Study: Fiber Reinforcement Effects on Shear Strength of Soft Clay

This report investigates the effects of fiber reinforcement on the shear strength of soft clay, a critical aspect of geotechnical engineering and construction. The study explores the use of recycled polyester fiber to enhance the properties of clay soil, addressing the challenges posed by its low shear strength and high compressibility. The research includes a literature review of existing studies, detailing the benefits of fiber-reinforced clay in construction, such as increased shear strength, compressive forces, and elasticity. The methodology involves direct shear tests on clay samples reinforced with varying percentages of recycled polyester fiber, comparing the results with those of natural clay. The findings reveal that the addition of fiber significantly increases shear strength, with an optimum fiber content identified. The report discusses the influence of normal stress, the internal angle of friction, and cohesion on the reinforced clay's behavior, concluding with an assessment of the effective shear strength and the long-term effects of drainage on the fiber-clay mixture. The report emphasizes the importance of this technique in addressing land limitations for development and improving infrastructure in areas with clay soil.

Effects of fiber reinforcement on Shear strength of soft clay
Introduction
The technology of using fibers in the clay reinforcement is not new. The civilization of ancient
time used hay and straw for muddy blocks reinforcements to make building blocks. By the use
of the same technique from the old civilization, the fibers can be reinforced to soils to create
strong blocks for construction. In the modern world fiber is used widely. The standard of soil
reinforced is actually defined as a mass of soil mixed with particles of fiber materials to improve
the mechanical behaviors of the soil composite. The effects of drainage and pressures of the pore
on the fiber-clay are important to shear strength of the fiber reinforced clay. Therefore, the
behavior of fiber-clay mass is investigated in order to get the performances of the shear strength.
The study tries to tries to investigate effects on the shear strength of soft clay. Soil stabilization
always tries to increase strength features because clay has high compressibility and is with low
shear strength. Due to the increase in demand of raw material for construction material, the
reinforcement of clay in order to improve its features. As a matter of facts the soil treatment has
been significant to the betterment clay in constructions. In rural areas, the mixing of clay and
straw makes the clay to improve material strength.
The objective the study
The objectives of the study is to:
a. Investigate the reinforced clay strength with other materials
b. Study the stress of the failure deviator of medium reinforced fiber with clay soil.
c. Establish the relationship between shear strength and fiber-clay
Key words: Shear strength, Recycled polyester fiber, clay
Benefits of the reinforced fiber clay
In the construction industry and making of structures, reinforced clay is widely used due to its
benefits. In the building and construction industry, blocks or bricks with high shear strength
which will make the material to be strong. The increase of shear strength is as a result of internal
friction angle. The structure made reinforced fiber-clay has high compressive forces in order to
crack. The modulus of elasticity is high also. This technology is used in the Chinese pottery,
blocks for building and tile making. It makes also the structure to be light. The fiber reinforced
clay adds lifespan to it.
Study of the scope
The focus is all about what happens when the clay is reinforced with fiber. Also to investigate
when the strength of clay increase after reinforcement. Also the shear strength parameters are
checked. There are two types of soils which are tested: one with fiber reinforced and another
without fiber. All the two experimental samples are controlled in terms of the moisture content as
well as density.

Problem statement
It usually known that clay soil has very low un-drained shear strength; requires a long period of
time to improve the shear strength to high value. Hence the adapted to clay from a specified
locality and the behavioral shear strength will be observed and evaluated.
Significance of the study
Due to normal land for developing properties and construction of infrastructures is reducing in
most township, and which is one of the promoters of economic development. The study is one of
the most important way of solving land limitation for development and how infrastructures are to
be made at areas where the clay soil is available. By this way structural and geotechnical design
will have found a solution to its problems.
Literature review
Shear Strength of Clay soil
The soil strength is optimum shear stress which it can support or the shear strength that can act
on a shear slip surface for which it’s falling with. Therefore the structural strength is the function
of shear strength. Shear strength of clay is opposition of particles between one another because
of particles interlocking.
The shear strength is mainly is as a result of inter forces of repulsion and attraction because of
the Van der Wal forces which may result the shear strength directly. The cone penetration testis
widely used to obtain the semi-surface stratigraphy and for estimation of parameters of
geotechnical engineering. It can be correlated empirically to shear strength un-drained which is
determined by trixial compression tests which were to be compared with the vane shear
outcomes as well as shear vane test outcome was continued in comparison to CPT results and
thus the findings concluded that depending on N values chosen, the shear strength un-drained has
slight rise or the double increase based the estimations from CPT into measurements situ shear
strength.
In order to calculate shear strength un-drained from the CPT data, the equations of correlation
must be utilized for pore water correction. The water pressure pore used equations of correlation
is measured by the penetrometer cone.
Background
The testing of strength in fiber-reinforced clay has been the addition of shear strength to the
composites. The fiber-reinforcements they are have same working feature as the planar
reinforcements in that material of polymer is put within the matrix of the soil and can distribute
stresses from failures which are potential planes in the surrounding mass by combining friction
along the soil-polymer interface. The fibers are distributed within the clay unlike the planar
materials which are put one direction, Hence, are considered having isotropic impacts on the
behavior of the soil.

