A rock strength criterion considering spatial properties of principal stresses
Based on the existing theories and experimental conclusions on the spatial damage surface characteristics of the principal stresses of rock materials,and in response to the problem that the conventional strength criterion has many parameters and the physical significance is not clear,it is put forward that there exists a strength curve in the bi-directional isotropic tensile stress point with the point of view that d(σ1-σ3)/dσm=3,by analyzing the characteristics of the change of the conventional triaxial compressive strength curves in the bi-directional isotropic tensile stress point(0,σtt,σtt).Meanwhile,a hyperbolic-type strength criterion containing two parameters of two-way isotropic tensile strength σtt and three-way isotropic tensile strength σttt is established,which takes into account both the average stress effect on the strength curves on the meridian and the π-plane,and the parameters have clear physical meanings.In order to verify its reasonableness and applicability,the strength criterion was utilized to fit and calculate the triaxial test data of 14 types of rocks in the published literature,and compared and analyzed with Burzynski's parabolic criterion and You Mingqing's exponential criterion,which have higher fitting accuracy.The results show that the fitting effect of this criterion is better for both conventional triaxial test data and true triaxial test data,with the correlation coefficients above 0.99,and the sizes of the fitted bidirectional isotropic tensile strengths σtt and the three-directional isotropic tensile strengths σttt are in a reasonable range;at the same time,the fitting results under different constraints corroborate the idea that there exists d(σ1-σ3)/dσm=3 at the bidirectional equal tensile stress points(0,σtt,σtt).It shows that the criterion is reasonable and applicable,and can provide some practical guidance value for the field of rock engineering.
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