Oswaldo Augusto Filho

Engineering geological data in support of municipal land use planning—a case study in Analândia, southeast Brazil

This paper presents a method for transforming the information of an engineering geological map into useful information for non-specialists involved in land-use planning. The method consists of classifying the engineering geological units in terms of land use capability and identifying the legal and the geologic restrictions that apply in the study area. Both informations are then superimposed over the land use and a conflict areas map is created. The analysis of these data leads to the identification of existing and forthcoming land use conflicts and enables the proposal of planning measures on a regional and local scale. The map for the regional planning was compiled at a 1:50,000 scale and encompasses the whole municipal land area where uses are mainly rural. The map for the local planning was compiled at a 1:10,000 scale and encompasses the urban area. Most of the classification and operations on maps used spatial analyst tools available in the Geographical Information System. The regional studies showed that the greater part of Analândia’s territory presents appropriate land uses. The local-scale studies indicate that the majority of the densely occupied urban areas are in suitable land. Although the situation is in general positive, municipal policies should address the identified and expected land use conflicts, so that it can be further improved.

Landslide analysis of unsaturated soil slopes based on rainfall and matric suction data

Shallow slope failures that occur as a result of a decrease in matric suction after water infiltration from intense rains (unsaturated soil conditions) are the main causes of slope instability in tropical and subtropical regions. This study analyzes the occurrence of shallow landslides in a highway cutting of residual soil originating from aeolian sandstone. Characterization of failure mechanisms and stability analyses have been carried out in different scenarios and supported by surface and subsurface investigations, instrumentation and monitoring of rainfall, matric suction, and water level, field tests, and laboratory tests. The results indicate that the reduction in matric suction induced by rainwater infiltration is the triggering mechanism of slope failure. Conventional slope stability analyses and analyses incorporating unsaturated seepage models present results compatible with the hydrological and geotechnical data collected in the study. On the basis of these analyses, and considering the frequent rainfall events in the study area, a critical geometric configuration is proposed for the triggering of landslides in highway cutting slopes of residual soils of aeolian sandstone.

Aplicação do Processo de Análise Hierárquica (AHP) no mapeamento de perigo de escorregamentos em áreas urbanas

The method of hazard mapping of landslides in urban areas adopted by the Ministerio das Cidades is the most currently used method in Brazil. In order to make it more systematic and to reduce the subjectivity in comparing and ranking hazardous areas, but without changing its fundamental approach, this paper proposes to incorporate the Analytic Hierarchy Process (AHP) into the analysis. To validate this proposal, this approach was tested in areas of landslide risk in the municipality of Sao Sebastiao (SP), previously mapped by the Geological Institute of the Geological Institute of the Environmental Secretariat of Sao Paulo State (IG/ SMA/SP), according to the traditional approach, i.e., without the systematic use of AHP. The results of the hazard mapping by the IG for one of these areas (Vila Baiana), exemplified in this work, were more conservative than those obtained using AHP. The application of AHP reduced the subjectivity and showed the ease and convenience in weighting the hazard indicators for hazard ranking. An analysis of the opinions of three experts in the parity judgment of landslide hazard indicators showed no discrepancies in the ranking of hazard.