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In addition to the intensity of precipitation, the different hydraulic and mechanical properties of a soil hill can also be responsible for landslides. More specifically, the same rainfall amount can trigger or not trigger a mass movement depending on its characteristics. This issue represents a great geotechnical hazard in mountainous regions such as Brazil, Italy, South Africa, Japan and Hong Kong. The understanding of each of the key factors involved in a rainfall-triggered landslide can be deepened and also quantified. Thus, this research defines, through a numerical model, which parameters are the key factors involved in slope stability. A homogeneous and unsaturated hill was studied. Its different hydraulic and mechanical properties were varied. Geometry and mechanical parameters were shown to exert the greatest influence on stability. Hydraulic parameters, for the same amount of rain, showed a lower influence. The fitting parameters of the soil–water characteristic curve of the materials had a low impact on stability when compared to other parameters assessed. Our conclusions can help future laboratory and field studies to focus more on the accuracy and confidentiality of the key parameters. The results are also important as they give direction to studies related to precipitation threshold definition.

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Abstract. This research aims to describe how rainfall can cause changes in the piezometric pore pressure and soil matric suction in a densely instrumented slope by the South BR-101 (Brazilian Numbered Highway), in the area of Morro do Boi, in the State of Santa Catarina, South Region of Brazil. The slope presented a history of instability movements instigated by intense rainfall, with debris accumulation on the highway and traffic interruption. The analyzed data are measured by six vibrating wire piezometers and eight electrical tensiometers attached to a datalogger, two conventional slope inclinometers and a rain gauge with an internal datalogger. A total of 2,552 readings corresponding to the vibrating wires and electrical resistance instruments, 29 inclinometers records and 7,143 rainfall records were collected over the first ten months of slope monitoring. The analysis results demonstrated that during the monitoring period there were no heavy rains. Three monitoring periods were identified by the frequency and intensity of rainfalls. The soil pore pressure monitoring instruments showed significant variations in the high frequency period and low intensity rainfall, and little variation in low frequency period and high intensity rainfall, which demonstrates greater runoff and little infiltration during the occurrence of more significant rainfall.