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    ICCBT 2008 - E- (37) pp449-468

    ICCBT2008

    Probabilistic Approach of Rock Slope Stability Analysis Using

    Monte Carlo Simulation

    M. S. Mat Radhi,Universiti Putra Malaysia,MALAYSIA

    N. I. Mohd Pauzi*, Universiti Tenaga Nasional,MALAYSIA

    H. Omar, Universiti Putra Malaysia,MALAYSIA

    ABSTRACT

    ___________________________________________________________________________

    Probabilistic analysis has been used as a tool to analyze and model variability and

    uncertainty for rock slope analysis. Uncertainty in rock slope may appear as scattered values

    of discontinuity length and persistence. This study is to develop the probabilistic approach of

    rock slope stability based on discontinuity parameters using Monte Carlo simulation. The

    probabilistic analysis was done using kinematic and kinetic analysis. Kinematic analysis is

    based on stereographic projection analysis and kinetic analysis is based on the deterministic

    analysis. Factor of Safety (FOS) is determined for each type of failure i.e. planar and wedgefailure. The slope that has FOS less than 1.00 is considered as not stable and FOS more than

    1.00 is considered as stable. Data of six slopes which is denoted as Slope S1, S2, S3, S4, S5

    and S6 show that, Slope S2, Slope S4, and Slope S6 have FOS of 0.953, 0.991, and 0.891

    respectively which show the slope as not stable. Whilst for wedge failure analysis, all the

    slopes show FOS greater than 1.00 which is stable, although the kinematic analysis

    (stereographic projection) shows otherwise. Probabilistic analysis is developed for rock slope

    stability using Monte Carlo Simulation. Monte Carlo simulation calculate the probability of

    failure for planar and wedge type of failure. The probability of failure (Pf) for planar failure

    at slope S2, S4, and S6 are 51.6%, 17.8%, and 49% respectively. Wedge failure analysis show

    0% probability of failure for dry slope cases while for wet slope cases, all slopes excluded the

    S1 has the probability of failure (Pf) varies from 7.7% to 75.2%. This shows that theprobabilistic analysis will give relevant and enhance results which can help to determine

    instability of rock slope. The development of probabilistic analysis using Monte Carlo

    simulation is useful tool to get an accurate data in stability analysis of rock slope which have

    great values of uncertainty.

    Keywords: Probabilistic Approach, Monte Carlo Simulation, Rock slope stability

    *Correspondence Authr: Nur Irfah Mohd Pauzi, Universiti Tenaga Nasional, Malaysia. Tel: +60389212020 ext

    6254, Fax: +60389212116. E-mail: [email protected]

    http://www.uniten.edu.my/newhome/content_list.asp?contentid=4017
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    1. INTRODUCTION

    Uncertainty and variability are common in engineering geology studies dealing with natural

    materials. This is because of rocks and soils are inherently heterogeneous, insufficient amount

    of information for site conditions are available and the understanding of failure mechanism isincomplete. There are many researcher have made efforts to limit or quantify uncertainty of

    input data and analysis results. Perhaps, slope engineering is the geotechnical subject most

    dominated by uncertainty since slopes are composed of natural materials [2]. Uncertainty in

    rock slope engineering may occur as scattered values for discontinuity orientations and

    geometries such as discontinuity length and persistence. Therefore, one of the greatest

    challenges for rock slope stability analysis is the selection of representative values from

    widely scattered discontinuity data. Since geotechnical engineering problems are

    characterized by uncertain variables, design is always subjected to uncertainties

    Application of probabilistic analysis has provided an objective tool to quantify and model

    variability and uncertainty. It makes the rock slope stability possible to consider uncertaintyand variability in geotechnical and geological parameters. There is several commercial

    available limit equilibrium codes (such as SWEDGE, ROCKPLANE, SLIDE, SLOPE/W)

    often incorporate probabilistic tools, in which variations in discontinuity properties can be

    assessed.

