INFLUENCE OF NATURAL FACTORS ON PIT WALL STABILITY: A CASE STUDY FROM THE KALMAKIR OPEN-PIT MINE

ACADEMIC RESEARCH IN MODERN SCIENCE

International scientific-online conference

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INFLUENCE OF NATURAL FACTORS ON PIT WALL STABILITY: A

CASE STUDY FROM THE KALMAKIR OPEN-PIT MINE

Ravshanov Z.Y.

Kadirkulov D.I.

Tashkent State Technical University named after

Islam Karimov, Uzbekistan.

https://doi.org/10.5281/zenodo.15760708

Abstract:

Pit wall stability in open-pit mines is directly affected by natural

geological and climatic factors. This study focuses on the Kalmakir open-pit
mine, assessing the effects of rainfall, seismicity, groundwater levels, and
lithological composition on slope deformation. Using field instrumentation,
laboratory testing, and numerical modeling with Slide2, various instability
scenarios were simulated. Results revealed that rainfall infiltration and elevated
groundwater levels drastically reduce the factor of safety (FoS), particularly in
weathered rock zones. Complementary slope monitoring data validated the
numerical findings. Recommendations include the implementation of real-time
drainage management, targeted reinforcement, and seasonal excavation
strategies.

Keywords:

pit wall stability, groundwater, rainfall infiltration,

geomechanics, Kalmakir mine, natural hazards, Slide2, safety factor.

Slope stability remains a major concern in large-scale open-pit mining

operations, especially in geologically complex regions with variable climatic
influences. Failures not only threaten human lives and equipment but also cause
production delays and economic losses. At the Kalmakir open-pit mine, past
incidents of localized wall collapses have prompted a focused investigation into
the natural contributors to instability. The present study combines field data,
laboratory testing, and numerical modeling to assess these impacts
comprehensively and develop targeted recommendations.

The Kalmakir deposit is part of the Almalyk ore district in southeastern

Uzbekistan. The deposit primarily consists of porphyritic granodiorite, quartz
diorite, and hornfels. The rock mass is moderately to highly fractured, with
weathered zones up to 15–20 meters deep.

Table-1 Key Geological Characteristics.

Parameter

Value / Range

Dominant

Lithology

Porphyritic Granodiorite

Fracture

Spacing

15–40 cm in upper 30 m

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Joint Condition

Rating

Fair to Poor

Weathering

Depth

Up to 20 m

Slope Angle

37–45° (bench), 50–55° (overall)

The study utilizes data from multiple instruments installed on site between

2021–2024.

Table-2 Instrumentation Summary.

Instrumen

t Type

Qua

ntity

Purpose

Piezomete

rs

4

Monitor groundwater table fluctuations

Rain

Gauges

Measure rainfall infiltration rates

Extensome

ters

2

Measure slope movement

Prism

Stations

8

Surface deformation tracking

Seismic

Sensors

Detect ground vibrations

Key Observations:



Rainfall: Peak precipitation in March–April and October–November.



Groundwater: Significant rise after 2–3 days of continuous rainfall.



Seismicity: Microseismic events (M = 3.5–5.2) occurred 1–2 times

per year.



Surface Deformation: Detected at benches B3–B6, correlating with

wet seasons.

Simulation of Rainfall and Groundwater Influence. Numerical models were

developed using Slide2 (Rocscience), implementing limit equilibrium analysis
under three primary scenarios:

Table-3 Input Parameters.

Parameter

Value Range

Cohesion (c)

20–60 kPa

Friction angle (φ)

28°–36°

Unit weight (γ)

21–24 kN/m³

Ru (pore pressure coef.)

0.2–0.5

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Water table depth

5–30 m (variable by season)

Simulated Scenarios: Scenario A: Dry season – base condition, Scenario B:

Peak rainfall (70 mm/week), no drainage, Scenario

C:

Elevated groundwater

table (10 m rise)

Table-4 Factor of Safety (FoS) Comparison.

Scenario

Avg. FoS (Upper

Slope)

Avg. FoS (Middle

Slope)

A – Dry

1.45

1.38

B – Rainfall

1.13

1.08

C – Groundwater

0.98

0.92

Observation:

When groundwater rises by 10 m, failure surfaces propagate

deeper and more extensively, especially in jointed granodiorite. While no major
earthquakes occurred during the monitoring period, small seismic events
accelerated minor slope movements, especially under saturated conditions.
Seismic shaking reduces frictional resistance temporarily, increasing the
likelihood of progressive failure. Deformation data from prism stations closely
matched predicted failure zones in Slide2 output maps. This validates the
model’s accuracy for real-time forecasting.

This study highlights the critical role of natural factors — primarily rainfall

infiltration and groundwater rise — in pit wall instability at the Kalmakir open-
pit mine. Through detailed data collection and numerical simulation, it was
shown that slope safety decreases significantly during wet periods, especially in
fractured and weathered rock masses. Integrating geotechnical monitoring with
adaptive drainage and excavation strategies can greatly reduce the likelihood of
failure and improve long-term slope management.

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Rocscience Inc. (2023). Slide2 User Manual.

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Kim, Y.J. et al. (2018). “Pore Pressure Changes and Pit Slope Failures.”

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