Plastic as Soil Stabilizer

PLASTIC AS A SOIL STABILZER (A.S. Aswathy, Greeshma.V.R, Arunachala College of Engineering for Women) ABSTRACT

INTRODUCTION

Soil stabilization is the permanent

Soil stabilization can be done in

physical and chemical alteration of soils to

many

enhance

properties.

using waste plastic fibers is an economic

Stabilization can increase the shear strength

method since the stabilizer used here

of a soil and control the shrink-swell

is waste plastic materials, which are easily

properties of a soil, thus improving the load-

available. A plastic material is any of a wide

bearing capacity of a sub-grade to support

range of synthetic or semi-synthetic organic

pavements and foundations. Stabilization

solids that are moldable. Plastics are

can be used to treat a wide range of sub-

typically organic plastics of high molecular

grade materials from expansive clays to

mass,

granular materials. Stabilization can be

substances. They are usually synthetic, most

achieved

commonly derived from petrochemicals, but

their

with

physical

a variety of

chemical

additives including lime, fly ash, and

ways.

but

But

they

the

often

stabilization

contain

other

many are partially natural.

Portland cement, as well as by-products such as lime-kiln dust and cement-kiln dust. These are the existing techniques to improve

PLASTIC AS A SOIL STABILIZER

soil stabilization. This paper presents the

In the investigation the waste

details of studies conducted on the possible

plastic materials has been chosen as the

use of waste plastic for soil stabilization. We

reinforcement material and it was randomly

think that the addition of plastic strips into

included in to the clayey soils with different

the soil will be a innovative technique to

plasticity

improve

strength, tensile

percentages of fiber content (0%, 1%,2%,

strength and California bearing ratio (CBR)

3%, 4%) by weight of raw soil. The use of

value of the soil in an economic way.

plastic

the

shear

indexes

fibers

in

at

five

different

unreinforced

soil

tremendously increases the CBR value, Shear Strength, Resistance to desiccation

cracking,

reduces

Consolidation

and

Swelling.

was performed on them. The samples examined for this purpose were prepared by

IMPROVED PROPERTIES OF SOIL BY USING PLASTIC AS SOIL STABILISER

adding 5, 15 and 25% cement and 0.1, 0.15, 0.2 and 0.5% polypropylene fibers. The sample which showed the maximum value of CBR after 90 days of curing was chosen

i)

CBR Value

as the optimum percentage of polypropylene

ii)

Increased shear strength

fibers for further evaluation of strength of

iii)

Reduction

the stabilized peat soil.

in

consolidation

settlement Effect of stabilization on CBR value

iv)

Reduction in swelling

v)

Reduction in cracks

vi)

Avoids disposal problems of

stabilized peat soil samples with cement and

plastic

polypropylene fibers after air curing for 90

The

results

of

CBR

tests

for

days .The CBR value of undisturbed peat i)

soil is 0.785%. With the addition of 50%

CBR VALUE The

California

bearing

ratio

(CBR) is a penetration test for evaluation of the mechanical strength of soil. To find out the change of CBR value of the fiber reinforced soil with respect to unreinforced soil, CBR test is conducted.

cement, it increased to 34% for unsoaked condition and 30% for the soaked condition. With the addition of 0.15% polypropylene fibers with 50% cement, this increased to 38% and 35% for unsoaked and soaked conditions. The results indicate that as cement amount in the mixture is increased,

In this study, in order to find the

the CBR values also increase and addition of

optimum percentage of fiber content for the

polypropylene

stabilized peat soil that would provide the

increase of the CBR values.

fibers

causes

a

further

maximum strength, peat soil samples at their natural water content were mixed with different

percentages

of

cement

INCREASED SHEAR STRENGTH

and

This experimental work has

polypropylene fibers and were cured in air

been performed to investigate the influence

for a period of 90 days and then CBR test

of Plasticity Index and percentage of waste

plastic materials on the shear strength of

due to the addition of the waste plastic fibers

waste plastic materials on the shear strength

and it is a non linear function. Up to a

of unsaturated clayey soils. For this purpose,

critical fiber content shear strength increased

clayey soils with different plasticity Indexes

considerably and later small reduction is

were

observed. However shear values are greater

used

and

mixed

with

different

percentage of waste materials to investigate the

shear

strength

parameters

of

unreinforced and reinforced samples in terms

of

direct

shear

than unreinforced soil. ii)

REDUCTION

IN

CONSOLIDATION

test.

