IMPLEMENTATION OF A ROCKFALL HAZARD RATING SYSTEM TO THE CUT SLOPES ALONG KIZILCAHAMAM-GEREDE SEGMENT OF D750 HIGHWAY

A rock fall hazard rating system (RHRS) was implemented to the cut slopes along Kizilcahamam-Gerede segment of D750 (Ankara-Istanbul) Highway. The RHRS developed by the Tennessee Department of Transportation was assessed for thirty five cut slopes which were 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 stages of the investigation consist of project conception, field investigations and application of this system, assessment and presentation of data. The cut slopes were classified by implementing the method which requires a scoring on an exponential scale assigned to various parameters related to the site and roadway geometry and geologic characteristics. The rating process was completed at two stages: Preliminary and Detailed Rating. Based on the Tennessee RHRS, nineteen cutslopes were assessed according to these two stages while the other sixteen cut slopes were able to be classified only with the preliminary rating stage. Different modes of slope failure (planar, wedge, toppling, rock fall with differential weathering, raveling) throughout the selected segments of the highway were investigated and 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 for these nineteen cut slopes. After the scoring process was completed all cut slopes were classified based on their hazard ratings from the point of the problems that they may cause in transportation.

Among these thirty five cut slopes, nineteen of them are rated as “A” slopes which are considered to be potentially hazardous, while a total of seven are rated as “C” slopes which pose no danger. In placing a slope into a “B” category, it is considered that they are not as prone as A slopes to create a danger and a total of nine B slopes are detected. The detailed rating is accomplished for these nineteen “A” slopes and as a result of the scorings, it has been seen that the final RHRS scores range from 164 to 591. The slopes with scores over 300 (both additive and multiplicative) can be counted as more hazardous slopes since they get very high scores both from site and roadway geometry and geologic hazard part.