By default, one can think of *RS2* as modeling the liner as being free draining, where water pressure does not build up behind the liner.

Applying a water pressure to a liner with groundwater is a bit complicated. You actually need to use a composite liner with a joint element or structural element between the soil and the liner. You can apply the water pressure through the joint.

Two sample files are attached to this article, which include a composite liner with a joint that gets pressurized by the groundwater pore pressure. The axial force increases by about 0.2 MN in Stage 3, which is about right for a thin walled cylinder subjected to a hydrostatic pressure of 0.1 MPa (10m*10kN/m^{3}). N=PR, where P is the water pressure and R is the tunnel radius (2m).

The first file (Pressurized Liner.fez) uses a groundwater analysis to compute the pore pressure. The second file (Pressurized Final Liner piezos.fez) uses piezo lines.

Composite liners are also discussed in Tutorial 15.

*Pressurized liner examples using groundwater analysis (left) and piezo lines (right)*