    Various probabilistic studies of rock slopes and mining areas have been carried out by these

    researchers [10, 11, 1, 9, 5, 6, 7, 14].Though in Malaysia, such research are very few and

    limited.

    In summary, this study is to determine probabilistic analysis of rock slope stability based on

    discontinuity parameters which is analyze and simulate probabilistic analysis method. Hence,

    it would become helpful for the engineers to design and monitor the rock slope. The main aim

    of this research is to determine probabilistic analysis of rock slope stability based on

    discontinuity parameters which will help the slope engineers in rock slope design and stability

    analysis.

    2. BASIC THEORY

    The development of road and highway constructions involved deep cutting into the slope, in

    order to minimize the traveling time and distance between the two places. Besides, the need of

    development on hilly areas for building and residential purpose has also increased and theselead to the concern of safety and stability of the slope for the public. The slope failure occur

    due to human and natural causes which consist of improper planning, design and

    implementation of the projects for human error while natural causes may be result of

    weathering process, weak material and geological setting of the area.

    In this research, cutting of rock slope is the major concern to be studied since a high degree of

    reliability is required because slope failure or even rock falls can rarely be tolerated. Rock

    slope stability is concern about analyzing the structural fabric of the site to determine if the

    orientation of the discontinuities could result in instability of the slope under consideration.

    Basically, there are four types of rock slope failures that always occurred at the rock slope

    which are planar failure, wedge failure, toppling failure, and circular failure.

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    Planar failure is movement occurs by sliding on a single discrete surface that approximates a

    plane and it is analyzed as two-dimensional problems which additional discontinuities may

    define the lateral extent of planar failures, but these surfaces are considered to be release

    surfaces, which do not contribute to the stability of the failure mass. Wedge failure happenedwhen rock masses slide along two intersection discontinuities both of which dip out of the cut

    slope at an oblique angle to the cut face, forming a wedge-shaped block. Toppling failure

    happened most commonly in rock masses that are subdivided into a series of slabs or columns

    formed by a set of fractures that strike approximately parallel to the slope face and dip steeply

    into the face. Circular failure is defined as a failure in rock for which the failure surface is not

    predominantly controlled by structural discontinuities and that often approximately the arc of

    a circle. Rock types that are susceptible to circular failures include those that are partially to

    highly weathered and those that are closely and randomly fractured.

    Applications of probabilistic analysis in geotechnical engineering have increased remarkably

    in recent years. This is ranging from practical design and construction problems to advancedresearch publications. A lot of study and research have been conducted regarding probabilistic

    analysis since geotechnical and geological engineering deal with material whose properties

    and spatial distribution are poorly known. Consequently, a somewhat different philosophical

    approach is necessary to overcome the uncertainty occurs in geotechnical and geological

    engineering.

    This paper explains on determining probability of failure of the rock slope which deals with

    the uncertainty in geotechnical and geological engineering parameter using Monte Carlo

    simulation. The Monte Carlo simulation used the extensive computational effort involved in

    the simulations required researchers to develop their own software to solve slope stability

    problems. The limitations and sometimes the complexities of probabilistic methods combined

    with the poor training of most engineers in statistic and probabilistic theory have substantially

    inhibited the adoption of probabilistic slope stability analysis in practice.

    3. METHODOLOGY

    Methodology of the research can be described by four stages; the first one is literature search

    and formulation of objective, the second one is data collection at the field, the third one is

    analysis and overview on the data collection and finally, the fourth stage is the developmentof the probabilistic approach using Monte Carlo simulation and finally suggestion for further

    work to be done for this research. The flow chart of the methodology is shown in Figure 1.

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    Figure 1. Methodology of the research

    The data collections at site are such as discontinuity data on the cut slope, classification and

    identification of grade weathering and lithology of the selected cut slope. Then, the analysis

    on the fieldwork data is done using kinematic analysis and kinetic analysis. The kinematic

    analysis is done using the data collection of geological structural at site. The DIPS 3.0

    software is used to give the analysis in Rosette Plot, Scatter Plot, Pole Plot, and Potential

    Instability.

