Slope Stability Analyses of Selected Road-Cut Slope Section from Agarfa Town-Wabe River Bridge, Bale Zone, Southeastern Ethiopia

Abstract

Infrastructure development is crucial for a country's economic, social, and cultural evolution. It involves not only construction but also sustainable practices that can boost the economy. However, the construction of civil engineering infrastructure such as roads, buildings, dams, and open-pit mines is often hindered by the instability of slopes along road cuts. This issue can have serious consequences for lives, properties, traffic flow, and car accidents. The road which connects Agarfa town to Wabe river bridge passes steep slope landscape to gentle slope with main to minor valleys and prone to slope stability failure. The study area was along a road between Agarfa town to Wabe river bridge. The aim of this study was to assess the stability of selected road sections by analyzing the geological and geotechnical properties of the materials that determine the FOS of the critical slope sections and proposing remedial measure. This study identifies eight different slope section out of these two structural controls (R1SS2 and R3SS2), three heterogenous rock slope R2SS1, R3SS1 and R5SS2 and other rock slope was homogenous basaltic slope (R4SS2) and two soil slope section (clay and silt clay) soils. From the field observation and kinematic analysis was show that different mode of failure such as planar, wedge and toppling occur at slope section R1SS2 and R3SS2. The FOS determined by deterministic methods such as Rocplane and swedge software. The stability analysis was conducted under four different scenarios, including static dry, dynamic dry, static saturated, and dynamic saturated conditions. Additionally, the soil laboratory test was conducted for four soil test pits to determining of shear parameter and for classification. From four soil sample two of them were homogenous soil slope (SS1 and SS3) and the other two was from heterogenous slope section (SS2 and SS4). The cohesion and frictional angle of the soil samples obtained from direct shear tests for SS1, SS2, SS3 and SS4 were 45.31K KN/m2, 38.68 KN/m2, 18.47 KN/m2, 17.65 KN/m2 and 19.16°, 19.22°, 23.21°, and 24.88°, respectively. Liquid limit, plastic limit and plastic index of SS1 were 73.5, 36 and 37.5, For SS2 were 68.9, 33 respectively. The study conducted slope stability analyses using deterministic, limit equilibrium and finite elements methods under different static and saturation conditions. The results showed that most of critical rock and soil slopes were unstable under static saturated and dynamic saturated conditions compared to static dry and dynamic dry conditions. The analyses identified rainfall, groundwater, and unfavorable orientation of rock discontinuities as causative factors for critical slope failures. Based on the findings, the study recommends remedial measures such as increasing the benching, lowering the slope angle and proper drainage systems in the critical slope failure sections.