Project: Laboratory shear strength studies of Soil …cistup.iisc.ac.in/presentations/Research project/CIST005.pdf2 grows about up to 15% every year. On the other hand, the number

Final Project Report

Project: Laboratory shear strength studies of Soil admixed with Plastic waste

Submitted to:

CiSTUP

Indian Institute of Science

Bangalore 560 012

Investigator:

Prof. G L Sivakumar Babu

Department of Civil Engineering

Indian Institute of Science

Bangalore 560012

12 July 2012

i

Executive summary SPECIFIC AIM/ OBJECTIVE OF THE PROJECT: Examine the use of

plastic waste in road construction. This is likely to lead to two advantages.

1. Use of waste in an appropriate manner. 2. The expected strength gain due to the presence of plastic waste is likely lead to

savings in the road construction material.

3. SUMMARY OF PROPOSED RESEARCH:

Over the last few decades there has been a steady increase in the use of plastic products

resulting in a proportionate rise in plastic waste in the municipal solid waste in large

cities and Bangalore is no exception. There is a need to examine the reuse of plastic waste

in road construction and in particular in subgrade and sub base materials.

Plastic-waste materials are produced plentifully such as polyethylene terephthalate (PET)

plastic bottles, polypropylene (PP) of plastic sack, and polypropylene (PP) of carpet. But

such materials have been used little for engineering purposes, and the overwhelming

majority of them have been placed in storage or disposal sites. These plastic wastes can

be cut into pieces and mixed with soil and the behaviour of the soil is similar to fibre

reinforced soil and the response of the plastic waste mixed soil can be examined using the

framework of fibre reinforced soil. Preliminary experiments show that addition of plastic

waste pieces lead to an improvement in strength response and there is a need to do

detailed studies in this direction.

The objectives are a) review of the studies on the use of plastic waste in road

construction, b) Experimental studies on plastic waste mixed soils for use in road

applications. Strength, volume change and permeability behaviour will be studied in

detail c) analysis of data and development of analytical methods for design d)

dissemination of knowledge to stake holders and conduct field trials if possible. All the above objectives have been nearly fulfilled and a few results have been

published in the Journal of Waste Management. A copy of the paper is enclosed as annexure.

Results of the work have also been presented in the Conference on “Modern Trends in

Pavement Engineering held on 15th July 2011, where many stakeholders of CiSTUP

participated.

Team: Sandeep Kumar Chousky, J Raja, Pawan Kumar, Geetha Manjari.

Laboratory Assistance: Anthony Raj

ii

Contents

CHAPTER 1 GENERAL INTRODUCTION

1.1 Introduction 1.2 Plastic waste versus soil reinforcement with discrete members/fibres 1.3 Advantages of soil reinforced with plastic waste/discrete fibres

CHAPTER 2 LITERATURE REVIEW

CHAPTER 3 MATERIALS AND METHODS

3.1 Introduction 3.2 Materials 3.2.1 Soil 3.2.1.1 Sand 3.2.1.2 Fly Ash 3.2.1.3 Red Soil 3.2.2 Plastic Waste 3.3 Experimental methods 3.3.1 Unconfined Compression (UCC) Test and compressibility tests 3.3.2 Consolidated Undrained Test 3.3.3 California Bearing Ratio (CBR) Test 3.3.4 Piping Test

CHAPTER 4 STRENGTH AND STIFFNESS BEHAVIOR

4.1 Introduction 4.2 Unconfined Compression (UCC) Test Results 4.2.1 Stress versus Strain Response 4.2.2 Strength Improvement due to Plastic Waste 4.3 Consolidated Undrained (CU) Test Results 4.3.1 Stress versus strain response 4.3.2 Effect of Plastic Waste on Soil Strength 4.3.3 Pore Pressure Curves 4.4 California Bearing Ratio (CBR) Test Results 4.4.1 Load-Displacement Curves 4.4.2 Effect of plastic waste on CBR value of different soils

CHAPTER 5 COMPRESSIBILITY BEHAVIOR

5.1 Introduction 5.2 Oedometer Test Results 5.3 Fly Ash 5.4 Red Soil 5.5 Effects of waste content on compression index of soils 5.6 Conclusions

iii

CHAPTER 6 SEEPAGE CHARACTERISTICS AND PIPING RESISTANCE

6.1 Introduction 6.2 Laboratory piping test 6.2.1 Experimental Setup 6.2.2 Materials used 6.2.3 Test Setup and Sample Preparation 6.2.4 Test Procedure 6.3 Seepage flow velocity and hydraulic gradient 6.4 Upward seepage rate of fly ash mixed with plastic and geogrid waste 6.5 Some Practical Applications 6.5.1 Fly Ash for Sheet Pile Wall Design 6.5.2 Cofferdam Seepage Analysis with plastic waste mixed sand 6.6 Summary and Conclusions

Appendix

iv

CHAPTER 1

GENERAL INTRODUCTION

1.1 Introduction The bottled water is the fastest growing beverage industry in the world. According to the

international bottled water association (IBWA), sales of bottled water have increased by 500

percent over the last decade and 1.5 million tons of plastic are used to bottle water every year.

Plastic bottle recycling has not kept pace with the dramatic increase in virgin resin

polyethylene terephthalate (PET) sales and the last imperative in the ecological triad of

reduce / reuse / recycle, has emerged as the one that needs to be given prominence. Fig. 1(a)

shows a typical group of the water bottles available in market used for the drinking purposes.

Fig. 1(a) Water bottles samples Fig. 1(b) Dumped water bottles

The general survey shows that 1500 bottles are dumped as garbage every second. PET is

reported as one of the most abundant plastics in solid urban waste (de Mello et al., 2009) Fig.

1(b) shows the plastic bottle present in garbage. Waste Recovery Program, WRAP (2005)

indicates that the reduction of waste benefits the natural environment with indubitable

economical advantages, since waste represents a large loss of resources and raw materials

that could be recovered, recycled or considered for other uses. In 2007, it is reported a

world’s annual consumption of PET bottles is approximately 10 million tons and this number

2

grows about up to 15% every year. On the other hand, the number of recycled or returned

bottles is very low (ECO PET, 2007). On an average, an Indian uses one kilogram (kg) of

plastics per year and the world annual average is an alarming 18 kg. It is estimated that

approximately 4-5% post-consumer plastics waste by weight of Municipal Solid Waste

(MSW) is generated in India and the plastics waste generation is more i.e. 6-9 % in USA,

Europe and other developed countries. As per data available on MSW, approximately, 4000-

5000 tonnes per day post consumer plastics waste are generated. Chen et al (2010) indicates

that reuse of plastic waste is an important step in the development of clean energy and in

conjunction with the promotion of new waste plastics recycling programs could contribute to

additional reductions in GHG emissions and fossil fuel consumption. Hence, there needs to

be concerted efforts in the reuse of plastic waste from water bottles and this study is in this

direction.

