Micromechanical characterization and upscaling homogenization analysis of heterogeneous Xiyu conglomerate

Abstract

Xiyu conglomerate, sampled from a reservoir bank slope in Kashgar, China represents a heterogeneous soil-rock composite characterized by complex mineral compositions and uneven particles. Its hydro-sensitive nature, weak cementation, and low intact core recovery rate pose significant challenges in multiscale mechanical characterization. To this end, a multiscale characterization framework integrating microscopic testing, statistical deconvolution, and homogenization method was proposed to bridge nano-to-macroscale mechanical responses. Mineral composition was quantified through backscattered electron signal (BSE) and energy-dispersive X-ray spectroscopy (EDS) analysis, complemented by atomic force microscopy (AFM) and micro-CT for surface topography and pore structure characterization. Nanoindentation coupled with Gaussian mixture model (GMM) deconvolution enabled discrimination of constituent mineral mechanical parameters (elastic modulus, indentation hardness and fracture toughness), revealing micromechanical behavior. The results show that the other minerals (hematite, rutile, pyroxene) exhibit the highest elastic modulus, followed sequentially by quartz, feldspar, mica, and clay minerals, with analogous evolution trends observed in hardness and fracture toughness. The elastic modulus for various mineral phase is positively correlated with the hardness. Increased fracture toughness in the Xiyu conglomerate accompanies increases in both elastic modulus and indentation hardness among minerals. Compared with the macroscopic uniaxial compression test, the three homogenization methods overestimate elastic moduli compared to experimental data, with generalized self-consistent (GSC) demonstrating superior predictive capability over Mori-Tanaka (MT) and self-consistent (SC) methods for heterogeneous conglomerates. The above multiscale characterization results provide critical benchmarks for predicting mechanical parameters in water conservancy infrastructure constructed within heterogeneous conglomerate formations of southern Xinjiang.