chapter 1 (sandy lean clay)

8/12/2019 Chapter 1 (Sandy Lean Clay)

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Chapter 1

INTRODUCTION

I.1. Background of the Study

Soil is a fundamental and ultimately finite resource that

fulfills a number of functions and services for society which

are central to sustainability. There are many different types

of soils, and each one has unique characteristics; color,

texture, structure, and mineral content. The depth of the soil

also varies. Soil is formed slowly as rock (the parent

material) erodes into tiny pieces near the Earth's surface.

Organic matter decays and mixes with inorganic material such

as rock particles, minerals and water to form soil

(EnchantedLearning.com, n.d).

In construction, soil plays a significant role. The

stability of the structure depends on the properties of soil.

Misconception of soil properties would result in unnecessary

maintenance costs or structure failure such as soil

settlement. The movement of the soil which caused by the

change of ground water table is one of the causes why

foundation settlement occurs. Some soils are also not capable

of supporting the weight or bearing pressure exerted by


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buildings foundation resulting to the footing to press or

sink into the soft soils, similar in theory to how a person

standing in the mud sinks into soft, wet clay (Foundation

SupportWorks, n.d).

Dealing with clayey soils constitutes great challenges to

geotechnical engineers, as structures on compressible clay can

create numerous problems. Construction without soil

improvement is impractical due to probable large settlements

that may occur (Bindu, Sobha, & Babu, 2011). Clay soils are

known to be one of the major factors causing foundation

problems. The ability of clay to expand and contract is

dependent to the change in moisture, shrink-swell phenomenon,

causing foundation problems and slope failure (Foundation

Repair Guide , 2004-2007).

Various soil improvement techniques such as soil

stabilization and soil reinforcement are developed to increase

the strength of soil. In the case of geotechnical engineering,

the inclusion of fibrous material in the soil mass in order to

improve the mechanical behavior of soil is widely developed

(Chaple & Dhatrak, 2013). Soil reinforcement is not a new

technique but a concept adapted from ancient time abundantly

demonstrated by nature in the action of tree roots (Chaple &

Dhatrak, 2013). Many ancient structures incorporated layers of


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natural tensile elements to reinforce the soil for

construction of stable structures.

Soil reinforcement is a procedure where natural or

synthesized additives are used to improve the properties of

soils (Hejazi). The natural fiber for improving soil

properties is advantageous because they are cheap, locally

available, biodegradable and eco-friendly. The natural fiber

reinforcement gives significant improvement in shear strength

and other engineering properties of the soil.

Many studies developed using natural fibers as

reinforcement on soil. Natural fibers such as sisal, coir,

bamboo and etc. are abundant in many countries like

Philippines. Coconut fiber, which is abundantly available in

the locality, is to be used as reinforcement on sandy lean

clay.

Coconut fiber, also known as coir, comes from the inner

husk of coconuts. According to the University of Florida

Extension, coconuts are the most widely grown nut in the world

and contribute significantly to the economy of many tropical

areas. The short, tough fibers can be woven or pressed

together for a number of uses. Unlike man-made fibers, coconut

is a renewable resource (Myers, 2010).In Philippines about one

third of arable agricultural land or 3.26 million hectares is


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planted to coconut representing sixty (64) out of total

seventy nine (79) provinces, and 1,195 out of the 1,554

municipalities in the country (AgFishTech Portal, n.d).

This study presents the influence of coconut fiber on the

shear strength of sandy lean clay.

I.2. Objectives

Objectives:This research project aims to investigate the

shear strength of sandy lean clay reinforced with coconut

fiber.

Specifically, it aims:

1.To determine the undrained shear strength of the sandylean clay with the following coconut fiber content by

dry weight:

a.0.2% coconut fiber by weight.b.0.4% coconut fiber by weight.c.0.6% coconut fiber by weight.d.0.8% coconut fiber by weight.e.1.0% coconut fiber by weight.

2.To determine if there are significant differences thatexist between the undrained sandy lean clay with :


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a.0.2% coconut fiber by weight.b.0.4% coconut fiber by weight.c.0.6% coconut fiber by weight.d.0.8% coconut fiber by weight.e.1.0% coconut fiber by weight.

