ABSTRACT
We have seen from the historical development of immersed tunnels that there are now two principal choices of immersed tunnel in use today. These are the concrete tunnel and the steel tunnel. Concrete tunnels comprise elements of either monolithic or segmental form, whereas steel tunnels can be formed of elements that are single shell, double shell, or sandwich construction. There are variations of each type, but both provide durable long-life structures that can be constructed safely. It is helpful to elaborate a little further on each type of construction to provide an introduction to current construction practice, and this chapter goes into further broad description by way of this introduction, but reference should be made to all subsequent chapters to understand the full detail of design and construction techniques.
MONOLITHIC CONCRETE ELEMENT CONSTRUCTION
