ERODIBILITY OF SOIL DERIVED FROM ROCKS OF THE SERRA DOS ORGÃOS SUITE: IMPLICATIONS FOR THE INSTABILITY OF CUTTING SLOPES

Abstract

Hillslope instability issues can be triggered by erosion processes in residual soil horizons. Identifying the causes and analysing these processes may not be a trivial task. Although the association between sliding and erosion is relatively frequent, causes and effects relationships are not always well defined and can hugely impact budgets of projects and works. Therefore, it is still necessary to go forward in foresee the erodibility of residual soils, which under critical conditions may drive to the instability of above soil horizons. The main purpose of this manuscript is to evaluate indices to support the erodibility forecast of residual soils and their potential to initiate landslides on hillslopes. Initially two profiles of residual soils were chosen both located at São João do Meriti and developed over rocks of Serra dos Orgãos suite. They were chosen based on evidences of erosive features and records of landslides. After sampling, the residual and pedological horizons were analysed regarding its mineralogy, physical indices and mechanical properties. Results have confirmed the field observations related to the high erodibility of residual horizons and its ability to initiate instability processes in the cut slopes in the municipality. This fundamental knowledge is helpful to assist the government authorities regarding the soil use and mainly for the need of avoiding deep cuts in slopes and then keep up the preservation of residual horizons and the safe equilibrium of hillslopes.