime

Commercially available Quick lime was obtained from local Market. The properties

of lime are presented in the table 4.7

Table 4.7 Properties of Lime

Property Value

Calcium hydroxide Ca(OH)2 90

Silica 1.5

Ferric Oxide 0.5

Magnesium Oxide 1.0

Alumina 0.2

Carbon dioxide 3

4.2.7 Muddanur Fly Ash

The fly ash collected from Raylaseema thermal power plant (R.T.P.P) Muddanur,

from Andra Pradesh, hence forth called as Muddanur fly ash (MFA) has been used in this

investigstion. It is a non-pozzolonic fly ah belonging ti the ASTM classification “F” the

physical and chemical properties of Muddanur fly ash are listed in table 3.8 and 3.9

respectively.

Table 4.8 Physical Properties of MFA

4.3 Tests

Conducted

Colour Light grey

Specific gravity 2.31

Grain size distribution

Silt size (%)Clay size (%)

5941

Atterberg’s limitsLiquid Limit (%)Plastic limit (%)

27.5Not possible

Maximum dry density (kN/M3)Optimum moisture content (%)

15.220.4

The experimental work was carried out in three stages. In the first stage basic tests

like Grain Sieve analysis and Atterberg’s limits, determining Optimum Moisture Content and

Maximum Dry Density for Black cotton soil alone and with combination of different

materials by heavy compaction method and Jodhpur mini compaction method respectively,

Second stage consisted of Unconfined Compressive tests and CBR are conducted on soil with

varying percentages of Cement, RBI Grade-81 stabilizer, Polypropylene fibre & their

combination, and In the third stage Static and Cyclic Plate load test were conducted in large

Model box for various combination of the materials used in present study. The objective of

conducting plate load test in large model box is to evaluate Modulus of subgrade reaction

which is useful parameter in the design of pavements. In addition to plate load test, for the

same combination cyclic plate load test were also conducted to Evaluate Co-efficient of

Elastic Uniform Compression (Cu) which is a useful parameter in the design of Machine

foundation resting on weak ground which is improved by various stabilisers.

4.3.1 Test Procedures

The test procedures of various experiments conducted in the investigation are briefly

explained as under.

4.3.1.1 Grain size Analysis

Grain size analysis was carried out by sieve analysis and hydrometer analysis as per

IS: 2720(part-4)-1985 method. Soil passing 425micron is washed through a 75micron sieve

so that silt and clay particles are separated from the sand fraction. Soil passing through

75micron sieve and the soil retained on it is separately collected in containers and kept them

in oven. The oven dried soil is weighed separately, soil passing 75micron sieve is used for

hydrometer analysis to separate silt and clay fraction.

4.3.1.2 Liquid limit

The liquid limit for all the samples were determined by the cone penetration method

as described in IS:2720, part 5-1985, owing to the difficulty in cutting a groove using

Casagrande’s device in certain cases. Liquid limit tests were carried out to secure a minimum

of five points for plotting the flow curve. The consistency of the soil specimens were

subjected such that the penetration is in between 14 and 28mm. the moisture ontent

corresponding to cone penetration of 20mm shall be taken as the liquid limit of the soil and

shall be expressed to nearest first decimal place.

4.3.1.3 Plastic limit

The plastic limit of the various samples was determined as per IS: 2720, part 5-1985.

The plastic limits reported are the average of three determinations.

4.3.1.4 Compaction

The compaction test was conducted using specially made apparatus (Mini

Compaction test apparatus), having a mould of internal diameter 38.1mm and external

diameter 46.1mm and 100mm in height. The mould has a detachable base plate and a

removable collar 35mm height. The hammer guide is of mass 13N and has three rods. The

bottom steel rod is 80mm long and 36.5mm in diameter acts as an energy transferring foot.

The top rod is 30mm long and 36.5mm in diameter acts as an energy transferring foot. The

top rod is 30mm long and 36.5mm in diameter. This rod is used to hold the frame in position

before dropping the hammer. The central rod is 195mm long and 18mm in diameter. This

central vertical rod passing through its axial bore, guides the hammer. Two hammers, one is

of 8N and the other is of 25N in mass, were used in the study. The hammer are 35mm in

height with a central bore of 19mm and fall freely through a height of 160mm (height of fall)

over the energy transferring foot.

In this mini compaction test, about 300grams of soil is used for each trial, required

amount of water is added to the soil and mixed thoroughly and stored in polythene bags for

moisture equilibrium. After allowing sufficient time for moisture equilibrium, the sample is

remixed thoroughly before compaction. The mould is cleaned, dried and greased lightly to

reduce the side walls friction and for easy extrusion of compacted sample after the test. The

mould is then fixed to the base plate. The soil is then compacted in the mould in three layers

by giving 45blows to each layer. (Sridharan et.al., 2005). Then the remaining procedure is

same as that compaction test as per IS: 2720(Part VII-1980)

4.3.1.5 Unconfined Compression TestAn axial load is placed onto a sample; the load is increased until the soil fails. This

load is known as the unconfined compressive strength. There is no lateral support on the soil

sample for this measurement. In the present study, Unconfined Compression test (UCC) was

conducted on Black cotton soil. Mould was prepared with respect to optimum moisture

content (OMC) and MDD obtained from modified compaction test and Jodhpur compaction

test for Black cotton soil samples respectively. Moulds for Unconfined compressive test

(UCC) were extracted from mould extractor. These were of sizes 3.8 cm in diameter and 7.6

cm in height. And these moulds were tested in compression testing machine for maximum

compressive strength achieved with variation in amount of stabilizers added.

