Abstract: In the course of driving through the gas fault or cutting through the coal seam, it often encounters the problems that the thickness of rock pillar protection and delay outburst issues in mine roadway. In order to explore the nonlinear coupling relationship between thickness of rock pillar protection and time, compression creep test of sandy mudstone, sandstone and mudstone are conducted by using triaxial rock creep apparatus RLW-2000 under step loading in this article. By analyzing the combination of classical rheological models and Matlab least squares iteration, an improved seven elements nonlinear constitutive model of viscoelastic plasticity is established as well as the calculation model based on the pillar of rock rheology critical safety thickness. The results of case study of Daping Mine in Western Henan show that when the life spans of anti-burst pillar of mud roadway in the depth of 612 m are 10, 20, 30 years, the corresponding protection thicknesses are 8.73, 23.56, 39.41 m. The theoretical safety rock pillar thickness is consistent with outburst case of Oct. 20th; the calculation model has certain reference significance for similar engineering.

Key words: coal-bearing rocks, creep test, delay outburst, safe thickness