1.0. INTRODUCTION
1.1. Slope Failure
A slope failure is the movement of rock, debris or earth down a slope. They result from the failure of the materials which make up the hill slope and are driven by the force of gravity. Slope failure are known also as landslips, slumps or land slide. A slope collapses abruptly due to weakened self-retain ability of the earth under the influence of a rainfall or an earthquake. Slope failure is a geological phenomenon that includes a wide range of ground movements, such as rock falls, deep failure of slopes, and shallow debris flows. It can occur in offshore, coastal and onshore environments. Although the action of gravity is the primary driving force for a landslide l andslide to occur, there are other contributi c ontributing ng factors affecting the original slope stability. s tability. In general, the factors which influence whether a landslide will occur typically include slope angle, climate, weathering, water content, vegetation, overloading, geology, and slope stability. These factors interrelate is important in understanding what causes slope failure along with an understanding of the impact humans have on these factors by altering natural processes. Typically, a number of elements will contribute to a slope failure, but often there is one which triggers the movement of material. Part of factors of slope failure are:
1.1.1. Steepness 1.1.1. Steepness of the Slope The natural tendency of steep slopes is to move some of its materials downwards until the natural angle of repose is found. The steeper a slope is, the more unstable it will be. Any form of slope modification whether by natural means such as a stream undercutting the banks of a river or workers removing a section of the base for roads will impact the stability of a slope.
1.1.2. Water 1.1.2. Water and Drainage Water is several times heavier than air.
During heavy rain when the soil
becomes saturated and water takes the place of air between the grains of soil, the earth in slopes becomes a lot heavier.
1
1.1.3. Soil 1.1.3. Soil Composition The composition of the soil making up the slope is a very important factor to consider when talking about slope failure. This is because different types of soils will have very different characteristics when it comes to frictional resistance to erosion and cohesion between the grains.
1.1.4. Vegetation 1.1.4. Vegetation The amount and type of vegetation found in a slope is also proportional to the strength of the slope. This is because vegetation, specifically its roots, holds the soil in place and makes it more resistant to erosion. 1.1.5. Joints 1.1.5. Joints and Fractures Joints and fractures are natural cracks in the rocks forming a slope. These are caused by the natural expansion of rocks due to cooling or the removal of overlying rocks due to to erosion. Because of these cracks, the cohesion between the rocks making up the slope is greatly reduced increasing increasing the likelihood of a landslide in the slope. sl ope.
1.1.6. Sudden 1.1.6. Sudden Shocks Sudden shocks like earthquakes, hurricanes, volcanic eruptions, the passage of heavy trucks, blasting and others may trigger the sudden mass movement of the soil in slopes.
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. Triggering factors of a slope failure can be climatic events can then make a slope actively unstable, leading to mass movements. Mass movements can be caused by increase in shear stress, such as loading, lateral pressure, and transient forces. The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock.
2
Geologists and engineering and engineering geologists can also use their knowledge of earth process and their ability to interpret surface geomorphology to determine relative slope stability based simply on site observations. Slope stability stability is affected by the factors of Strength of soil s oil and rock, Type of soil and stratification, stratification, Discontinuitie Discontinuitiess and planes of weakness,
Groundwater Groundwater
table
and seepage through the slope, External loading, Geometry of the slope. Slope stability is based on the interplay between two types of forces, driving forces and resisting forces.
i.
Driving forces Promote down slope movement of material, whereas resisting forces deter movement.
So, when driving forces overcome resisting forces, the slope is unstable and results in mass wasting. 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. 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.
ii.
Resisting forces Resisting forces act oppositely of driving forces. The resistance r esistance to down slope movement
is dependent on the shear strength of the slope material. And shear strength is a function of cohesion ability of particles to attract and hold each other together and internal friction between grains within a material. Water contributes to resisting forces when sediment pores are partially filled with water. The thin film of water acts as a binder, making the particles cohesive.
The ratio of resisting forces to driving forces is the safety factor (SF): SF =
If Safety Factor > 1 (SAFE) If Safety Factor < 1 (UNSAFE) ( UNSAFE)
3
1.3. Retaining wall A retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil. A basement wall is thus one kind of retaining wall. But the term usually refers to a cantilever retaining wall, which is a freestanding structure without lateral support at its top. These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side. The walls must resist the lateral pressures generated by loose soils or, in some cases, water pressures. A retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil (Crosbie and Watson, 2005). The term usually refers to a cantilever retaining wall, which is a freestanding structure without lateral support at its top (Ching et. al., 2006). These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side. The walls must resist the lateral pressures generated by loose soils or, in some cases, water pressures (Raj, 2003).
