pbl report geotechnical engineering

8/19/2019 PBL report GeoTechnical Engineering

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1.0 INTROCDUCTION

1.1 Slope Failure

Slope failure, also referred to as mass wasting, is the down slope movement of rock

debris and soil in response to gravitational stresses. Three major types of mass wasting

are classified by the type of down slope movement: falls, slides, and flows and also

represents one of the most active processes in modifying the landscape in areas of

significant relief. Mass wasting involves material other than weathered debris (notably in

rock slides) but most mass wasting phenomena occur in a thick mantle of regolith, the

rock and mineral fragments produced by weathering. The general term landslide is used

to describe all rapid forms of mass wasting. Some of the Slope failure factors are :

a) Slope Gradient

Slope gradient is probably the major cause of mass wasting. Generally speaking,

the steeper the slope, the less stable it is. Therefore, steep slopes are more likely

to experience mass wasting than gentle ones. A number of processes can

oversteepen a slope. One of the most common is undercutting by stream or

wave action. This removes the slope's base, increases the slope angle, and

thereby increases the gravitational force acting parallel to the slope. Wave

action, especially during storms, often result in mass movements along the

shores of oceans or large lakes. Excavations for road cuts and hillside buildingsites are another major cause of slope failure. Grading the slope too steeply, or

cutting into its side, increases the stress in rock or soil until it is no longer strong

enough to remain at the steeper angle and mass wasting ensues. Such action is

analogous to undercutting by streams or waves and has the same result, thus


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explaining why so many mountain roads are plagued by frequent mass

movements.

b) Water Content

The amount of water in rock or soil influences slope stability. Large quantities of

water from melting snow or heavy storms greatly increase the likelihood of slope

failure. The additional weight that water adds to a slope can be enough to cause

mass movement. Furthermore, water percolating through a slope's material

helps to decrease friction between grains, contributing to a loss of cohesion. For

example, slopes composed of dry clay are usually quite stable, but when wet,

they can quickly lose cohesiveness and internal friction and become an unstable

slurry. This occurs because clay, which can hold large quantities of water,

consists of platy particles that easily slide over each other when wet. For this

reason, clay beds are frequently the slippery layer along which overlying rock

units slide down slope.

c) Overloading

Overloading is almost always the result of human activity and typically results

from dumping, filling, or piling up of material. Under natural conditions, a

material's load is carried by its grain-to-grain contacts, and a slope is thus

maintained by the friction between grains. The additional weight created by

overloading increases the water pressure within the material, which in turn

decreases its shear strength, thereby weakening the slope material. If enough


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material is added, the slope will eventually fail, sometimes with tragic

consequences.

1.2 Slope stability

Slope stability is the potential of soil covered slopes to withstand and undergo

movement. Stability is determined by the balance of shear stress and shear strength. A

previously stable slope may be initially affected by preparatory factors, making

the slope conditionally unstable. Slope stability is based on the interplay between two

types of forces which is driving forces and resisting forces. The driving forces promote

downslope movement of material while the resisting forces deter 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 and the main for

resisting force is the material's shear strength.

Safety Factor (SF) = The ratio of resisting forces to driving forces:

SF =

If SF > 1 then safe

If SF < 1 then unsafe

1.3 Retaining wall

Retaining structures are built for the purpose of retaining or holding back a soil mass

(Cheng and Jack, 2005). A simple retaining wall simply depends on its weight to achieve

stability hence as call as the gravity wall. In case of taller walls, large lateral pressure

tends to overturn the wall, and for economical reasons, cantilever walls are more


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preferable. As for a cantilever wall, it has a part of its base extending underneath the

backfill and the weight of the soil above this part of the base to help prevent overturning

(Craig, 1993). The material placed behind the retaining wall is highly desirable to be free

draining and granular material. Clayey soils make extremely objectionable backfill

material because of the excessive lateral pressure they create.

