Slope stability assessment of various road cuts with effects of weathering at North West Black Sea Region (Turkey)

Ersöz, Timur
Rocks containing pore spaces, fractures, joints, bedding planes and faults are prone to weathering due to effects of temperature differences, wetting-drying, chemistry of solutions absorbed, and other physical and chemical agents. Especially cut slopes are very sensitive to weathering activities because of disturbed rock mass and topographical condition by excavation. During and right after an excavation process of a cut slope, weathering and erosion may act on this newly exposed rock material. These acting on the material may degrade and change its properties and the stability of the cut slope in its engineering lifetime. In this study, the effect of physical and chemical weathering agents on shear strength parameters of the rocks are investigated in order to observe the differences between weathered and unweathered rocks. Also, slope stability assessment of twenty cut slopes located at North West Black Sea region of Turkey are studied by the effect of these weathering agents which may alter the parameters like strength, cohesion, internal friction angle, unit weight, water absorption and porosity. In order to compare the condition of the rock materials and analyze the slope stability, the parameters of weathered and relatively fresh rock materials are found with in-situ tests such as Schmidt hammer and laboratory tests like uniaxial compressive strength, point load and direct shear. In order to reflect the relation between Schmidt rebound values and UCS two new functions are developed. Moreover, slake durability and methylene blue tests are applied to investigate the response of the rock to weathering and presence of clays in rock materials, respectively. In addition to these studies, stability conditions of the road cuts are determined by two empirical systems namely Slope Mass Rating (SMR) and Slope Stability Probability Classification (SSPC). Furthermore, the performances of the weathered and relatively fresh zones of the cut slopes are evaluated and 2-D slope stability and rockfall analysis are modeled. Success rates of empirical solutions and limit equilibrium analyses are compared with field observations, with recommendations for further research for the cut slopes. According to this, SSPC method is found to give results similar to the field performances of the cuts slopes, compared to SMR. It is found that two testing cycles are insufficient to assess the field durability of the rocks based on the slake durability test results. According to field observations and stability analyses, periodic maintenance of the drainage channels is suggested for some road cuts due to surficial failures and degradations.