1.3.1. Types of retaining wall
i.
Gravity Gravity walls depend on their mass stone, concrete or other heavy material to
resist pressure from behind and may have a 'batter' setback to improve stability by leaning back toward the retained soil. For short landscaping walls, they are often made from mortar less stone or segmental concrete units masonry units. Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing in frost areas.
ii.
Cantilevered Cantilevered retaining walls are made from an internal stem of steel-reinforced,
cast-in-place concrete or mortared masonry often in the shape of an inverted T. These walls cantilever loads like a beam to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counter fort on the back, to improve their strength resisting high loads. Buttresses are short wing walls at right angles to the main trend of the wall. 4
iii.
Sheet Piling Sheet pile retaining walls are usually used in soft soils and tight spaces. Sheet
pile walls are made out of steel, vinyl or wood planks which are driven into the ground. For a quick estimate the material is usually driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment.
iv.
Bored Pile Bored pile retaining walls are built by assembling a sequence of bored piles,
proceeded by excavating away the excess soil. Depending on the project, the bored pile retaining wall may include a series of earth anchors, reinforcing beams, soil improvement operations and shotcrete reinforcement layer.
v. Anchored An anchored retaining wall can be constructed constructed in any of the aforementioned aforementioned styles but also includes additional strength using cables or other stays anchored in the rock or soil behind it. Usually driven into the material with boring, anchors are then expanded at the end of the cable, either by mechanical means or often by injecting pressurized pressurized concrete, which expands to form a bulb in the soil.
Figure 1.3.1: Types 1.3.1: Types of Retaining Wall
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2.0. OBJECTIVE
To determine the soil properties of experimented site.
To conduct a slope stability analysis. To propose a retaining wall structure design.
3.0. RESEARCH METHODOLOGY
3.1. Flowchart Site Visit
Soil Sampling
Sieve Analysis
Compaction Test
Atterberg Limit
Soil Classificat C lassification ion
Direct Shear Box
Soil Engineering Properties
Slope Stability Analysis
Ordinary Slice
Geostdio Software
Method
Page 7
6
Page 6
Failure Plane & Safety Factor
Retaining Wall Design
?????
??????
Proposed Finished Design
3.2. Site Visit th
The first site visit was conducted on 12 September 2015 to identified the exact location of slope failure that located at Jalan Bantayan Minintod, Inanam. During the second site visit on th
28 September 2015 photo was taken at the site for Research propose. It was found that the slope failure is 14m height and 7m wide. The physical properties that can be seen during the site visit it was found that the slope was very steep and low amount of vegetation, also the condition of soil was found very dry and dusty, the soil was also yellow in colour.
Figure 3.2 : Jalan Bantayan Minintod, Inanam
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3.3. Sieve Analysis Test
Sieve analysis was conducted to determines the relative proportions of different grain sizes as they are distributed distributed among certain size ranges. The grain size analysis is widely used in classification of soils. The size distribution is often of critical importance to the way the material performs in use. Being such a simple technique of particle sizing, it is probably the most common. The largest particles are of sieve No. 10 with sieve opening of 2.00 mm. The soil samples are broken into individual particles particles using a mortar and a pestle. The idea is to break up particles, not to break the particles themselves. The weight of the sample is determined, M to 0.1 g. The stack of the sieves is prepared and weigh. A sieve with larger sieve openings is placed above a sieve with smaller sieve openings. openings. A bottom bottom pan should be placed under the No. 200 sieve. As mentioned before, the sieves is used in this experiment using different size of sieve. The soils prepared in Step 2 are poured into the stack of sieves from the top. The cover is placed on top of the stack of sieves. The stack of sieves was run through a sieve shaker for about 10 minutes. The amount of soil retained on each sieve and in the bottom of the pan is i s weighed.
3.4. Compaction Test
Compaction test were used to determine the relationship between moulding water content and dry unit weight of soils. Soil placed as engineering fill is compacted to a dense state to obtain satisfactory engineering properties such as, shear strength, compressibility, or permeability. In addition, foundation soils are often compacted to improve their engineering properties. Laboratory compaction tests provide the basis for determining the percent compaction and moulding water content needed to achieve the required engineering properties, and for controlling construction to assure that the required compaction and water contents are achieved. There are several means of achieving compaction of a material. Some are more appropriate for soil compaction than others, while some techniques are only suitable for particular soils or soils in particular conditions. Some are more suited to compaction of non-soil materials such as asphalt. Generally, those that can apply significant amounts of shear as well as compressive stress, are most effective.
