Rainfall Effects on Pore Pressure Changes in a Coastal Slope of the Serra do Mar in Santa Catarina

Abstract

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.

The Key Parameters Involved in a Rainfall-Triggered Landslide

“…This work used characteristics and mean parameters related to real soil slopes. Its validation was achieved via its application to values obtained from the instrumentation of a road slope in the southern region of Brazil [39].…”

“…For an unsaturated soil element, a change in volumetric moisture content is related to a change in suction [5] by the following equation: This work used characteristics and mean parameters related to real soil slopes. Its validation was achieved via its application to values obtained from the instrumentation of a road slope in the southern region of Brazil [39].…”

“…Based on real instrumentation data [39,52], the initial suction profiles were modeled as being able to reach a maximum, over which suction returns to zero.…”

“…After defining and listing all the input parameters involved, each one was assigned a reference value based on the available literature [39,53]. The hydraulic soil properties were derived from the silty sand SM average results of experimental SWCC presented by [53].…”

“…The hydraulic soil properties were derived from the silty sand SM average results of experimental SWCC presented by [53]. The mechanical properties of the soil were derived from the silty sand SM average results of the geotechnical properties of the slope soil in [39]. Two additional realistic values, one higher and one lower than the referential value, were primarily tested in order to have at least one of each: slope stability and instability.…”