Abstract: The Zhongtiaoshan tunnel crosses rich and highpressure water Tertiary formation for a long distance. To guarantee the structural stability and operation safety, a treatment scheme of gravel filling + grouting reinforcement is put forward to solve the argillization of foundation, which improves the bearing capacity of soft foundation of heavyhaul railway tunnel effectively. Then a drainage and pressurerelief technology for invert bottom is developed, the drainage ducts are laid on surface of primary support of invert to conduct dewatering, thus reducing the structural damage risk of tunnel foundation during operation caused by dynamic groundwater pressure.

Key words: tunnel, highpressure groundwater, Tertiary formation, gravel filling, grouting reinforcement, foundation drainage