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3.5. Atterberg Limit Test
Laboratory testing for Atterberg Limits includes plastic and liquid limit tests used to determine the soil’s plasticity index. index. At a minimum, soil classification and index testing should be performed on soil and rock samples extracted from subsurface borings drilled during slope stability stabili ty investigations. investigations . The mass of a soil sample is measured prior to conducting a particle size analysis to assist in the determination of the in-situ water content. Once the sample is dry the material is placed in a set of sieves and the particle size is analyzed. Based on the results of this test the material is classified in accordance with the AASHTO and USCS soil classification classification systems. The natural water content of extracted extracted soil samples is also determined as part of the A gency’s A gency’s routine testing; this allows for the determination of the liquidity index. The following tests provide insight on how a soil with plastic characteristics characteristics will perform or behave.
3.5.1. Plastic Limit The plastic limit (PL) is the moisture content at which a soil transitions from being in a semisolid state to a plastic state. For additional references, see AASHTO T90 - Standard Method of Test for f or Determining the Plastic Limit and Plasticity Index of Soils.
3.5.2. Liquid Limit The liquid limit (LL) is defined as the moisture content at which a soil transitions from a plastic state to a liquid state. For additional references, see AASHTO T89 - Standard Method Method of Test for Determining the Liquid Limit of Soils.
3.5.3. Plasticity Index The larger the percentage of clay minerals and the more active the clay mineral, the more complex and difficult the behaviour of the soil can be to predict. The plasticity index, or PI, is a useful indicator to screen for potential problems including swelling, creep, strain softening and changes in behaviour due to physiochemical effects. In general, higher values of PI are more indicative of poor performing soils. The plasticity index (PI) is defined as the difference between the liquid limit and the plastic limit of a soil. The PI represents the range of moisture contents within which the soil behaves as a plastic solid.
9
3.5.4. Liquidity Index The liquidity index (LI) is used for scaling the natural water content of a soil sample to the limits. LI is a good indicator of geologic history and relative soil properties. It can be calculated as a ratio of difference between natural water content, plastic limit, and liquid limit. The liquidity index is a measure of the relative consistency of a cohesive soil in its natural state. If the in-situ moisture content, Wn is equal to the LL then LI = 1 or if Wn is equal to PL then LI = 0. Therefore, for a soil in a plastic state LL > Wn > PL the LI varies from 1 to 0. Sensitive clays are soils, in an undisturbed state, whose Wn
> LL but if the soil becomes
disturbed could transform transform into a liquid state; thus a sensitive clay would have a LI > 1.
3.6. Shear Box Test
Direct Shear Box Test was conducted to determine the cohesion and angle of internal friction of a dry granular soil. The direct shear test is the oldest and simplest form of shear test. A soil sample is placed in a metal shear box and undergoes a horizontal force. The soil fails by shearing along a plane when the force is applied. The test can be performed either in stresscontrolled or strain-controlled environment. In addition the test is typically performed as a consolidated-drained test on cohesion less soils. The test procedure that the Agency follows is outlined in AASHTO T236 - Standard Method of Test for Direct Shear Test of Soils Under Consolidated Drained Conditions. To conduct this experiment first, make sure that the alignment screws are screwed through the top half of the shear box into the bottom half of the shear box and the gap screws are screwed into the top half of the shear box and touching the bottom half of the shear box. Place the shear box into the shearing device. Apply a normal load to the specimen using the load transfer plate and the loading hanger. Remove the alignment screws from the shear box. Turn the gap screws a half turn clock wise and then tow turns counter clockwise. This should increase the gap between the two halves of the shear box. Begin the data acquisition system. Record the input voltage output and voltage from the channels needed. Once data acquisition has begun start the shearing device. Record the transducer output every 10 seconds after it has begun to change from the initial reading. Continue recording the output until the output is constant or drops for three consecutive readings. Stop the data acquisition system. Perform the test with normal loads 5.5kg, 10.5kg, and 15.5kg.