    Limit equilibrium method which is also known as kinetic analysis is carried out to determine

    factor of safety for each cases of potential instability. The probabilistic approach is developed

    using Monte Carlo Simulation Method for rock slope stability analysis. The development of

    this probabilistic approach is done using spreadsheet software such as EXCEL and

    probabilistic simulation is done using RISKAMP. These two software are link together and

    the analysis is simulated which is called Monte Carlo Simulation.

    Probabilistic approach is carried out by simulating the results according to number of

    iteration. For each number of iteration, it would give the Factor of Safety (FOS) from where

    the probability of failure can be obtained. The simulation carried out here are for 10, 100, 500,

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    1000, 5000, and 10000 no of iteration. The input data needed for the development of

    probabilistic approach is the kinematic and kinetic analysis data. The kinematic analysis

    inputs are the dip and dip direction data, friction angle, cohesion, and slope angle. The outputs

    data are the type of failure of the slope whether it is planar, wedge, toppling or combination of

    the two type of failure.

    The kinetic analysis requires input data such as slope properties, cohesion, friction angle, and

    groundwater table. The outputs from this analysis are the FOS of the slope. If FOS is less than

    1, the slope is considered fail and if the FOS is more than 1, the slope is stable. The output

    from kinetic analysis only gives one value of FOS. Then, when the simulation is carried out

    for 10 times, 100 times, 500 times, 1000 times, 5000 times and 10000 times, the RiskAMP

    software would gives many results of FOS and probability of failure, Pf for that particular

    slope.

    4. RESULTS AND ANALYSIS

    4.1 Pos Selim Area

    The probabilistic analysis which is developed for this study has been tested using data from

    Pos Selim Highway. This probabilistic analysis is used to get accurate result and to determine

    the uncertainties in geotechnical data. The probabilities of failure of the slope are the outcome

    of this research.

    Pos Selim Highway is located in Perak and can be accessed from Simpang Pulai or Cameron

    Highland. The highway is part of the Malaysian Plan for East West second Link and divided

    into eight packages. The highway starts from Simpang Pulai in Perak and ends at Kuala

    Berang in Terengganu. Package two has been awarded to MTD Construction Sdn. Bhd. under

    a Fixed Turnkey Lump Sum contract of total RM 282 million. The construction of the

    highway in package two has started in May 1997 and was scheduled for completion in April

    2000 [8]. Due to continuous cut slope failure along the highway, the construction of this

    project was delayed [12]. Now in the year of 2005, the project has been opened to be used for

    the public.

    Along the terrain of Pos Selim Highway, there are two types of main lithological units which

    are igneous and metasediment rock (Figure 4.1). The igneous rocks consist of granite and

    metasediment rocks consist of quartz mica schist, quartz schist and closely foliated phylite.Granite rock covers over 65% while metasediment is about 35% [8].

    Locations of slope study are distributed over three granite slopes and three schist slopes.

    These slopes have been labeled as a S1, S2, and S3, which cover the granitic areas and S4, S5,

    and S6 cover the schist areas (Table 1).

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    S

    S

    Figure 2. Pos Selim Area with granite and schist formation

    Table 1: Study Locations and Lithology

    Slope Location Lithology

    S1 Ch 2 + 960 Granite

    S2 Ch 9 + 100 Granite

    S3 Ch 17 + 600 Granite

    S4 Ch 18 + 280 Schist

    S5 Ch 18 + 800 Schist

    S6 Ch 20 + 750 Schist

    4.2 Kinematic Analysis

    Kinematic analysis is done to plot the discontinuity data such as dip and dip direction into

    graphical method. The graphical method which are discussed in this analysis are pole plot,

    rosette plot, scatter plot. From these plots, the potential instability for each slope can be

    determined.