1.2 Plastic waste versus soil reinforcement with discrete members/fibres Plastic waste when mixed with soil behaves like a fibre reinforced soil. Plastic waste/fibres

are distributed throughout a soil mass; they impart strength isotropy and reduce the chance of

developing potential planes of weakness. Hence uses of plastic waste for improving the

engineering properties of soil are taken up in the present study. Mixing of plastic

waste/fibres with soil can be carried out in a concrete mixing plant of the drum mixer type

(Lindh 1990) or with a self propelled rotary mixer (Santoni and Webster 2001). Plastic waste/

fibres could be introduced either in specific layers or mixed randomly throughout the soil. An

earth mass stabilized with discrete, randomly distributed plastic waste/fibres resembles earth

reinforced with chemical compounds such as lime, cement etc in its engineering properties.

1.1.3 Advantages of soil reinforced with plastic waste/discrete fibres

The following are the specific advantages of soil mixed with plastic waste.

Improves strength, stiffness, ductility and toughness of soil.

Maintains strength isotropy which resists shear band formation.

Improves the piping resistance of soil.

Increases resistance against liquefaction under dynamic loading conditions.

Reduces compressibility of soil.

3

Reduces desiccation cracking and increase tensile strength of clays.

CHAPTER 2

LITERATURE REVIEW

Plastic bottle recycling has not kept pace with the dramatic increase in virgin resin

polyethylene terephthalate (PET) sales and the last imperative in the ecological triad of

reduce / reuse / recycle, has emerged as the one that needs to be given prominence. The

general survey shows that 1500 bottles are dumped as garbage every second. PET is reported

as one of the most abundant plastics in solid urban waste (de Mello et al., 2009). Waste

Recovery Program, WRAP (2005) indicates that the reduction of waste benefits the natural

environment with indubitable economical advantages, since waste represents a large loss of

resources and raw materials that could be recovered, recycled or considered for other uses. In

2007, it is reported a world’s annual consumption of PET bottles is approximately 10 million

tons and this number grows about up to 15% every year. On the other hand, the number of

recycled or returned bottles is very low (ECO PET, 2007). On an average, an Indian uses one

kilogram (kg) of plastics per year and the world annual average is an alarming 18 kg. It is

estimated that approximately 4-5% post-consumer plastics waste by weight of Municipal

Solid Waste (MSW) is generated in India and the plastics waste generation is more i.e. 6-9 %

in USA, Europe and other developed countries. As per data available on MSW,

approximately, 4000-5000 tonnes per day post consumer plastics waste are generated. Chen

et al (2010) indicates that reuse of plastic waste is an important step in the development of

clean energy and in conjunction with the promotion of new waste plastics recycling

programs could contribute to additional reductions in GHG emissions and fossil fuel

consumption. Hence, there needs to be concerted efforts in the reuse of plastic waste from

water bottles and this study is in this direction.

The plastic waste mixed soil behaves as reinforced soil, similar to fibre reinforced soil. The

concept of soil reinforcement has dramatically changed the function of soil as a construction

material. The introduction of the soil reinforcing techniques has enabled engineers to

effectively use unsuitable in-situ soils as reliable construction materials in a wide range of

civil engineering applications. Reinforced soil construction is an efficient and reliable

technique for improving the strength and stability of soils. The technique is used in a variety

4

of applications, ranging from retaining structures and embankments to subgrade stabilization

beneath footings and pavements. It is noted that, in the literature very few studies are

available on the use of plastic mixed soil. The possible advantages of using the plastic wastes

are that the plastic waste can be consumed in useful geotechnical engineering applications. In

one of the earliest papers on the use of plastic waste in combination with soil, Consoli et al

(2002) indicates that one of the most promising approaches is the use of fibre-shaped waste

materials in the combination with soil and cement. Materials such as polyethylene

terephthalate (PET) plastic bottles are profusely and widely produced, yet used little for

engineering purposes, and the overwhelming majority of them are placed in storage or

disposal sites. The plastic waste when mixed with soil results in improvement of soil

response in the case of roads and embankments, soil being a natural resource, the quantity of

soil can be reduced. Thus, it offer two advantages; one is the reuse of plastic waste materials

and the other is the reduction in consumption of natural material like soil. In the present

study, an approach for recycling of plastic water bottles in the field of geotechnical

engineering as reinforcing material is proposed and illustrated with a simple example.

In the recent years, several researchers are trying to develop solutions for the reuse of

different types of wastes generated which has become one of the major challenges for the

environmental issues in many countries. Wastes such as plastic waste tire shreds mixed with

soil behave similar to fibre reinforced soils and several researchers presented technique of

using discrete fibres to enhance the strength of soil. Most of them used different types of

fibres as reinforcing materials, such as natural fibres, glass fibres, plastic fibres,

polypropylene and polyester fibres. Experimental results reported by various researchers

(Shewbridge and Sitar, 1989, Maher & Gray, 1990; Maher and Ho, 1994, Li et al. 2001, Rao

& Balan, 2000, Consoli et al., 2002, 2003, 2004, 2009, Sivakumar Babu & Vasudevan 2008

a, b; Sivakumar Babu & Chouksey 2010) showed that the fibre reinforced soil is a potential

composite material which can be advantageously employed in improving the structural

behaviour of soils. The tests were carried with different types of fibres in different

proportions and the effects of fibre in improving strength and stability of soil were

identified.

Shewbridge and Sitar (1989) conducted experiments with sand reinforced with fibres to

observe the deformation pattern and to quantify the width of shear zone in sand. The results

showed that deformation pattern of reinforcement was found curve- linear and symmetric

about the centre of the shear zone. Maher and Gray (1990) carried out triaxial compression

5

tests on sand reinforced with discrete, randomly distributed fibres and observed the influence

of various fibre properties on soil behaviour. Using the experimental results they have

proposed a force equilibrium model based on statistical analysis for randomly distributed

discrete fibre reinforced sand. Maher and Ho (1994) reported that the fibre reinforcement

increased the shear strength and ductility of clay. Li et al. (2001) carried out centrifuge model

test to study the behaviour of fibre reinforced cohesive steep slope using poly propylene

fibres. It was found that critical height of slope can be increased due to reinforcing.

Consoli et al. (2002) carried out an experimental study of the utilization of the polyethylene

fibres derived from plastic wastes in the reinforcement of uncemented and artificially

cemented sand and showed that the plastic waste improved the stress strain response of

uncemented and cemented sands. This is perhaps one of the earliest attempts advocating the

use of plastic waste. Consoli et al. (2003) proposed a field application for such materials

designed for increasing the bearing capacity of spread foundations when placed on a layer of

fibre-reinforced cemented sand built over a weak residual soil stratum. Consoli et al. (2004)

carried out triaxial compression test on cemented and uncemented sand reinforced with

various types of fibres to study the effect of fibres on mode of failure, ultimate deviator

stress, ductility and energy absorption capacity. They observed that the inclusion of fibres

changed the mode of failure from brittle to ductile.

Studies were also conducted on tire shreds as reinforcing material (Hataf and Rahimi 2006,

Yoon et al. 2008). Hataf and Rahimi (2006) carried series of laboratory tests on the model of

shallow footing resting on reinforced sand. Tire shreds were used as reinforcement elements.

