Study on Strength Theory Effect of Plastic Zone Distribution of Roadway Surrounding Rock

The plastic zone of surrounding rock is an important basis for evaluating the stability of roadway, and the distribution of plastic zone is closely related to the strength theory. The equation of boundary line of plastic zone is derived by using the approximate plastic condition method. According to specific parameters, the plastic zone is calculated. When the lateral pressure coefficient increases from 0.3 to 1, almost all the plastic zones calculated by different strength criteria have four shapes: butterfly, curved rectangle with concave horizontal direction and convex vertical direction, approximate ellipse, and circle, but the butterfly shape based on DP1 is not obvious. There are differences in the maximum plastic radius calculated by different strength criteria with the same lateral pressure coefficient from large to small: DP3 criterion, DP2 criterion, Mohr–Coulomb criterion/UST (b = 0)/DP5 criterion, UST (b = 0.25), DP4 criterion, UST (b = 0.5), UST (b = 0.75), Matsuoka–Nakai criterion, UST (b = 1), Mogi–Coulomb criterion, Lade–Duncan criterion, and DP1 criterion. With the increase in lateral pressure coefficient, the difference between the results calculated by different strength criteria is smaller. When K0 = 0.3, the maximum plastic radius is distributed at 43°∼47°. The results of this paper show that the strength theory effect of plastic zone distribution cannot be ignored, which enriches the theory of approximate plastic condition method and can provide an important reference for roadway stability evaluation and support design.