Gaussian Random Fields for Modelling the Influence of Soil and Dredging Variation on Shear-Keys of Immersed Tunnels

Immersed tunnels are buoyant structures, which are constructed by immersing elements to the seabed and covering them with sand and rocks to counter the buoyancy and for protection afterwards. From a structural point of view, an immersed tunnel is a flexible system with segments. Between elements the displacement degrees of freedom are coupled, but the rotations are not coupled or restrained. Discontinuous loading in the longitudinal direction or discontinuous bedding conditions will result in a response variation over the length of the flexible tunnel. If the response between two segments is not equal, shear forces are transferred on the segment joints by shear-keys. The foundation of an immersed tunnel is influenced by many factors related to soil but also to construction and dredging tolerances. Because of the geometrical limitation of the tunnel due to immersion and buoyancy requirements, the size and therefore the capacity of these shear-keys is limited. A combination of soil stiffness and dredging depth including their spatial variability is researched in a simple structural model in a systematic and probabilistic approach. For these effects, Gaussian random fields with different covariance lengths are investigated. This research shows that the maximum shear forces are found when the covariance length is in the same order as the segment dimensions.

Keywords: Gaussian random fields, immersed tunnels, covariance length, shear-key