Figure 1.3.1 : Simple retaining wall

Figure 1.3.2 : Cantilever retaining wall


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2.0 LITERATURE REVIEW

Slope stability is a way to protect any slope from sliding or side collapse, or against

weather conditions and erosions. So it is very important for the engineer to analyses the

slope stability before any construction are being carried out to ensure the slope is safe

and does not risk any human life.

According to (Chandler, 1991), during site investigation, which is in the relation to the

slope stability, the main aims of site investigation are : a) to obtain an understanding of

the development and nature of natural slopes, and of the processes which have

contributed to the formation of different natural features; b) to assess the stability of

various forms of slopes under given conditions; c) to assess the risk of instability in

natural or artificial slopes, and to quantify the influence of engineering works or other

modifications to the stability of an existing slope; d) to facilitate the redesign of failed

slopes, and the planning and design of prevention and remedial measures; and e) to

analyze slope failures which have occurred and to define the causes of failure.

Site investigations can be consider under 3 main headings which are: a) desk study; b)

field study; and c) laboratory work. For desk study, the aim here is to obtain all available

information with regard to the site and its geological environments. It will involve a

search through records, maps, (topographical and geological), and any other

information which is relevant to the geology, history and present condition of the site.

As for field study, it is to record accurately the topography of the site, to determine the

precise nature of the geological deposits underlying the site and to determine their

engineering properties, either by the collection of good quality samples which can be

tested subsequently in the laboratory, or by performing tests in-situ. And lastly is the


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laboratory works which is done to obtain information, additional to that obtained

from in situ tests, on the composition and properties of the materials encountered on

any site. Laboratory tests can be grouped under three main headings: a) tests

for classification and identification; and b) tests for engineering properties (Bromhead,

1992). The first group include tests to determine the particle-size distribution of the

material, index property tests (Liquid and Plastic Limits), specific gravity tests, and tests

to determine the bulk density and water content of the soils. While the second group of

tests includes those to determine the engineering properties of the soils such as

permeability, compressibility and shear strength.

According to (Leventhal, 1987) the accurate measurement of the shearing resistance or

shear strength of a material is essential in attempting to predict future instability or to

assess the present or past stability condition. As stated previously, shear strength tests

must be performed on samples of the highest quality if reliable information is to be

obtained. Even when this condition is satisfied, however, there may still be cases where

the shear strength measured in the laboratory differs from that mobilised in situ. Shear

strength properties of soils are defined by two parameters, apparent cohesion c and the

angle of shearing resistance υ .

The shear box was probably the first type of apparatus used for the measurement of the

shearing resistance of soils. The apparatus consists essentially of a square brass box

split horizontally at the level of the centre of the soil specimen which is held between

metal grills and porous stones. The horizontal force acting on the upper part of the box

is gradually increased until the specimen fails in shear. The shear force at failure s f is

divided by the cross-sectional area A to give the shearing stress t f at failure. The

vertical stress s n is provided by a vertical load on the sample, normally by dead-weights


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and a lever system. The horizontal load is applied by pushing the lower part of the box

by means of an electric motor and gearbox. Volume changes are monitored by a dial

gauge mounted to show the vertical movement of the top loading platen.

Figure 2.0.1 : Shear test example

Figure 2.0.2 : Results of shear box test


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The factor of safety of a slope in soil possessing cohesion and friction can be written as

Where the factor safety for retaining wall is if it is more than 2, it is considered unsafe

and if it is less than 2, it is considered safe.


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3.0 Problem details

3.1 Problem Statement

Prelude:

Kinabalu Times, 18 Jan 2013

Kota Kinabalu: Villagers of a small kampong at suburban of Kota Kinabalu city

have alarmed the authority of a possible slope failure located next to their housing

area.

The slope was cut during the construction of a road two years ago but the

contractor failed to provide adequate measures to ensure the safety of the

villagers.

It‟s village chief, Mr. Ali Rahman said they feared the safety of schoolchildren going

to and back from nearby secondary school. “During rainy seasons, the soil becomes

wet and soggy, and tragedy can happen in any minute” he added.

