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THE EFFECTIVENESS OF GEOSYNTHETIC TO PREVENT SLOPE EROSION
I.
MUHAMAD IQMAL BIN MUHAMAD SHAH
AA07076
A Final Year Project submitted in partial fulfillment of the requirements for the award of
the degree of Bachelor of Civil Engineering
Faculty of Civil Engineering & Earth Resources
Universiti Malaysia Pahang
DECEMBER 2010
ABSTRACT
Slope failure or landslide always related to the slope works at the hilly area. One
of the factors that contribute to this problem when slope surface is exposes to the rainfall
or surface run-off that eroded particle from slope surface. Suitable protected layer and
types of vegetation is important in this final year project. This final year project was
carried out to determine the actual value of sedimentation when using protected layer
compared to unprotected layer or bare control slope, also carried out the soil
classification at the case study. Geogrid were selected to be used in this study and two
types of grass were selected as earth cover is Signal grass and Japanese millet. From the
shear strength test of soil at Bukit Gambang, the average of shear strength is 183.17 kPa
with angle of friction 37.1°. From the soil classification test, this soil is sand soil with
absence of fine gravel and little silt and clay. To ensure the successfully of this study,
four (4) slope model were develop to determine the sedimentation value of the slope
surface. Actual values of sedimentation were determined by using total suspended solid
method. This study conclude that slope surface that contain Japanese millet not effective
either control or protected slope model. Slope surface that protected with Geogrid shows
effectiveness where can reduce sedimentation up to 6.98x lO g/mL per m 2. Side
analysis form this study shows that Signal grass have effectiveness to protect slope
surface by reducing 2.72x10 3 g/mL per m2 sedimentation. The usage of Geogrid with
Signal grass totally shows the effectiveness to solve slope surface erosion problem that
can reduce sedimentation up to 3.86x1(1 3 g/mL per m2.
V
ABSTRAX
Kerja-kerja membuat cerun di lereng4ereng bukit sentiasa dikaitkan dengan
punca kegagalan cerun. Salah satu faktor yang menyumbang kepada ketidakstabilan
cerun adalah permukaan cerun yang terdedah dengan air yang menyebabkan hakisan
permukaan cerun. Kajian terhadap lapisan dan tanaman tutup bumi menjadi perkara
penting didalam kajian projek sarjana muda mi. Tujuan kajian mi dijalankan adalah
untuk mendapatkan nilai sebenar hakisan dan membezakan dengan permukaan cerun
yang tidak diberi perlindungan serta mengklasifikasikan jenis tanah di tapak kajian.
Lapisan yang digunakan didalam kajian mi ialah lapisan geogrid dan terdapat dua jenis
tanaman tutup bumi yang telah dikenal pasti sesuai digunakan iaitu Signal grass dan
Japanese millet. Ujian kekuatan ricih tanah di Bukit Gambang mendapati purata
kekuatan ricih tanah ialah 183.17 kPa dengan satah kegagalan sebanyak 37.1°. Dari ujian
pengekiasan tanah, tanah mi dikelaskan sebagai tanah pasir yang mengandungi batu
kelikir halus, sedikit kelodak dan tanah hat. Bagi memastikan kajian mi berjaya, empat
(4) buah model cerun dibina khas untuk mendapatkan niiai hakisan terhadap permukaan
cerun tersebut. Nilai sebenar hakisan dapat ditentukan dengan rnenggunakan kaedah
pepejal terampai. Kesimpulan kajian mi mendapati permukaan cerun yang menggunakan
rumput Japanese millet tidak berkesan samada dengan Geogrid atau tidak. Permukaan
cerun yang dilindungi dengan Geogrid adalah lebih baik dengan mengurangkan kesan
hakisan sebanyak 6.98x104 g/mL per m2. Kajian sehingan mendapati Signal grass juga
mempunyai keberkesanan dengan mengurangkan hakisan sebanyak 2.72x10 3 g/mL per
M2 . Penggunaan Geogrid dengan Signal grass sememangnya berkesan bagi menangani
masalah hakisan permukaan cerun dengan mengurangkan hakisan sebanyak 3.86x103
gImL per m2.
