SINDH ENGRO COAL MINING COMPANY
DRAFT TECHNICAL NOTE ON SLOPE
STABILITY ANALYSES FOR REVISED
DUMPSITE GEOMETERY
Doc No. J-909/SS/02-R00
MARCH 2025
HEAD OFFICE: 24 D1, NESPAK COLONY PHASE-1, LAHORE
PHONE: +92 42 35181331-3
EMAIL: berkeley.associates@yahoo.com
BRANCH OFFICE:
108, LUXUX MALL, GULBERG GREENS,
ISLAMABAD
PHONE: +92 314 5108150
EMAIL: aqadeer.berkeley@gmail.com
TABLE OF CONTENTS
1.
2.
INTRODUCTION ....................................................................................................... 2
1.1.
General.............................................................................................................. 2
1.2.
Background ....................................................................................................... 2
1.3.
Objectives .......................................................................................................... 3
1.4.
Site Conditions .................................................................................................. 3
METHODOLOGY ...................................................................................................... 5
2.1.
Slide2 Analysis .................................................................................................. 5
3
RESULTS AND DISCUSSION ................................................................................... 7
4
CONCLUSION ........................................................................................................ 12
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1. INTRODUCTION
1.1.
General
Sindh Engro Coal Mining Company (SECMC), hereinafter called as the Client, has been
granted a 30-year Mining Lease for Thar Block-II by Mines & Minerals Development
Department, Government of Sindh that is further extendable to 30 years. Currently,
SECMC is operating a 7.6 Mt/a open pit lignite coal mine in Block II, Tharparkar. SECMC
uses truck and shovel method to remove overburden (waste) and produce lignite coal
The overburden is being dumped in-pit and ex-pit waste dump location. The height of
individual lift is 20 m and slope angle ranges between 37° to 39°. Waste dump material
includes Clay, silt and sand.
A significant concern has arisen at the Ex-Pit dump, located adjacent to the Mine, due to
increased rainfall spells causing flooding, blowouts, and large-scale water accumulation.
The resulting soil erosion and landslides are damaging critical infrastructure. Currently, the
Ex-Pit dump lacks a surface runoff drainage system, leaving mine infrastructure and local
farmlands vulnerable.
SECMC has hired Berkeley Associates Pvt Ltd. (BAL) for Ex Pit Dump Reclamation Pilot
Project. In this regard, M/s BAL is working on devising an innovative yet efficient system
for reclamation of this Ex Pit Dump by employing methods of Surface Protection and
efficient drainage system. Out of many options that were shared with SECMC for Surface
Protection (via Email on March 23, 2025), the Client suggested to employ an additional
method requiring that the two slopes are further extended so that the angle of repose lies
between 19-22 degree.
As suggested by the Client, BAL has revised the Geometry of the Ex Pit Dump and
evaluated it for slope stability. This Technical Note provide details of slope stability
analyses carried out by BAL on the revised dump geometry.
1.2.
Background
Slope stability analyses are a critical aspect of geotechnical engineering, ensuring the
safety of natural and man-made slopes. The objective of this study was to evaluate the
stability of a given slope using Slide2 software.
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1.3.
Objectives
The key objectives of this study are outlined below:

Perform slope stability analysis using Slide2 for the existing slope geometry.

Carry out a revised analysis based on the geometry modifications suggested by
the client.