    4.2.1 Pole plot

    From the six slopes that have been chosen for study, about 637 of discontinuity data have

    been collected for analysis. From Figure 3, it can be seen that joint is the most dominant and

    common at field, followed by fault and lastly foliation. The percentage occurrence of joint

    from field measurement is 79.7%, while fault is 10.9% and another 9.4% is foliation. S1, S2

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    0

    20

    40

    60

    80

    100

    120

    S1 S2 S3 S4 S5 S6

    Joint Fault Foliat ion

    (Figure 4), and S3 show that joint is dominant and higher which are 97%, 81%, and 97%

    respectively from field measurement. S4, S5 (Figure 5), and S6 show that percentage of joint

    decrease which is 63%, 70%, and 67% respectively.

    Figure 3. Discontinuity data showing percentage of joint, fault and foliation at S1, S2, S3, S4,

    S5 and S6.

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    Figure 4. Pole Plot at S2

    Figure 5. Pole Plot at S5

    4.2.2 Scatter Plot Analysis

    Scatter plot data (Figures 6) collected for six numbers of slopes, the total number of plot is

    584. Table 2 has summarized scatter plot for each slope which shows three category of plot;

    one, two, and three plots. The importance of the scatter plot is to distinguish any discontinuity

    data that have the same value of dips and dips direction, where in pole plot it does not show

    the poles that share the same value.

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    Figure 6: Scatter plot data

    Table 2. No. of Scatter plot for each study slope

    Slope One Plot() Two Plot() Three Plot() Total Plot

    S1

    S2

    S3

    S4

    S5

    S6

    89

    98

    91

    85

    81

    94

    10

    7

    4

    6

    9

    3

    1

    1

    1

    1

    3

    0

    100

    106

    96

    92

    93

    97

    Total 538 39 7 584

    4.2.3 Rosette PlotAnalysis

    There are 525 of planes out of 637 discontinuities that have been plotted into rosette plot

    (Figure 7) covering S1, S2, S3, S4, S5, and S6. Dips direction of each slope is plotted into

    respected bin at interval of 10 degrees. Table 3 shows the maximum and minimum

    frequencies of plotted plane for each slope, which are 10 and 1 respectively. Each slope has

    only two bin of maximum frequency, whilst the number of bin for minimum frequency varies

    between two and four.

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    Figure 7. Rosette Plot

    Table 3. No of plotted plane in Rosette Plot for each study slope

    SlopePlotted

    Planes

    Maximum Plot

    (Bin No)

    Minimum

    Plot (Bin No)

    Total

    Discontinuity

    S1 92 6a& 24a 4c, 12c, 16c, 22c, 29c, &

    34c112

    S2 98 7b& 25b 1c, 5c, 13c, 19c, 23c,&

    31c115

    S3 92 13a& 31a 6c, 10c, 24c, & 28c 102

    S4 79 7a& 25a 4c, 5c, 9c, 21c, 22c, &

    27c100

    S5 84 6a& 24a 4d, 11d, 14d, 22d, 29d, &

    32d108

    S6 80 18a& 36a 8c, 16c, 26c, & 34c 100

    Total 525 118 38 637

    a = frequency of 10, b = frequency of 9, c = frequency of 1, d = frequency of 2.

    4.2.4 Potential Instability

    Potential instability analysis is determined using stereoplot computer software, DIPS. This

    analysis facilitates the determination of possible kinematic sliding of weathered rock slope in

    types of planar, wedge, and toppling failure. Planar and wedge failure analysis is referred to

    the work by Hoek and Bray [4], but toppling failure analysis is referred to Goodman and Bray

    [3].

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    Table 4 Continue

    5-6% 86/122 J1 Joint Granite

    S3 >10% 68/220 J2 Joint Granite

    CH 17600 3-4% 52/79 J3 Joint Granite

    7-8% 71/313 J4 Joint Granite

    8-9% 45/87 J1 Joint Schist

    S4 6-7% 65/322 J2 Joint Schist

    CH 18280 6-7% 74/208 J3 Joint Schist

    6-7% 66/237 J4 Joint Schist

    >12% 35/98 J1 Foliation Schist

    S5 10.5-12% 71/252 J2 Joint Schist

    CH 18800 4.5-6% 87/176 J3 Joint Schist

    4.5-6% 62/315 J4 Joint Schist

    >10% 62/261 J1 Joint Schist

    S6 7-8% 19/191 J2 Joint SchistCH 20750 6-7% 68/292 J3 Joint Schist

    4.3 Kinetic Analysis

    Kinetic analysis is carried out by applying direct formula using single fixed values (typically,

    mean values). Therefore, the stability analysis is carried out using only one set of geotechnical

    parameter. Factor of safety, based on limit equilibrium is widely used to evaluate slope

    stability because of its simple calculation and results.