It was found that addition of 10% shreds by volume contributed to improvement of bearing

capacity, expressed in terms of the bearing capacity ratio (BCR) in the range of 1.17 to 1.83

where as use of 50% tire shreds increased BCR to values in the range of 2.95 to 3.9 for

different sizes of shreds. Yoon et al. (2008) presented a method for the reuse of waste tires

called ‘tirecell’ for soil improvement. The results indicated that tirecell reinforced sand

produced higher bearing capacities and lower settlements.

Sivakumar Babu et al. (2007) presented the results based on numerical analysis of stress

strain response of fibre reinforced sand. Numerical simulation results indicate that the

presence of random reinforcing material in soils make the stress concentration more diffused

and restricts the shear band formation. Numerical simulation results also indicate that pull-out

resistance of fibres governs the stress strain response of random-reinforced soil. Sivakumar

Babu and Vasudevan (2008a, 2008b and 2008c) presented comprehensive experimental

results using compacted soil-fibre specimens, with coir fibres randomly distributed in the soil

6

specimen. Experiments were carried out for various fibre parameters such as fibre content,

fibre length and fibre diameter. Results showed that the improvement in strength and stiffness

response, reduction in compression indices, reduction in swelling behaviour of soil. It is also

observed that fibres reduce the seepage velocity of plain soil considerably and thus increase

the piping resistance of soil. Based on critical state concepts, Sivakumar Babu and Sandeep

Chouskey (2010) proposed a constitutive model to obtain stress strain response of coir fibre

reinforced soil as a function of fibre content.

The above literature review clearly indicates that studies are available on the use of wastes

from plastic water bottles are limited. The soil mixed with plastic waste is expected to

behave as a fibre reinforced soil. The patented procedures for the use of fibre-reinforced soil

in the field are also available (Freed 1988)). To promote the recycling of plastic wastes on a

large-scale in geotechnical applications where bulk utilization of waste materials is possible,

work is carried out and presented in this report.

7

CHAPTER 3 MATERIALS AND METHODS

3.1 Introduction As discussed in the preceding chapters about the materials used in the analysis of the fibre

reinforced soil, in this chapter the basic characteristics of the materials from various

classification and other tests is discussed. In the present study materials used for the

experimental studies and the methods followed to study the behaviour of fibre reinforced soil

is detailed. In the present study the materials used are sand, Raichur fly ash, red soil, plastic

waste (from water bottles), geogrid waste.

3.2 Materials The section describes the materials used in the study of fibre reinforced soil. 3.2.1 Soil

Sand, fly ash and red soil are used in the present study. 3.2.1.1 Sand

Sand is a naturally occurring granular material made up of fine rock particles. It comprises of

particles, or granules, ranging in size from 75μm to 4.75 mm. The most common constituent

of sand is silica (silicon dioxide, or SiO2), usually in the form of quartz. Sand collected from

the local area is used in this study. The basic properties of sand obtained are tabulated below:

Table 3.1: Characteristics of Sand

Properties ValuesSpecific Gravity, G 2.65 Moisture Content, (%) 10 Dry density, (kN/m3) 17.2 Relative density, (%) 60 Maximum void ratio, (emax) 0.76 Minimum void ratio, (emin) 0.45 Void ratio, (e) 0.57 Effective size, (D10) (mm) 0.15

8

Coefficient of uniformity, (Cu) 1.53 Coefficient of curvature, (Cc) 0.939 Angle of internal friction, (Φ) 30

3.2.1.2 Fly Ash

Fly ash is generally captured by electrostatic precipitators or other particle filtration

equipments before the flue gases reach the chimneys of coal-fired power plants, and together

with bottom ash removed from the bottom of the furnace is in this case jointly known as coal

ash. Depending upon the source and makeup of the coal being burned, the components of fly

ash vary considerably, but all fly ash includes substantial amounts of silicon dioxide (SiO2)

(both amorphous and crystalline) and calcium oxide (CaO), both being endemic ingredients

in many coal-bearing rock strata. Fly ash material solidifies while suspended in the exhaust

gases and is collected by electrostatic precipitators or filter bags. Since the particles solidify

while suspended in the exhaust gases, fly ash particles are generally spherical in shape and

range in size from 0.5 µm to 100 µm. They consist mostly of silicon dioxide (SiO2), which is

present in two forms: amorphous, which is rounded and smooth, and crystalline, which is

sharp, pointed and hazardous; aluminium oxide (Al2O3) and iron oxide (Fe2O3). Fly ashes are

generally highly heterogeneous, consisting of a mixture of glassy particles with various

identifiable crystalline phases such as quartz, mullite, and various iron oxides.

In the present study Raichur fly ash with chemical composition SiO2 (63.23), Al2O3 (26.25),

TiO2 (1.10), Fe2O3 (3.51), MgO (0.50), CaO (0.20), K2O (0.64), Na2O (0.26), LOI (4.01) is

used. From the grain size distribution curve (shown in Fig. 3.1) it is observed that fly ash is

uniform graded with 95% of particle size between 75.0µ to 2.0mm. The coefficient of

uniformity, Cu of fly ash is 2.36 (<4) indicates that fly ash is uniformly graded.

Table 3.2: Classification test results of Fly Ash Properties Value Liquid limit,(%) 32.07 Specific gravity 2.01 Dry Density, (g/cc) 1.27 Optimum moisture content,(%)

22

Coefficient of uniformity, Cu 2.36

Coefficient of curvature, Cc 1.05

9

Table 3.3: Comparison of Chemical composition of different Fly ash

Composition or property

Raichur pond ash(i)

Indian fly ashes Range(ii)

United states fly ashes(iii)

Silica (SiO2) 63.23 53-63 28-59

Alumina (Al2O3) 26.25 27-37 Jul-38

Iron oxide (Fe2O3)

3.51 3.3-6.1 Apr-42

Lime (CaO) 0.2 0-3 0-13

Magnesia (MgO) 0.5 0-0.8 -

Soda (Na2O) 0.26 0.1-0.4 -

Potash (K2O) 0.64 0-0.9 -

Fig. 3.1 Particle size distribution curve of fly ash 3.2.1.3 Red Soil

The soil used in the present study is collected from IISc Bangalore campus from different

locations. Red soils generally form from sedimentary rocks. The red color in soil usually

indicates a high amount of iron, in the form of iron oxide. The iron oxide can be inherited

10

from the parent material or can form as a result of intense weathering over a long period of

time. This is the main type of soil available in Bangalore and surrounding areas. This type of

soil is also available in a large region of our country.

Table 3.4: Basic characteristics of red soil

Properties Values Liquid limit (%) 39.0 Plastic limit (%) 26.0 Shrinkage limit (%) 20.0 Specific gravity (G) 2.65

Optimum moisture content (%) 17.8 Maximum dry unit weight (kN/m3) 17.6 Silt + clay size (%) 10.0 Sand size (%) 90.0

3.2.2 Plastic Waste

The used water bottles i.e. disposed plastic (PET) water bottles have been cut into pieces and

used. Polyethylene terephthalate (PET) is the polymer used in the manufacture of plastic

bottles. Polyethylene terephthalate has a molecular formula of (C10H8O4)n. Its solubility in

water is negligible at less than 0.4 percent. The melting point is 473 F to 500 F (245 C to 260

C). Polyethylene terephthalate is incompatible with strong oxidizing agents and strongly

alkaline materials. The extent of polymerization of polyethylene terephthalate varies from

product to product. Plastic water bottle wastes in the form of chips are used as reinforcing

material.

