Mechanical behavior and compositional variation of weathered granite soil with different degrees of weathering

Granite undergoes varying degrees of weathering when subjected to weathering processes, resulting in weathered granite soil (WGS) with different degrees of weathering. This study focuses on granite residual soil (GRS) and completely weathered granite (CWG) within WGS of varying weathering degrees. Initially, a one-dimensional compression test and a consolidated undrained triaxial test are employed to investigate and compare the mechanical characteristics. Subsequently, the microscopic evolution mechanisms from the fresh granite (FG) to WGS are analyzed through X-ray diffraction, fluorescence spectroscopy, and scanning electron microscopy tests. Finally, various relationships between the physical and mechanical parameters of WGS and their weathering characteristics are developed. The findings reveal that GRS exhibits a smaller compression index than CWG but possesses a larger compression modulus. CWG demonstrates a higher critical stress ratio and effective internal friction angle at the critical state, and the CWG's dynamic elastic modulus exceeds that of GRS. Upon normalization to yield E/E_dmax, GRS confidence region resides below that of CWG. As weathering increases, the primary minerals in granite undergo weathering to produce secondary minerals, and the overall structural integrity declines. Furthermore, a strong correlation exists between the physical and mechanical parameters of WGS and its weathering indices. This study offers invaluable insights into the mechanical characteristics and microstructural mechanisms of WGS. Moreover, offering theoretical underpinning for future pertinent engineering construction endeavors.