    From this study, three slopes out of six slopes have been identified potential planar failure

    which is S2, S4, and S6. Through these three slopes, only three joint sets have fall and satisfy

    with conditions for planar failure. Table 5 below shows factor of safety for each joint set for

    wet and dry case for planar failure.

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    Table 5. Results of Factor of Safety for Planar Failure

    SlopeJoint Set

    I.D.

    Slope

    Face

    (deg)

    Planar

    Failure

    (deg)

    Mean Friction

    Angle (deg)

    Factor of

    Safety

    (Wet)

    Factor of

    Safety

    (Dry)J1 77 30 Stable Stable

    J2 80 30 Stable Stable

    J3 33 30 Stable Stable

    S1

    J4

    63

    72 30 Stable Stable

    J1 59 30 0.879 0.953

    J2 82 30 Stable Stable

    J3 80 30 Stable Stable

    S2

    J4

    63

    48 30 Stable Stable

    J1 86 30 Stable Stable

    J2 68 30 Stable Stable

    J3 52 30 Stable Stable

    S3

    J4

    73

    71 30 Stable Stable

    S4 J1 63 45 30 0.899 0.991

    J2 65 30 Stable Stable

    J3 74 30 Stable Stable

    J4 66 30 Stable Stable

    S5 J1 102 35 30 Stable Stable

    J2 71 30 Stable Stable

    J3 87 30 Stable Stable

    J4 62 30 Stable Stable

    S6 J1 63 62 30 0.767 0.891

    J2 19 30 Stable Stable

    J3 68 30 Stable Stable

    For wedge planar failure case, five slopes have been identified potential to fail which are S2,

    S3, S4, S5, and S6. Nine intersections of joint sets have been identified and satisfied for this

    type of failure. The results for factor of safety for each intersection joints are shown in Table

    6 below for wet and dry case.

    Table 6. Results of Factor of Safety for Wedge Failure

    SlopeIntersection

    Joint

    Slope Face

    (deg)

    Dip of

    intersection

    (deg)

    Mean

    Friction

    Angle (deg)

    Factor of

    Safety

    Factor of

    Safety

    (Dry)J1J2 58 30 1.296 Stable

    J1J3 36 30 1.411 Stable

    S2

    J1J4

    63

    33 30 Stable Stable

    J3J1 43 30 0.931 StableS3

    J3J4

    73

    48 30 0.999 Stable

    S4 J1J3 63 56 30 1.395 Stable

    J2J3 17 30 1.434 StableS5

    J3J4

    102

    38 30 0.831 1.572

    S6 J1J3 63 30 30 Stable Stable

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    0

    0.5

    1

    1.5

    2

    2.5

    10 100 500 1000 5000 10000

    No of Iter ation

    Mean

    ofFoS

    Wet Slope Dry slope

    Figure 9. Mean of FOS at J1J2, S2 for each iteration.

    0

    0.2

    0.4

    0.6

    0.8

    1

    10 100 500 1000 5000 10000

    No of Iteration

    Pf

    Wet Slope Dry Slope

    Figure 10. Probability of wedge failure at J1J2, S2 for each iteration.

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    0

    0.5

    1

    1.5

    2

    2.5

    1.44

    1.56

    1.68 1.

    81.92

    2.04

    2.16

    2.28 2.

    42.52

    2.64

    Factor of Safety

    Frequency

    0

    0.5

    1

    1.5

    2

    2.5

    3

    3.5

    0.27

    0.39

    0.51

    0.63

    0.75

    0.87

    0.99

    1.11

    1.23

    1.35

    1.47

    Factor of Safety

    Frequency

    0

    2

    4

    6

    8

    10

    12

    14

    1.38

    1.54 1.

