Case studies on Q-slope method use for slope stability analyses

The use of the Q-slope value is a relatively new approach for the stability investigations of rock slopes. In this study, four different slopes in Giresun and Ordu cities of Turkey were investigated to assess whether the Q-slope approach is usable for varying slope heights, or not. A back analysis was carried out for a landslide in a case study quarry located in Kovanlik municipality of Giresun city. Carrying out detailed investigations on the geotechnical drill cores and the field studies, the Q-slope value of the rock mass of the Kovanlik quarry was determined as 0.58. According to the Q-slope approach, the slope which had a landslide under the case of 49° general slope angle and 225 m height should have been stable at a general slope angle of 59°. It has been found that the Q-slope approach is not favorable for a high slope with the height of 225 m. Two roadway excavations with steep slope angles and low heights smaller than 25 m were also investigated within this study. According to the Q-slope value, the roadway slopes which are stable for more than 3 years are estimated to be unstable. Therefore, the Q-slope approach was found also misleading for slopes with low heights like those under 25 m. On the other hand, the Q-slope method usability is confirmed obtaining parallel results with the observations from another case study slope with a height of 78 m. Although it has become a popular empirical method in the recent years, it is recommended to revise the Q-slope approach or limit its use depending on the slope height parameter.