Upon contacted, the Public Work Department (JKR) representative, Ir. Lim

confirmed of receiving the public complain. Ir. Lim said a geotechnical company

has been commissioned to assess the slope stability, to determine the soil

properties in that area and to purpose the retaining wall structure design. “Upon

receiving their technical report, the department will ensure swift suitable measures

are taken to solve this problem” he assured.


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3.2 Objective

a) To assess the slope stability

b) To determine the soil properties in that area

c) To propose the retaining wall structure design

3.3 Slope details

Location : Jalan Bantayan Minintod, Kota Kinabalu, Sabah.

Slope physical properties :

a) Steep slope

b) Clayey looks

c) Place is currently under construction to improve the safety of factor

14m

7m

=63.435

Figure 3.2 .1 : Slope of location


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Based from the sketching of the slope;

15.653sin 90 = 14sin

x = 63.435 m

3.4 Work Flow Chart

Site Visit

1) Sieve analysis

Soil Sampling

3) Atterberg Limit Test2) Compaction Test

Soil Classification

4) Direct Shear Test

Soil Engineering Properties

Cullman Method GeoStudioSlope Stability Analysis

Retaining Wall DesignRankine Method QuickRWall 4.0

Recommendation of Retaining Wall


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4.0 Methodology, Results & Discussion

4.1 Experiment 1: Sieve Analysis

Objective:

To classify soil sample according to USCS standard based on its grain size distribution.

Results:

Mass of oven-dry specimen, = 2500

Sieve

Opening

(mm)

Sieve

weight

before

sieving (g)

Sieve weight

+ weight of

soil retained

after sieving

(g)

Mass

retained

(g)

% Mass

retained

Cumulative

% mass

retained

% Finer

3.35 1017 1563 546

27.43718

593

27.437185

93

72.562

814

2.36 1039 1253 214

10.75376

884

38.190954

77

61.809

045

2 1077 1121 44

2.211055

276

40.402010

05

59.597

99

1.4 979 1114 135

6.783919

598

47.185929

65

52.814

07

0.6 928 1147 219

11.00502

513

58.190954

77

41.809

045


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0.425 793 872 79

3.969849

246

62.160804

02

37.839

196

0.3 827 1192 365

18.34170

854

80.502512

56

19.497

487

0.15 790 1007 217

10.90452

261

91.407035

18

8.5929

648

0.075 795 936 141

7.085427

136

98.492462

31

1.5075

377

Pan 1004 1034 30

1.507537

688 100 0

= –

= 2500 – 1990

= 510

Since the mass loss of soil after sieving is less than 2% of total weight of soil before, the

data is acceptable.

Analysis of Data:

The soil will be classified according to USCS standard step by step.

Table 4.1.2: Data from Sieve Analysis


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a) The soil is a „coarse -grained soils‟ because more than 50% of the soils is retaine d

on No. 200 sieve. (The percentage retained of soils on No. 200 sieve is, 100% −

1.5075% = 98.4925% )

b) Thus, in accordance to plasticity chart, the fraction of soil is low plasticity clay.

(The analysis using the plasticity chart is explained further in the next

experiment; The Atterberg Limits)

Conclusions:

Based on the classification of soils using USCS standard, the type of soils that was

experimented is low plasticity clay. Thus, the type of soil is coarse with a fraction of low

plasticity clay. Since t he soil if of coarse type, the experiment to determine the soil‟s

angle of internal friction and its cohesion is by shear box testing.

