Thesis Proposal.docx

8/14/2019 Thesis Proposal.docx

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Chapter 1: Introduction

Project Background

The rapid increase rate of economy and social development in Malaysia has sparked demand

for road infrastructure that is able to connect different cities in shortest and fastest waypossible. The outlying cities of Kuala Lumpur - Selangor have now aggressively taken part to

contribute to local industry which made them appear on the radar as being the busy cities.

Transportation system is now forced to reach out to these cities to accommodate their rapid

progress.

The KL-Kuala Selangor Expressway, abbreviated as LATAR Expressway is a newly built

highway connecting Ijok, a township in Kuala Selangor and Templer which is located near

Rawang. LATAR highway was officially opened for operation on June 2011 and it marked

the fourth highway built by the government in Klang Valley east-west link after Federal

Highway, NKVE and Shah Alam Expressway.

The highway stretches to 33 km end to end which takes about 18 minutes to complete the

whole course. It is carefully planned and designed to feature 4 interchanges which merge to

three existing major highways for ease of access namely Guthrie Corridor Expressway, PLUS

North-South Expressway and the future West Coast Highway.

Since its opening, several slope failures have been recognized along the stretch of LATAR

Expressway which cause disturbance to the smoothness of traffic and rehabilitation process is

being carried out as of now.

Basically, landslide is defined as movement of rock or earth down the slope where the shear

stress exceeds the shear strength of the withholding material. This paper is to provide a report

on the causes of failure by performing shear strength and consolidation tests on the soil at the

site.


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Problem Statement

There are many factors affecting the failure of a slope and rainfall is one of the biggest

factors in Malaysia. Our country receives rainfall of 2000mm to 3000mm annually. This

amount of rainfall requires a proper and efficient drainage system to channel the excess water

back to nature.

There were problems at some part of the internal drainage system of LATAR Expressway

which has led to saturation of water in the soil supporting the pavement at the slope after

some time. The problems may arise during construction or design stage which will be

discovered after an interview session with their representatives.

Excess water penetrates the ground making the slope in active stage thus decreasing the

overall strength of the slope. Furthermore, the excess water penetration along with the

existing ground water directly increased the pore water pressure. The slope becomes instable

as the different planes are sliding between each other. The increase moisture content reducesthe shear strength of slope and therefore decreases the slope safety. Over time, the weight of

the pavement becomes an excess burden which pushes the slope to slide down causing the

slope to fail.

Research Objectives

1. To investigate the shear strength of soil of the slope when it fails by Triaxial test2.

Consolidation test

3. To compare the lab result against the professional test results to gain insight on theaccuracy of the tests.

Scope of Research

1. To conduct brief laboratory tests to meet the above objectives2. Record observations and readings from the laboratory test3. Compile and analyse the data obtained to gain useful conclusions4. Comparison of lab results and analysis against results obtained professionally on

limited conditions only.


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Literature Review

The Concept of Slope Instability

Slope stability is based on the interplay between two types of forces: driving forces and

resisting forces. Driving forces promote downslope movement of material. Resisting forcesdeter the movement. When driving forces overcome resisting forces, the slope is unstable and

results in mass wasting. The main driving force in most land movements is gravity. The main

resisting force is the material's shear strength.

Driving force are mainly gravity, it is to be noted that gravity does not act alone as slope

angle, climate, slope material, and water contribute to the effect of gravity. Mass movement

occurs much more frequently on steep slopes than on shallow slopes.

On a slope, the force of gravity can be resolved into two components: a component acting

perpendicular to the slope and component acting tangential to the slope.

Water plays a key role in producing slope failure. In the form of rivers and wave action,

water erodes the base of slopes, removing support, which increases driving forces.

Water can also increase the driving force by loading, i.e., adding to the total mass that is

subjected to the force of gravity. The weight (load) on the slope increases when water fills

previously empty pore spaces and fractures. An increase in water contributes to driving forces

that result in slope failure.


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Resisting forces act oppositely of driving forces. The resistance to downslope movement is

dependent on the shear strength of the slope material. Shear strength is a function of cohesion

which is the ability of particles to attract and hold each other together and internal friction,

which is friction between grains within a material. Chemical Weathering (interaction of water

with surface rock and soil) slowly weakens slope material (primarily rock), reducing its shearstrength, therefore reducing resisting forces.

The shear strength of the slope material is decreased by increasing the pore water pressure

(pressure that develops in pore spaces due to the increased amount of water).

Type of Slope Failures

Slope failure, is the downslope movement of rock debris and soil in response to gravitational

stresses. Three major types of slope failures are classified by the type of downslopemovement namely falls, slides, and flows.


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There are three primary triaxial tests conducted in the laboratory, each allowing the soil

response for differing engineering applications to be observed. These are:

Unconsolidated Undrained test (UU)

Consolidated Undrained test (CU)

Consolidated Drained test (CD)

The unconsolidated undrained (UU) test is the simplest and fastest procedure, with soil

specimens loaded whilst only total stresses are controlled and recorded. This allows the

undrained shear strength cu to be determined, which is suitable for assessing soil stability in

the short-term (e.g. during or directly following a construction project). Note this test is

generally performed on cohesive soil specimens.

The consolidated drained (CD) test on the other hand is applicable to describing long-term

loading response, providing strength parameters determined under effective stress control

(i.e. and c). The test can however take a significant time to complete when using cohesive

soil, given the shear rate must be slow enough to allow negligible pore water pressure

changes.

Finally the consolidated undrained (CU) test is the most common triaxial procedure, as it

allows strength parameters to be determined based on the effective stresses (i.e. and c)

whilst permitting a faster rate of shearing compared with the CD test. This is achieved by

recording the excess pore pressure change within the specimen as shearing takes place.

The stresses applied to a soil or rock specimen when running a triaxial compression test are

displayed in Figure below. The confining stress c is applied by pressurising the cell fluid

surrounding the specimenit is equal to the radial stress r, or minor principal stress 3. The

deviator stress q is generated by applying an axial strain a to the soilthe deviator stress

acts in addition to the confining stress in the axial direction, with these combined stresses

equal to the axial stress a, or major principal stress 1. The stress state is said to be isotropic

when 1 = 3, and anisotropic when 1 3.


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Chapter 3Methodology

Triaxial Test Procedure

The following is a basic outline of the triaxial test procedure:

1. The specimen is a cylindrical sample normally 100 mm (4 in.) in diameter by 200mm (8 in.) high (Figure 1a). The sample is generally compacted in the laboratory;

however, undisturbed samples are best if available (which is rare).

2. The specimen is enclosed vertically by a thin "rubber" membrane and on bothends by rigid surfaces (platens) as sketched in Figure 1b.

3. The sample is placed in a pressure chamber and a confining pressure is applied(s3) as sketched in Figure 1c.

4.

The deviator stress is the axial stress applied by the testing apparatus (s1) minusthe confining stress (s3). In other words, the deviator stress is the repeated stress

applied to the sample. These stresses are further illustrated in Figure 2a.

5. The resulting strains are calculated over a gauge length, which is designated by"L" (refer to Figure 2b).

6. Basically, the initial condition of the sample is unloaded (no induced stress).When the deviator stress is applied, the sample deforms, changing in length as

shown in Figure 2c. This change in sample length is directly proportional to the

stiffness.


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