Settlements of Immersed Tunnels

Most immersed tunnels are placed in underwater trenches and add little net load to the foundation soils. Reloading settlements, compression of foundation courses and construction activities can nonetheless result in appreciable settlements of tunnel elements which can threaten tunnel alignments, joints between individual elements, or the structural integrity of the tunnel elements. This paper describes the design and construction of the Second Hampton Roads Tunnel. It provides assessment of tunnel displacements and describes the settlement performance of the tunnel. For example, settlement data from the First Hampton Roads Tunnel correlate well with those from the second tunnel. Rational methods for forecasting total and differential tunnel settlements are shown to produce reasonably reliable results when construction factors are fairly considered. Soil compressibility data for reloading are essential for such settlement analyses.