Research on the variations in the weathering of large open-air stone relics from macro- and microperspectives: a case study of the Leshan Giant Buddha

The nature of stone relic bodies is mainly determined by their stratigraphic properties; large open-air stone relics are affected by the stratigraphic span in space and have variations in weathering, and the systematic study of these variations is relevant to the prevention and treatment of weathering and restoration on the premise of the research and development of materials. Traditional research on the weathering of stone relics is usually focused on local or small-scale analysis, which uses qualitative evaluations by employing engineering geology techniques to determine weathering levels. However, quantitative research is relatively rare because large open-air stone relics lack systematic and comprehensive research. To systematically study the degree of weathering of large stone relics and quantify their variations, a method for determining the degree of weathering variation in large stone relics from macro- and micro perspectives was established by using a variety of experimental methods with combined testing to carry out a systematic study of the degree of weathering. The results show that there are obvious variations in the degree of weathering of large open-air stone relics and stratigraphic stratification of the rocks forming these relics have been carried out through field investigations and identifications using rock-thin sections. There are variations in mineral composition and elemental content between different layers, and SiO2/(CaO+Al2O3 + Fe2O3) was chosen to characterize the loss of colloids from large open-air stone relics. Al2O3/(K2O+CaO) was chosen to react with the degree of chemical weathering of large open-air stone relics, and a comprehensive comparative analysis of the variations between the layers of large open-air stone relics was carried out. The microscopic pore structures also differ between different layers, and the permeability of layers with dominant distributions of large pore-size pores is greater, which provides more convenient channels for water seepage, thus leading to more severe weathering. This study provides a new quantitative method for studying the weathering variations of large stone relics and provides a scientific basis for the prevention and control of weathering damage to large stone relics.