Abstract:  The original roof ripping design for the connection between shaft No. 2 and the main tunnel of Muzhailing tunnel on the WeiyuanWudu expressway is improved to allow roof ripping construction in soft rock with significant geostress. A new roof ripping design with a smalldiameter prestressed anchor cable as the key technology is proposed based on the highstrength prestressed support theory, in which the joist and the support beam are cancelled to achieve the idea of "support replaced by cable". The structure and technology of the smalldiameter prestressed anchor cable, as well as the design and implementation scheme of roof ripping and supporting, are studied and applied to the roof ripping construction for the connection section between inclined shaft No. 2 and main tunnel of Muzhailing tunnel. The monitoring results of the surrounding rock deformation show that the proposed method is safe and effective.

Key words:  high geostress soft rock tunnel, roof ripping construction, long span, prestressed anchor cable, support replaced by cable, supporting structure