Analytical method for elastic-brittle-plastic analysis of a circular tunnel in a non-hydrostatic in-situ stress field considering the unified strength criterion

•Analytical method evaluates the circular tunnel's stability in a brittle rock mass.•Failure zones develop under a general condition of a non-hydrostatic stress field.•Three-dimensional analyses address impacts of tunnel axial stress on failure zone.•Brittle failure causes rapid growth of failure zone along minor geostress direction.•Failure zone changes in shape, size and mode with different geostress differences.