ASSESSMENT OF A ROCK FALL HAZARD RATING SYSTEM ALONG KIZILCAHAMAM-GEREDE SEGMENT OF D750 HIGHWAY IN TURKEY

The scope of this study is to implement a rock fall hazard rating system to the cut slopes along Kizilcahamam-Gerede segment of D750 (Ankara-Istanbul) Highway. The rating system developed by the Tennessee Department of Transportation was assessed for thirty five cut slopes selected based on a reconnaissance survey along D750 Highway, between Kurtbogazi Dam (50 km northwest of Ankara) and Aktas village (15 km to Gerede town of Bolu province). The route is suitable for the purpose of this study since a majority of cut slopes located along there are susceptible to slope instabilities.

The basic principles of Tennessee RHRS are used in the study and the rules which offers guidance for assessing rock fall hazard, particularly those aspects regarding geologic character of rock slope are followed. The stages of the investigation include project conception, field investigations and rating processes in the frame of this system. The rating process was completed at two stages: Preliminary and Detailed Rating. The slopes were classified based on a scoring system with an exponential scale assigned to various parameters related to the site and roadway geometry and geologic features in the detailed rating. In the detailed ratings, the slope and highway related parameters such as slope height, ditch effectiveness, average vehicle risk, road width, percent desicion site distance and rockfall history were identified and different modes of slope failures (planar, wedge, toppling, differential weathering, raveling) were considered for the geologic characterization.

Based on the preliminary ratings, a total of nineteen slopes are rated as “A” which are considered to be potentially hazardous slopes, while a total of seven are rated as “C” slopes which pose no danger. In placing a slope into a “B” category, a total of nine “B” slopes are detected. “B” slopes are not as prone as A slopes to create a danger. It has been seen that the final RHRS scores range from 164 to 591 for A slopes. The slopes with scores over 300 (both additive and multiplicative) can be counted as more hazardous slopes when compare to others since they get very high scores both from site and roadway geometry and geologic hazard part. A total of nine cut slopes, which have got the highest scores from both additive and multiplicative ratings, can be counted as the most hazardous ones.