Engineering geological characterization and assessment of complex rock slope failures in Mudurnu, Turkey

Mudurnu County, situated in northwestern Turkey, is a prominent settlement area because it is located on major trade routes (i.e., the Silk Road and the Crimean Road) and has served as a trading town and a military base in the Byzantine, Seljuk, and Ottoman periods. Mudurnu County is affected by regional complex rock slope instabilities that pose a substantial hazard to the settlement area and generate regional risk to human life, buildings, houses, and industrial facilities. Mudurnu, because of its invaluable historical structures, has been nominated for the UNESCO World Heritage List. Yet, those historical structures are threatened by the rock instabilities. The aim of the paper is to characterize the rock mass on the western slopes of the Mudurnu Valley, through geomechanical evaluation of the rock and empirical assessment of the slope instabilities. The engineering geological and geomechanical properties of the area were acquired via a 3D point cloud together with field scan-line surveys. The western slope of the Mudurnu Valley was divided into 11 geomechanically uniform sectors. Classification of the sectors using the SMR and Q-slope methods demonstrated that the rock mass was prone to complex planar, wedge, and toppling failures. Proper identification of such complex failures was performed using a decision tree methodology. Estimation of the probabilities of the complex failures was accomplished using empirical classifications and field observations. It was found that Sector 8 was the most critical for combined toppling and wedge failures, as well as toppling with a combination of planar and wedge failures. In addition, Sector 6 was the most critical for combined toppling and planar failures.