3.To determine if there is a significant relationshipbetween coconut fiber reinforcement and the undrained

shear strength of the sandy lean clay.

4.To determine the optimum percentage by dry weight ofcoconut fiber reinforcement for sandy lean clay.

I.3. Hypothesis

1.There is no significant difference between theundrained shear strength of sandy lean clay reinforced

with varying percentage of coconut fiber.

2.There is no significant relationship between thecoconut fiber relationship and the undrained shear

strength.

I.4. Scope and Limitations


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The focus of the study is on the utilization of coconut fiber

as reinforcement in sandy lean clay.

The scope and limitations of the study are the following:

1.The shear strength of the sandy lean clay soil reinforcedwith coconut fiber will be tested using unconfined

compression test.

2.The sandy lean clay soil will be randomly mixed withcoconut fiber having a percentage by weight of 0.20,

0.40, 0.60, 0.80 and 1.00.

3.The coconut fiber will have a uniform length of 25mm allthroughout the study.

4.The extraction of coconut fiber will be done manually.5.The coconut fiber to be used will be extracted from a

completely ripened coconut.

I.5. Significance of the Study

In construction industry, soil as one of the primary

criterion in planning and designing a project requires a lot

of tests in order to ensure a safety design specification.

Soils compressive strength and its ability to resist shear

failure differ depending on its type. Also the design of

foundations, roads and pavements varies on soil.


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Treatment of sandy lean clay with natural fiber offers

economical, ecological and environmental benefits. The coconut

fiber is abundantly available throughout the country, produced

at cheaper costs. It is advantageous to use coir fiber as

reinforcement because of its cost effectiveness and easy

adaptability. The coconut fiber is an eco-friendly product;

hence it will not create any environmental problems.

This study would be beneficial to geotechnical engineers

in terms of the strength of the soil. This kind of method

could be used to avoid various foundation problems and

anticipated soil movement.

I.6. DEFINITION OF TERMS

1.Coconut Fiber a fiber obtained from the fibrous husk(mesocarp) of the coconut (Cocos nucifera) from the

coconut palm, which belongs to the palm family (Palmae)

(Lloyd, n.d).

2.Undrained Shear Strength- The resulted strength of halfof the unconfined compressive strength of soil (Soil

Mechanics).


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3.Unconfined Compression Test measures the shearstrength of the soil. The unconfined compression test is

by far the most popular method of soil shear testing

because it is one of the fastest and cheapest methods of

measuring shear strength. The method is used primarily

for saturated, cohesive soils recovered from thin-walled

sampling tubes. The unconfined compression test is

inappropriate for dry sands or crumbly clays because the

materials would fall apart without some land of lateral

confinement (Chaoyang University of Technology).

4.Sandy lean clay A lean clay (CL) with more sandcontent than gravel and is abbreviated as s(CL). It has

a less than 70% fines and less than 15% gravel (Soil and

Rock Classification and Logging, 2003). It should have a

liquid limit of less than 50%, inorganic, plasticity

index of greater than 7, plotted at the CL group in the

plasticity chart for USCS and have a greater than 30%

passing No. 200.

5.Lean Clay Clay with a low liquid limit and have thesymbol CL (Elementary Soil Engineering).


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CHAPTER II

REVIEW OF RELATED LITERATURE

Soil provides the basic support for all civil engineering

structures such that geotechnical engineers include soil as

the most widely used as engineering materials (Zaniewski &

Mamluok, 2011). It is a unique natural material, and its

properties are governed not only by the particles size

distribution, particles shape, and density of particle

packing, but also by the presence of water and air in the

voids (Das, 1981). To identify specific textures in soils,

common descriptive terms such as gravels, sands, silts and

clays are being used (Budhu, 2007).

CLASSIFICATION OF SOIL

Soil can be classified according to USDA, AASHTO USCS,

and engineering behavior (Das, 1981).