A
TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE i
DECLARATION
DEDICATION iii
ACKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES xii.
LIST OF FIGURES xiii
LIST OF SYMBOLS xvi
LIST OF APPENDICES xviii
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Problem statements 4
1.3 Objectives 6
1.4 Scope of works 6
1.5 Significant of study 10
VI'
CHAPTER 2 LITERITURE REVIEW
2.1 Introduction 11
2.2 Type of soil 12
2.2.1 Cohesive soils 13
2.2.2 Cohesionless soil 14
2.3 Particle size and gradation analysis 15 2.4 Soil classification 16
2.4.1 Unified Soil Classification System (USCS) 17
2.5 Slope vegetation 19
2.5.1 Function of vegetation 19
2.6 Slope 21
2.6.1 Types of slope 21
2.6.1.1 Finite slope 22
2.6.1.2 infinite slope 22
2.6.2 Landslide 23
2.6.3 Landslide chronology in Malaysia 23
2.6.4 Types of landslide 25
2.7 Rainfall 27
2.8 Use of Geosynthetic 28
2.8.1 Separation or stabilization 28
2.8.2 Drainage 29
2.8.3 Erosion control 29
2.8.4 Reinforcement 30
2.9 Woven Geosynthetic 30
2.9.1 Geogrid 30
2.9.2 Geoweb 31
viii
CHAPTER 3 METHODOLOGY
3.1 General 32
3.2 Preliminary research 33
3.3 Preparation of slope model 35
3.4 Laboratory testing 36
3.4.1 Soil classification 36
3.4.2 Particle size distribution 37
3.4.3 Sieve analysis test 37
3.4.4 Particle size analyzer 38
3.4.5 Moisture content 39
3.4.6 Liquid limit and plastic limit test 40
3.4.7 Specific gravity 42
3.4.8 Standard proctor test 43
3.4.9 Undrained Unconsolidated Shear Strength 44
3.4.9.1 Triaxial specimen 46
3.4.9.2 Undrained Unconsolidated test 46
3.5 Preparation of soil sample 47
3.6 Rainfall rate test 48
3.7 Sedimentation test 49
3.7.1 Total Suspended Solid 49
3.8 Report writing 50
CHAPTER 4 RESULT AND DISCUSSION
4.1 Introduction 51
4.2 Natural moisture content 52
4.3 Specific gravity 52
4.4 Particle size distribution 53
4.4.1 Result for soil sample at Bukit Gambang 54
lx
4.4. 1.1 Mechanical sieve analysis result 54
4.4.1.2 Particle size analyzer 55
4.5 Standard proctor test 56
4.6 Atterberg limit 57
4.7 Shear strength test result 59
4.8 Undrained shear strength classification 65
4.9 Rainfall rate test 65
4.10 Summary of soil classification 66
4.11 Total suspended solid result test 66
4.11.1 Japanese millet grass for control model 67
4.11.2 Signal grass with for control model 73
4.11.3 Japanese millet grass with Geogrid 79
4.11 .4 Signal grass with Geogrid 85
4.12 Erosion rate classification
4.12.1 Japanese millet protected model VS Japanese 91
millet control model
4.12.2 Signal grass protected model VS Signal grass 93
control model
4.12.3 Signal grass control model VS Japanese millet 95
control model
4.12.4 Signal grass protected model VS Japanese millet 97
protected model
4.13 Factor influence the experimental result 99
4.13.1 Disturbance of the soil sample 99
4.13.2 Handling equipment 100
4.13.3 Time constraint 100
4.13.4 Slope model not evenly leveled 101
4.13.5 Unsuitable rainfall sprinkler 101
4.13.6 Geogrid installation 101
x
CHAPTER 5 CONCLUSIONS AND RECOMMENDATION
5.1 Conclusions 102
5.2 Recommendation 104
REFERENCES 106
APPENDICES A-E 109
xi
LIST OF TABLES
TABLE NO. TITLE
PAGE
XII
2.1 USCS classification system
3.1 Typical laboratory testing and their method
4.1 Moisture content result
4.2 Specific gravity
4.3 Particle size percentage
4.4 Plastic limit result
4.5 Atterberg limit result
4.6 Shear strength parameters
4.7 Result undrained shear strength classification
4.8 Comparison between control and protected model with
Japanese millet grass
4.9 Comparison between control and protected model with
Signal grass
4.10 Comparison between Signal grass and Japanese millet grass
in control model