4.2 Experiment 2: Atterberg Limits Test

Objective

To determine the liquid limit and plastic limit of sample

Results

The equations used to obtain the result are:

Mass of water = Mass of container + wet soil - (Mass of container + dry soil)

Mass of dry soil = (Mass of container + dry soil) - (Mass of container)


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Moisture content (%) =Mass of water

Mass of dry soil × 100%

Test Number 1 2 3 4 5

Penetration (mm)

28

.9

2

7

28

.5

21

.6

20

.2

23

.3

20

.1

21

.7

20

.2

27

.7

25

.7

26

.7

33

.8

32

.7

34

.9

Average

Penetration (mm) 28.13 21.7 20.667 26.7 33.8

Mass of Container(g) 8.119 7.928 22.501 21.058 19.575

Mass of container

+ Wet Soil (g) 10.9113 9.735 24.222 26.132 24.410

Mass of container

+ Dry Soil (g) 10.261 9.348 23.856 24.974 23.216

Mass of Water (g) 0.649 0.387 0.3663 1.158 1.194

Mass of Dry Soil

(g) 2.141 1.419 1.354 3.916 3.640

Moisture Content

(%) 30.342 27.265 27.051 29.573 32.797

Container Number 1 2 3 4

Mass of Container (g) 8.059 87.7212 7.6516 87.2409

Mass of Container + Wet Soil 8.8985 89.2477 9.4797 89.6503

Table 4.2.1: Data for Casagrande Method


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(g)

Mass of Container + Dry Soil

(g) 8.7561 89.0148 9.1579 89.2081

Mass of water (g) 0.1424 0.2329 0.3218 0.4422

Mass of Dry Soil (g) 0.6971 1.2936 1.5063 1.9672

Moisture Content (%) 20.427 18.004 21.364 22.4786

Analysis

a) To determine the liquid limit of the sample by using Casagrande method, the

graph of moisture content against number of blows is plotted on the semi-log

graph. The value of liquid limit (LL) is the correspondent value of moisture

content when the number of blows is 25.

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35

P e n e t r a t i o n

( m m

)

Moisture Content (%)

Table 4.2.2: Data for Plastic Limit

Figure 4.2.1: Graph of Moisture Content Vs Number of Blows


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Therefore, the value of liquid limit for the sample is 26.80%

b) The average value of plastic limit:

PL = 20.427+18.004+21.364+22.4794

= 20.568%

c) The value of Plastic Index:

PI = LL - PL

= 26.80-20.568

= 6.232%


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d) Based on the plasticity chart above, the value of Liquid Limit and Plastic Index

fall at the region of CL or OL. Since the sample does not contain organic matter,

the sample can be classified as CL which means low plasticity clay or lean clay.

Conclusion

Therefore, the sample taken has a liquid limit of 26.80%, plastic limit of 20.0568% and

plastic index of 6.232%. This sample is classified as low plasticity clay or lean clay.

4.3 Experiment 3: Shear Box Test

Objective:

Figure 4.2.3: Plasticity Chart


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To determine the cohesion and angle of internal friction of a dry granular soil.

Results:

a) Loose States

Table for Shear Load versus time (Loose States) with corresponding weights

Times

(s)

Shear Load (N)

5.5kg 15.5kg 25.5kg

20 0.6 0 0

40 2.9 0 0

60 6.7 4.3 0

80 10.8 12.4 0

100 5.1

120 13.9

Table for Vertical Displacement versus time (Loose States) with corresponding weights

Times

(s)

Shear Load (N)

5.5kg 15.5kg 25.5kg

20 7.2 5 2.1

40 50.8 27.5 6.8

60 91.1 61.9 8.1

80 86.2 9.5

100 35.2


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120 68.8

Table for Horizontal Displacement versus time (Loose States) with corresponding

weights

Times

(s)

Shear Load (N)

5.5kg 15.5kg 25.5kg

20 0 1.6 0

40 0 6.9 29.1

60 69.2 12.5 24.8

80 34.1 21.2

100 19.3

120 17.1

140 -28.1

b) Dense States

Table for Shear Load versus time (Dense States) with corresponding weights

Times

(s)

Shear Load (N)

5.5kg 15.5kg 25.5kg

20 3.2 4 0

40 4.6 5.8 2.8


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60 6.8 8.4 5.8

80 8.8 8.4 9.8

100 10.2 11.8

Table for Vertical Displacement versus time (Dense States) with corresponding weights

Times

(s)

Shear Load (N)

