Monitoring and Analysis of a Reactivated Landslide with Uncertain Boundaries in an Urban Area

A landslide was triggered in January 2024 in an urban area in Ankara, Türkiye. During reconnaissance survey, it was found out that an old landslide which was stabilized at the same site almost 30 years ago was reactivated by an excavation in the sliding mass.A site investigation and monitoring program was executed which revealed that the depth and mechanism of the old landslide was altered such that the new landslide had roughly a rotational mechanism while the old landslide was more translational. After the excavation started in January 2024, the landslide movement continued with an increasing displacement rate. So, it was decided to analyze the landslide and design a stabilization system using reinforced concrete bored pile rows. The analyses were carried out by both limit equilibrium and finite element methods.Although the boundaries of the landslide were determined at the upper parts (crown, main scarp and sides) of the sliding mass, the boundaries at the lower part were uncertain due to the on-going construction activities in the excavated area. So, a series of analyses were carried out to estimate the probable toe of the sliding mass. The depth of the landslide observed from inclinometer readings and idealized soil profile obtained from site investigations were utilized as input in the analyses while the uncertainty both in the soil parameters and landslide geometry were considered for probable failure scenarios.The analyses have revealed that the most probable landslide toe was almost in the middle of the excavation area,which was then proved by site observations. The potential parametric and geometric uncertainties wereevaluated in the design of the geostructure for landslide stabilization. The effects of the spacing of the pile rows and pile cap dimensions were also investigated in this stage.

Keywords: Uncertainty, Landslide, Geostructure, Pile, Monitoring, Rotational, Translational, Stabilization.