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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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