5.5kg 15.5kg 25.5kg

20 34.2 0 17

40 84.4 0 20.2

60 94 8 33.2

80 94 48.4 70

100 89.6 110

120 134.2 17

Table for Horizontal Displacement versus time (Dense States) with corresponding

weights

Times Shear Load (N)


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(s) 5.5kg 15.5kg 25.5kg

20 0 0 4.2

40 10 0 8

60 24.4 0 9.8

80 33.4 1 11

100 1 13.2

120 1

Calculation:

a) Loose States

• For case no. 1 where the mass of the hanger is 5.5kg:

The value of Normal stress, σ =

=

= 14987.5 Nm -2

The value of Shear stress, τ = .. .

= 3000 Nm -2



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=

= 42237.5 Nm -2


= 3444.444 Nm -2



=

= 69487.5 Nm -2


= 3861.111Nm -2

Data for shear stress and normal stress (loose states)

Shear stress, τ (kN/m 2) Normal stress, σ (kN/m 2)

3.000 14.9875


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3.444 42.2375

3.861 69.4875

b) Dense States



=

= 14987.5 Nm -2


= 2444.444 Nm-2



=

= 42237.5 Nm -2



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= 2833.333 Nm -2



=

= 69487.5 Nm -2

The value of Shear stress, τ =.

. .

= 3277.780 Nm -2

Data for shear stress and normal stress (dense states)

Shear stress, τ (kN/m 2) Normal stress, σ (kN/m 2)

2.444 14.9875

2.833 42.2375

3.278 69.4875

a) Loose Soil

τ = c + σ tan ø

From graph, the apparent cohesion, c = 2000 N/m 2

tan ø = (τ – c)/ σ


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= (3861.111 - 2000) Nm -2 / 69487.5 Nm -2

= 0.0268

Angle of internal friction, Ø = 1.534 ˚

b) Dense Soil

τ = c + σ tan ø


tan ø = (τ – c)/ σ

= (3277.78 – 1875) Nm -2 / 69487.5 Nm -2

= 0.020

Angle of internal friction, Ø = 1.160 ˚

0

10000

20000

30000

40000

50000

60000

70000

80000

0 10000 20000 30000 40000 50000 60000 70000 80000

Figure 4.3 .1 : Loose ( Shear stress vs normal stress )


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Discussion

a) Based on the result obtained, the angle of internal friction, ø for loose state is

1.534° and for dense state is 1.160°. Conclusion:

The cohesion for loose is 2000 N/m 2 and dense state is 1875 N/m 2 while angle of

internal friction for loose and dense state is 1.534˚and 1.160˚respectively.

4.4 Experiment 4: PROCTOR COMPACTION TEST

Objective :

0

10000

20000

30000

40000

50000

60000

70000

0 10000 20000 30000 40000 50000 60000 70000

Figure 4.3 .1 : Dense ( Shear stress vs normal stress )


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To determine the maximum dry unit weight of compaction of soils.

Results :

Mass of dry soil used : 2.5 kg

Classification of soil : SW (USCS Classification)

Measurement of mould :d=100 mm, h=100 mm

Volume of mould :7.85x10 -4 m3

Mass of base : 3.242 kg

Trial No 1 2 3 4 5

Mass of wet soil + mould +

base (kg)

5.22 5.312 5.242 5.192 5.169

Mass of wet soil (kg) = W 1.378 1.47 1.381 1.342 1.327

Buld density of soil, ρ (kg/m 3) 1869.74 1994.57 1873.81 1820.9 1800.54

Container No 1 2 3 4 5

Mass of container (g) 84 8 8 7 7

Mass of wet soil + container

(g)

104 28 28 26 27

Mass of dry soil + container (g) 10.62 24.02 23.53 21.52 22.07

Mass of water (g) 3.38 3.98 4.47 4.48 4.93

Mass of dry soil (g) 16.62 16.02 15.53 14.52 15.07

Water content (%), w 0.169 0.199 0.224 0.236 0.247

Dry density of soil, ρd(kg/m 3) 1599.44 1663.53 1530.89 1473.22 1443.9


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=ρ/(1+w)

Table 4.4.1: Results of the Standard Proctor Compaction Test.

