Numerical analysis and field experiments of a new drainage system with pressure valves for single shield TBM

Single shell segmental lining can withstand a maximum water head of about 50 m. If the water pressure exceeds this value, it is necessary to partially reduce groundwater pressure acting behind the tunnel lining.This paper presents a novel TBM tunnel drainage technology that employs adjustable pressure valves to regulate the volume of incoming water. This method not only reduces the impact of tunnel drainage on the surrounding groundwater environment but also effectively decreases the water pressure behind the lining, lowering the risk of structural damage and enhancing the load-bearing capacity of the lining. This represents an integration of prevention and drainage in the engineering concept of groundwater control.The study commenced with field experiments in the Daxiang Mountain Tunnel of the Fuzhou Intercity Railway, focusing on the effects of different drainage hole spacings and pressure valve settings on tunnel water inflow, pressure behind segmental linings, and strain on the linings’ inner surfaces. A numerical model was subsequently constructed to compare and validate these field monitoring results, which demonstrated a high level of agreement. Finally, a parametric analysis was conducted, and the results indicate:

• (1)
  Although increasing the spacing between drainage holes effectively controls groundwater discharge, the resulting higher water gradient near these holes significantly increases bending moments at the foot of the side wall and invert of the lining, thus elevating the risk of structural disorders in the lining.
• (2)
  At segmental linings with drainage holes spaced at 3.6 m, the installation of pressure valves set to 400 kPa reduced the drainage volume from 2.18 m³/(D·m) to 1.56 m³/(D·m) compared to the full drainage scenario. This reduction satisfies the groundwater conservation requirements of the Daxiang Mountain area and significantly lowers the risk of structural damage to the lining caused by high water gradients near the drainage holes. Consequently, the load-bearing capacity of the segmental tunnel structure is effectively utilized.

The research outcomes of this paper can offer guidance for the drainage countermeasure design in similar TBM tunnel projects.