INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,  
MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)  
ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
Stability Analysis of Planned Disposal Slope Using Bishop Method at  
PT. XYZ  
1Efa Octavia Jawak, 2M. Eka Onwardana, 3Johana Sihol Marito Purba, 4Ruth Meivera Siburian,  
5Swingly Purba  
1,2 Department of Mining Engineering, Faculty of Technology Mineral, Institute Sains and Technology  
TD. Pardede Medan  
3,4,5 Department of Industrial Engineering, Faculty of Technology Industri, Institute Sains and  
Technology TD. Pardede Medan  
DOI : https://doi.org/10.51583/IJLTEMAS.2025.1412000064  
Received: 16 December 2025; Accepted: 24 December 2025; Published: 05 January 2026  
ABSTRACT:  
Mine disposal is a critical facility that requires a stable slope design to ensure operational safety and the  
sustainability of mining activities. This study aims to analyze the stability of the planned mine disposal design  
at PT. XYZ, South Sumatra, and to evaluate the necessity of design improvement through a resloping  
approach. The initial disposal design applied a slope angle of 35°. The slope stability analysis results indicate  
that, at several locations, this slope angle produced factor of safety (FoS) values below the required stability  
criteria, classifying the disposal slopes as unstable.  
As a mitigation measure against slope failure risks, the slope geometry was modified by reducing the slope  
angle to 20°. The evaluation results demonstrate that the implementation of resloping significantly increased  
the FoS values to meet the disposal slope stability criteria. Therefore, a disposal slope design with a 20°  
inclination is recommended as a safer alternative for implementation at PT. XYZ to enhance operational safety  
and reduce the potential for slope failure.  
Keywords: Mine Disposal, Slope Stability, Factor of Safety, Resloping, Mining Geotechnics.  
INTRODUCTION  
PT. XYZ is one of the coal mining companies operating in South Sumatra Province using an open-pit mining  
system. In open-pit mining activities, safe and optimal mine design planning is a critical factor that directly  
affects occupational safety, operational efficiency, and the sustainability of mining operations. One of the key  
components of mine design planning is the disposal design, which serves as a dumping area for overburden  
(OB) materials generated from mining activities.  
Mine disposal facilities are designed to accommodate large volumes of waste material; therefore, the stability  
of disposal slopes must be carefully planned and evaluated. Slope failure at disposal areas may result in serious  
consequences in terms of safety, operational disruptions, and environmental impacts. Consequently, each  
disposal design plan must undergo a geotechnical analysis to ensure that the proposed slope geometry yields  
factor of safety (FoS) values that satisfy the required slope stability criteria.  
In relation to the planned development of a new disposal area, PT. XYZ prepared an initial disposal slope  
geometry and requested a slope stability evaluation through geotechnical analysis. This analysis aims to assess  
whether the proposed design produces acceptable FoS values or still presents potential instability. In this study,  
slope stability analysis was conducted using the Slide software with the Bishop method, which is one of the  
widely applied limit equilibrium methods for slope stability assessment. The results of this analysis are  
expected to provide an overview of the stability level of the disposal design and to serve as a basis for  
recommending design improvements to enhance the safety and reliability of the mine disposal facility.  
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,  
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
Research Objectives  
This research aims to:  
Analyze the stability of mine disposal slopes in the initial design planned by PT. XYZ using  
geotechnical analysis.  
Determine the factor of safety (FoS) values of the disposal slopes generated from the initial design as a  
basis for assessing slope stability.  
Evaluate the safety level of the disposal design against potential slope failure based on the required  
slope stability criteria.  
Analyze the effect of slope geometry modification (resloping) on the improvement of the factor of  
safety of the disposal slopes.  
Provide recommendations for a safer disposal slope design based on the results of slope stability  
analysis using the Slide software with the Bishop method.  
LITERATURE REVIEW  
Slope Stability  
Slope stability is one of the most common issues encountered in mining construction engineering.  
Disturbances to slope stability can affect worker safety, cause environmental damage, damage mining  
equipment, reduce production intensity, and disrupt mining operations [1]. Therefore, slope stability analysis is  
essential to prevent failures caused by landslide hazards.  
Slope stability in mining activities is influenced by several factors, including local geological conditions, the  
overall geometry of the slope, external factors such as vibrations from blasting activities or operating  
mechanical equipment, and the excavation techniques used in slope formation. A commonly used approach to  
express the stability of a mining slope is through the factor of safety (FoS). This factor represents the ratio  
between resisting forces that maintain slope stability and driving forces that induce slope failure.  
The data required for a basic calculation of the factor of safety (FoS) include:  
1. Slope geometry data, which are primarily required to construct slope cross-sections, including slope angle,  
slope height, and haul road or berm width.  