Table 3.5 Basic characteristics of Plastic waste

Properties Values Length, (mm) 8.0

thickness, (mm) 0.1

Specific gravity 1.33

Tensile Load, (N) 350.0

3.3 Experimental Methods

11

This section gives the details of the experiment procedure of various tests like UCC, CU,

oedometer test, Californian Bearing Ratio test and piping tests conducted on fibre reinforced

material for the analysis.

3.3.1 Unconfined Compression (UCC) Test and compressibility tests:

The maximum load carrying capacity of subsoil is determined by its shear strength and

compressibility. The shear strength is usually determined with compression tests in which an

axial load is applied to the specimen and increased till the specimen fails. The unconfined

compression test gives the undrained shear strength of the soil in a simple and quick way. In

unconfined compression test the specimen is not subjected to any lateral pressure during the

test. One –dimensional compression test were also done using consolidation tests.

3.3.2 Consolidated Undrained Test

The standard consolidated undrained test is compression test, in which the soil specimen is

first consolidated under all round pressure in the triaxial cell before failure is brought about

by increasing the major principal stress. It may be performed with or without measurement of

pore pressure although for most applications the measurement of pore pressure is desirable.

This method determines the angle of internal friction (φ) and cohesion (c) strength parameters

of soils by triaxial compression testing. When pore pressures are measured, the effective

values of internal friction and cohesion,(φ') and (c') respectively, can be calculated.

3.3.3 California Bearing Ratio (CBR) Test

The California bearing ratio (CBR) is a penetration test for evaluation of the mechanical

strength of road subgrades and base courses. It was developed by the California Department

of Transportation. CBR is defined as the ratio of force per unit area required to penetrate a

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

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

for penetrations of 2.5mm and 5mm. When the ration of 5mm is consistently higher than at

2.5mm, the ratio at 5mm is used.

C.B.R. = (Test load/Standard load) ×100

Standard load is defined as the load obtained from the test on crushed stone which has a CBR

value = 100%.The following table (Table 3.6) gives the standard loads adopted for different

penetrations for the standard material with a C.B.R. value of 100%.

12

Generally the CBR value at 2.5mm penetration will be greater than that at 5.0mm

penetration. In such cases, the CBR2.5mm is selected for design. If CBR5mm> CBR2.5mm, the

test is repeated. If the identical results follow, the bearing ratio at 5mm penetration is taken

for the design.

Table 3.6: Standard load for different penetrations

Penetration of plunger, (mm) Standard load, (kg)

2.5 1370.0

5 2055.0

7.5 2630.0

10 3180.0

12.5 3600.0

3.3.4 Piping Test:

This section gives the details of the experiment procedure of the test to find critical hydraulic

gradient and upward seepage rate of fly ash blended with plastic waste and geogrid waste.

The sample is prepared at (96% of MDD) on dry side of optimum water content. Plastic

waste and geogrid waste are randomly distributed over the sample and mixed with fly ash

Mould is of size 10.0cm diameter and 11.0cm height as shown in Fig.3.2 and compacted in

three layers by uniformly dropping a weight of 500.0g plate from a height of approximately

50.0cm with 10 drops per layer.

13

Fig 3.2 Sample compacted at 96% of MDD kept for saturation.

The water tank shown in Fig. 3.2 is filled to sufficient head with water before connecting the

stand pipe to the bottom of the sample. After preparing the sample in the mould the standpipe

is connected to the mould from the bottom. Before allowing the water to flow through the

sample, the necessary readings like exit gradient are noted. Open the value at the bottom and

allow the sample to saturate with sufficient head (preferably for 24hrs). After the specimen is

saturated, the water level of the water supply tank is gradually raised to apply the hydraulic

gradient to the testing specimen.

The head is increased in steps of 0.5cm or less to determine the precise head of failure at

which piping occurs with time of observation (say 30min). Discharge is measured using

graduated cylinder and noted. The above procedure is repeated for different heads as long as

the particle in the sample gets detached due to upward movement of particles.

14

CHAPTER 4 STRENGTH AND STIFFNESS CHARACTERISTICS

4.1 Introduction

Literature concerning the strength and stiffness of plastic waste reinforced soils clearly

indicates there are limited studies in this area and there is need for detailed studies in this

area. Strength is an important aspect which governs the stability of reinforced soil structures,

and knowledge of stiffness of these soils is required to calculate ground movements and to

obtain solutions to problems of soil-structure interaction. Comprehensive experimental

investigation is conducted and experimental results concerning the strength and stiffness

aspects of plastic waste reinforced soils are examined in detail in this chapter. The results are

discussed in the following manner.

(i) Unconfined Compression (UCC) Test Results

(ii) Consolidated Undrained (CU) Test Results

(iii) California Bearing Ratio (CBR) Test Results

The general observable trends and conclusions from the above studies are presented at the

end of the chapter.

4.2 Unconfined Compression (UCC) Test Results

15

The improvement in the unconfined compressive strength (UCS) of soil by the inclusion of

plastic waste is discussed in this section. The stress levels at 2% strain were calculated by

dividing the load with corrected cross-sectional area of the specimen. The results for the

various percentages of plastic waste are summarized in the plot given below.

4.2.1 Stress versus Strain Response

Stress vs. strain (%) response is presented for various plastic waste parameters and confining

pressures. The figure presents the stress vs. strain response for plastic waste reinforced soil

with various fibre contents for a fibre length of 4mm and fibre diameter of 0.1 mm.

It is clear from these results that the unconfined compressive strength increases as the %

content increases. The results show that the stress-strain behaviour is considerably improved

by incorporating plastic waste into the soil.

4.2.1.1 Sand mixed with plastic waste

Fig 4.1 Stress-Strain Curve from UCC Test for sand mixed with plastic waste

4.2.1.2 Flyash mixed with plastic waste

16

Fig. 4.2 Stress-Strain Curve from UCC test for fly ash mixed with plastic waste

4.2.1.3 Red soil mixed with plastic waste

Fig. 4.3 Stress-Strain Curve from UCC test for red soil mixed with plastic waste

4.2.2 Strength Improvement due to Plastic Waste

17

In general from the above curves it can be observed that with the increase in the percentage

of plastic waste, the strength of the soil improved.

In the case of flyash mixed with plastic waste, \the increase in strength at 2% strain was

found to be 16.33% for 0.5% plastic waste, 29.84% for 0.75% plastic waste and 38.11% for

1% plastic waste. In the case of sand mixed with plastic waste, \the increase in strength at 2%

strain was found to be 37.11% for 0.5% plastic waste, 64.24% for 0.75% plastic waste and

71.21% for 1% plastic waste. In the case of flyash mixed with plastic waste, \the increase in

strength at 2% strain was found to be 39.5% for 0.5% plastic waste, 65.11% for 0.75% plastic

waste and 72.12% for 1% plastic waste.

