Post on 03-Apr-2018
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PRESENTATION OUTLINE
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ABSTRACT OF RESEARCH PAPER
In order to improve the strength of soil many methods are incorporated
Including fiber reinforcement, cementious material or mixing other soil.
All of the above mentioned method need research related to the test of
Soil strength and its behavior under high stress.
Unfortunately there are limited number of test conducted on
mechanically improved soil under low confining pressure and the soil
behavior is not fully understood.
The aim of this research paper is to test fiber reinforced cementious soil
under high confining pressure of 20 MPa using GDS triaxial test system
and study its mechanical behavior .
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Material and Equipment
Portaway sand was fiber reinforced and cemented and test using GDS
High pressure triaxial testing system under confining pressure of 1,4,10,20MPa both un drained and drained test have been conducted.
Discrete monofilament polypropylene fibres were used to strengthen
soil along with ordinary Portland cement. Their characteristics were
22 mm in length, 0.023 mm in diameter, specific gravity of 0.91, tensile
strength and elastic modulus of 120 and 3,000 MN/m2 respectively,
and linear strain of 80% at failure.
Standard methods were used to prepare sample of size 50mm diameter
And length of 100mm.
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Microphotographs of Portaway sand
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Drained behaviour at high pressures:-
a) Effect of fibre and cement on sand
b) Effect of confining pressure
c) Effect of fibre and cement on shear strength parameters
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A) Effect of fibre and cement on sand
Effect of addition of 0.5% fibre
and 5% cement at 4MPa
The Graph is between deviator
stress and axial strain.
%
1. Addition of fiber has
increased peak deviator
stress for both clean sandand cemented sand
2. Cement also plays important
roll since it also increases
deviator stress more than
fiber effect.
0
4
8
12
q(MPa)
s '3 = 4 MPa
Sand, Cement & FibreSand & CementSand & FibreSand only
(a)
0 10 20 30
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A) Effect of fibre and cement on sand
0
0.4
0.8
1.2
1.6
q/p'
(b)
s
Sand, Cement & Fibre
Sand & CementSand & FibreSand only
%
The Graph is between deviator
stress ratio and axial strain.
s '3 = 4 MPa
1. At 4MPa confining pressure
graph lines tends to
converge on unique stressratio of 1.3.
2. Cement also plays important
roll since it also increases
deviator stress more than
fiber effect.
Effect of addition of 0.5% fibreand 5% cement at 4MPa
0 10 20 30
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A) Effect of fibre and cement on sand
The Graph is between volumetric
strain and axial strain.
Effect of addition of 0.5% fibre
and 5% cement at 4MPa
0
5
10
15
0 10 20 30
v
(%)
(c)
%
1. Fiber also reduces
volumetric strain and graph
lines gets more flatter.2. Cement also plays important
roll since it also reduces
volumetric strain more than
fiber effect.
s '3 = 4 MPa
s
Sand, Cement & FibreSand & CementSand & FibreSand only
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0
50
100
150
200
250
0 5 10 15 20
increa
seqmax
(%)
p' (MPa)
% increase in sand with fibre & cement
% increase in sand with f ibre
A) Effect of fibre and cement on sand
The Graph is between increase
in qmax(%) and confiningpressure.
1. The effect of fiber decreaseswith increase in the confining
pressure. At low confining
press the effect of fiber is
more prominent.
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B) Effect of confining pressure
0 10 20 30 40a (%)
0
10
20
30
q(Mpa)
Fibre reinforced cemented sand
10MPa
4MPa
1MPa
(a)
0 10 20 30 40a (%)
0
10
20
30
q(Mpa)
Fibre reinforced sand
10MPa
4MPa
1MPa
(a)
1. Both graphs show that addition of fiber in cemented soil sampleincrease the peak deviator stress and delays axial strain. Similar
effect of cement addition in soil samples can also be observed.
