This study addresses the challenges of excessive fluidity and poor bonding performance in ultraretarded solidification mine tailings waste-based shotcrete. The research investigates the fundamental mechanical properties of this material by optimizing the proportions of mineral powder (A), soil-rock waste (B), and water content (C). Comprehensive analysis was conducted through mechanical property testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) to elucidate the hydration mechanisms. The results demonstrate that a mineral powder content of 20 % (A1B2C3 to A1B1C1) yields optimal performance, with compressive, splitting tensile, and flexural strengths reaching 138.5 %, 163 %, and 154 % of baseline values, respectively. Maximum compressive strengths of 16.12 MPa, 24.18 MPa, and 32.08 MPa were achieved under specific mix conditions (C1A1B1). Additionally, increasing the content of A and C was found to extend the setting time of the cementitious material. The optimal mix ratio, comprising 20 % A, 25 % B, and 4 % C, exhibited enhanced hydration degree and superior macroscopic performance. Field construction tests confirmed that the material's viscosity, fluidity, and rapid-setting properties meet practical engineering requirements.

A key and urgent scientific issue is how to characterize the complex intergranular contact state and mechanical behavior evolution of sand-fines mixed materials and then show how this state contributes to the static and dynamic properties of such materials. Both theoretical analyses and experimental data suggest that the mixes have different intergranular contact states as the fines content (FC) increases, and the mixed materials can be classified as sand -like, in -transition, or fines -like. The capability of the Rahman semi -empirical formula to predict the threshold fines content FCth-which distinguishes the regime of fines in sand (sand -dominated behavior) from that of sand in fines (fines -dominated behavior)-is verified using the basic material and mechanical properties of mixed materials from the literature. Developed from the method for determining the theoretical minimum void ratio, a new method that allows unified characterization of the critical intergranular contact state parameters FCin-min and FCin-max for in -transition soils is established based on the binary packing model, and FCin-min and FCin-max can be determined simply through explicit expressions that use some material physical indices of pure -sand and pure -fines materials. The proposed procedure offers significant advantages for evaluating the critical intergranular contact state and mechanical properties of sand-fines mixed materials in geotechnical engineering practice.