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3.7. Slope Stability Analysis
Slope stability analysis is performed to assess the safe design of a human-made or natural slopes and the equilibrium conditions. The main objectives of slope stability analysis are finding endangered areas, investigation of potential failure mechanisms, determination of the slope sensitivity to different triggering mechanisms, designing of optimal slopes with regard to safety, reliability and economics, designing possible remedial measures, barriers and stabilization. The presence of water has a detrimental effect on slope stability. Water pressure acting in the pore spaces, fractures or other discontinuities in the materials that make up the pit slope will reduce the strength of those materials. Choice of correct analysis technique depends on both site conditions and the potential mode of failure, with careful consideration being given to the varying strengths, weaknesses and limitatio l imitations ns inherent in each methodology. Slope Stability has been analyse using Ordinary Method of Slices, then the result from Ordinary Method of Slices has been compare using Geostudio Software.
3.7.1. Ordinary Method of Slices
In method of slices, also called OMS or the Fellenius method, the sliding mass above the failure surface is divided into a number of slices. The forces acting on each slice s lice are obtained by considering the mechanical (force and moment) equilibrium for the slices. Each slice is considered on its own and interactions between slices are neglected because the resultant forces are parallel to the base of each slice. However, Newton's third law is not satisfied by this method because, in general, the resultants on the left and right of a slice do not have the same magnitude and are not collinear. This allows for a simple static equilibrium calculation, considering only soil weight, along with shear and normal stresses along the failure plane. Both the friction angle and cohesion can be considered for each slice. In the general case of the method of slices, the forces acting on a slice are shown in the figure below. The normal (Er, El) and shear (Sr, Sl) forces between adjacent slices constrain each slice and make the problem statically indeterminate when they are included in the computation.
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3.8. Retaining Wall Design
A design of retaining wall wall was design and was check check for it factor of safety safety check against overturning and sliding using Rankine Theory. For factor of safety against overturning = MR / MO ≤ 1.55 ≤ 1.55 Where, MR = Stabilising moment or restoring moment MO = overturning moment. Also factor of safety check against Sliding FOS = Resisting force to sliding/Horizontal sliding/Horizontal force causing sliding. FS = µ∑ µ∑W/Pa ≥ 1.55 If the wall is not safe against sliding, then a shear key is to be provided. It is provided either below the stem or at the end of heel. It should not be provided at the end of toe. If shear key is provided, then it should be designed taking the effect of passive pressure. Stability requirements of Retaining Wall following conditions must be satisfied for stability of wall. It should not overturn. It should not slide. It should not subside for example Maximum pressure at the toe should not exceed the safe bearing capacity of the soil under working condition.
3.8.1. Earth Pressure (P)
Earth pressure is the pressure exerted by the retaining material on the retaining wall. This pressure tends to deflect the wall outward. There are two types of earth pressure and they are Active earth pressure or earth pressure (Pa) and Passive earth pressure (Pp). Active earth pressure tends to deflect the wall away from the backfill. Earth pressure depends on type of backfill, the height of wall and the soil s oil conditions.
Figure 3.8.1 : Lateral : Lateral Earth Pressure 12
4.0.
Results 4.1.
Sieve Analysis After conducting conducting sieve analysis analysis test, the mass retained was recorded. The cumulative mass retained and % finer was computed and tabulated on table 4.1.1 below. By using data from table 4.1.1, graph of soil particle distribution was plotted on graph 4.1.1.
Sieve Opening (mm)
Sieve weight (g)
Sieve Weight + Mass of soil retained (g)
3.35
1017
1563
546
27.437
27.437
72.563
2.36
1039
1253
214
10.754
38.191
61.809
2
1077
1121
44
2.211
40.402
59.598
1.4
979
1114
135
6.784
47.186
52.814
0.6
928
1147
219
11.005
58.191
41.809
0.425
793
872
79
3.970
62.161
37.839
0.3
827
1192
365
18.342
80.503
19.497
0.15
790
1007
217
10.905
91.407
8.593
0.075
795
936
141
7.085
98.492
1.508
Pan
1004
1034
30
1.508
100
0
Mass Retained (g)
% Mass Retained
Cumulative % Mass Retained
% Finer
Table 4.1 :Sieve Analysis
13
Soil Particle Distribution 80 70 60
) 50 % ( 40 r e n i F 30 20
10 0 0.001
0.01
0.1
1
10
Sieve size (mm) Graph 4.1. Soil Particle Distribution Distribution of Soil Sample
Based on graph 4.1.1,
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Since sand has the highest percentage, therefore the type of soil is S.
