Stable creep upper and lower thresholds in roadway (tunnel) surrounding rock and it’s determination method

Based on the rock creep characteristics and the formation mechanism of stable creep termination trajectory line,the existence of rock stable creep upper and lower thresholds is revealed and the test determination method is giv-en. The influence of the different loading paths and different load termination levels on surrounding rock deformation zoning is analyzed. With the above work,the basic properties of stable creep upper and lower thresholds in surrounding rock are found. In order to obtain the determination method of internal and external boundary stress of the plastic hard-ening zone in the surrounding rock,not only the linear relationship between the hoop stress and the radial stress in the elastic zone is utilized,but also the fitting lines of the stable creep upper and lower thresholds under different confining pressures are used. The results have an important reference value for the correct establishment of the strain softening model,the scientific research on the deformation zone of surrounding rock and the quantitative design of supporting pa-rameters.