Fast Prediction of a Rock–Soil Mixture Strength Parameter

Rock–soil mixtures are a special kind of engineering material formed in the Quaternary period. This material’s structure is between that of homogeneous soil and fragmented rock and is heterogeneous. Its strength depends not only on the mechanical properties of the soil and rock but also on the relative proportions of soil and rock and the particle sizes; a practical method for quickly and accurately predicting the strength of the rock–soil mixtures would be important for the design and safe operation of high-fill slope projects. By combining experimental data with an extensive database containing strength test data, this paper addresses the factors that influence a shear strength parameter of rock–soil mixtures, the internal friction angle, φ, and proposes an equation for predicting this internal friction angle. This equation uses four factors: the d₄₀ particle size fraction from a standard particle size distribution curve, the uniformity coefficient C_u, the curvature coefficient C_c, and the prepared sample’s dry density (ρ_d). The prediction results are verified by both internal checks and by comparing the predictions to data from the literature. The research results show the following: (1) the proposed equation is useful for predicting the strength of rock–soil mixtures; the prediction errors are generally less than 5 % with the maximum errors not exceeding 10 %; (2) the internal friction angle φ of the rock–soil mixtures is nonlinearly correlated with the four influencing factors d₄₀, C_u, C_c, and ρ_d; and (3) the d₄₀ particle size fraction has the greatest effect on φ, followed by ρ_d; the effects of C_u and C_c are smaller.