4.3 Consolidated Undrained (CU) Test Results

The improvement in deviator stress at failure for soil by the inclusion of plastic waste is

discussed in this section. Deviator stress at various strain levels were calculated by dividing

the deviator load with corrected cross-sectional area of the specimen. Pore pressure curves

were also plotted in order to study how the plastic waste affected pore water behaviour.

Experimental results for various confining pressures and discussed in the following sections.

4.3.1 Stress versus strain response

Deviator stress vs. strain (%) response is presented in for various plastic waste percentages

and confining pressures. The stress vs. strain response for plastic waste reinforced soils with

various fibre contents at a confining pressure of 50 kPa are also presented. Similarly the

stress-strain curves for plastic waste reinforced soil with various fibre parameters tested at

various confining pressures.

From the stress-strain curves, deviator stress at failure (peak deviator stress) and

corresponding strain for various cases is obtained. It is clear from these results that deviator

stress increases as the plastic waste content increases. Further it is observed from these results

that as the strain increases the deviator stress also increases. In most cases maximum deviator

stress occurred at about 6 % to 8% of strain. The results show that the stress-strain behaviour

is considerably improved by incorporating fibres into the soil. The increase in strength is due

to the confinement, which results in the increase of cohesion and friction of plain soil and

further the fibres reduce chance of slippage of soil particles.

4.3.1.1 Sand mixed with plastic waste

18

Fig 4.4 Stress-Strain Curves for Confining Pressure = 50kPa

19


Fig. 4.6 Stress-Strain Curves for Confining Pressure = 150kPa

4.3.1.2 Fly ash mixed with plastic waste


20



4.3.1.3 Red soil mixed with plastic waste

21



22


4.3.2 Effect of Plastic Waste on Soil Strength

From these figures, it is clear that deviator stress at failure increases as the plastic waste

content increases. This aspect can be observed for all the three confining pressures. A

reasonable estimation of the increase in strength can be done by comparing the deviator stress

levels for 5% strain level. In the case of fly ash mixed with plastic waste at 50 kPa confining

pressure, 0.5% plastic waste showed an increase in strength of 8.79%, 0.75% plastic waste

showed an increase in strength of 26.67% and 1% plastic waste showed an increase in

strength of 40.8%. For a confining pressure of 100 kPa, 0.5% plastic waste showed an

increase in strength of 7.56%, 0.75% plastic waste showed an increase in strength of 14.82%

and 1% plastic waste showed an increase in strength of 24.44%. And finally for 150 kPa

confining pressure, 0.5% plastic waste showed an increase in strength of 5.88%, 0.75%

plastic waste showed an increase in strength of 8.83% and 1% plastic waste showed an

increase in strength of 12.94%. The increase in strength was higher for lower confining

pressures for all the percentages of plastic waste. Similarly sand mixed with plastic waste, red

soil mixed with plastic waste showed the same trend of increment in strength.

4.3.3 Pore Pressure Curves

The pore pressure curves were plotted by plotting the excess pore pressure for the various

23

strain levels as obtained from the CU Tests.

4.3.3.1 Fly Ash

Fig 4.13 Pore Pressure Curves for Confining Pressure = 50kPa

Fig. 4.14 Pore Pressure Curves for Confining Pressure = 100kPa

24


4.3.3.2 Red Soil

25



26


It was observed throughout that the excess negative pore pressure increased throughout due

to plastic waste reinforcement. Thus the Effective Stress (Total Stress – Pore Pressure) for

any given strain will be more with the inclusion of plastic waste. This indicates that the Fly

Ash will exhibit a higher stiffness with the addition of plastic waste. In general this increase

in negative pore pressure was more for greater percentages of plastic waste.

4.4 Proposed Model

Babu et al. (2010a, b) proposed generalized constitutive model based on critical state

soil mechanics framework for the prediction of stress-strain-pore water pressure response and

long term settlement for municipal solid waste. The model accounts volumetric strain due to

elastic, plastic, creep and biodegradation for the predictions. Babu and Chouksey (2010)

proposed a constitutive model for the prediction of stress-strain and pore water pressure

response based on critical state soil mechanics framework. The model accounts fiber effect

present in soil which is used for the prediction of the stress-strain and pore water pressure

response of fiber reinforced soil. Based on the model proposed by Babu and Chouksey

(2010), stress ratio for unreinforced soil is expressed as:

q

p

(4.1)

where, the deviatoric stress and mean effective stress are given by ' '1 3( )q and

' '1 3( 2 ) / 3p .

It is observed from experiments that deviatoric stress and stress ratio are functions of

27

plastic waste present in soil. A typical observations of stress ratio versus strain (in %)

presents in Figs. 9(a), 9(b) and 9(c) for plastic waste mixed soil at confining pressure of 50,

100 and 150 kPa.

The experimental observations of stress ratio with strain show that up to a certain

strain level, stress ratio increases and becomes constant. Hence, to model the behavior of

plastic waste mixed soil, it can be assumed that the stress ratio increases and subsequently

becomes constant with increase in strain. This can be expressed as an exponential form as a

function of plastic waste as follows:

2q

ep

(4.2)

where is percentage of plastic waste present in soil ( = 0.0, 0.50, 1.0 and 2.0) and is

material constant.

2p q e (4.3)

Therefore, taking differential both sides,

2p d dp dq e dq q e d (4.4)

2p d dp e dq q e d (4.5)

Let us assume that the slope of the yield curve at any point ,p q be . Since q decreases

with p , the sign of is negative.

dq dp (4.6)

Substituting value of dq in equation (5)

2p d dp e dp q e d (4.7)

2p d e dp q e d (4.8)

By rearranging Eq. (8) can be written as:

2 2

q e dd dp

pe e p

(4.9)

The Eq. (9) defines a yield locus. Since for this model, the successive yield loci are

geometrically similar, is a function of (stress ratio) only. Therefore, any yield curve

passing through a known point can be obtained by integrating Eq. (9).

28

00 02 2

p

p

q e dd dp

pe e p

(4.10)

Here in the equation (4.10) is function of stress ratio. Now, our objective is to find the

in terms of stress ratio. The value of is obtained by energy dissipated equation. (Wood,

1990)

2 2

2 2

'

'

2 2

p M qM

p q

Multiplying numerator and denominator by 22 e

2 22

2'

' 2

2 2

p M q e

p q e

(4.11)

On simplification of Eq. (4.11)

22 22

2 2

M e

e

(4.12)

Substituting value of in Eq. (4.10)

0

2 22 2 2 2

0 02 2

2 22 2 2 2

p

p

q e dd dp

pM e M ee e p

e e

(4.13 )

On simplification of Eq. (13)

2 2

2 2 2 2 20

2ln 1 1n 2

q p qe

M p p M p q

(4.14)

On further simplification of Eq. (4.14) with expanding exponential series and assuming

higher terms are neglected, final expression turns to:

0 exp 2ln 2 1 2ln 2p

q Mp e ep

(4.15)

Thus, Eq. (4.15) represents the equation for deviatoric stress which incorporates

behavior of plastic waste under different loading conditions. When the plastic wastes are

29

ignored, it reduces to standard form of the modified cam clay model i.e. when plastic

waste 0 , above equation changes to:

0' 1p

q Mpp

(4.16)

The proposed model requires the same parameters as the modified cam clay model. These

parameters are frictional constant 6sin / 3 sinM , compression index ( ),

recompression or swelling index ( ), p is mean effective stress 1 32 / 3 and 0p is a

pre-consolidation pressure. All these model parameters are obtained from standard triaxial

and one dimensional compression tests. The compression and recompression indices ( and

κ) are obtained from the compression test results presented earlier for red soil. The slope of

loading path in e-log p curve is given by and the slope of unloading path is given by .