Graph 4.4.1: Graph of Proctor Curve for the soil sample.

From graph 4.4.1,

, = 1663.53 3

, = 0.19 %

, = × 9.81

= 1663.53 × 9.81

= 16.32 / 3

Conclusion :

1400

1450

1500

1550

1600

1650

1700

0 0.05 0.1 0.15 0.2 0.25 0.3

D r y

D

e n s

i t y o

f s o

i l

Water Content (%)

Proctor Curve

1663.53 kg/m^3


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The maximum dry density is 1663.53 kg / m 3. Therefore, the unit weight is 16.32 kN/m 3

.

4.5 Determination of Factor of Safety (FOS) for Slope

To determine the factor of safety for the slope, the group are using manual calculation

and software.

I. Manual Calculation (Culmann Method)

For the manual calculation, the equation used is;

=4 sin β cos ∅

(1 − cos( −∅ )

cd =c

F.Sc

tan ∅ =tan ∅

. ∅

From the shear box testing result, ∅= 1.160 °


Safe depth of cut = 14m

Unit weight of the soil, = 16.32 kN / m 2

Angle of horizontal to cut surface, β = 63.435

(The angle of friction, ∅ used is the result from the dense soil because it has lower value

of ∅ compared to loose sample and this will result in lowest possible value of the factor

of safety for the slope.)


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Calculation

F.S ф фd cd F.Sc

1 1.16 16.59 0.113

2 0.58 16.87 0.111

3 0.38 16.96 0.11

= 0.111

0

1

2

3

4

0 1 2 3 4F.S ф

F.Sc

Figure 4.4.2 : F.Sc vs F.S ф


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Significance Factor of Safety for Design,

Safety Factor Significance

Less than 1.0 Unsafe

1.0 - 1.2 Questionable safety

1.3 – 1.4 Satisfactory for cuts, fills; questionable for dams

1.5 – 1.75 Safe for dams

From the above table, since the = 0.111 which is less than 1.0,

therefore the slope is unsafety and a retaining wall is needed to avoid slope failure.

II. Software Calculation

For software calculation, the group is using software called Geoslope Design. By

inputting the necessary parameter such as the slope‟s height, angle, angle of internal

friction, unit weight and cohesion. The result is as follows.

Source: Liu C. & Evett J. B., (2005). Soils and Foundations. Singapore: Pearson Prentice Hall


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The green coloured area is the critical area where the slope failure may occur. The

factor of safety for the slope is 0.109 which is less than 1.0. Thus, the slope is unsafe.

There is also other possible slope failure but since the slope failure is the most critical.

Comparison for manual calculation and software calculation

Manual Software

Factor of safety = 0.111 Factor of safety = 0.109


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5.0 RETAINING WALL DESIGN

5.1 Proposed Wall Retaining Structure (Manual)

Kh = 1 – sin υ 1 + sin υ

Kp = 1+ sin υ 1− sin υ

= 0.960 = 1.041

Ph = 1/2 Kh H 2 ɣ Pp = 1/2 Kp H 2 ɣ

= 1/2 (0.960) (16.5) 2(16.32) = 1/2 (1.041) (12.5) 2(16.32)

123

4

5

6

7


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= 2132.698 kN/m = 1327.275 kN/m

Component Weight Component (kN/m) Moment arm (m) Righting moment

kN.m/m

1 14x15x23.5x0.5 = 822.5 7.83 6440.175

2 2x14x23.5 = 658 10.5 6909

3 14x15x23.5x0.5 = 822.5 13.167 10829.583

4 21x2.5x23.5 = 1233.75 10.5 12954.375

5 2x10x23.5 = 470 10.5 4935

6 14x5x16.32x0.5 = 571.2 14.83 8472.8

7 4.5x16.32x14 = 1028.16 18.75 19278

Total ΣMv = 5606.11 ΣMr = 69818.928

Analyse the factor of safety for Sliding.

