Integrated Geological, Geotechnical and Hydrogeological Model Applied to Environmental Impact Assessment of Road Projects in Brazil

Abstract

This paper discusses the use of an integrated geological, geotechnical and hydrogeological model as a tool for environmental impact assessment of new road projects in Brazil. The method consists of a geomechanical characterisation of rock masses and an identification of soil behavior along the proposed road alignment. It uses a morphostructural analysis integrated to a hydrogeological model in a Geographic Information System (GIS) platform aiming to identify environmental risks. Lineaments extracted from satellite imagery and digital terrain models (DTM) were analysed to identify patterns of orientation across the area of the project. Morphostructural domains were defined and grouped in areas of similar pattern. For each domain a statistical analysis of directions of lineaments was carried out to identify the main morphostructural directions. Structural field data was gathered for each domain. A systematic structural survey was performed in quarries and/or natural outcrops, identifying the rock type(s) and main discontinuities characteristics/parameters. The orientation data was statistically analysed in stereonets and sets of discontinuities were identified based on the maximum concentrations and the 85 % confidence interval. The integration of data was performed in a GIS environment. For each morphostructural domain, the lineament directions were compared to the field structural data and the main directions that control groundwater flow were identified. The hydrogeological model was also entered in the GIS and crossed with the product of the lineaments analysis to identify zones of higher hydraulic gradients and possible flow paths. The environmental impacts of the project were assessed, based on the integrated models developed.