4.2.
Atterberg Atterberg Limits
From the fall cone test conducted, value of penetration and mass of soil was obtained. Computing these data, mass of water and mass of dry soil were obtained and tabulated in table 4.2.1 below. From the mass of water and penetration value, graph of penetration versus moisture contain was plotted in graph 4.2 below. Result obtained from plastic limit test on the other hand, was computed and tabulated on table 4.2.2 below.
15
Table 4.2.1. Data from fall cone cone test test Test Number
1 2 3 4 5 28.9 27 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
Penetration (mm)
Average Penetration (mm) 28.13333333 8.1195 Mass of Container (g) Mass of container + Wet 10.9113 Soil (g) Mass of container + Dry 10.2614 Soil (g) 0.6499 Mass of Water (g)
21.7
20.66666667
26.7
33.8
7.9288
22.5019
21.058
19.5758
9.7352
24.2223
26.1321
24.4103
9.3482
23.856
24.974
23.2163
0.387
0.3663
1.1581
1.194
Mass of Dry Soil (g)
2.1419
1.4194
1.3541
3.916
3.6405
Moisture Content (%)
30.3422
27.2650
27.051
29.574 29.574
32.798
Penetration Penetration Vs. Moisture Content C ontent 40 35
) m m ( n o i t a r t e n e P
30 25 20 15 10 5 0 0
5
10
15
20
25
30
35
Moisture content (%) Graph 4.2. Graph of Penetration vs. Moisture Content
From graph 4.2,
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Table 4.2.2. Data from plastic plastic limit test test 1
2
3
4
Mass of Container (g)
8.059
87.7212
7.6516
87.2409
Mass of Container + Wet Soil (g)
8.8985
89.2477
9.4797
89.6503
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
Container Number
From table 4.2.2,
Hence, the plasticity index
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4.3.
Proctor compaction Test
From compaction test conducted, the mass of wet soil and mould was determined. Dry density for each trial was computed and tabulated in table 4.3.1 below. From the table 4.3.1, two parameters were obtained. Table 4.3.1 Data from proctor compaction test Trial No Mass of wet soil + mould + base (kg) Mass of wet soil (kg) = W Bulk density of soil, ρ (kg/m3) Container No Mass of container (g) Mass of wet soil + container (g) Mass of dry soil + container (g) Mass of water (g) Mass of dry soil (g) Water content (%), w Dry density of soil, ρd(kg/m3) =ρ/(1+w)
1
2
3
4
5
5.22
5.312 5. 312
5.242 5. 242
5.192
5.169
1.978
2.07
1.981
1.942
1.927
931.262
974.576
932.764
914.313
907.25
1 84
2 8
3 8
4 7
5 7
104
28
28
26
27
10.62
24.02
23.53
21.52
22.07
3.38 16.62
3.98 16.02
4.47 15.53
4.48 14.52
4.93 15.07
0.169
0.199
0.224
0.236
0.247
796.631
812.824
761.989
739.734
727.546
Proctor Curve 820 810
MDD
800 3
790
m / g 780 K 770 y t i s 760 n e 750 D 740 730
OPC
720 0
0.05
0.1
0.15
0.2
0.25
0.3
Water content, Wc (%) Graph 4.3. Proctor Curve indicating Maximum Dry Dry Density & Optimum Water Content
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From Graph 4.1.1,
The dry unit weight of soil is = 4.4.
Direct Shear Box Test 4.4.1. Loose state Table 4.4.1.1: Table of Shear Force over time for different weights. Times (s)
Shear Force (x0.01 mm) 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 4.4.1.2: Table of Vertical Displacement over time for different weights. Times (s)
Vertical Displacement Displacemen t 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
86.2
9.5
80 100
35.2
120
68.8
19
Table 4.4.1.3: Table of Horizontal Displacement over time for different weights. Times (s)
Horizontal Displacement (x0.002 mm) 5.5kg
15.5kg
25.5kg
20
0
1.6
0
40
0
6.9 6.9
29.1
60
69.2
12.5
24.8
34.1
21.2
80 100
19.3
120
17.1
140
-28.1
Calculation for normal stress and shear stress; (a) For 5.5kg
20
(b) For 15.5kg
(c) For 25.5kg
21
Table 4.4.1.4: Table of Maximum Shear Stress and its Normal Stress.