    71.86

    2.02

    2.18

    2.34 2.

    52.66

    2.82

    2.98

    Factor of Safety

    Frequency

    0

    2

    4

    6

    8

    10

    12

    0.17

    0.33

    0.49

    0.65

    0.81

    0.97

    1.13

    1.29

    1.45

    1.61

    1.77

    Factor of Safety

    Frequency

    0

    10

    20

    30

    40

    50

    60

    70

    1.29

    1.47

    1.65

    1.83

    2.01

    2.19

    2.37

    2.55

    2.73

    2.91

    3.09

    Factor of Safety

    Frequency

    0

    10

    20

    30

    40

    50

    60

    70

    0.07

    0.25

    0.43

    0.61

    0.79

    0.97

    1.15

    1.33

    1.51

    1.69

    1.87

    Factor of Safety

    Frequency

    (a) Wedge Failure Wet Slope (left) and Dry Slope (right) for 10 iteration

    (b) Wedge Failure Wet Slope (left) and Dry Slope (right) for 100 iteration

    (c) Wedge Failure Wet Slope (left) and Dry Slope (right) for 500 iteration

    Figure 11. Histogram of FOS calculated in probabilistic analysis for combination of joint set 1

    and 2 at S2.

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    0

    200

    400

    600

    800

    1000

    1200

    1400

    1 .2 4 1 .4 4 1 .6 4 1 .8 4 2 .0 4 2 .2 4 2 .4 4 2 .6 4 2 .8 4 3 .0 4 3 .2 4

    Factor of Safety

    Frequency

    0

    200

    400

    600

    800

    1000

    1200

    1400

    0 .0 4 0 .2 4 0 .4 4 0 .6 4 0 .8 4 1 .0 4 1 .2 4 1 .4 4 1 .6 4 1 .8 4 2 .0 4

    Factor of Safety

    Frequency

    0

    20

    40

    60

    80

    100

    120

    1.31

    1.49

    1.67

    1.85

    2.03

    2.21

    2.39

    2.57

    2.75

    2.93

    3.11

    Factor of Safety

    Frequency

    0

    20

    40

    60

    80

    100

    120

    140

    0.06

    0.26

    0.46

    0.66

    0.86

    1.06

    1.26

    1.46

    1.66

    1.86

    2.06

    Factor of Safety

    Frequency

    0

    100

    200

    300

    400

    500

    600

    700

    1.2

    1.4

    1.6

    1.8 2

    2.2

    2.4

    2.6

    2.8 3

    3.2

    Factor of Safety

    Frequency

    (d) Wedge Failure Wet Slope (left) and Dry Slope (right) for 1000 iteration

    0

    100

    200

    300

    400

    500

    600

    700

    -0.01

    0.19

    0.39

    0.59

    0.79

    0.99

    1.19

    1.39

    1.59

    1.79

    1.99

    Factor of Safety

    Frequency

    (e) Wedge Failure Wet Slope (left) and Dry Slope (right) for 5000 iteration

    (f) Wedge Failure Wet Slope (left) and Dry Slope (right) for 10000 iteration

    Figure 11: Histogram of FOS calculated in probabilistic analysis for combination of joint set 1

    and 2 at S2 (continued).

    The result could be interpreted that the increase in the number of iteration in Monte Carlo

    simulation, the result becomes even details and thus increase the accuracy of calculation of

    factor of safety of the rock slope. Probability of failure for dry slope at slope S2 is zero which

    means the slope is stable and when the slope in wet condition, the probability of failure is in

    the range of 0.752 to 0.802.

