Three-Dimensional Nonlinear GZZ Strength Criterion of Sandy Dolomite: Verification by True Triaxis Test and Analysis of Intermediate Principal Stress Effect

In response to the complex mechanical characteristics of sandy dolomite in the Central Yunnan Water Diversion (CYWD) Project, this study constructs a multi-parameter strength prediction model (the power function relationship between UCS and SH, I_s(50), Vp, ρ, n, with an R² value ranging from 0.593 to 0.973) through in-situ tests (Schmidt rebound, point load, wave velocity test) and laboratory tests (uniaxial compressive strength and triaxial compression). It also proposes a three-dimensional constitutive model parameter calibration method based on the Generalized Zhang-Zhu (GZZ) criterion. True triaxial tests demonstrate that the intermediate principal stress (σ₂) exerts a significant influence on the brittle-ductile transition and strength properties of sandy dolomite, as evidenced by a 133% increase in peak strength of σ₁ at σ₂ = 0.8 σ₁. By calibrating parameters (GSI = 84.57, a = 0.5, s = 0.4285), the theoretical yield surface predicted by the GZZ criterion shows a high degree of agreement with the experimental data (average error < 5%), thereby confirming its applicability in a three-dimensional stress field. The parameter sensitivity analysis indicates that a has a significant effect on the yield surface morphology (the yield surface is expanded twofold when a = 0.8), while s only causes the overall translation. Engineering case studies further indicate that optimized parameters (a = 0.7, s = 0.45) effectively reduce the extent of the plastic region in surrounding rock by 23%, providing a robust tool for engineering stability analysis of deep sandified rock mass engineering.

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