Fourteen-Year Creep Monitoring and Benchmark Velocity Parameters of Natural Slopes at ‘Serra do Mar’, Brazil

Abstract

This paper presents the analysis and results of a 14-year monitoring of creep behavior along a 100m high slope at Serra do Mar, Brazil. The slope is located nearby a roadway and an industrial area and was suffering from creep movements triggered by an excavation at its foot. Creep movements were especially severe during the rainy periods due to water table fluctuation. Inclinometer readings from 2009 to 2011 showed that the creep movement involved a soil mass around 15 to 20m thick and was in the so-called tertiary phase, with relatively high acceleration. Prediction models showed that the slope failure would probably occur in another two to three years, which required immediate implementation of mitigation actions. By the end of 2011, several horizontal deep drains were installed along the slope to reduce the water table level. Since then, the inclinometers showed that creep acceleration was eliminated and creep velocity was substantially reduced, bringing the slope back to primary and secondary, stable creep movements. Monitoring results of Horizontal Deep Drains show that flow volumes increase substantially during the rainy seasons, showing that the solution efficiently stabilizes the slope. With the basis of monitoring results for both secondary and tertiary creep phases as well as comparison with instrumentation results from other monitored slopes in the region, benchmark parameters related to creep velocity and acceleration for Serra do Mar slopes are discussed and presented. This constitutes the first organized study on slope movement velocities at Serra do Mar and presents an important contribution for researchers and designers.