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    5. CONCLUSIONS

    For the planar failure shown in Table 8 for 10000 number of iteration, deterministic

    analysis of J1 at S2 gives 0.879 and 0.953 for wet and dry slope cases, while in probabilistic

    analysis it gives 76.3% and 51.6% respectively. For J1 at S4, deterministic analysisshows the lowest values of FOS; 0.899 and 0.991. But probabilistic analysis gives

    the result of 38% and 17.8% for wet and dry slope cases. For planar failure of J1 at S6 gives

    the high values of probability failure which is 62.9% and 49% and deterministic analysis

    results are 0.767 and 0.891 respectively. These indicate that the slope has high possibility

    of planar failure at J1 for S2 and S6, compare to J1 of S4. The Slope of S2, S4, and S6 also

    show that probability of failure is high even the slopes are in dry condition.

    For wedge analysis shown in Table 9 for 10000 number of iteration, high probability of

    failure are determined at J1J2 and JIJ3 of S2, with 75.2 % and 57.9% respectively,

    J3J4 of S3 with 48.2%, and J 1J3 o f S4 with 43% . Eve n deterministic values show

    the FOS is more and equal to 1.00, it still has a higher probability to fail in these

    circumstances. For example in slope S2 for wedge failure in Table 9, the FOS values is 1.434

    but the probabilistic analysis result show otherwise where its probability of failure is 0.77 for

    wet slope. This means that although factor of safety calculation said the slope is stable but the

    probabilistic analysis run using Monte Carlo has detailed out the calculation and indicates the

    slope is not stable.

    Others intersection shows the lower results of probabilistic analysis with less than 40% for

    each cases. The probabilistic analysis for wedge failure show that in dry condition, the value

    of Pfis equal to 0, which mean that the slope is stable.

    Table 8. Comparison of results for the deterministic and probabilistic analysis

    (iteration of 10000) for planar failure

    Deterministic ProbabilisticJoint Set Potential

    Slope Analysis (FOS) Analysis (Pf)

    InstabilityI.DWet Dry Wet Dry

    J1 No Stable Stable 0 0

    J2 NoStable Stable 0 0

    S1J3 Planar Stable Stable 0 0

    J4 No Stable Stable 0 0

    J1 Planar 0.879 0.953 0.763 0.516

    S2 J2 No Stable Stable 0 0

    J3 No Stable Stable 0 0

    J4 No Stable Stable 0 0

    J1 No Stable Stable 0 0

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    Table 8 continue

    S3 J2 No Stable Stable 0 0

    J3 Planar Stable Stable 0 0

    J4 No Stable Stable 0 0

    J1 Planar 0.899 0.991 0.38 0.178

    S4 J2 No Stable Stable 0 0

    J3 No Stable Stable 0 0

    J4 No Stable Stable 0 0

    J1 Planar Stable Stable 0 0

    S5 J2 No Stable Stable 0 0

    J3 No Stable Stable 0 0

    J4 No Stable Stable 0 0

    J1 Planar 0.767 0.891 0.629 0.49

    S6 J2 No StableStable 0

    0

    J3 No Stable Stable 0 0

    Table 9. Results of wedge failure for the deterministic analysis and the

    probabilistic analysis (iteration of 10000)

    Deterministic Probabilistic

    Set Set PotentialSlope No. I No. 2 Instability Analysis (FOS) Analysis (Pf)

    Wet Dry Wet Dry

    S1 J2 J3 No Stable Stable 0 0

    J1 J2 Wedge 1.296 Stable 0.752 0

    S2 J1 J3 Wedge 1.411 Stable 0.579 0

    J1 J4 Wedge Stable Stable 0.203 0

    J3 J4 Wedge 0.999 Stable 0.482 0

    S3 J3 J1 Wedge 0.931 Stable 0.203 0

    S4 J1 J3 Wedge 1.395 Stable 0.43 0

    J3 J2 Wed e 1.434 Stable 0.77 0S5 J3 J4 Wedge 0.831 1.572 0.386 0

    S6 J1 J3 Wedge Stable Stable 0.32 0

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    Acknowledgements

    The authors would like to thanks Universiti Putra Malaysia (UPM) for the funding of this

    project and Universiti Tenaga Nasional (UNITEN) for their constant support andencouragement.

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