Evaluate the stability of both configurations and report any failure conditions
identified.
1.4.
Site Conditions
1.4.1. Location
The analysis was conducted for a site within Sindh Engro Coal Mining Company
(SECMC), Pakistan’s leading coal producer. SECMC operates the country’s first openpit lignite mine in Block II of the Tharparkar region, located in Sindh province, Pakistan.
1.4.2. Soil Conditions
The site consists of waste dump material generated from mining activities, forming a
heterogeneous mix of various soil compositions. Due to the variability in material
properties, multiple soil layers exist within the dump. To ensure a conservative
stability assessment, the most critical soil layer was selected based on direct
shear test data (provided by the Client), which identified sand as the least stable
material among the available soil layers. For the purpose of the analysis, the entire
slope was modelled using this lowest-parameter sand to represent the most critical
condition.
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1.4.3. Slope Geometry
To accurately analyse slope stability, two slope geometries have been considered
during the design assessment. The initial geometry (Geometry A) represents the
original design profile, developed based on preliminary site evaluations and
engineering judgment. Subsequently, a revised geometry (Geometry B) was proposed
by the client, reflecting adjustments aimed at optimizing both stability and
constructability. Both configurations are defined by specific coordinates and slope
angles to represent the terrain profile with precision for stability analysis. The graphical
representations of Geometry A and Geometry B are shown below:
Geometry A: Initial Slope Geometry
Geometry B: Revised Slope Geometry (Client Suggested)
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2. METHODOLOGY
The methodology involves numerical modeling of slope stability using Slide2 software. The
analysis process includes defining the material properties, setting appropriate boundary
and loading conditions, and applying the Strength Reduction Method (SRM) to assess the
factor of safety and overall stability of the slope.
2.1.
Slide2 Analysis
2.1.1. Static Loading Conditions
2.1.1.1 Input Parameters
 Material Properties
The site consists of waste dump material generated from mining activities, resulting in
a heterogeneous mix of various soil compositions. Due to the inherent variability in
material properties, multiple soil layers are present within the dump profile. To ensure
a conservative and reliable stability assessment, the most critical soil layer was
identified based on direct shear test data provided by the Client. The test results,
summarized in the “Direct Shear” sheet of the Geotechnical Data file, identified sand
as the least stable material among the available layers. For the purpose of analysis,
the entire slope was modeled in Slide2 using the parameters of this critical sand layer,
which exhibits a cohesion of 0 kPa, an internal friction angle of 36°, and a dry unit
weight of 14.9 kN/m³. The Mohr-Coulomb constitutive model was adopted to
represent the material behavior during the stability assessment.
 Loading Conditions
No external loading or groundwater conditions were considered in this analysis. The
stability assessment was conducted under dry conditions to evaluate the inherent
strength of the slope material.
2.1.2. Modelling Approach
 Analysis Method
The slope stability analysis was carried out using Slide2, which applies the Limit
Equilibrium Method (LEM) to compute the Factor of Safety (FOS). Various search
algorithms were employed to locate the critical failure surface, ensuring the
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identification of the lowest FOS corresponding to the most likely slip mechanism. The
analysis accounts for soil strength, geometry, and applied loads, providing a reliable
assessment of slope stability.
 Critical Slip Surface Search and FOS Calculation
The software systematically searches for potential failure surfaces and computes the
FOS by balancing the driving and resisting forces along these surfaces. The selected
analysis method ensures the slope stability is assessed under the most critical
condition, offering a conservative and dependable evaluation.
2.1.2
Earthquake Analysis
In Slide2, earthquake loading was incorporated using the pseudostatic analysis method,
which simulates seismic effects by applying an equivalent horizontal seismic load to the
slope model. A horizontal seismic coefficient of 0.2g was adopted, in accordance with the
Building Code of Pakistan for the Thar region. This coefficient represents the expected
Peak Ground Acceleration (PGA) for the site. The application of this seismic coefficient
enabled the evaluation of slope stability under earthquake loading conditions, ensuring
that the design remains within acceptable safety limits during seismic events.
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RESULTS AND DISCUSSION
3
3.1.
Static Loading Condition
3.1.1. Factor of Safety — Initial Geometry
The Factor of Safety (FOS) values obtained from Slide2 using different limit equilibrium
methods are as follows:

Ordinary/Fellenius: 1.36

Bishop Simplified: 1.42

Janbu Simplified: 1.36

Janbu Corrected: 1.41

Spencer: 1.41

GLE/Morgenstern-Price: 1.41
Figure 3.1-1: Calculated critical slip surface and FOS(1.415) for Janbu Corrected
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3.1.2. Factor of Safety — Revised Geometry
The Factor of Safety (FOS) values obtained from Slide2 using different limit equilibrium
methods are as follows:

Ordinary/Fellenius: 2.33

Bishop Simplified: 2.33

Janbu Simplified: 2.33

Janbu Corrected: 2.37

Spencer: 2.33

GLE/Morgenstern-Price: 2.33
Figure 3.1-2: Calculated critical slip surface and FOS(2.374) for Janbu Corrected
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3.2.
Seismic Loading Condition (Pseudostatic Analysis)
3.2.1. Factor of Safety — Initial Geometry
The Factor of Safety (FOS) values obtained from Slide2 using different limit equilibrium
methods are as follows:

Ordinary/Fellenius: 0.93

Bishop Simplified: 0.97

Janbu Simplified: 0.93

Janbu Corrected: 0.96

Spencer: 0.98

GLE/Morgenstern-Price: 0.98
Figure 3.2-1: Calculated critical slip surface and FOS(0.967) for Janbu Corrected
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3.2.2. Factor of Safety — Revised Geometry
The Factor of Safety (FOS) values obtained from Slide2 using different limit equilibrium
methods are as follows:

Ordinary/Fellenius: 1.44

Bishop Simplified: 1.48

Janbu Simplified: 1.44

Janbu Corrected: 1.49

Spencer: 1.48

GLE/Morgenstern-Price: 1.48
Figure 3.2-2: Calculated critical slip surface and FOS(1.497) for Janbu Corrected
3.3.
Interpretation of Factor of Safety
The slope stability analysis was conducted in Slide2 under both static and seismic
(pseudostatic) loading conditions. For the static loading condition, the Factor of Safety
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(FOS) values ranged between 1.36 and 1.42 for the initial geometry, and between 2.33
and 2.37 for the revised geometry.
Under seismic loading, simulated using the pseudostatic analysis method with a horizontal
seismic coefficient of 0.2g, the FOS values were observed to range from 0.93 to 0.97 for
the initial geometry, and from 1.44 to 1.49 for the revised geometry.
These results reflect the expected reduction in slope stability under seismic conditions
compared to static conditions and highlight the sensitivity of Factor of Safety to both
loading conditions and geometrical configurations.
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4
CONCLUSION
The slope stability assessment for the mining dump site was conducted using Slide2 under
both static and seismic (pseudostatic) loading conditions. The calculated Factors of Safety
(FOS) for the initial and revised geometries are summarized in Table 3.1.
Recommended
Loading
Condition
Geometry
Factor of Safety
Minimum FOS
(FOS)
(Yukon Guidelines,
2023)
Static Condition
Seismic Condition
(Pseudostatic)
Initial Geometry
1.36 – 1.42
> 1.3
Revised Geometry
2.33 – 2.37
> 1.3
Initial Geometry
0.93 – 0.97
> 1.0
Revised Geometry
1.44 – 1.49
> 1.0
Under static conditions, the initial geometry resulted in FOS values ranging from 1.36 to
1.42, while the revised geometry exhibited higher FOS values ranging from 2.33 to 2.37.
For the seismic loading condition, modeled using the pseudostatic analysis method with a
horizontal seismic coefficient of 0.2g, the FOS for the initial geometry dropped to a range
of 0.93 to 0.97, which is below the generally accepted minimum threshold for seismic
stability. In contrast, the revised geometry maintained FOS values between 1.44 and 1.49,
exceeding the required limit for earthquake loading.
The results clearly reflect the influence of both loading conditions and slope geometry on
overall stability. In particular, the FOS for the initial geometry under seismic conditions falls
below the minimum acceptable value of 1.0, as specified in the Yukon Government’s
Guidelines for Mine Waste Management Facilities (2023). This outcome suggests the need
for further investigation through borehole drilling and laboratory testing to confirm the
actual subsurface conditions and refine the geotechnical parameters.
If site investigations confirm the conservative nature of the current soil strength
assumptions, flattening the slope—as previously suggested by the Client—remains the
only viable stabilization measure, though this approach involves considerable practical and
operational challenges.
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