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B) Effect of confining pressure
0
0.4
0.8
1.2
1.6
2
q/p'
(b)
0 10 20 30 40a (%)
10MPa
4MPa
1MPa
Fibre reinforced cemented sand
0
0.4
0.8
1.2
1.6
2
q/p'
(b)
0 10 20 30 40a (%)
Fibre reinforced sand
10MPa
4MPa
1MPa
1. Both graphs show that addition of fiber in cemented soil sampleincrease the peak deviator stress and delays axial strain. Similar
effect of cement addition in soil samples can also be observed. For
fiber reinforced soil the graph lines tend to intersect at unique
stress ratio of 1.3.
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C) Effect of fibre and cement on shear strength parameters
25
35
45
55
65
75
0 5 10 15 20
max
p' (MPa)
Sand with cement & fibre
Sand with cement
Sand with fibreSand only
25
35
45
55
65
75
0 200 400 600
max
p' (kPa)
Sand with cement & f ibre
sand with cement
Sand with fibre
Sand only
1. Graph on left shows that increase in confining pressure diminishesthe effect of fiber on friction angle .It can be observed on right
graph that cement in clean soil show more shift in graph then fiber
addition.
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C) Effect of fibre and cement on shear strength parameters
0
10
20
30
40
50
0 10 20 30 40
q(MPa)
p' (MPa)
sand with fibre & cement
Sand with fibre
Sand only
0
500
1000
1500
2000
0 200 400 600 800 1000
q(kPa)
p' (kPa)
Poly. (Sand with fibre & cement)Poly. (Sand with fibre)Poly. (Sand only)
1. Graph on left shows that failure envelops of all sample followssame path .It can be observed on right graph that at low confining
pressure fiber addition shifts the graph line upwards to form
cohesion intercept. This cohesion in soil is due to cement addition.
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Un drained behaviour at high pressures:-
a) Effect of fibre and cement on sand
b) Effect of confining pressure
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B) Effect of confining pressure
0
4
8
12
16
20
0 10 20 30 40
q(MPa)
a %
Fibre reinforced cemented sand
20MPa 10MPa
4MPa 1MPa
(a)
1. At low confining pressure the soil sample shows gradual
behavior. This behavior is effect by addition of fiber and
cement.
2. At high confining pressure the soil sample shows brittle
behavior by delaying axial strain. This behavior is effect by
addition of fiber and cement
0
2
4
6
8
0 10 20 30 40
q(MPa)
a %
Fibre reinforced sand
1MPa
4MPa
10MPa
(a)
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0
4
8
12
16
20
0 5 10 15 20 25
q(MPa)
p' (MPa)
(c)
Fibre reinforced cemented sand
0
2
4
6
8
0 2 4 6 8 10 12
q(MPa)
p' (MPa)
FL
(c)
20MPa 10MPa
4MPa 1MPa
Fibre reinforced sand
B) Effect of confining pressure
1. Fiber addition to sample increases the strength of soil and
shifts the failure envelop graph upwards.
1MPa
4MPa
10MPa
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0
10
20
30
40
50
0 10 20 30 40
q(MPa)
p' (MPa)
sand with fibre & cement
Sand with fibreSand only
0
4
8
12
16
20
0 5 10 15 20 25
q(MPa)
p' (MPa)
(c)
B) Effect of confining pressure
drained tests
ndrained tests
1. Both drained and un drained test shows that stress path ofdrained test is crossed by soil test in un drained conditions
proving that soil can attain more strength in un drained
conditions.
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Conclusion
1. Both drained and un drained test shows that addition of fiber
increases the strength and increases the friction angle.2. Both test shows that cement plays an important role in
producing cohesion in soil and its strength.
3. More research is recommended for this field as complete
behavior of soil fiber interaction is not understood well.
4. Arrangement of fibers in soil structure also plays an importantroll.
5. Also other soil of good strength can be mix in proportion to
improve the target soil.
6. It was observed that at confining pressure of 10MPa the
effectiveness of fiber was lost where as the cement plays its roll
with minor effects.