Discussion: Session 1: Geotechnical and hydraulic

H. Oudy Rijks waterstaat

With reference to Paper 1, how accurate are your measurements of the siltation depth, and do the uplift forces affect the river flow and siltation?

T.N. Burt, Paper I In the case of the Conwy tunnel, some physical model tests of the uplift forces were done by Delft Hydraulics. They built a scale model of the tunnel element and checked the forces over a whole range of conditions, studying wave and current effects, different angles to the flow, and salinity and buoyancy effects. If you have both fresh water and saline flow in the same estuary then it is quite possible, if it is not very dynamic, that you would get a saline layer forming in the trench. Therefore, as the element goes down, the buoyancy suddenly starts to change and you have to compensate.