I am trying to model (unsaturated rock, transient flow) a tunnel at depth being first excavated then filled, before being closed (t = t_final). At time t = t_0, I assume that the tunnel has already been excavated and that filling can begin. During filling, I need the tunnel to stay dry, so I assign a head boundary condition (= elevation of the base of the tunnel) with constraints (min = - pump rate from t_0 to t_final and = 0 at t_final; max = 0) at each tunnel node. For the filling period, I also assume that the tunnel is more (by a factor of about 2) permeable (K) and porous than the surrounding rock.
When looking at the results, I find that the pressure in the tunnel tends to get much higher than that of the surrounding rock, which should not happen. What am I doing wrong?
Thanks.