4.3.1.6California Bearing Ratio Test (CBR) The ratio expressed in percentage of force per unit area required to penetrate a soil

mass with a circular plunger of 50 mm diameter at the rate of 1.25 mm/min to that required

for corresponding penetration in a standard material. The ratio is usually determined for

penetration of 2.5 mm and 5 mm. Where the ratio at 5 mm is consistently higher than that at

2.5 mm, the ratio at 5 mm is used.

The dry density for a remoulding shall be either the field density or the value of the

maximum dry density estimated by the compaction tests [IS: 2720 (Part-7)1980, and IS: 2720

(Part-8) 1983] or any other density at which the bearing ratio is desired. The water content

used for compaction should be the optimum water content or the field moisture as the case

may be.Soil Sample - The material used in the remoulded specimen shall pass a 19 mm IS

Sieve. Allowance for larger material shall be made by replacing it by an equal amount of

material which passes a 19 mm IS Sieve but is retained on 4.75 mm IS Sieve. A filter paper

shall be placed over the specimen and the adjustable stem and perforated plate shall be placed

on the compacted soil specimen in the mould. Weights to produce a surcharge equal to the

weight of base material and pavement to the nearest 2.5 kg shall be placed on the compact

soil specimen. The whole mould and weights shall be immersed in a tank of water allowing

free access of water to the top and bottom of the specimen.The tripod for the expansion

measuring device shall be mounted on the edge of the mould and the initial dial gauge

reading recorded. This set-up shall be kept undisturbed for 96 hours noting down the readings

every day against the time of reading. A constant water level shall be maintained in the tank

through-out the period. The free water collected in the mould shall be removed and the

specimen allowed to drain downwards for 15 minutes. Care shall be taken not to disturb the

surface of the specimen during the removal of the water. The weights, the perforated plate

and the top filter paper shall be removed and the mould with the soaked soil sample shall be

weighed and the mass recorded. The mould containing the specimen, with the base plate in

position but the top face exposed shall be placed on the lower plate of the testing machine.

Surcharge weights, sufficient to produce an intensity of loading equal to the weight of the

base material and pavement shall be placed on the specimen. If the specimen has been soaked

previously, the surcharge shall be equal to that used during the soaking period.

To prevent upheaval of soil into the hole of the surcharge weights, 2.5 kg annular

weight shall be placed on the soil surface prior to seating the penetration plunger after which

the remainder of the surcharge weights shall be placed. The plunger shall be seated under a

load of 4 kg so that full contact is established between the surface of the specimen and the

plunger. The load and deformation gauges shall then be set to zero (In other words, the initial

load applied to the plunger shall be considered as zero when determining the load penetration

relation). Load shall be applied to the plunger into the soil at the rate of 1.25 mm per minute.

Reading of the load shall be taken at penetrations of 0.5, l.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 7.5,

l0.0 and 12.5 mm (The maximum load and penetration shall be recorded if it occurs for a

penetration of less than 12.5 mm). The plunger shall be raised and the mould detached from

the loading equipment. About 20 to 50 g of soil shall be collected from the top 30 mm layer

of the specimen and the water content determined according to IS : 2720 (Part-2) 1973. If the

average water content of the whole specimen is desired, water content sample shall be taken

from the entire depth of the specimen.

4.3.1.7Cyclic Plate Load test

The equipment for the test was assembled in the Material Testing Laboratory, Civil

Engineering Department, Bangalore University. According to the details given in IS:

1888:1982, the test set up is shown in plate no 1. After the set up has been arranged the initial

readings of the dial gauge should be noted and first increment of static load should be applied

to plate. This load shall be maintained constant throughout for a period till no further

settlement occurs or the rate of settlement becomes negligible. The final readings of the dial

gauges should then be recorded. The entire load is then removed quickly but gradually and

the plate allowed rebound. When no further rebound occurs or the rate of rebound becomes

negligible, the readings of the dial gauges should be again noted. The load shall then be

increased gradually till its magnitude acquires a value equal to the proposed next higher stage

of loading, which shall be maintained constant and the final dial gauge readings should be

noted as mentioned earlier. The entire, load should then be reduced to zero and final dial

gauge readings recorded when the rate of rebound becomes negligible.

The cycles of loading, unloading and reloading are continued till the estimated

ultimate load has been reached, the final values of dial gauge readings being noted each time.

The magnitude of the load increment should be such that the ultimate load is reached in five

to six increments. The initial loading and unloading cycles up to the safe bearing capacity of

the soil should be with smaller increments in load. The duration of each loading and

unloading cycle upon the type of soil under investigation.IS 5249(1992)

Coefficient of Elastic Uniform Compression from Cyclic Plate Load Test

From the data obtained during cyclic plate load test, the elastic rebound of the plate

corresponding to each intensity of loading shall be obtained as shown in Fig. . The load

intensity versus elastic rebound shall be plotted as shown in Fig. .The value of Cu, shall be

calculated from the equation given below Cu=P/Se

Plate no 1