2. Soil and rock mechanical properties, including:  
a. Internal friction angle (φ)  
b. Cohesion (c)  
c. Water content (ω)  
d. Rock density  
3. External factors, including:  
a. Vibrations resulting from blasting activities  
b. Loads from operating mechanical equipment  
Methods of Slope Stability Analysis  
One of the methods developed to analyze slope stability is the Limit Equilibrium Method (LEM). The limit  
equilibrium method evaluates the balance between resisting forces and driving forces acting on a slope. Slope  
stability analysis is expressed in terms of the factor of safety. This method presents fundamental principles for  
designing stable natural or artificial slopes, identifies potential failure mechanisms, and determines the factor  
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
of safety for specific geotechnical conditions. In the limit equilibrium method, slope stability conditions are  
expressed using a factor of safety index. The factor of safety is calculated using force equilibrium, moment  
equilibrium, or a combination of both approaches ([2]).  
Several calculation methods are included within the limit equilibrium framework, such as the Bishop  
Simplified method and the Janbu Simplified method. The analysis is performed by dividing the soil mass along  
the potential failure surface into slices; therefore, these approaches are also referred to as the method of  
slices[3]  
Bishop Simplified Method  
The Bishop Simplified method is widely used in slope stability analysis due to its simplicity, computational  
efficiency, and ability to produce sufficiently accurate factor of safety results ([4]). In this method, the normal  
forces at the base of each slice are determined from vertical force equilibrium. The method is applied to  
automatically search for critical circular failure surfaces in order to obtain the minimum factor of safety.  
A key requirement for applying the Bishop Simplified method is the accuracy and reliability of the input data.  
The parameters used in the analysis must represent actual field conditions. Strength parameters and  
groundwater data must be derived from appropriate site investigations, as these parameters significantly  
influence the calculated factor of safety. The pore water pressure ratio plays an important role in determining  
slope stability, as it directly affects the resulting factor of safety values.  
Where:  
ru= Pore Water Pressure Ratio  
γ = Unit Weight of Soil (kN/m²)  
u = Pore Water Pressure (kN/m²)  
h = Average Slice Height (m)  
b= Width of the i-th Slice (m)  
From a mathematical standpoint, this method can be expressed as follows:  
FK = Factor of Safety  
α
= Inclination angle of the i-th slice (°)  
= Effective soil cohesion (kN/m²)  
= Width of the i-th slice (m)  
c
b
Wᵢ  
Φ’  
Uᵢ  
= Weight of the i-th soil slice (kN)  
= Effective internal friction angle (°)  
= Pore water pressure of the i-th slice (kN/m²)  
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,  
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
The value of FK in the above equation appears on both the left-hand side and the right-hand side. Therefore, to  
calculate the magnitude of the factor of safety, a trial-and-error method must be used by assuming an initial  
value of the factor of safety.  
Relationship between the Slope Safety Factor (FK) and Slope Stability  
Slope failure in mining operations generally occurs along a specific surface known as the slip surface. Slope  
stability depends on the driving forces and resisting forces acting along this slip surface.  
The resisting force is the force that counteracts and prevents slope failure, whereas the driving force is the  
force that causes slope failure to occur. The ratio between the resisting forces and the driving forces acting on  
the soil mass is referred to as the safety factor (FK) of the mining slope.  
Systematically, the safety factor of a slope can be expressed by the following equation:  
The basic concept of the relationship between the forces acting to obtain the factor of safety value for a slope  
slice is as follows:  
Mathematically, the factor of safety equation presented above can be formulated as follows:  
Description:  
τ = Resisting forces  
S = Driving forces  
L = Length of the slip surface  
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W = Total weight of the slice  
c = Cohesion  
α = Inclination angle of the slip surface  
φ = Internal friction angle  
Limit Equilibrium Method  
The Limit Equilibrium Method has been used for several decades to safely design geotechnical structures [5]  
The Simplified Bishop Method is one of the most commonly used limit equilibrium methods for analyzing  
slope stability [6]. Although the Bishop method is considered less rigorous in slope stability analysis because it  
does not account for horizontal force equilibrium, this method is relatively simple and practical to apply. In  
many cases, it produces results with acceptable accuracy [4]  
DISCUSSION  
Results of Physical Properties Testing  
Physical properties testing was conducted to determine the physical properties of the lithology in the study  
area. The physical properties data used in this study are obtained from tests carried out by PT XYZ, as  
presented in the table below.  
Results of Mechanical Properties Testing  
Mechanical properties testing was conducted to obtain the values of the internal friction angle and cohesion,  
which were subsequently used as material input parameters in slope stability analysis. The results of the rock  
mechanical properties tests were obtained from laboratory testing conducted by PT. XYZ and are presented in  
the table below.  
Cohesi (Kpa), Residual  
Max Average  
84.6 38.84  
Sudut Geser Dalam (o), Residual  
Litology  
Claystone  
Min  
11.8  
Min  
6.11  
Max  
22.15  
Average  
13.66  
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XIV, Issue XII, December 2025  
Siltstone  
Sandstone  
Coal  
20.6  
4.9  
82.9  
115.4  
113.8  
40.88  
41.73  
67.87  
13.87  
8.47  
6.67  
28.9  
23.8  
30.9  
21.93  
17.4  
19.9  
16.1  
Research Layout Map  
The geotechnical analysis was conducted on Sections A–E, as shown in the figure below.  