The U.S. Department of Agriculture (USDA) is a textural

classification system that is based on the particle-size

limits as described under the USDA system in Fig. 2.a that is:

sand size having 2.0-0.05mm in diameter, silt size having

0.05-0.002mm in diameter, and clay size having smaller than

0.002mm in diameter (Das, 1981).


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The American Association of State Highway and

Transportation Officials (AASHTO) is a system that classifies

soil into seven major groups: A-1 through A-7. Soils

classified under groups A-1, A-2, A-3 are granular materials

of which 35% or less of the particles pass through the no. 200

sieve. Soils of which more than 35% pass through the no. 200

sieve are classified under groups A-4, A-5, A-6 and A-7. These

soils are mostly silt and clay-type material (Gillesania,

2006).

Chart


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The Unified Soil Classification System (USCS) was first

developed by Professor A. Casagrande (1948). The USCS is based

on the characteristics of the soil that indicate how it will

behave as a construction material. In the USCS, all soils are

placed into one of three major categories. They are: coarse-

grained, fine-grained, and highly organic (Rossiter, n.d)

Figure 2.1.a AASHTO Classification Chart


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Figure 2.1.b USCS Classification Chart

Fig. 2.1.a USDA Textural Classification


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The e

th

ei

r

ph

ys

ical properties (Das, 1981).

There are many different types of soils, and each one has

unique characteristics, like color, texture, structure, and

mineral content (EnchantedLearning.com, n.d). Generally, soils

are called gravel, silt or clay.

Soil Reinforcement

Reinforced soil is the technique where tensile elements

are placed in the soil to improve stability and control

deformation. To be effective, the reinforcements must

intersect potential failure surfaces in the soil mass

(Nicolon, n.d). It serves as an initial lateral confinement

that allows the soil to mobilize more shearing resistance

(Budhu, 2007)

Generated strain of reinforcements from the strain of

soil mass creates tensile load in the reinforcement in which

Figure 2.1.c USCS Classification Chart continuation


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it acts to restrict soil movement and impart additional shear

strength, thus reinforcement system gives greater shear

strength than the soil mass alone (Nicolon, n.d).

The term reinforced soil describes any soil mass which

has had its shear strength improved by combining it with

resisting elements; these resisting elements, or

reinforcements may take the form of bars, strips, tube, grids

or sheets (Pedley, 1990).

Reinforcing of soil can be done in different ways such as

soil nailing, soil dowelling, using of geosynthetics and using

fibers that are randomly mixed with soil. Soil nailing is a

technique used for stabilizing either vertical or steep cut

slopes and is executed incrementally; after each stage of

excavation the reinforcements or nails are installed (Pedley,

1990). Soil dowelling is used for the stabilization of

shallow, unstable or creeping slopes (Pedley, 1990).

Geosynthetic is manufactured from a polymeric material such as

geogrids or geotextiles which can be used as reinforcement to

increase shear strength of soils, thereby providing a more

competent structural material (Post Construction Best

Management Practices Manual). Reinforcing the soil with short,

randomly-distributed short fibers appear to be a very


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promising soil stabilizing technique for a variety of

applications (Leshchensky, 2013).

Reinforcement with natural fiber in composites has

recently gained attention due to low cost, easy availability,

low density, acceptable specific properties, ease of

separation, enhanced energy recovery, CO2 neutrality,

biodegradability and recyclable in nature (Verma, Gope,

Shandilya, Gupta & Maheshwari, 2013).

Coconut Fiber

Coconut fiber is a natural fiber that can be easily

obtained in many tropical areas and is considered as

environment friendly material owing and their biodegradability

and renewable characteristics (Bujang, Awang, & Ismail, 2007).

It is reasonably waterproof and resistant to salt water and

microbial degradation (Picha, 2003).

Coconut fiber known to have the greatest shearing

strength that even on its wet conditions the property of the

coir fiber remains. Coir fiber is usually used as fuel. Hence,

it can be used for several civil engineering applications such

as ground improvement (Kar, Pradhan, & Naik, 2014).


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chapter 1 (sandy lean clay)

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