Abstract

Slope instabilities are one of the most frequent natural hazards capable of causing severe failures both at regional and large scales. Mudurnu, which is settled on a steep valley, is affected by regional rock slope instabilities. These instabilities constitute a hazard and create an important risk to the community since they threaten human lives, settlement areas, and historically-important structures. In order to minimize the hazard and risk associated with slope instabilities, rock masses along the valley were characterized and the potential failure mechanisms were defined. The west side of the valley, which is the focus of the research, is characterized by Cretaceous pelagic discontinuous limestone, and is prone to complex failures. The aim of the study is to characterize the rock mass along the valley, divide the area into geomechanically-uniform sectors, define possible modes of failure (kinematics) and ultimately quantify the potential failure (kinetics) and the associated risk. For the study, in addition to the field work and scan-line survey measurements, an Unmanned Aerial Vehicle (UAV) was utilized to collect high-resolution images from problematic locations that were not accessible. Then, a point cloud of the area was generated. The images were interpreted and the resulting structural representation of the rock mass was compared with information gathered from the scan-line survey in the field. Afterwards, it was used to identify the possible modes of failure along the valley. Since seismic activity in the area is significant due to the proximity of the North Anatolian Fault Zone (NAFZ), which is the most active fault system in Turkey, dynamic loading was also considered for the stability analyses.

Introduction

Mudurnu is a county of Bolu province located in northwestern Turkey. It is an important midpoint between the capital city, Ankara, and the largest city in the country, İstanbul (figure 1). The county center is located in a valley that suffers from regional rock instabilities both in the west and east sides of the valley. The instabilities are the result of the combined effect of geology, topography, weathering, human-made activities and seismicity. The total population of the county is 18.880 and the number of people who live in the county seat is 5.132 [1]. According to the inventory of Mudurnu Municipality, 84 of the damaging hazards that occurred between 1961 and 2016 were caused by rockfalls and mass movements due to precipitation, weathering and secondary effects of earthquakes. The valley can be defined as a high-risk region, given the slope instability casualties that have occurred in the past and those that have the potential to occur. The instabilities throughout the valley threaten human lives, houses, buildings and small industrial facilities. Moreover, instabilities create a risk for the historically important structures located in Mudurnu such as mansions, historical mosques and a Turkish bath from Ottoman period, and a wooden clock tower by which Mudurnu has been nominated as a candidate for the UNESCO World Heritage.

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