Willy A. Lacerda

Mechanisms of the Recent Catastrophic Landslides in the Mountainous Range of Rio de Janeiro, Brazil

Catastrophic mass movements occurred in January 2011 in a mountainous area of Rio de Janeiro leaving more than 1,500 dead people and large destruction. Heavy thunderstorms occurred on January 11th (~100 mm/day) and 12th (~150 mm/day) and triggered thousands landslides on steep slopes with trees and block rich debris materials converged into the river channels, hence avalanches down valley. Through fieldwork, mainly translational slides and debris flow types were observed, as well as some rotational slides and rock fall. Initial studies show that translational slides occurred in saprolite soil with 1–3 m depth and on more than 30° slopes. Debris flows initiated in small catchments with very steep slopes and run out along the valley bottom where colluvial soils are present. This study focuses geological analysis and correlation between soil properties and geotechnical behavior in order to explain this catastrophic slope movement mechanisms and processes.

Landslides and Disasters in Southeastern and Southern Brazil

Abstract Landslide conditions and problems involve functional relationships among natural elements (climate, topography, rocks, soil, vegetation and fauna) and artificial elements (related to land use) of the landscape, which may change over space and time. Two characteristic rainfall regimes might express rainfall–landslide relationships in southern and southeastern Brazil: less intense events of longer duration tend to favor deep rotational failures along channel banks and road cuts, colluvium-deposit creep in valley bottoms, and shallow translation failures on steep lands; extreme rainfall events tend to favor shallow translational slides and debris flows on steep lands, block-rich debris avalanches along main valley bottons and rock falls on vertical scarps. Landslide disasters are commonly associated with less frequent, intense, and spatially nonuniform rainfall events during the summer rainy periods. Critical events have prevailed along the highly populated coastal region, especially in the upper portion of steep mountain slopes. In this text the authors draw special attention to case studies of historical landslide disasters in the most populated area of Rio de Janeiro State, and also include some other case studies in southeastern and southern Brazil.

The Community-Based Alert and Alarm System for Rainfall Induced Landslides in Rio de Janeiro, Brazil

The community-based alert and alarm system for rainfall induced landslides in Rio de Janeiro, locally called A2C2 (Sistema de Alerta e Alarme Comunitario para Chuvas Fortes), may be considered the second tier of the citywide landslide early warning strategy initiated, between the late 1980s and the early 1990s, with the SIGRA and the—still operational—Alerta-Rio projects. The A2C2 landslide early warning system was deployed between 2011 and the first few months of 2012; it is currently employed in 103 informal communities of the city. Herein, the main characteristics of the A2C2 system are presented together with a preliminary analysis on its behaviour during this initial phase of deployment.

Shear strength of soils derived from the weathering of granite and gneiss in Brazil

Abstract Research on the properties of residual soils has been continuing in Brazil since the pioneering work by Vargas in 1953. A great number of earth dams built since then and the initiation of graduate courses since 1960 have increased the rate of in-depth studies on this theme. This contribution considers the more recent research on the properties of these soils, mainly shear strength parameters.