Analysis of Existing Slope Reinforcement Design on Clay Shale Soil and Its Alternative Modifications: A Case Study of the Awunio – Lapuko Road Section Sta 4+955 – 5+015 in the Southeast Sulawesi Province

Abstract

On the Awunio -Lapuko road section, there was a landslide from STA 4+955 to STA 5+015, causing the roadside to collapse. The probable cause is water infiltration into the soil, affecting the clay shale properties. An analysis of the existing slope stability and its planning needs to be carried out. Water management planning and alternative reinforcement are necessary if the stability does not meet the requirements. Slope stability analysis is conducted on the existing slope and existing design using manual calculation methods and the GEO5 program. The stability considered includes shear stability, tilting, and overall stability.The analysis reveals that the existing slope stability is safe from landslides. However, this contradicts the field observations. Therefore, a crack soil approach is used in this study to assess the landslide conditions in the field, resulting in a safety factor (SF) of 0.95 for the road slope. The existing design, a 2.5 m high retaining wall with bored piles of 50 cm diameter and a depth of 8 m, yields slope stability with an SF of 7.91, indicating safety but being excessively costly. The water management system planning indicates that the drainage channel capacity can handle the water discharge from rainfall. Introducing subdrains improves the slope stability from SF 0.95 to 1.38, but additional reinforcement is still needed. An alternative design with a 2.5 m high retaining wall and bored piles of 40 cm diameter and 3 m depth yields a slope stability 3.29. Replacing the retaining wall structure with natural stone using bored piles of 30 cm diameter and 3 m depth results in an SF of 2.18. If an alternative subdrain with additional gabion reinforcement is implemented, the slope stability becomes 2.23. Additionally, an alternative design using geotextiles results in slope stability with an SF of 1.77. All alternative reinforcements are deemed safe and meet stability requirements