Semnan University Press Journal of Transportation Infrastructure Engineering 2423-5350 6 1 2020 06 17 Effect of Rainfall Infiltration on the Stability of Unsaturated Soil Slopes with Fluid-Mechanical Coupled Analysis Effect of Rainfall Infiltration on the Stability of Unsaturated Soil Slopes with Fluid-Mechanical Coupled Analysis 83 99 4226 10.22075/jtie.2020.19178.1432 FA Danesh Sattari PhD Candidate, Department of Soil Mechanics, Faculty of Civil Engineering, University of Tabriz, Iran Masoud Hajialilue Bonab Professor, Department of Soil Mechanics, Faculty of Civil Engineering, University of Tabriz, Iran Akbar Arab Javadi Professor, College of Engineering Mathematics and Physical Sciences, University of Exeter, UK Journal Article 2019 11 26 Nowadays, transportation is one of the most important components of national economy. Every year, many hills and natural slopes are excavated to build transport infrastructure. The stability of trenches created by excavations is important during construction and operation. In nature, these treches are mainly unsaturated and should be analyzed with theory of unsaturated soils. One of the main causes of trench instability is rainfall and water infiltration. In this research, using theory of unsaturated soils and finite difference numerical method, rainfall infiltration trend and its effect on pore water pressure variations, saturation percent, deformations and finally its stability during rainfall event was investigated. For his purpose, in addition to field and laboratory test for estimation of geomechanical parameters of the materials, the RETC software was used to obtain soil-water characteristics parameters. Results showed that the factor of safety decreases with increasing duration of low-intensity rainfall from 1.283 to 1.221 in 5 months, but the rate of decline is not sufficient to cause complete instability. But for short-term high-intensity rainfall, due to the lack of infiltration and water flow in the slope, maximum impact occurred in the upper 2 m of the slope, and in this zone, in addition to weight increasing, suction and shear strength of the unsaturated soil have decreased. Due to conjugate effect of these two factors, within 48 hours, the factor of safety decreased to 0.981 and led to instability of trench. Nowadays, transportation is one of the most important components of national economy. Every year, many hills and natural slopes are excavated to build transport infrastructure. The stability of trenches created by excavations is important during construction and operation. In nature, these treches are mainly unsaturated and should be analyzed with theory of unsaturated soils. One of the main causes of trench instability is rainfall and water infiltration. In this research, using theory of unsaturated soils and finite difference numerical method, rainfall infiltration trend and its effect on pore water pressure variations, saturation percent, deformations and finally its stability during rainfall event was investigated. For his purpose, in addition to field and laboratory test for estimation of geomechanical parameters of the materials, the RETC software was used to obtain soil-water characteristics parameters. Results showed that the factor of safety decreases with increasing duration of low-intensity rainfall from 1.283 to 1.221 in 5 months, but the rate of decline is not sufficient to cause complete instability. But for short-term high-intensity rainfall, due to the lack of infiltration and water flow in the slope, maximum impact occurred in the upper 2 m of the slope, and in this zone, in addition to weight increasing, suction and shear strength of the unsaturated soil have decreased. Due to conjugate effect of these two factors, within 48 hours, the factor of safety decreased to 0.981 and led to instability of trench. https://jtie.semnan.ac.ir/article_4226_5a46e14316be92975cca927571d9a962.pdf