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Omar, Heryanti Awang
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Civil Engineering, Building, Construction & Architecture

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Journal : Civil Engineering Journal

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Quantifying Slope Stability and Landslide Susceptibility Through Rainfall-Induced Geotechnical Assessment Nasir, Nur Fazielah; Mohamad, Habib M.; Haziq Rosly, Mohammad; Omar, Heryanti Awang; Hamansa, Harryanshah
Civil Engineering Journal Vol. 11 No. 12 (2025): December
Publisher : Salehan Institute of Higher Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.28991/CEJ-2025-011-12-017

Abstract

Landslides are a major hazard to people and infrastructure, especially in areas with weak geology and high rainfall. This study examined soil properties and slope stability in Ranau (RNU) and Kota Belud (KB), Sabah. Soil tests showed that RNU had 2–21% clay with cohesion of 3.49–9.7 kPa, while KB soils contained 2–17% clay, more sand and gravel, and much lower cohesion of 0.5–1.1 kPa, indicating weaker strength and higher permeability. Rainfall data from 2013–2023, provided by the Malaysian Meteorological Department, were used to develop Intensity-Duration-Frequency (IDF) curves. Results showed that 1-hour intensities increased from 0.92 mm/hr at ARI-2 to 2.18 mm/hr at ARI-100, reflecting the variation of extreme rainfall. Slope stability was analyzed using GeoStudio’s SEEP/W and SLOPE/W to simulate infiltration and compute the Factor of Safety (FOS). In RNU, FOS rose from 2.481 to 2.565 after 24 hours, showing stable slopes. In KB, FOS declined from 2.495 to 2.379 under ARI-100 rainfall, along with higher pore-water pressures. Both slopes remained above the safe limit of 1.50, but KB proved more vulnerable to long rainfall. Compared with earlier studies, this research introduces a decade-long dataset combined with numerical modelling to demonstrate the dynamic response of tropical slopes. The findings provide practical contributions to slope design, drainage management, and disaster risk reduction in regions experiencing similar climatic and geological conditions.
Evaluating Rainfall Effects on Soil Parameters and Slope Stability Using Hydrology Procedure (HP26) Omar, Heryanti Awang; Nasir, Nur Fazielah; Rosly, Mohammad Haziq; Mohamad, Habib Musa; Majain, Nelly; Afizah Asman, Nurul Shahadahtul
Civil Engineering Journal Vol. 12 No. 2 (2026): February
Publisher : Salehan Institute of Higher Education

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.28991/CEJ-2026-012-02-018

Abstract

Rainfall-induced slope failures are a major geohazard in tropical regions, often triggered by intense or prolonged rainfall that alters soil strength and pore water pressure conditions. This study evaluates the effects of rainfall duration on slope stability in Kota Belud and Ranau, Sabah, by applying Hydrology Procedure 26 (HP26) rainfall data with numerical modelling using SEEP/W and SLOPE/W under the Limit Equilibrium Method (LEM). Soil parameters were derived from site investigations, with strength values including cohesion (0.5-9.7 kPa) and friction angle (25.7°-30°). The results showed that short-duration rainfall (1 hour) had minimal impact on stability, while prolonged (24-hour) rainfall significantly increased pore water pressure, reducing the factor of safety (FOS) by 25-30%. A localized weak zone in Ranau was identified, with cohesion decreasing from 7 kPa to 5 kPa between 7.4 m and 13.5 m depth, corresponding to potential slip surfaces. Findings align with previous research on infiltration-driven failures, but this study demonstrates the practical use of HP26 rainfall design data for tropical slope analysis. The novelty lies in linking rainfall duration, soil-water interactions, and FOS reduction through a standardized rainfall procedure, providing a framework for improved slope risk assessment in rainfall-prone terrains.
Co-Authors Afizah Asman, Nurul Shahadahtul Hamansa, Harryanshah Haziq Rosly, Mohammad Majain, Nelly Mohamad, Habib M. Mohamad, Habib Musa Nasir, Nur Fazielah Rosly, Mohammad Haziq