4.11 Comparison between Signal grass and Japanese millet grass
in protected model
18
36
52
53
54
58
58
60
65
91
93
95
97
LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Pacific ring of fire at equator line 3
1.2 Signal grass in specimen box 7
1.3 Japanese millet grass in specimen box 7
1.4 Slope surface in specimen box 8
1.5 Geogrid KG 60/60 8
1.6 Slope model with rain simulator 9
2.1 Landslide at MRSM Bentong 11
2.2 Semi log graph 16
2.3 Lateral, tap, and sinker roots of a woody root system 20
2.4 infinite slope 22
2.5 Landslide distribution in Malaysia for 1973 to 2007 24
2.6 Landslide distribution based on geomorphology form 1973 24
to 2007
2.7 Types of landslide 26
3.1 Flow process of methodology 34
3.2 Slope model 35
3.3 Set sieve analysis 38
3.4 Particle size analyzer 39
3.5 Cone penetration set 41
3.6 Apparatus for plastic limit test 41
3.7 Density bottle 42
3.8 Standard proctor test 43
3.9 Triaxial compression machine 44
xlii
Al V
3.10 Rain gauge 48
3.11 Total suspended solid standard apparatus 50
4.1 Particle size distribution curve for coarse grained of 55
soil sample at Bukit Gambang
4.2 Particle size distribution curve for fine grained of sample 56
4.3 Dry unit weight VS moisture content graph 57
4.4 Moisture content (%) versus penetration (mm) 58
4.5 Plasticity chart for laboratory classification of fine grained soils 59
4.6 (a) Triaxial compression test result for soil sample BH 1 60
4.6 (b) Triaxial compression test result for soil sample BR 2 62
4.6 (c) Triaxial compression test result for soil sample BR 3 63
4.7 Soil sample at BR 1 61
4.8 Soil sample at BR 2 63
4.9 Soil sample at BH 3 64
4.10 Graph of erosion rate for control model with Japanese millet 67
grass (00)
4.11 Graph of erosion rate for control model with Japanese millet 68
grass (10°)
4.12 Graph of erosion rate for control model with Japanese millet 69
grass (20°)
4.13 Graph of erosion rate for control mode! with Japanese millet 70
grass (30°)
4.14 Graph of erosion rate for control model with Japanese millet 71
grass (400)
4.15 (a) Runoff water collected at 400 slope 72
4.15 b) Slope surface failures 72
4.16 Graph of erosion rate for control model with Signal grass (0) 73
4.17 Graph of erosion rate for control model with Signal grass (10 0) 74
4.18 Graph of erosion rate for control model with Signal grass (20 0) 75
4.19 Graph of erosion rate for control model with Signal grass (30°) 76
4.20 Graph of erosion .rate for control model with Signal grass (40) 77
4.21 Graph of erosion rate for control model with Signal grass (50) 78
4.22 Condition of soil when failed at 50° slope. 79
xv
4.23 Graph of erosion rate for protected model with Japanese millet 79
grass (0°)
4.24 Graph of erosion rate for protected model with Japanese millet 80
grass (100)
4.25 Graph of erosion rate for protected model with Japanese millet 81
grass (200)
4.26 Graph of erosion rate for protected model with Japanese millet 82
grass (300)
4.27 Graph of erosion rate for protected model with Japanese millet 83
grass (400)
4.28 Slope surface condition failed at 40° slope. 84
4.29 Graph of erosion rate for protected model with Signal 85
grass (0°)
4.30 Graph of erosion rate for protected model with Signal 86
grass (100)
4.31 Graph of erosion rate for protected model with Signal 87
grass (200)
4.32 Graph of erosion rate for protected model with Signal 88
grass (300)
4.33 Graph of erosion rate for protected model with Signal 89
grass (400)
4.34 Graph of erosion rate for protected model with Signal 90
grass (500)
4.35 Protected slope model VS control slope model using 92
Japanese millet grass
4.36 Protected slope model VS Control slope model using 94
Signal grass
