Comportamento geomecânico de frente de intemperismo em filito da região do Quadrilátero Ferrífero

Abstract

Low-grade metamorphic rocks are known for their low mechanical strength and also for their possibly elevated alterability. In the Quadrilátero Ferrífero, southeast region of Brazil, this set of characteristics results in frequent problems of instability of mining and road slopes associated with phyllites, mainly. Despite the significant production of iron ore, little is known about the geotechnical properties of the materials that compose the weathering front. The aim of this thesis is to discuss the variation of mineralogical, physical, chemical and mechanical properties in four phyllites weathering grades. The methodology included the field classification of the four weathering grades and mapping of the spatial distribution of these grades in a road slope for sampling and geological characterization. The mineralogy was defined by petrography and X-ray diffraction (XRD). Chemical evaluations utilized X-ray fluorescence (XRF) and chemical indexes. Physical properties were defined based on physical indexes, mercury porosimetry, colorimetry, and alterability (slake durability tests, wetting and drying cicle, and rock leaching. Resistance data were obtained with Schmidt hammer, field and laboratory, point load test (PLT) and direct shear (natural and saturated condition). The results show that structural features such as discontinuities and metamorphic foliations are relevant role in the distribution of rocks with different slope change intensities. The variations of physical and mechanical properties define better when compared to mineralogical ones. Despite the tropical conditions of the region, chemically the front is poorly developed, with a predominance of physical weathering over the chemical. It should be emphasized that cemented levels, identified in the foliation planes, directly influence the geomechanical properties of the weathering front. The aforementioned characteristics generate heterogeneous and anisotropic rock massifs. Consequently, the definitions of geomechanical models become complex, making it difficult to predict the behavior of engineering structures on or inside the rock mass