Abstract: Many technical issues are encountered during the construction of the Yima No. 1 tunnel on the Xi′anYinchuan highspeed railway in the waterrich loess stratum, including water seepage on the tunneling face, soft surrounding rock spalling, primary support deformation and collapse, and soft foundation of the tunnel bottom. As a result, an indepth study on surface dewatering excavation and soft foundation reinforcement is conducted, and the dewatering and reinforcement effect is analyzed. The findings are as follows: (1) Because the designed water gushing volume is largely different from the actual one based on experience, a deepwell drainage test should be performed first to provide a reference for water gushing volume parameter design. (2) The practice demonstrates that advanced surface dewatering for the tunnel crossing deep waterrich soft plastic loess soil layer is feasible. Surface dewatering which is superior to intunnel drainage, can improve the stability of the surrounding rock and facilitate tunnel construction. (3) When tunnel foundations are reinforced with steel tube piles in waterrich softplastic loess stratum, many disadvantages occur, including large disturbance to tunnel excavation, complex pile formation, and low water stop and reinforcement effect, whereas Soletanche grouting performs better.

Key words: waterrich loess tunnel, seepage and water gushing, surface dewatering excavation, soft foundation reinforcement