4.37 Control slope model using Signal grass VS Control slope 96
model using Japanese millet grass
4.38 Protected slope model using Signal grass VS Protected slope 98
model using Japanese millet grass
LIST OF SYMBOLS
A - Area
BH - Bore hole
C - Cohesion
C. - Undrained shear strength
C' - Effective cohesion
C - Clay
CL - Low plastic clay
GCLs - Geosynthetic clay liners
Us - Specific gravity
IL - Liquidity index
Ip - Plasticity index
I - Rainfall intensity
LI - Liquidity index
LL - Liquid limit
M - Silt
P1 - Plasticity index
PL - Plastic limit
UU - Undrained unconsolidated
UV - Ultraviolet
OMC - Optimum moisture content
S - Sand
SP - Poorly sand
w - Natural moisture content
WL - Liquid limit
WP - Plastic limit
xv'
Ws - Shrinkage limit
Q - Flow rate
z - Depth
a - Stress
a' - Effective stress
03 - Confining pressure
av - Overburden pressure
P - Density
Y - Bulk unit weight
Ydzy - Dry unit weight
- Internal angle of friction
- Effective angle of friction
tf - Stress at failure
OF - Degree Fahrenheit
°C - Degree Celsius
0 - Degree
xvii
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Natural Moisture Content and Specific Gravity 109
B Particle Size Distribution Result and Standard Proctor 112
Test Result
C Atterberg Limit Test Result 121
D Shear Strength Result 123
E Rainfall Rate Test Result and Erosion Rate Result 130
xviii
CHAPTER 1
INTRODUCTION
1.0 Introduction
Highlands's area is a beautiful place to serve as travel, entertainment or as a
residence for people who like beautiful scenery, fresh air and away from the bustling
city. Highland areas in Malaysia including Cameron Highland, Genting Highland,
Fraser's Hill and Bukit Tinggi often become tourist attractions from within and
outside the country. Nowadays, highland areas in Malaysia are becoming more
sought-after the settlers who want to open the forest highlands. With activities such
as the development is expected to increase revenue, but instead have happened.
Malaysia has received a drastic current modernization began early 80s, where
there are many infrastructure development ahead run in the city or village. Not
exempt development on high ground and the slope of the hill-slope. Since developing,
many buildings can be built higher and also due to modernization, many residential
areas built in the hills because of the fmancial status changes dramatically. At that
time and now, housing in the area of land represents a high status to the buyer, but
buyers are not realizing the danger living in hilly area.
IL
November 1993, Malaysia shocked by landslides against the Highland Tower
which has claimed iiiany lives. The event was a great impact for Malaysia where the
effects of modernization has been shown to respond to the community. Since the
incident, the government has taken various measures to prevent landslides from
happening again, but the result disappointed. Since 1993, there are many cases
follow-up occurred after the landslide and also involves death and property loss.
While Malaysia can be categorized as a country that is safe from natural
disasters such as earthquakes, hurricanes and tsunamis, but Malaysia is not free from
landslides caused by climatic conditions and form of the hilly terrain. Malaysia
generally has a mountainous terrain in the middle of the country from north Malaysia
to the west coast. Titiwangsa Mountains range is the oldest in Malaysia which there
are many hills around. Mountainous also is an obstacle to the transport system to get
to the eat coast and northern Malaysia. Normally the way to go to the north and the
east coast, the road were be built on the hillside of the work involves cutting and trim
hill.
