Abstract: The safety of surrounding rock and support structures of deep-buried soft rock tunnel is faced with great challenges under the action of high external water pressure. Drainage structure is a common engineering treatment to alleviate the impact of external water pressure on the surrounding rock and support structure of soft rock tunnel. A simple seepage-stress coupling scheme for tunnel’s surrounding rock-lining structure is first established. The drainage effect of the drainage structures of a deep-buried soft rock tunnel crossing a fault zone is investigated through seepage-stress coupling analysis in construction period and operation period. Under the combined action of grouting ring and drainage structures, the hydraulic gradient near tunnel lining is small while the hydraulic gradient of grouting ring is large. As a result, the grouting ring bears most of the external water load, while the tunnel lining bears a small part of the external water load. In addition, under the deformation compatibility between soft rock and lining, the co-bearing effect between grouting ring and lining is finally formed, which effectively improves the safety of the tunnel in operation period.

Key words: water conveyance tunnel, soft rock, high external water pressure, drainage structure, seepage-stress coupling analysis