The average value of material constant ( ) used for prediction of stress-stain and pore water

pressure behavior is taken as 0.52 for analysis in the present study. It can be noted from the

results that, the compression parameters ( and ) decrease and frictional constant (M)

parameter increases as percentage of plastic waste increases. The experimental results clearly

point out that the plastic waste mixed soil improves stress-strain behavior.

Fig. 4.19: CU experimental results for stress strain response at confining pressure of

(50 kPa)

30

Fig. 4.20: CU experimental results for pore water pressure response at confining pressure of

(50 kPa)

4.4 California Bearing Ratio (CBR) Tests

The CBR tests were performed both under soaked and unsoaked conditions. Separate tests

were performed for various percentages of plastic waste. CBR is a basic penetration test to

determine the shear resistance of soil. The effect of plastic waste reinforcement was done

both by comparing the CBR values, as well as the load displacement curves under unsoaked

and soaked conditions. All tests were performed as described in Chapter 3.

4.4.1 Load-Displacement Curves

The CBR tests were performed sequentially for various percentages of plastic waste under

both unsoaked and soaked conditions. The load-displacement response for both the

conditions are summarised in the plots shown below.

31

Fig 4.19 Load-Displacement Curves for unsoaked conditions (Sand)

Fig 4.20 Load-Displacement Curves for soaked conditions (Sand)

32

Fig 4.21 Load-Displacement Curves for unsoaked conditions (Fly Ash)

Fig 4.22 Load-Displacement Curves for soaked conditions (Fly Ash)

33

Fig 4.23 Load-Displacement Curves for unsoaked conditions (Red Soil)

Fig 4.24 Load-Displacement Curves for soaked conditions (Red Soil)

From the load-displacement curves, it is clear that the penetration resistance of soil increases

substantially on addition of plastic waste. The increase in resistance was observed to be

greater for higher percentages of plastic waste. The difference was more clear-cut for higher

strains under soaked conditions. This increase in strength can be more clearly characterised

by computing and comparing the CBR values, as mentioned in the following section.

4.4.2 Effect of plastic waste on CBR value of different soils

Under unsoaked conditions, the CBR of plain sand was found to be 14.3, which increased to

34

18.01 for 0.5% plastic waste, 19.8 for 1% and 24.6 for 1.5%. Under soaked conditions, the

CBR of plain Fly Ash was found to be 13.1, which increased to 14.9 for 0.5% plastic waste,

18.2 for 1% and 22.0 for 1.5%.

In the case of red soil, the CBR under unsoaked conditions was found to be 24.08, which

increased to 26.1 for 0.5% plastic waste, 31.6 for 0.75% and 42.1 for 1%. Under soaked

conditions, the CBR of plain Fly Ash was found to be 15.6, which increased to 19.6 for 0.5%

plastic waste, 22.6 for 0.75% and 26.1 for 1%.

In the case of Fly Ash, the CBR under unsoaked conditions was found to be 15.4, which

increased to 20.4 for 0.5% plastic waste, 23.3 for 1% and 30.4 for 1.5%. Under soaked

conditions, the CBR of plain Fly Ash was found to be 5.6, which increased to 7.2 for 0.5%

plastic waste, 8.1 for 1% and 9.6 for 1.5%. Significant amount of research has been done

correlating the CBR value of soil to its stiffness, but the credibility of those correlations

remains highly questionable because of the empirical single parameter nature of the CBR test.

But since the other tests performed with plastic waste mixed fly ash also suggest an increase

in stiffness, the comparison of the CBR values can be taken as a fair indication of the increase

in stiffness of soil due to addition of plastic waste.

35

CHAPTER 5

COMPRESSIBILITY AND PERMEBAILITY BEHAVIOUR

5.1 Introduction

Performance of structures such as embankments and roads is greatly affected by the high

compressible nature of the subsoil/ soil used for the construction of these structures. Even

though, several studies have been carried out for improving the shear strength of soil with

fibres, very few studies have been conducted for developing the methods to control the

compressibility when soil is mixed with plastic waste. In the present study one dimensional

consolidation tests were carried out on plastic waste reinforced soil to study the

compressibility behaviour. Based on experimental test results, it was observed that the

compressibility and permeability reduced significantly with addition of a small percentage of

plastic waste to the soil. An empirical relation has been formulated among void ratio,

permeability and percentage of plastic content. A practical application of permeability

reduction is also investigated by analysing a seepage problem.

5.2 Oedometer Test Results

To investigate the effects of plastic waste on the engineering properties of soils, one-

dimensional consolidation test was performed for different percentages of plastic waste

mixed sand.

Fig 5.1.Sand mixed with plastic waste

The experiments were carried out in a standard consolidation apparatus as per ASTM D2435-

04 specifications. Based on the total compression under each normal stress, a relationship

between void ratio (e) versus normal pressure (p) was obtained. The results in the form of e

versus log p for plain sand and sand mixed with different percentages of plastic wastes (0%,

36

0.5%, 0.75%, 1%) are presented in Fig. 5.2. The effect of permeability of plastic waste mixed

sand was studied by calculating the coefficient of consolidation, time taken for 90%

compression etc. The void ratio decreased with an increase in plastic waste percentage (Fig

5.2).

Table 5.1 Compression index at various percentages of plastic waste

Percentage

of plastic

waste(%)

Compressibility

Index (Cc)

Recompression

Index (Cr)

0 0.076 0.041

0.5 0.073 0.026

0.75 0.071 0.021

1 0.069 0.017

It is quite evident from Table 5.1 that the compressibility of sand decreases with the

reinforcement. The permeability was determined at different vertical stresses and it was

plotted against void ratios at different percentages of plastic waste (Fig. 5.3). The plot clearly

shows a decrease in the void ratio and permeability with an increase in plastic waste content.

The void ratios obtained from the corresponding vertical stresses were plotted in the form of

an e versus log k response. The decrease in permeability is due to the effect of the external

pressure and also the decrease in the void ratio due to the addition of plastic waste. Using

these results, an empirical relation has been formulated correlating the void ratio, fibre

content and permeability.

37

Fig. 5.2 e Vs log p curves for different percentages of plastic waste

Fig. 5.3 e Vs log k curves for different percentages of plastic waste

The void ratio in the general equation was divided by a normalizing factor (1+exp(-µχ)), where

µ is the interaction factor and χ is the percentage of plastic waste. The parameter µ considers

the effect of interaction between sand and the plastic waste added to it. The normalized plot

between void ratio and permeability is shown in Fig 5.4.

