Nonlinear creep model of rock in tensile or compressive stress and its parameter identification

Abstract：Based on the power function fitting analysis of acceleration creep curves of rocks in tensile and compressive stress,a nonlinear expression of viscous components in the visco-plastic creep model was derived,which then incorporated with the Burgers creep model to achieve the building of a new nonlinear creep model.This new model can well describe the decay,steady-state and acceleration creep stages of rocks in tensile or compressive stress.Combined with creep test results of red sandstones in Chongqing under uniaxial direct tension and uniaxial compression,compiled the Quasi-Newton algorithm（BFGS） by Matlab program,which helps to identify the parameters of creep model of rocks in tension and compression.The results indicate that squared value of identification parameters correlation coefficient,R2,is more than 96%;and the new nonlinear creep model does better in fitting creep curves of rocks in tension and compression than the modified Nishihara model as well as in applicability to the tensile and compressive features of rocks,thus further verifying this model＇s validity in describing the rock creep deformation in tension and compression.