Quantitative assessment of calcareous cementation in moraine soils: insights from an integrated mineralogical and granulometric analysis

Calcareous cementation in moraine soils remains insufficiently studied, despite its critical role in influencing mechanical behavior and slope stability. To address this gap, a series of tests were conducted, including field surveys, X-ray diffraction (XRD) tests, Scanning Electron Microscope (SEM) analysis, energy-dispersive X-ray spectroscopy (EDS) tests, grain sieve tests, and dilute hydrochloric acid (HCl) pretreatment tests. XRD results revealed widespread carbonate cementation in the study area, primarily composed of calcite and dolomite (5.09–30.26%). SEM and EDS mapping revealed that calcium carbonate is mainly a rigid cementing agent, bridging grains and contributing to the structural integrity of moraine soils. HCl pretreatment significantly reduced calcareous mineral content and relatively increased the proportion of silicate minerals. It also led to a decrease in gravel content and an increase in fine particles (< 0.25 mm), thereby shifting the cumulative grain size distribution (CGSD) curves. A new Sigmoid-TL CGSD model is proposed to quantify these changes in (CGSD) curves, serving as an indirect measure of calcareous cementation. The model parameters (k, γ, ΔA) are closely correlated with the degree of cementation, providing a robust mathematical representation of its influence on soil structure. Additionally, calcareous cementation is susceptible to degradation from external factors, such as road excavation and acid rain, which may increase the risk of instability and debris flow development.