The relationship obtained was:

(1)

38

Where, e= void ratio

e*= e/(1+exp(-µχ))= normalized void ratio

m, c = slope and y-intercept

µ= Interaction factor

k= permeability

Fig. 5.4 Normalized e Vs log k curves

The equation was generalized by taking µ= 0.2. It was observed that the width between two

lines in the general plot was 0.03 and it decreased to 0.0085 in the normalized plot. A

regression analysis was carried out and the standard error and R2 value were found to be

0.0052 and 0.88, respectively. There is a certain complexity involved in the determination of

the factors that influence the parameter, µ. It is mainly affected by tortuosity, grain size,

specific surface area, fibre arrangement, etc.

5.3 Fly Ash

To investigate the effects of plastic waste on the compressibility characteristics of fly ash, a

series of One-dimensional consolidation tests were performed for different percentages of

plastic waste. The results in the form of e versus log p for plain fly ash and fly ash mixed

with different percentages of plastic wastes (0%, 0.5%, 0.75%, 1%) are presented in Fig. 5.5.

39

Fig 5.5 e versus log p curves for flyash mixed with different percentages of plastic

5.4 Red Soil

Fig 5.6 e versus log p curves for red soil mixed with different percentages of plastic

From the e-logp curves of soils (sand, fly ash, red soil) mixed with different percentages of

plastic waste (0%, 0.5%, 0.75%, 1%), it can be observed that the initial void ratio was higher

for plain soil and lower when plastic waste was added. As the percentage of plastic waste

increased in soil, the density of plastic waste being less, more voids were occupied with

plastic waste and resulted in overall reduction of void ratio. Thus the compressibility of soil

decreased with the increase in plastic waste.

40

5.5 Effects of waste content on compression index of soils

From the oedometer test data, the e-logp curves are obtained. The slope of compression line

and the recompression line from these curves gives compression index and recompression

index respectively. These indices for different soils mixed with plastic waste are tabulated

below.

Table 5.2 Flyash Compressibility Indices

Percentage of

plastic waste (%)

Compressibility

Index(Cc)

Recompression

Index (Cr)

0 0.065 0.019

0.5 0.064 0.018

0.75 0.063 0.016

1 0.061 0.013

Table 5.3 Red soil Compressibility Indices

Percentage of plastic waste

(%)

Compressibility Index(Cc)

Recompression Index (Cr)

0 0.116 0.019 0.5 0.094 0.018 0.75 0.064 0.014

1 0.031 0.011

From the above results, it can be observed with the increase in the percentage of plastic waste

from 0.5% to 1%, the compression and recompression indices is reduced. This results implies

reduction in compressibility.

5.6 Conclusions

1. From the results it was observed that the initial void ratio was higher for plain soil and

lower when plastic waste was added. As the percentage of plastic waste increased in soil, the

density of plastic waste being less, more voids were occupied with plastic waste and resulted

in overall reduction of void ratio.

2. The slope of e-log p curve decreases as the plastic waste content increases from 0.5% to

1%. It indicates that the compressibility of soil reduces as the plastic waste content increases.

3. The permeability of sand decreases with an increase in the percentage of plastic waste. On

addition of 1% plastic waste, the permeability gets halved when compared to plain sand.

41

4. A normalizing factor was introduced to generalize the relation between permeability and

void ratio at different contents of plastic waste and an empirical relation was generated

between these parameters.

42

CHAPTER 6

PIPING AND SEEPAGE RESISTANCE OF FLY ASH MIXED WITH PLASTIC WASTE

6.1 Introduction

In this chapter utilization of fly ash by adding plastic waste and geogrid waste products is

described for an effective utilization in geotechnical engineering. Fly ash is a material which

is highly vulnerable to surface runoff and internal piping. This can be improved by adding

plastic waste and geogrid waste which improves the shear resistance of the composite. The

experiment results conducted on fly ash composite shows that piping resistance of the

composite is increased and the permeability is decreased due to the addition of plastic waste

and geogrid waste.

6.2 Laboratory Piping Test

This section gives the details of the experiment procedure of the test to find critical hydraulic

gradient and upward seepage rate of fly ash blended with plastic waste and geogrid waste.

Before the test sample is prepared the basic characteristics of fly ash like particle size

distribution, specific gravity of fly ash, maximum dry density, optimum moisture content of

the fly ash using standard proctor test and gradation properties are determined. The basic

characteristics of fly ash are given in Table 6.1.

6.2.1 Experimental Setup

The apparatus used in the test are specimen mould (Acrylic material), water tank, stand pipe,

graduated measuring jar and scale as shown in Fig. 6.1.

6.2.2 Materials used

In the present study Raichur pond ash with chemical composition SiO2 (63.23), Al2O3

(26.25), TiO2 (1.10), Fe2O3 (3.51), MgO (0.50), CaO (0.20), K2O (0.64), Na2O (0.26), LOI

(4.01) is used. From the grain size distribution curve (shown in Fig. 6.2), it is observed that

fly ash is uniform graded with 95% of particle size between 75.0µ to 2.0mm. The coefficient

of uniformity, Cu of fly ash is 2.36 (<4) indicates that fly ash is a uniformly graded.

Plastic waste from used water bottle is cut in the form of strips of length between 10-20mm

and aspect ratio (L/D) between 20 and40 is used.

43

Fig. 6.1 Sample compacted at 96% of MDD kept for saturation

6.2.3 Test Setup and Sample Preparation

Before the sample is prepared, calculations like weight of soilto be added, fibres and amount

of water to be added are calculated. The sample is prepared at (96% of MDD) on dry side of

optimum water content. Plastic waste and geogrid waste are randomly distributed over the

sample and mixed with fly ash as shown in Figs. 6.3-6.4 and is kept in a mould of size

10.0cm diameter and 11.0cm height as shown in Fig. 6.1 and compacted in three layers by

uniformly dropping a weight of 500.0g plate from a height of approximately 50.0cm with 10

drops per layer.

Fig. 6.3 Fly ash mixed with randomly distributed plastic waste

44

Fig. 6.4 Fly ash mixed with randomly distributed geogrid waste

6.2.4 Test Procedure

The water tank shown in Fig. 6.1 is filled to sufficient head with water before connecting the

stand pipe to the bottom of the sample. After preparing the sample in the mould the standpipe

is connected to the mould to the bottom of the sample. Before allowing the water to flow

through the sample initial head is noted. Value is opened at the bottom and allow the sample

to saturate with sufficient head (preferably for 24hrs). After the specimen is saturated, the

water level of the tank is gradually raised to apply the hydraulic gradient to the specimen.

The head is increased in steps of 0.5cm or less to determine the precise head of failure at

which piping occurs with time of observation (30min). Discharge is measured using

graduated cylinder. The above procedure is repeated at different heads until detachment of

particles due to upward flow is observed.

