Study of geotechnical characteristics of fine-grain borrow resources of Azaroud reservoir dam

The provision of borrow resources for earthen dams is a fundamental aspect of feasibility studies for dam construction. Inability to supply borrow resources with appropriate geotechnical and economic characteristics renders the construction of the dam unjustifiable. The objectives of constructing the Azaroud Dam on the Azaroud River in Tonekabon (Western Mazandaran) are to address the shortages of drinking and agricultural water downstream of the dam. This study investigates the geotechnical characteristics of the fine-grained borrow resources required for the dam's construction, which were identified approximately 6.5 kilometers downstream, covering an area of about 18 hectares. To assess the physical, chemical, and mechanical properties, fifteen wells were drilled to a depth of 5 m, and sampling was conducted. Subsequently, tests for grain size distribution, Atterberg limits, plasticity index determination, swelling potential, and divergence were performed, and classification was conducted based on ASTM standards. The grain size distribution curve and Atterberg limit tests indicated that about 74% of the particles fall within the clay range, predominantly belonging to high-plasticity clays (CH). The average activity of the clay minerals in the materials (0.39) reveals a predominance of illite and kaolinite, which are classified as almost inactive minerals with low swelling potential. Additionally, Chen's experimental method, along with pinhole and double hydrometric tests, demonstrated that the soil's swelling potential is low and that the materials are completely non-divergent. The results of Crumb and Sherard tests corroborated these findings. In conclusion, the identified fine-grained borrow resources are entirely suitable for the dam body, posing no risk of swelling or divergence.