SETTLEMENT

In order to determine the shear strength parameters (C and φ) of unreinforced and

In order to assess the effect of

reinforced samples, a series of shear box

random fiber inclusion on consolidation

tests at vertical normal stresses of 100-300

settlement,

KPa and strain rate of 0.2% mm/min were

conductivity,

carried out in accordance with ASTMD

conducted according to ASTM D2435-96. In

3080.shear stresses were recorded as a

the current investigation all samples were

function of horizontal displacement up to

prepared using the same dry density and

total displacement of 17 mm to observe the

molding moisture content equal to 70% of

post failure behavior as well. Verification

the liquid limit.

tests were also performed in order to examine

the

repeatability

of

swelling oedometer

and

hydraulic tests

were

Consolidation settlements results

the Effects of random fiber inclusion on

experiments. Effects of stabilization on shear strength

consolidation settlement of soil samples were evaluated as function of fiber length,

Soil can be non-liner variation because

the

reinforcement

materials

exhibited a distribution with In general angle of internal friction increased with fiber content. The variation of with percentages of fiber contents leads to a conclusion that the behavior of the fiber included. The shear strength of fiber reinforced soil is improved

content and consolidation pressure. Prior to the fiber inclusion, consolidation settlement of unreinforced soil sample was determined. A Constant pressure, increasing the fiber contents from 1 to 8% resulted in reducing consolidation settlement of the samples. This is a common trend with all fiber lengths

examined.

Maximum

and

minimum

fibers having 5mm length which is a

consolidation settlements of 7.5 and 2.6 mm

substantial

were

the

constant fiber contents, an increase in the

sample

fiber length from 5 to 10mm resulted in a

reinforced by 8% fibers having 5mm length .

slight increase in swelling. As a whole,

This shows a reduction in consolidation

however, the increase in the fiber length did

settlement of approximately 25%.

not have a significant effect on swelling

respectively

unreinforced

measured

sample

REDUCTION

and

IN

for

the

SWELLING

Oedometer was used for swelling saturated on molding; they showed no affinity for further water absorption after flooding

the

oedometer

water

bath.

Therefore, they did not exhibit much free swelling in order to be able to assess the effects

of

fiber

inclusions

on

this

characteristic. Therefore, volume changes during

the

unloading

stage

of

the

reduction

in

swelling.

For

reduction. This was particularly true when the fiber contents remained constant. It can therefore be concluded that with the increase in fiber contents and lengths, the soil/fiber surface interactions were increased. This resulted in a matrix that binds soil particles and

effectively

resists

tensile

stresses

produced due t swelling. Resistance to swelling is mainly attributed to cohesion at the

soil/fiber

interfaces.

consolidation tests were measured and used as an indication of the possible effects of

DESICCATION

fiber inclusion on swellings. The swellings presented were measured after unloading the maximum consolidation pressure of 200kPa.

CRACKS

Oedometer

rings

were

used

to

investigate the effects of random fiber inclusion on desiccation cracking of the soil. After molding, confining rings containing

Effects of swelling test

the specimen were placed in open air in the

It can be seen that by increasing the fiber content, the amount of swellings decreased.

The

unreinforced

sample

produced the highest swelling of about 3.4mm. This was reduced to approximately 1.5mm for the sample reinforced with 8%

laboratory at a temperature of about 30°C. Samples were regularly weighed and when no

changes

in

three

consecutive

measurements were observed, they were considered completely dried. Then, samples were used for observational examination of

the

extent

of

cracking.

solution to waste treatment with the advent of soil reinforcement.

Effects

of

desiccation

Observational

cracks

examination

of

samples after desiccation showed that by increasing the fiber contents and lengths, the extent and depth of cracks were significantly reduced. It can be seen that extensive, deep and wide cracks were formed in the unreinforced sample. The reinforced sample, however, has mainly experienced separation from the metal ring with no visible sign of cracks forming within the sample. This clearly shows the effectiveness of random fiber inclusion in resisting and reducing desiccation cracking which is of paramount importance in surface cracking of clay covers used in landfills. Therefore, it can be concluded that random fiber inclusion seems to be a practical and effective method of increasing tensile strength of the clayey soils to

resist

volumetric

changes.

CONCLUSION Plastic is one of the major toxic pollutants of our time. Being a nonbiodegradable substance, composed of toxic chemicals, plastic pollutes earth, air and water. Beside all these ill effects we here suggested one method which drastically change the view by which the people are concerned it today. Here without affecting the normal texture of the soil we are stabilizing it with the fiber format of the plastic. REFERENCES 1. Carol J. Miller and Sami Rifai, (2004), “Fiber

Reinforcement

Containment

Soil

for

Waste

Liners”,

(ASCE)

Journal,(1-5). 2. S. A. Naeini and S. M. Sadjadi ,(2008) ,” Effect of Waste Plastic Materials on Shear Strength of Unsaturated Clays”, EJGE

REDUCE

ENVIRONMENTAL

HAZARDS The most important point is the environmental concern regarding the effects of waste plastic in soil and the problems and threats that is related with their excessive usage and disposal. This gives an effective

Journal,

Vol

13,

Bund

k,(1-12).