Analysis on Structural Characteristics of Grout and Rock Distribution in Complex Geological Mixtures after Grouting Reinforcement and Its Mechanical Strength

Soil rock mixture (SRM) is a common geo-material, which usually needs to be treated by grouting reinforcement. The grouting effect is tied to the grouting method, grout property, and geological condition, which are difficult to be quantitatively analyzed. The main obstacle in developing a rigorous theory for evaluating the grouting effect is the heterogeneity of SRM. This paper aims at developing a preliminary theoretical model and an empirical formula for predicting the overall strength of grouted SRM based on the actual morphological structure of grout-rock skeleton and its heterogeneity. A discrete element model was established for analysis of grout vein structures and validation of the theoretical approach. Two morphological parameters called “grout vein uniformity” and “block-skeleton conversion ratio” were proposed to quantify the influence of spatial distribution of grout vein and rock blocks in grouted SRM. Finally, an empirical formula was established for estimating the uniaxial compressive strength of grouted SRM, with a complete description of rock conversion ratio as a function of grout proportion and rock proportion. The ability of the approach to capture the influence of the grouting effect was verified by comparing the predicted values with the numerical values and the laboratory test results of this study. The improvement of the mechanical property of the stratum can be quickly assessed according to the obtained correlations as a general rule. Specifically, the normalized UCS increases in a linear fashion over grout proportion at a rock-soil ratio between 0.6 and 0.8. However, the theoretical model may overestimate the strength when the rock-soil ratio is higher than 0.9. It is open to improvement by further studies for the systemization of a more rigorous and robust approach in estimating and accommodating the uncertainties when applied in grouting operation guidance in the real world.