Shear Stress, (kN/ m2)
Normal stress, (kN/m2)
3.000
14.9875
3.444
42.2375
3.861
69.4875 Shear Diagram
80000.00 70000.00
) 2 m 60000.00 / N 50000.00 k ( Τ , s s e r t S r a e h S
40000.00 30000.00 20000.00 10000.00 0.00 0
10000
20000
30000
40000
50000
60000
70000
80000
Normal Stress , Σ (kN/m2 ) Graph 4.4.1.1: Shear graph for Direct Shear Test (Loose).
Equation of line is given by;
From the graph plotted, the apparent cohesion, c = 2000N/m 2
( ) 22
4.4.2. Dense state
Table 4.4.2.1: Table of Shear Force over time for different diff erent weights. Times (s)
Shear Force (x0.01 mm) 5.5kg
15.5kg
25.5kg
20
3.2
4
0
40
4.6
5.8
2.8
60
6.8
8.4
5.8
80
8.8
8.4
9.8
10.2
11.8
100
Table 4.4.2.2: Table of Vertical Displacement over time for different weights. Times (s)
Vertical Displacement 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
23
Table 4.4.2.3: Table of Horizontal Horizontal Displacement over time for different weights. Times (s)
Horizontal Displacement (x0.002 mm) 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 for normal stress and shear stress; (a) For 5.5kg
24
(a) For 15.5kg
(b) For 25.5kg
25
Table 4.5.2.4: Table of Maximum Shear Stress and its Normal Stress.
Shear Stress, (kN/ m2)
Normal stress, (kN/m2)
2.444
14.9875
2.833
42.2375
3.278
69.4875 Shear Diagram
80000.00 70000.00
)
60000.00
2
m50000.00 / N k ( Τ , s s e r t S r a e h S
40000.00 30000.00 20000.00 10000.00
0.00 0
10000
20000
30000
40000
50000
60000
70000
80000
Normal Stress , Σ (kNn/m2 )
Graph 4.5.2.1: Shear graph for Direct Shear Test (Dense).
Equation of line is given by;
From the graph plotted, the apparent cohesion, c = 1875N/m 2
( )
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4.5.
Slope Stability Analysis 4.5.1. Method of Slice
Table 4.5.1.1: Calculations of Method of Slices of Graph 8.1.1 Slice No.
(kN/m)
1
55.11
64
2
104
53.5
3
139.04
45
4
167.48
37.8
5
126.4
30
6
79
25.9
7
28.44
17.3
(kN/m)
(kN/m)
49.53
24.158
83.601
61.861
98.316
98.316
102.649
132.335
63.2
109.465
34.507
71.065
8.457
27.153
ΣΣ
Since F.S < 1.5, therefore the slope fails.
27
4.5.2. Computer Software (Geostudio) Using computer software, data from laboratory test was keyed in and the results of computer analysis is shown in figure 4.5.2.1 and 4.5.2.2 below.
Table 4.5.2.1. Shear plane and its Factor of safety for dense state
Table 4.5.2.2.Shear plane and its Factor of safety for loose state
28
4.6.
Retaining Wall Design With the result from slope stability analysis conducted. Retaining wall can be design. To design retaining wall, Rankine method was used. Next, the calculation was confirmed with computer software (QuickRWall).
4.6.1. Design trial 1 (Rankine Method)
29
Component
Weight of Component, (kN/m)
Moment Arm From From A, (m)
Righting Moment
1
(51)(23.5) (51)(2 3.5) = 1198.5
5.000
5992.500
2
(16)(23.5) (16)(2 3.5) = 37.6
3.333
1253.208
3
(4)(23.5) (4)(2 3.5) = 94
2.000
188.000
4
(8)(23.5) = 188
4.000
752.000
5
(4)(7.5) (4)(7 .5) = 31.6
1.000
31.600
6
(0.25)(7.5) = 1.975
2.083
4.1139
∑ = 1890.075
∑ = 8221.4219
∑ , FAIL against sliding ∑∑ , FAIL against overturning 30
̅ ∑ ∑∑ ̅
∑
31
, FAIL against bearing Capacity 4.6.2. Design trial 2 (Rankine Method)
1 5
4
6 3 2
32
Component
Weight of Component, (kN/m)
Moment Arm From From A, (m)
Righting Moment
1
1128
8.5
9588.000
2
423
8.5
3595.000
3
329
3.5
1151.500
4
564
6.000
3384.000
5
2.963
4.125
12.222
6
63.2
2
126.400
∑ = 2510.163
∑ = 17857
∑ , FAIL against sliding
33
∑∑ , OK! ̅ ∑ ∑∑ ̅
34
∑ , FAIL against bearing Capacity
35
4.6.3. Design trial 3 (Rankine Method) 1.5m
5m
1.5m
7
1
5
6
14m
4 2
6m
3
5m
A
4.5m
5m
5.5m
36
Component
Weight of Component, (kN/m)
Moment Arm From From A, (m)
Righting Moment
1
1645
7
11515
2
2115
7.5
15862.5
3
587.5
7
4112.5
4
246.75
10
2467.5
5
246.75
4
987
6
442.4
13
5751.2
7
82.95
10.5
870.98
∑ = 5366.35
∑ = 41566.68
∑ , PASS against sliding ∑∑ , PASS against overturning overturning
37
̅ ∑ ∑∑ ̅
38
∑ , PASS against bearing Capacity
39
5.0.