Factor of Safety Analysis  
To analyze slope stability and ensure safe slope conditions, slope design modeling was carried out to  
determine the Factor of Safety (FoS) using Rocscience Slide v6 software, as shown in the figure below. The  
analysis employed the Bishop method, incorporating material definition data based on the results of the  
mechanical properties testing described above.  
Section A–A’  
Based on the geotechnical analysis of the disposal design plan for Pit 6 at Section A–A’, a Factor of Safety  
(FoS) value of 2.29 was obtained. According to the Regulation of the Minister of Energy and Mineral  
Resources of the Republic of Indonesia No. 1827 of 2018, the Factor of Safety for waste dumps shall be  
calculated using residual cohesion and residual internal friction angle values, with a minimum FoS of 1.5.  
Therefore, Section A–A’ can be classified as stable.  
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Section B–B’  
Based on the geotechnical analysis conducted at Section B–B’, a Factor of Safety (FoS) value of 1.062 was  
obtained. This indicates that Section B–B’ is unstable. Therefore, resloping is required to improve the  
stability of Section B–B’.  
Section C–C’  
Based on the geotechnical analysis of Section C–C’, a factor of safety (FK) value of 3.1 was obtained,  
indicating that Section C–C’ is considered stable.  
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Section D–D’  
Based on the geotechnical analysis of Section D–D’, the factor of safety (FK) obtained is 1.191 for the right  
side and 1.092 for the left side. These values indicate that the disposal slope at Section D–D’ is unstable.  
Therefore, resloping is required for this section.  
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Based on the geotechnical analysis of Section E–E’, the factor of safety (FK) obtained is 1.42 for the right side  
and 1.398 for the left side. These values indicate that the disposal slope at Section E–E’ is unstable. Therefore,  
resloping is required for Section E–E’.  
Results of Back Analysis  
Results of Resloping Analysis for Section B–B’  
To obtain a stable factor of safety (FK), a change in the slope angle was carried out. The initial slope angle of  
35° was modified to 20°. The resulting FK value after resloping is 1.509. Therefore, the disposal slope can be  
considered stable.  
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Results of Resloping Analysis for Section D–D’  
To obtain a safe factor of safety (FK), the slope angle was modified. The initial slope angle of 35° was  
changed to 20°. The resulting FK values after resloping are 1.509 for the left side and 1.546 for the right side  
of the slope. Therefore, the disposal slope can be considered stable.  
RECOMMENDATIONS  
1. For the mudtrap position at Section B–B’, it is recommended to provide sufficient spacing so that it is  
not located too close to the disposal face.  
2. For Sections B–B’, D–D’, and E–E’, it is recommended to use a slope angle of 20°, a bench width of  
15 meters, and a bench height of 10 meters in order to achieve a factor of safety (FK) greater than 1.5.  
3. Sections A–A’ and C–C’ have stable FK values using the originally planned geometry, with a slope  
angle of 35°.  
CONCLUSION  
Based on the results of the slope stability analysis conducted on the planned mine disposal design, it is found  
that the initial disposal geometry does not yet meet the required factor of safety criteria. This condition  
indicates a potential slope instability that may increase the risk of slope failure, particularly under long-term  
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loading conditions and the influence of external factors such as rainfall and the mechanical properties of the  
disposal material.  
Design improvement efforts through the application of the resloping method have proven effective in  
increasing the disposal slope factor of safety to values exceeding the recommended minimum limit.  
Modifications to the slope geometry, especially in terms of slope angle and bench height, provide a more  
stable stress distribution and reduce the driving forces that may lead to slope failure.  
Therefore, the implementation of resloping can be recommended as an effective technical solution to enhance  
the stability of mine disposal slopes. The results of this study emphasize the importance of periodic  
geotechnical evaluations of disposal designs to ensure operational safety, the sustainability of mining  
activities, and the mitigation of environmental risks in mining areas.  
REFERENCES  
1. J. R. Almenara dan H. D. Lelono, “Batu Hijau Open Pit Slope Design Based on Geotechnical  
Models and Past Performance.”  
2. “Metode Irisan-ii.”  
3. S. Lereng Dengan Jenis Tanah Lempung Berpasir pada Kondisi Tidak Jenuh, K. Jenuh Sebagian,  
dan Kondisi Jenuh Yota Pentawan, dan L. Afriani, “Simulasi Penggunaan Program Geostudio  
Slope/W 2007 dalam Menganalisis,” 2017.  
4. A. W. Bishop, “First Technical Session: General Theory oj Stability of Slopes the Use of The Slip  
Circle in The Stability Analysis of Slopes,” 1954.  
5. F. P. Dwikasih dkk., “Pengaruh Struktur Ketidakmenerusan Pada Kestabilan Lereng Penggalian  
Batuan.”  
6. O. A. Cherianto Parluhutan Rajagukguk Turangan dan S. Monintja, “Analisis Kestabilan Lereng  
Dengan Metode Bishop (Studi Kasus: Kawasan Citraland sta.1000m),” Jurnal Sipil Statik, vol. 2,  
no. 3, hlm. 139–147, 2014.  
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