Malaysia's position is located in the middle of the equator line to receive hot
and humid weather throughout the year also located in a circle of Pacific Ring of Fire
that shows in Figure I.I. A climatic condition such as this is a major contributor to
landslides where the weathering process that occurs at very high line is the equator.
Malaysia also received high rainfall throughout the year starting from early October
until late January next year because of changes in the northeast monsoon winds.
Even though Malaysia is safe from earth quake, but Malaysia still can have the effect
form that activity and there is still no evident that says Malaysia are not suffer from
earth quake activity or massive movement of earth crust.
Figure 1.1: Pacific ring of fire at equator line
Source: Google earth
Water is a dangerous agent compared to wind, water not only can dissolve,
but it's scraping and drifting the soil particle. A part form factor land and climatic
conditions, there are several additional factors, such as less monitoring and
maintenance and the attitude not to know about the circumstances surrounding
highlands contribute to landslides. High land clearing activity not controlled can also
affect the geological origin of the region. Until now, there are many projects actively
carried out in the highlands, for example the construction of such roads in the
Simpang Pulai-Gua Musang-Lojing the recorded cases of concern.
Development in the hills that are not managed and controlled to give worst
impact to the country, when there is landslide occurs especially to the victim family
or community. Because landslides occur blinking of an eye and people who live on
high ground are not prepared, always is a victim of landslides. Effects of landslides
not only claimed lives and property, even harming the economy of the country as the
issue had to spend big to repair the destruction and damages. Also, there are some
people who suffer emotional disturbances because of past landslides.
4
1.2 Problem Statements
Development on high ground indeed invites the problem of landslides.
Generally, plateau areas are places where rain water catchment' s supplying water in
lowland areas. When the occurrence of development activities carried out, cutting of
forests in the highlands can disrupt the original ecology of the area. With activities
that also, it changed the pattern of water flow at the top of the hill. Time when it
rained, the water can easily infiltrate into the soil pores and loosen the bonds of soil
and the occurrence of landslides.
Landslides can occur in two ways, first by nature, and the second with the
man-made. However, as a result of man-made landslide that makes this worse
compare than nature. As an example, construction of roads in the hillside, Cut and
trim work involves hills and the result is there is a slope failure along the road.
Unfortunately, due to the progress of an area, work like this should be done.
However, it must be carefully planned and reviewed, also supervision and
maintenance that must be implemented consistently.
Slope failure is the main enemy really is water, because in Malaysia, the
rainfall for each year is quite high. Safe and well construction on slope can siphon
water out well from the slope. Certainly the increasingly steep slope, the speed of
water flow rate and increasingly dangerous conditions the slope. With the right
techniques must be adopted when the design of a slope. Most of the problems of
landslides or other words slope failure occurred due to poor technique and lack of
maintenance. This is because of slope failure cannot be predicting when it happen
when and where, so the design of a slope should first ensure its effectiveness.
Pattern of slope failure are many ways, including erosion slope. When the
occurrence of erosion slopes, the mountain has been lost from the water layer of
defence. Thus, water is easy to infiltrate into the hills and help to collapse. The main
5
factor is the occurrence of slope erosion processes of weathering, where hot and cold
conditions cause cracks in the surface and rain which came down to help eliminate
the particle of the soil. For problems like this, usually require in-depth study to
determine where the appropriate conditions are used to prevent erosion problems on
the surface slope.
Normally, the surface slope erosion solved by providing a special layer to
prevent soil movement from top to bottom. To prevent the erosion rate is by planting
grass on the surface of the slope to slow water runoff in surface slope. Surface slope
maintenance is important to ensure the safety of slopes. This is because the surface
slope acts as a barrier from water absorbed into the surface. This is important,
because surface slopes are low maintenance compared to the costs when a landslide
occurrence. So on the surface treatment is indeed important to guarantee the safety of
slopes.
