Influence of weathering on the Hoek‒Brown parameters of a syenogranite

Understanding the geomechanical properties of rocks is essential for predicting their behavior under field stresses. Weathering can significantly affect these properties, impacting the durability and safety of engineering structures over time. Therefore, the present study aimed to investigate the influence of weathering on the geomechanical properties and intact rock parameters of the Hoek‒Brown failure criterion (m_i and σ_ci) of a syenogranite. An experimental campaign was conducted using samples of a syenogranite collected in the southeast region of Brazil, with rock blocks ranging from sound rock conditions to moderately weathered conditions. Laboratory tests, including physical indices, uniaxial and triaxial compression tests, direct tensile tests, and petrographic analysis, were performed to characterize the material at the alteration levels studied. The results allowed us to conclude that weathering action on the syenogranite significantly influenced all individually evaluated geomechanical properties, but this influence was much more noticeable from slightly weathered to moderately weathered materials. Statistical analysis, including the Tukey test, revealed that geomechanical properties of W1 and W2 are statistically similar, while both differ significantly from W3. Furthermore, determining the Hoek‒Brown envelopes for the assessed alteration degrees led to the conclusion that the behavior of these envelopes and the parameters m_i and σ_ci do not solely depend on the weathering effect but may be influenced by other microstructural factors, such as mineral composition, grain size and fabric, cementing materials, and the weathering degree. Thus, this study advances the understanding of how weathering affects the Hoek‒Brown parameters, contributing valuable knowledge to rock mechanics applications.