Secondary Development And Application Of ANSYS Based On Rock Nonlinear Unified Elastic-Plastic Model

At present,the Mohr-Coulomb strength theory is widely used in rock engineering,but the Mohr-Coulomb strength theory ignores the influence of the intermediate principal stress on the rock strength.The Mohr-Coulomb strength theory is a linear strength theory and cannot reflect the nonlinear characteristics of the rock strength envelope.The Drucker-Prager criterion includes the intermediate principal stress,but it cannot reflect the difference in rock strength on different meridians.The nonlinear unified strength theory of rock proposed by Zan Yuewen theoretically makes up for the above shortcomings.It combines the advantages of unified strength theory and Hoek-Brown strength criterion,which can reflect the influence of intermediate principal stress on rock strength and the nonlinearity of rock strength envelope.This paper firstly derives the elastic-plastic constitutive relation based on the nonlinear unified strength theory of rock.At the same time,combined with the efficient operation function and excellent data processing module of ANSYS software,and using the ANSYS user programmable secondary development tool UPFs,the corresponding secondary development subroutine USERMAT.F was written.The main functions of ANSYS,the compiling,linking and activation of UPFs,the method of subroutine realization and the writing steps are also described in detail in this paper.By comparing the elastic-plastic analytical solution of circular tunnel under hydrostatic pressure with the numerical solution obtained by the developed program,the correctness of the secondary development model program is proved.At the same time,the variation law of the circular tunnel stress field under different principal stress magnitudes is analyzed.The results show that with the increase of the intermediate principal stress effect,the stress in the plastic zone changes obviously,and the plastic radius decreases.Then,the secondary development model program is applied to the conventional triaxial experimental numerical simulation of Darley Dale sandstone and the field triaxial experimental numerical simulation of marble in Jinping II Hydropower Station.It can be found that the two have a high degree of agreement and the curves almost overlap.At the same time,by changing the intermediate principal stress coefficient,it is found that the simulated stress results of Darley Dale sandstone with b=0.15 and marble with b=0.34 are in the best agreement with the experimental results.The main reason is that the conventional triaxial test ignores the effect of ?₂ on the damage of cylindrical specimens at the macroscopic level,and when the specimen is divided into numerous units,the effect of intermediate principal stresses still exists on the tiny units inside the specimen from the microscopic point of view.Finally,the generated customized version of ANSYS program is used to analyze the rock slope excavation project in the Bayan Obodong mining area.From the analysis of the displacement angle,it can be found that when b=0,1,the displacement value of the numerical simulation is quite different from the measured displacement value of the project.When b=0.6-0.86,the numerical calculation result and the measured result meet the error requirements,and when b=0.74,the error between the numerical calculation result and the measured result is the smallest,and it is the closest to the measured displacement value.From the point of stress analysis,the excavation of the rocky slope in the Bayan Obodong mining area is a process of unloading,and some tensile stress areas will appear on the failure surface and the top of the slope after excavation.With the increase of the intermediate principal stress effect,the yield range of the slope is reduced,especially at the foot of the slope,the yield change is relatively obvious.