6.3 Seepage Flow Velocity and Hydraulic Gradient

Seepage velocity is a parameter which combines the effects of porosity and tortuosity of the

actual flow path among and around the mineral grains.Actual seepage flow velocity is the

seepage flow divided by the pore area. The relationship between actual seepage flow velocity

and hydraulic gradient is shown in Figs. 6.5-6.6 for plastic and geogrid waste. In all cases, the

relation between actual seepage flow velocity and hydraulic gradient is nonlinear expect in

the initial stages. Plastic waste and geogrid waste appeared to effectively restrict soil particles

movement and the resistance to the piping is improved. There is an increase in critical

45

hydraulic gradient from 0.45 for 0% plastic waste to 0.56 for 1% is observed for plastic waste

which shows an increase of about 24% compared to plain fly ash. For geogrid waste as the

fibre content increases the critical hydraulic gradient increases from 0.45 for 0% geogrid

waste to 0.58 for 1% geogrid waste where there is an increase of about 29% which is higher

than that of plastic waste due to increased shear resistance offered by geogrid waste.

Fig. 6.5 Variation of seepage velocity vs. hydraulic gradient with plastic Waste

Fig. 6.6 Variation of seepage velocity vs. hydraulic gradient with geogrid Waste

46

6.4 Upward Seepage Rate of Fly Ash Mixed With Plastic and Geogrid Waste

The slope of the plotted lines in Figs. 6.5-6.6 indicates the upward seepage rate. From Fig.

6.7 it is observed that the fly ash mixed with 0% fibre content, the upward seepage rate is

2.30x10-4cm/s and decreased to a value of 2.00x10-4cm/s, 1.90x10-4cm/s for plastic waste and

geogrid waste of 1.0%. In all cases, the upward seepage rate has marginal decrease with the

increase in the waste content.

Fig. 6.7 Variation of hydraulic conductivity for plastic waste and geogrid waste

6.5 Some Practical Applications

The excessive seepage and piping at the tail end are the two important considerations one

should take into account in the design of sheet pile walls. Optimum combination of plastic

waste and geogrid waste mixed with fly ash can be used efficiently in reducing the seepage

and can be a cost-effective solution with reduced maintenance.

47

6.5.1 Fly Ash for Sheet Pile Wall Design

Fig.

Fig 6.8 Sheet pile wall

A sheet pile as shown in Fig. 6.8 is driven into the fly ash composite to a depth of 7.0m and

the upstream water level is at a height of 6.0m. Upward seepage rate of the fly ash composite

for plastic waste and geo grid waste for different percentage are taken according to Fig. 6.7.

An impervious layer exists at a depth of 8.0m below ground level. A flow net is drawn for the

above case and the no. of flow lines and equipotential lines of the flow net are determined

and the discharge through the medium is calculated in cumecs/m. The exit gradient obtained

from the seepage of piping tests shown in Figs. 6.5-6.6 is used for calculating the safety

factor against piping for different percentage of both plastic waste and geo grid waste. From

Fig. 6.9 it is observed that factor of safety against piping is increased from 0.98 to 1.4 for

1.0% geogrid waste. Geogrids mixed fly ash exhibits an improved piping resistance at 1.0%

of fibre inclusions due to high shear strength offered by the geogrid waste.

48

Fig. 6.9 Variation of factor of safety against piping with different percentage of fibres

Fig. 6.10 Variation of dischrage with fibre content

From Fig. 6.10 it is observed that amount of seepage decreases with increase in the

49

percentage of fibres. The percentage decrease in seepage is more for geogrids in the order of

21% compared to decrease for fly ash blended with plastic waste.

6.5.2 Cofferdam Seepage Analysis with Plastic Waste Mixed Sand

To investigate the practical significance of reduction in permeability for sands, an example

problem on cofferdam seepage from Craig (1997) was simulated using the finite element

package Phase2 (Rocscience, 2006). A plain strain model was used with the inclusion of

sheet piles and the ponded water (Fig. 5). Triangular elements were used to discretise the

model into 2406 elements and 1264 nodes.

Fig. 6.11 Finite Element Model for the Cofferdam Seepage Problem

The analysis was carried out in 3 stages, (1) Installation of sheet pilings, (2) Excavation of

soil inside the dam and (3) Pumping of water inside the dam. For a permeability of 4x10-7

m/s (as given in problem), the discharge entering the dam was found to be 2.02x10-6 m3/s,

and the value given in Craig (1997) is 2x10-6 m3/s. The values of permeability for plain sand

and 1% plastic waste corresponding to 100kPa pressure were then used and it was observed

from the flow diagrams (Fig. 6a) that the discharge entering the dam decreased from 3.07x10-

6 m3/s to 1.51x10-6 m3/s.

Fig. 6.12 (a) Pressure Head Contours and Flow Vectors. (b) Flow Net

The flow net for this arrangement was generated for hydraulic gradient calculations (Fig.

50

6.12b). One of the critical problems to be considered for sheet pile design in such

groundwater conditions is that of piping. It is evident from previous results that the void ratio

of sand decreases with the addition of plastic waste, which will in turn increase the critical

hydraulic gradient. A higher critical hydraulic gradient ensures a greater factor of safety

against piping. For the current problem it was found that the factor of safety increased from

1.2 for plain sand to 1.4 for sand reinforced with 1% plastic waste.

6.6 Summary And Conclusions

Experimental investigations have been carried out on flyash mixed with plastic waste and

geogrid waste and their effect on the seeapge potential and piping resistance is studied. The

following are important finding of the present research.The present study reveals that the

addition of discrete and randomly distributed fibre inclusions in fly ash is an effective method

in improving the piping resistance of the fly ash and is cost effective. Flyash blended with

geogrid waste shows and improved resistance to the piping phenonmen compared to the

plastic waste blended with flyash due to the higher shear resistance offered by the geogrid

waste compared to the plastic fibre.

The upward seepage rate is decreased for fly ash composites due to decrease in void ratio and

the blocking of pore spaces of fly ash by fibres replacing fly ash solids. The upward seepage

rate has a marginal decrease with increase of the fibre content.

For the steady state seepage case performed on the sheet pile wall constructed with a fly ash

mixed with plastic and geogrid waste can effectively restrict soil particles movement and the

resistance to the piping is improved.

A similar case was also analysed on plastic waste mixed sand for a cofferdam seepage

problem, and even in this case, the addition of plastic waste was found to increase the overall

stability against piping.

51

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Appendix Objectives proposed and achieved Objective Status

1 review of the studies on the use of plastic

waste in road construction

Presented in Chapter 2

2 Experimental studies on plastic waste mixed

soils

Presented in all chapters

3 Strength, volume change and permeability

behaviour

Presented in 4, 5 and 6 chapters

4 analysis of data and development of

analytical methods

Presented in Chapter 4 and 6

5 dissemination of knowledge to stake holders

and conduct field trials if possible.

Results of the work have

also been presented in the

Conference on “Modern

Trends in Pavement

Engineering held on 15th

July 2011, where many

stakeholders of CiSTUP

participated.

Project: Laboratory shear strength studies of Soil …cistup.iisc.ac.in/presentations/Research project/CIST005.pdf2 grows about up to 15% every year. On the other hand, the number

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