Discussion
Based on the results obtained from soil classification test, the soil sample was found that high percentage of sand (58.08%) was discovered inside the soil sample. Using USCS classification system, this particular soil sample can be classified as SW. It cause by the soil’s particle distribution is in w ell graded state. The soil sample was found to have maximum dry density of 814.17 kg/m 3 with the optimum water content of 0.19% while its dry unit weight is 7.9kN/m 3. After conducting direct shear box test, engineering properties of the soil was obtained. The soil was discovered to have value of cohesion of 2000 N/m 2 for loosely and 1875 N/m2 for densely compacted soil. The soil’s angle of friction on the other hand, indicates value of 1.534 loosely compacted soil and 1.16 for densely compacted soil.
After obtaining results from f rom all laboratory laboratory test, analysis of slope failure was conducted. conducted. Based on analysis using method of slice, safety factor of failing slope was 0.122 while safety factor obtained by using Geostudio software was found to be 0.117. The value of safety factor only differs by 0.05 which was acceptable. From the value obtained in slope analysis, retaining was designed. The retaining wall designed possess a height of 14 m, top width of stem 5m and width of bottom stem 8m and a footing of 15 m long, the retaining wall also design with depth of key is 5m and 5m width. The wall designed passed all 3 factor of safety (sliding, overturning & bearing capacity) and finally the safety factor was computed in computer software (QuickRWall) to re-examine on its safety design.
6.0.
Conclusion
For the conclusion, soil sample from the site was classified to be of SW from the USCS classification system. The slope stability analysis has shown that the shear plane is at a factor of safety of 0.117. Thus, a designed has been proposed for a retaining wall structure which consist of a retaining wall supported by a footing and key to have more shear stability and moment stability.
40
7.0. REFERENCE
Abramson, L. W., Thomas, S., Sharma, L. S. & Boyce, G. M. (2001). Slope Stability and Stabilization Methods . Pg 1-2.
Bowles, J. E. (1984). Engineering Properties of Soil and Their Measurements. Singapore: McGraw Hill International Book Company.
Liu, C. and Evett, J. B. (2005). Soils and Foundations. Foundations. Singapore: Pearson Prentice Hall.
Mansour,
A.
E.,
2009.
Sieve
analysis .
[online]
Available
at:
[Accessed 12 October 2012].
Raj, P. P. (2003). Soil Mechanic & Foundation Engineering . India. Pg 445.
Robert, W. D. (2001). Soil Testing Manual: Procedures, Classification Data, and Sampling practices. New York: McGraw-Hill.
Shroff, A. V. and Dhananjay, L. S. (2003). Soil Mechanics and Geotechnical Geotechnical Engineering. Tokyo: Taylor & Francis. Singh, A., 1990. Soil Engineering In Theory and Practice. 2nd ed. New Delhi: CBS Publishers & Distributors.
41
8.0. APPENDICES
8.1. Method Of Slice 8.1.1. Graph Of Method Of Slice
42
8.2. Geostudio Result Of Slope Stability Bantayan Minintod (Loose Soil)
43
44
8.3. Geostudio Result Of Slope Stability Bantayan Minintod (Dense Soil)
45
46
8.4. QuickRWall Result 8.4.1. Design Detail
47
8.4.2. Stem Flexural Capacity
48
8.4.3. Stem Shear Capacity
49
