Investigation of the classification system for Xiyu conglomerate based on engineering geological and fabric characteristics

Abstract Xiyu conglomerate is a significant and extensively distributed geological formation in western China. A clear understanding of its properties and the establishment of a classification system are essential for selecting appropriate research methods to investigate its engineering mechanical behavior. Based on geological data from eight typical Xiyu conglomerate geological belts and seven hydropower projects, this study summarizes the main engineering geological characteristics, and analyzes the fabric characteristics of various components of the conglomerate through laboratory tests and statistical analysis. A comprehensive classification system is proposed for Xiyu conglomerate based on two key criteria: (1) grain size distribution, quantified by the d 50 (median grain diameter), and (2) cementation type, identified via mineralogical and geochemical analysis. This system divides Xiyu conglomerate into nine distinct categories, each defined by specific engineering geological and petrofabric properties. The results reveal that, even within the same region, the grain size composition and distribution of Xiyu conglomerate are highly heterogeneous. While the chemical composition of the cementing materials is generally consistent, notable differences in cement properties arise primarily from variations in mineral content, particularly the proportion of calcareous material (dolomite, calcite, and quartz). Conglomerates with gray or grayish‐blue matrices typically exhibit higher calcareous content, whereas those with earth‐yellow or khaki matrices contain less calcareous material and are predominantly argillaceous‐cemented. Additionally, Xiyu conglomerate shows higher porosity compared to conventional rocks. The proposed classification method based on engineering geological and fabric characteristics offers a geological basis for further determining the engineering mechanical properties of various Xiyu conglomerate types. This approach holds potential for addressing the challenges related to unclear classification and difficulty in accurately defining mechanical parameters for Xiyu conglomerate across different regions.