Impact of stained- and cemented-type sandstone natural fractures on stress-weathered cracking behavior

Abstract

Rock material, such as sandstone, frequently shows a wide range of fracture characteristics and mechanical responses due to variations in weathering grades and the existence of natural fractures. These natural fractures in sandstone are regularly cemented by different minerals or cementation removed by weathering and/or stained with iron, which can affect the stress-induced fracture pattern and rock strength. These effects, along with fracture orientation and location on mechanical behavior and failure modes resulting from quasi-static loading, are poorly understood. The focus of this paper is to assess the effects of cemented and stained natural fractures on stress-induced sandstone failure mechanism and mechanical behavior, with a focus on natural fracture angle and location. To investigate sandstone mechanical behavior and failure mechanism, six unconfined compressive tests were conducted on specimens with pre-existing natural fractures at different angles (∅) to estimate unconfined compressive strength (UCS) and failure modes. ANSYS was also utilized for finite-element modeling and simulation to analyze comprehensive 3D fractured models. The results revealed that UCS of sandstone decreased with increasing fracture angles of 0°, 20°, 30°, 45°, 50°, to 60°, respectively. Sandstone with a 90° fracture angle exhibits higher UCS than samples with a 0° fracture angle. The findings indicated that sandstone with 0° and 20° fracture angles had multiple fracturing, while specimens with 90° fracture angles provided axial splitting. On the other hand, the shear failure in sandstone specimens occurred as the fracture angle superseded 50°. The simulation results demonstrate that fracture location affects only the UCS of sandstone.