Control mechanism of outburst-preventing rock pillar thickness in roadway on delayed water inrush in fault

In order to explore the interaction between the thickness of rock pillar for prevention of water inrush and the delayed water inrush in roadway, firstly, the corresponding "six-element" nonlinear viscoelastic-plastic rheological model was established by combining the material constitutive relation with the rock triaxial creep test results. And the "six element" model was fitted by using the method of least squares in Matlab. Secondly, on the basis of analyzing the relationship between the confined water of fault zone and the mudstone pillar for prevention, the influence mechanism of the delayed water inrush in the roadway working face was discussed and the formula for the creep failure time (t) of the mudstone pillar for prevention was deduced. Based on the elastic mechanics equation of creep failure time formula and the integral of the creep failure time (t) in the direction of the main rupture surface, the functional relationship between the thickness of the protective rock pillar (L) and the delayed water inrush time (T) was established. Finally, the elasticity theory and the Gaussian numerical analysis method were used to verify the thickness of mudstone pillar for prevention. The results of case study of Zhaogezhuang coal mine in Kailuan shows:there is a direct function between the delayed water inrush (T) of the working face of the roadway and the protective thickness (L). When the thicknesses of rock pillar for prevention are 10, 20, 30, 40 m, the corresponding delay of water inrush are 20, 42, 67, 94 d. This calculation results are in good agreement with the successive water inrush accidents (lagging 1-3 months) under the corresponding working conditions of the mine, which has certain guiding significance for the actual groundwater calamity prevention and control in mine.