Análise do processo de adensamento aplicado ao fechamento de reservatório de rejeito de bauxita

Abstract

During the conception of the project for the closure of a tailings dam, the stages of geotechnical and environmental monitoring are defined. One aspect of geotechnical monitoring is tracking the consolidation process in the tailings layer, which can cause differential settlements on the surface. Predicting this process allows preparation for the time it will take until settlements become irrelevant. The estimation identifies the period during which the reservoir may still require surface adjustments before reforestation can take place, mainly because depression points tend to accumulate water, hindering vegetation growth. The present study aimed to analyze the performance of two methodologies for predicting the consolidation process, comparing them with field results, and to present the steps involved in the closure of a reservoir from national and international legal perspectives, including geotechnical, environmental, and social contexts. The first methodology involved obtaining input parameters for the Classical Consolidation Theory through piezocone and vane tests. The second methodology consisted of numerical modeling using the PLAXIS 2D program, employing input parameters obtained from triaxial and consolidation induced by permeation tests. The field values were obtained through topographic monitoring. The methodologies were analyzed under various assumptions to reproduce the field scenario, with the variation of the modulus of elasticity being most relevant for the first methodology, and the consideration of a desiccated crust over the tailings layer being most relevant for the second. When comparing the scenarios with field results, the numerical modeling demonstrated the best adherence, highlighting the potential of finite element analyses in complex geotechnical problems such as tailings dams.