F.S sliding = (μ)( ΣV) + Pp = 0.55 5606 .11 +1327.2752132 .698

= 2.068 > 1.50 Safe against sliding

Analyse the factor of safety for Overturning.

Mo = Ph (H/3) = (2132.698) (16.5/ 3)

= 11729.9367 kN.m/m

Noted that for the calculation of active and passive pressure, the cohesion isconsidered cohesion less.

Noted that the passive pressure at toe is not considered in the manualcalculation.


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F.S overturning = ΣMrΣMo =69818.928

11729.9367

= 5.95 > 1.50 Safe against overturning

Analyse the factor of safety for Bearing Capacity Failure.

x = ΣMAΣV =ΣMr − ΣMo

ΣV = 69818.928 − 11729.937

5606.11

= 10.362 m

e = Base2

– x = 212

− 10.362 = 0.138< L/6 (i.e. 21/6 = 3.5)

My = Qe = 5606.11 (0.138) = 775.064 kN.m

X = Base2

= 212

= 10.5 m

Iy =3

12=

1(21) 3

12= 771.75 m 4

A = bh = (1)(21) = 21 m 2

q =

± ±

qL = 5606 .1121

+ 775.064(10.5)771.75

= 277.503 / ^2

qR = 5606.1121

− 775.064(10.5)771.75

= 256.413 / ^2

F.S bearing capacity failure 277.503 / ^2 < 620 / ^2 (Assumed allowable

pressure bearing)

620277.503

= 2.234 > 1.5 Safe against bearing capacity


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5.2 Proposed Wall Retaining Structure (Software)

For the design of the retaining wall using software, QuickRWall is used. The following

picture is the recommended retaining walls.


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5.3 CONLUSION & RECOMMENDATION

For conclusion, the slope is unsafe since the factor of safety (FOS) is considered

in manual calculation or from using software is less than 1. The slope is considered fail

and unsafe. The soil has a liquid limit of 26.80%, plastic limit of 20.0568% and plastic

index of 6.232%. This sample is classified as low plasticity clay or lean clay known from

the previous experiment. Thus, a retaining wall is recommended to be built to avoid

slope failure in the future. Based from all the data obtained, a retaining wall for the

slope is assumed. It is assumed by using the Rankine method including using the

software known as QuickRWall 4.0 to get the most suitable retaining wall for the slope.

Since The allowable pressure bearing for the structure is 620 kPa which for the design

assumed is only 277.530 kPa thus making the structure safe against failure. The friction

coefficient assumed in the manual calculation and software is 0.55. As for the calculation

of active and passive pressure, the cohesion is considered cohesion less soil, thus using

the equation of a cohesion less soil of Rankine Theory while the software's calculation

includes the cohesion. Also, the active pressure's height is from top structure to bottom

of foundation while the passive pressure is from bottom structure to top of foundation.

Noted that the passive pressure at toe is not considered in the manual calculation as it is

calculated separately from the manual. That is why the answer for factor of safety of

overturning is different from software's calculation. The selection criteria is not based on

the cost, difficulty in building the retaining wall and other factors. Since the most

important factor in this project is only to avoid slope failure, other factor such as the

cost of building and the difficulty in building the retaining wall will not be discussed.


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6.0 REFERENCE

Bromhead, E.N. 1992. The stability of slopes . Blackie, London.

Chandler, R.J. 1991. Slope stability engineering . Thomas Telford, London.

Craig, R. F. Mekanik Tanah . Johor Darul Ta'zim: Universiti Teknologi Malaysia.

Leventhal, A.R. and Mostyn, G.R. 1987, Slope stabilisation techniques and their

application in Slope Instability and Stabilisation , ed. by B. Walker and R. Fell,

Balkema, Rotterdam.

Liu, C. and Evett, J. B. (2005). Soils and Foundations. Singapore: Pearson Prentice Hall.

pbl report geotechnical engineering

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