Slope Stability Assessment of Weak and Weathered Rocks with BQ System

Rock slopes can be affected by weathering and human activities. Depending on the type of the rock, the impact of weathering and excavation can change. This leads some strength reductions and consequently some stability problems. Limit equilibrium analyses are widely used to assess slope stability but empirical methods are also very useful and quick. Basic quality (BQ) system is very popular method which is developed in China to assess slope stability of the rock slopes. Generally it leans on strength and rock soundness/GSI to determine slope stability. In this study, rock slope stabilities were assessed with limit equilibrium method and BQ system. 55 cut slopes located in Western Black Sea Region of Turkey were used to evaluate the stability conditions. 39 of the cut slopes are located in flysch deposits consisting mudstones and sandstone/limestone alternations. Other rock types are granite, basalt, andesite, granodiorite, serpentinite and tuff. According to the field observations, degree of weathering of most of the cut slopes are moderate (38), and the rest are slightly (10) and highly (7). Uniaxial compressive strength, point load strength index and Schmidt hammer tests were applied to find strength values. According to the tests, most of the rocks are in the category of weak and medium strong (5–50 MPa) throughout the study area. The field observations revealed that all cut slopes are stable except surficial failures due to weathering and excavation. According to limit equilibrium analyses, all cut slopes are stable, but only surficial failures were observed due to degradation which is completely coherent with the field observations. However, BQ System revealed that most of the results are not coherent with the field observations and limit equilibrium results. It is concluded that rocks stronger than 50 MPa can be assessed properly by BQ System in the study area.