Challenges in the Construction of Segmental Retaining Wall in Clayshale Hilly Area: A Case Study in Indonesia

Abstract

Clayshale is one of the problematic soils commonly encountered in Indonesia. The main concerns related to clayshale behavior include the effects of wet–dry cycles (slaking) on the mass behavior and the vertical swelling pressure of the soil. Clayshale is highly unstable, both on flat ground and especially on sloped areas. The reduction in shear strength of clayshale can vary significantly depending on the duration of weathering exposure, which ultimately affects the stability and safety of any overlying structures. This paper presents a case study addressing the challenges and mitigation efforts in the construction of a retaining wall on clayshale terrain located in the hilly area of West Java, Indonesia. The retaining wall, with a maximum height of 9.5 meters, was constructed using a reinforced soil system with geosynthetics in a limited area underlain by clayshale. Proper selection of fill material, excavation method, and construction procedure were carried out in parallel to maintain slope stability. The reinforced soil wall, using geosynthetic strips as reinforcement, was built with selected fill material sourced from an external quarry to avoid contamination with clayshale. Laboratory testing, including mineralogical analysis and slake durability testing, indicated that the clayshale contained significant clay minerals, particularly montmorillonite and illite, with total clay mineral contents ranging from approximately 24.72% to 60.04%. The slake durability results showed that most samples had low durability, confirming the susceptibility of the material to disintegration when exposed to water or wetting–drying cycles.To obtain an accurate and representative design, additional soil investigations were performed at the proposed MSE Wall area. Numerical analysis was conducted using PLAXIS 3D to evaluate the safety factor. Several mitigation measures were implemented during construction, including staged excavation, temporary slope protection, replacement of degraded clayshale with granular material, use of selected imported backfill, installation of non-woven geotextile as a separator, and application of a double protection system consisting of geomembrane and concrete topping to minimize water infiltration.