A.K.Choudhary*, J.N.Jha**,K.S.Gill**

*National Institute of Technology, Jamshedpur

**Guru Nanak Dev Engg. College, Ludhiana

Introduction

Laboratory Investigation

Result and Discussion• Peak deviator stress and strain at failure• Elastic moduli• Shear strength parameters

Conclusions

References

IntroductionSoil ReinforcementConventional method of soil reinforcemento Inclusions:Oriented in preferred direction and introduced

sequentially in alternate layerso Plane of weakness: Develop parallel to the oriented

reinforcements

Randomly distributed discrete fiber reinforced soilo Similar to admixture stabilization in preparationo Maintenance of strength isotropy and absence of potential

plane of weakness

Major geotechnical project Local availability of Good quality soilTransportation of good quality soil incur good amount of

project costReplacement of soil by local Industrial wastelike flyash if

found suitable; Reduction in construction cost and encouragement for sustainable development

FlyashDisposal of flyash :Big problem, Can’t be used due to low strengthFiber if added as admixture may improve engineering

behaviour Flyash properties depends on nature of coal burnt and are

source sensitiveRequire separate study for different sources

Present ProblemTo study the effect of fiber inclusion on the strength

characteristics of flyash obtained from local thermal power station by carrying Triaxial test (unconsolidated undrained)

Effect of aspect ratio and fiber content on peaK deviator stress, elastic moduli and shear strength parameters

Laboratory Investigation• Physical and Engineering Properties of Fly ash. 

Property Value• Specific Gravity 2.09• Grain size distribution (%)

Sand: 16.0Silt: 82.0Clay: 2.0

• Liquid Limit (%) 44.0• Plastic Limit Non -plastic• Optimum moisture content (%) 36.50• Maximum dry density (kN/m3) 10.52

Physical and Engineering Properties of Fibers

Property Value• Type Polyethylene

(Synthetic)• Colour White

• Cut length, lf (mm) 5,10,15 (variable)• Dia. of fiber df (mm) 0.20 (constant)• Aspect ratio (lf / df) 25,50,75 (variable)• Fiber content, fc 0.25,0.50,1.0

(% by mass of dry fly ash) (variable)

• Tensile strength (Mpa) 60 -120• Tensile elongation (%) Greater than 100

Sample preparation/Result & discussion• Dry mixing of flyash and fiber

(Even distribution of fiber)• Amount of water added (corresponds to OMC of flyash)• Length of specimen =76.2mm • Diameter of specimen= 38.1mm• Confining pressure: 98.1kPa, 96.2kPa,294.3kPa• Strain rate:1.20mm/minute

Peak deviator stress vs Fiber contentSr.No. df lf lf / df Confining

pressure(kPa)

Fiber content

(%)

Peak deviator

stress (kPa)

1.0 0.20 5.0 25 98.10 Nil 177

0.25 255

0.50 294

1.0 372

2.0 0.20 10.0 50 196.20 0.25 436

0.50 488

1.0 549

3.0 0.20 15.0 75 294.30 0.25 706

0.50 763

1.0 1044

Peak deviator stress vs Aspect ratioSr.No. df lf Confining

pressure(kPa)

Fiber content

(%)

lf / df Peak deviator

stress (kPa)

1.0 0.20 5 98.10 0.25 25 255

10 50 275

15 75 367

2.0 5 196.20 0.50 25 415

10 50 488

15 75 604

3.0 5 294.30 1.0 25 570

10 50 692

15 75 1044

Strain at failure vs Fiber contentSr.No. df lf lf / df Confining

pressure(kPa)

Fiber content

(%)

Strain at failure

(%)

1.0 0.20 5 25 98.10 0.25 3.50

0.50 3.50

1.0 6.50

2.0 10 50 196.20 0.25 3.50

0.50 4.50

1.0 6.50

3.0 15 75 294.30 0.25 6.0

0.50 7.50

1.0 10.50

Elastic moduli vs Fiber contentSr.No. df lf lf / df Confining

pressure(kPa)

Fiber content

(%)

Initial tangent modulus

(kPa)

Secant modulus at

failure (kPa)

1.0 0.20 5 25 98.10 0.25 7848 7286

0.50 9810 8400

1.0 10791 5723

2.0 10 50 196.20 0.25 14715 12457

0.50 15696 10844

1.0 16677 8446

3.0 15 75 294.30 0.25 20209 11767

0.50 21092 10173

1.0 21876 9943

Shear strength parameter vs Fiber contentSr.No. df lf lf / df Fiber

content(%)

CohesionCuu

(kPa)

Angle of internal friction

Øuu˚

1.0 0.20 5 25 0.25 49.0 18˚26’

0.50 59.0 22˚15’

1.0 98.0 23˚18’

2.0 10 50 0.25 59.0 23˚12’

0.50 69.0 24˚12’

1.0 108.0 25˚17’

3.0 15 75 0.25 69.0 25˚28’

0.50 88.50 26˚34’

1.0 118.0 30˚58’

The increase in peak deviator stress may be due to the shear transfer mechanism which has been induced by the inclusion of fibers

The increase in aspect ratio provides more surface area that causes increase in resistance, resulting in higher strength of reinforced flyash

The failure of specimens in case of reinforced fly ash is of progressive nature indicating ductile behavior induced by the fiber inclusions

ConclusionsMixing of synthetic fiber can increase the strength of

flyash.The stress- strain behaviour of flyash improved

considerably due to increase in fiber content and aspect ratio

Elastic moduli increases with increase in fiber content and aspect ratio

Shear strength parameter;cohesion and angle of internal friction also increases with increase in fiber content

Thankyou.................