Stability of an immersed tunnel in offshore conditions under deep water wave impact

One of the special design requirements for the immersed tunnel of the Busan–Geoje Fixed Link in South Korea has been the stability of the tunnel under wave impact with up to 9.2 m significant wave height. A large part of the tunnel is placed in a trench and is founded on soft marine clay which is reinforced by cement deep mixing (CDM) columns to limit and control the settlements caused by the weight of the tunnel and its protection material. Being beyond the scope of any design standard the problem of the tunnel stability under wave impact has been investigated and verified by a combination of physical model tests and numerical modelling. This paper provides a detailed description of the methodology applied to solve this particular problem and a discussion of the results and consequences for the design of the tunnel.