With the existence of problems such as this, a study should be conducted to
investigate the effectiveness of the layer to treat this slope erosion problem.
Consistent with the title of this study, expected a new discovery or improvement on
how to prevent this problem The appropriate parameters must be studied in order get
good results and thus solve the puzzle about this problem.
b
1.3 Objective
The objectives of this study are:
1. To determine the soil properties at the Bukit Gambang area.
2. To analyze the effectiveness of Geosynthetic due to different types of
vegetation.
1.4 Scope of works
Studies that were implemented are related to the slope erosion involving the
study of soil properties and methods to prevent erosion. To implement this study, the
study of slope should be done, but it is difficult for outside research takes a long time
and uncertain circumstances. As solutions, this study was implemented to model
slope outside, which is smaller but still similar to the conditions outside. To ensure•
the success of this study, there are three processes to be carried out, the first study the
situation of soil properties in Bukit Gambang. Second, develop four slope models as
tool for this study. Finally, is comparing the effectiveness of Geosynthetic layer
between protected and control model and also due to different types of vegetation.
To studying soil properties in Bukit Gambang, soil usually be taken at the
surface slope. This soil are taken in Eukit Gambang and then brought back to the
laboratory for more in-depth study for soil classification. For research that utilizes
Geosynthetic, there are four soil specimens should be develop, two of it is the control
model are fertilized with two different types of grass and the other two are protected
model which protect by Geosynthetic material also fertilized with two different types
of grass. All of the slope models were using the same soil that taken from Bukit
Gambang.
7
There is two types of grass were planted for this study, first is Signal grass
where it is low-growing decumbent perennial, with trailing stems that root at the
nodes. It forms a dense soil cover, with a canopy usually under 40 cm when grazed
and Figure 1.2 shows a photo of Signal grass. The second grass is ordinary corps
field grass that suitable to adapt in wet soils and requires no soil preparation or care
called Japanese Millet grass. Figure 1.3 shows a photo of Japanese Millet grass.
Figure 1.2: Signal grass in specimen box
Figure 1.3: Japanese millet grass in specimen box
8
Specimen box were develop specifically for this study and specimen box has
dimensions measure 500 mm wide x 1000 mm long x 356 mm high (1 foot). Figure
1.4 shows the illustration of the slope surface in specimen box. There are many types
of Geosynthetic, and Geogrid were used for this study. Geogrids is only one of
Geosynthetic material can let grass grows on it and there is a standard size in the
market. In this study, Geogrids with a biaxial strength of 60 kN/m horizontally and
60 kN/m vertically were used and Figure 1.5 shows a photo of Geogrids.
Figure 1.4: Slope surface in specimen box
\ -
;.
I .-
: -3
- -) .-)•_ .
Figure 1.5: Geogrids KG 60/60
9
Slope model were also developed specially for the purpose of this study, it is
used to replicate the original slope. Slope model are constructed with a dimension of
1000 mm length x 500 mm wide x 1000 mm high. Specimen box were placed on the
top of slope model, where the soil are tested with various slope angles. The top of the
slope model can be rotated until 500 maximum. Slope surface in specimen box were
rotate for every 100 each starting from 00 until 500. Therefore, the study required 6
types of angles of rotation and 24 data of the erosion rate were collected.
To study the erosion rate, rain simulators were constructed to resemble the
actual rain or other words to make the process of weathering with the actual situation.
This study is implemented in open areas and rainfall simulator were accordance with
Malaysia average heavy rainfall with intensity 83.3 mm/hr. Rainfall simulations were
carried out for 1 hour for each specimen at a certain slope angle. To determine the
rate of erosion, the water runoff are collected and determine using the total
suspended solid apparatus, to knowing the particles of the soil has been eroded every
hour. Figure 1.6 shows the slope model and rain simulator illustration.
DIA WJ2lrn
PVC pipe
Specimen Box
b,soorn
I LOOm
Guer(WarCollector) -"
Slope Model Frame
Figure 1.6: Slope model with rain simulator
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