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<p>Rapid urban expansion in Hosaina Town, southern Ethiopia, has increased the demand for safe and sustainable infrastructure. The town is underlain by highly variable residual volcanic soils and weak pyroclastic rocks, whose engineering behaviour is poorly documented, introducing uncertainty in foundation design, slope stability assessment, and construction planning. This study provides a comprehensive characterization of soils and rocks to support reliable engineering decision making.</p><p>Field investigations covered approximately 52&#xa0;km², combining geological and engineering geological mapping, in-situ testing, and laboratory analyses. Eighteen test pits were excavated to obtain representative soil samples. Two dominant soil types were identified based on the Unified Soil Classification System: dark gray clay and red to reddish-brown silt. Clay soils contained 34–70% clay, 21.5–50.8% silt, and 3–18% sand, with moderate to high plasticity (liquid limits 32–72%, plasticity indices 10–52%) and free swell values of 35–93%, indicating high expansivity. Silt soils exhibited lower plasticity (liquid limits 29–43%, plasticity indices 5–14%) and free swell values of 31–50%. Shrinkage limits ranged from 6.2% to 25.1%, while direct shear tests showed cohesion of 18–69 kN/m² and internal friction angles of 14°–23°.</p><p>Rock strength showed significant variation: ignimbrite measured between 13 and 29 MPa, while tuff was remarkably weak—dropping below 5 MPa where Schmidt hammer testing became ineffective.</p><p>The study concludes that thick, expansive clay soils pose the most critical geotechnical challenge due to high plasticity and swelling–shrinkage behaviour, while weak volcanic rocks, particularly tuff, exacerbate foundation instability and construction difficulties. These conditions are expected to significantly influence foundation performance and the development of infrastructure in Hosaina Town. The findings provide essential guidance for foundation design, urban planning, and risk mitigation in areas underlain by soils and weak rock formations.</p>

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Engineering Geological Characterization of Hosaina Town in Central Ethiopia

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月11日

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  • Alemayehu Paulos,
  • Matebie Meten

摘要

Rapid urban expansion in Hosaina Town, southern Ethiopia, has increased the demand for safe and sustainable infrastructure. The town is underlain by highly variable residual volcanic soils and weak pyroclastic rocks, whose engineering behaviour is poorly documented, introducing uncertainty in foundation design, slope stability assessment, and construction planning. This study provides a comprehensive characterization of soils and rocks to support reliable engineering decision making.

Field investigations covered approximately 52 km², combining geological and engineering geological mapping, in-situ testing, and laboratory analyses. Eighteen test pits were excavated to obtain representative soil samples. Two dominant soil types were identified based on the Unified Soil Classification System: dark gray clay and red to reddish-brown silt. Clay soils contained 34–70% clay, 21.5–50.8% silt, and 3–18% sand, with moderate to high plasticity (liquid limits 32–72%, plasticity indices 10–52%) and free swell values of 35–93%, indicating high expansivity. Silt soils exhibited lower plasticity (liquid limits 29–43%, plasticity indices 5–14%) and free swell values of 31–50%. Shrinkage limits ranged from 6.2% to 25.1%, while direct shear tests showed cohesion of 18–69 kN/m² and internal friction angles of 14°–23°.

Rock strength showed significant variation: ignimbrite measured between 13 and 29 MPa, while tuff was remarkably weak—dropping below 5 MPa where Schmidt hammer testing became ineffective.

The study concludes that thick, expansive clay soils pose the most critical geotechnical challenge due to high plasticity and swelling–shrinkage behaviour, while weak volcanic rocks, particularly tuff, exacerbate foundation instability and construction difficulties. These conditions are expected to significantly influence foundation performance and the development of infrastructure in Hosaina Town. The findings provide essential guidance for foundation design, urban planning, and risk mitigation in areas underlain by soils and weak rock formations.