Field Monitoring of Deformation Effects Caused by Landslides with Fiber Optic Methods

Abstract

Landslides are among the most dangerous natural disasters that occur frequently worldwide, often triggered by intense rainfall, earthquakes, snowmelt, or human activities. Beyond their direct impact on human life, landslides are significant for their potential to damage structural and lifeline systems (residential buildings, hospitals, railways, pipelines, etc.) and their adverse effects on ecological balance. Since the beginning of the 21st century, extreme meteorological events related to climate change have increased the frequency and intensity of landslides worldwide. In Türkiye, the fact that seismic events significantly contribute to initiating landslides apart from climatic conditions has raised the importance of landslide risk assessment and management processes, necessitating the development of effective prevention and action strategies. Among the most crucial strategies are the adoption of effective landslide monitoring methods and the consequent development of early warning systems. In landslide monitoring, numerous methodologies have been defined, encompassing extensometers, inclinometers, geodetic approaches, and remote sensing or satellite images. However, these methods face limitations in real-time data flow and short response time in data transmission. Fiber optic technologies, in contrast, offer significant advantages over other methods, including high accuracy, long-distance measurement capabilities, and resilience to adverse environmental conditions. These systems enable real-time detection of ground movements and deformations through integration of early warning mechanisms for landslide risks. This thesis examines the potential of fiber optic systems, a light-based technology, in landslide monitoring through a pilot landslide site in Yalova, Türkiye. The region was chosen due to its intense rainfall, active fault lines, and the continuously observed mass movement. The susceptibility of the region to landslides has been substantiated through the application of Limit Equilibrium Methods (LEM) conducted in the context of this thesis. In analyzing data obtained from fiber optic cables, instead of the traditional Optical Time Domain Reflectometer (OTDR) method, which is the point sensing method, the Brillouin Optical Time Domain Analyzer (BOTDA) technology, which is Distributed Strain and Temperature Sensing (DSTS) method, was preferred, enabling continuous measurements along the cable length. In the case study, fiber optic cables with diameters of 3 mm and 4.5 mm were integrated into the BOTDA system, and a monitoring section, about 50 m in length, was installed through a planned configuration in the Yalova region. The deformations (strains) experienced by these cables due to seismic activity and precipitation were monitored over 50 days. In the most active point of the monitoring area, strain values exhibited considerable variations, ranging between -2000 to 7000 με for the 3-mm fiber cable and -500 to 2000 με for the 4.5-mm fiber cable. With its limited global precedents, this research is expected to lead the way in establishing advanced monitoring and early warning systems in Türkiye.