Ho and Maher tested the randomly distributed fibers in kaolinite clay test using compression
which unconfined. From the result, it was discovered the fibers raises the compressive strength
of clay and ductility as well toughness of clay. The tests conducted by Al Wahab and El-Kedrah
tested on clay of plasticity which is medium, it was found the strength of clay increased when
reinforced with fiber. And this finding shows how the shear strength is influenced by fiber
reinforced in the clay.
Shear Strength of Clay reinforced with clay
Different research have been doing research to get new method of reinforcing clay with different
methods and approaches. The use of fiber to reinforce clay has be proved to be the most
significant by raising the shear strength of clay soil. The highest shear strength usually occur at
the highest optimum moisture content while the smallest occur within saturated state.
When Pashazadeh did study of clay reinforced with polypropylene fiber, figure below shows
Path of the reinforce clay and unreinforced clay with fiber.
In Turkey, a research conducted, for reinforcing clay soil with fiber it gave optimum
compressive strength of 0.2% of content of polypropylenes
The kinds of fiber length as well as type of fiber tested and the results are given as below. The oil
fiber has the highest shear strength increase to clay which is about 0.75.From the table below we
can see the shear strength increased as a result of fiber reinforcement in the soil.
The use of natural fiber such as coconut and sisal is widely used because of their durability,
strength, low cost and weight. Also waste materials can be used to reinforce soil such as fly ash
that has been used in concrete reinforcement, proven effectively to be increasing the compressive
strength. When the fly ash is mixed with cement decreases the time of curation with increasing
water content. The strength of fly ash relied on disposed fly ash, portion of cement and mixture
with water content
Table 2.2
Material used
The clay soil used in this study and the recycled polyester fiber. The soil used for investigation is
of minimal liquid limit. The liquid as well as the plastic soil limits are approximated to 22 and 30
respectively. In the figure below it can be observed clay contain 49%, silt 29% and soil 22%. The
length of polyester used was 22mm.The physical properties polyester fiber that has been recycled
is in the figure below.

To estimate and evaluate the mixture, direct shear strength were done on three normal stresses:
300kPa, 200kPa and 100kPa. After series of unconfined compression tests, conducted on the clay
combined with polyester fiber of natural sample specimens.
The experiments were done on different polyester content.
Table
Preparation of the sample
The clay soil and polyester are ground and mixed at a constant moisture content. This composite
was mixed at optimum moisture content as per Protor compaction test. The mixture was mixed in
a metallic container to prevent water loss, later used for evaluation of the soft clay reinforced
with recycled polyester fiber. The recycled polyester and clay were mixed by hands until the
contents were fully mixed. Then right quantity of water was added to the mixture and stirred to
mix. The shear strength test was performed according to the required standards and conditions.
Methodology
Test results and discussions
In this study there were carried different tests on four specimens e.g. specimens of natural clay,
recycled polyester specimens, specimens of with nano-SIO2 and specimens containing recycled
clay with nano-SIO2. The evaluation was done on the effects of clay nano-SIO2, recycled
polyester with nano-SIO2 on behavior of the clay soil its shear strength and elastic modulus.
The curves was obtained
Direct Shear Test
The effects of reinforced fiber (recycled polyester) on the shear strength of soft clay
The relation between the clay and the recycled fiber is shown by the graph below.
The shear strength of the polyester reinforced with clay happens at large specimens large
specimens in comparisons to natural clay. The normal stress contributes to clay strength increase
to the peak, when recycled polyester is included. Normal stress increases due to interlocking of
the soil particles and contact forces. When recycled polyester of 0.5% increases the shear
strength of 112kPa to 201kPa in comparison to natural clay, that is about 80%. While the peak
stress of clay increases from 21% to 68%. For further increase of recycled polyester by 0.3% is
not reasonable to raise the peak strength to 112 kPa to 201 kPa. Due to that, the optimum content
is 0.3% of recycled polyester.
When there is an increase of the content of recycled polyester from 0.3% to 0.5% the internal
angle of cohesion and friction will increase by8% and 19% respectively. It means the fiber
materials increases the angle of internal friction. The connection of with enough clay particles

that make a contribution fiber friction strength and the clay particles. Thus improvement of the
shear strength parameters specimens which are treated.
Conclusion
The envelopes failure is determined from the trixial testing indication of effective shear strength
of the clay when it is reinforced with fibers, that is for a short term results testing. The results
obtained from trixial ICD tests show that the strength reinforced clay was low for a longer-term
absolutely drained conditions, giving evidence that efficient strength of the fiber-clay mixture
can significantly reduce with drainage and time. However, this reduction in strength initially was
attributed to move along the fiber-clay interface, the outcome from program testing show that the
impacts of fibers on the pressures of the pore during testing of ICU may provide a higher
estimated effective strength.