Stability Analysis of Unsaturated Cut Slopes Due to Rainfall Infiltration (Case Study-Khoda Afarin Main Irrigation Canal)

The stability of unsaturated slopes during rainfall is an important natural hazard. Past studies have shown that slope failures generally occur during or after rainfall. A review of past studies shows that instability of natural or excavated slopes for infrastructure construction occurs mainly during or after rainfall. Due to rainfall infiltration into unsaturated soil, the apparent cohesion and shear strength provided by matrix suction reduces d, resulting in slope instability. Library studies for this research, revealed that in recent years, extensive studies have been conducted on the rainfall infiltration in unsaturated slopes and their effect on shear strength and stability. But much of the research has been on high-intensity rainfall over a short period of time, however, some instability of slopes occurs during long-term rainfall or after rainfall. In addition to field research and physical modeling, numerical methods have also been developed to solve complex problems of unsaturated soils within the framework of various scientific theories in recent years. In this paper, in addition to considering the results of previous studies, the stability of the excavated soils with multiple berms has been investigated by considering transient fluid-mechanical coupled analysis.Khodafarinn Irrigation network is one of the largest water resources development projects in northwestern Iran. The length of its main canal is 144 km. According to the topography of the project area, excavations were required to construct the main canal and its structures. The stability of the slopes created by excavation is of great importance for canal construction and operation. One of the critical slopes created along the main canal is in the trench created at the site of the Golmali cut and cover which was selected as a case study.

FLAC 2D is one of the most applicable geotechnical software based on the FDM and complex LAC 2D is one of the most applicable geotechnical software based on the FDM and complex geotechnical problems can be modeled by using FISH. The general framework of the study is that geometrical characteristics and materials parameters of the slope were first extracted using in situ and laboratory tests and then the average monthly rainfall was obtained from the meteorological station statistics. Then, transient fluid-mechanical coupled analysis was prepared for rainfall infiltration and deformation analysis using TPFlow. As a result of the analysis, pore water pressure, degree of saturation and deformation were calculated and according to results, the stability of slope was evaluated by using the shear strength reduction method. Filter paper test and RETC code were used to extract the SWRC and HCF of unsaturated soil parameters by Van-Genuchten model. Table.1 shows the parameters used in the analysis.