In 2007, together with partner Invacon, I build a software package for the precise positioning under water of (tunnel) elements.
The approach also allows for the precise positioning of sections of bridges and other large objects and constructions, that need to be placed or transported with greatest accuracy while floating in water, hanging from cranes or moved on vehicles.
Contractors were Dutch construction companies BAM Civiel Projecten and Van Hattum en Blankevoort.
This software was first used during the second half of 2008 for the construction of the Bjørvikatunnel in Oslo, Norway. 6 tunnel elements were subsequently immersed.
In 2010 the software was used to immerse the second vehicle tunnel under the river Tyne in Newcastle, UK. (4 tunnel elements)
Before immersion the element is fitted with a number of measuring targets.
The positions of these targets is exactly known relative to the final (design) position.
During the manouvering of the element, these targets are continuously tracked by robotic total stations and/or GPS equipment using RTK corrections.
The software continuously calculates a 3D model of the element and presents all information relevant for the element position to the commander and crew.
Presentations consist of (map) top and side views of the element relative to the final position, as well as schematic and numerical views.
This way the actual position can be tracked in absolute and relative (to the design position) sense.
GIS Magazine (2009 nr. 4) published an article about the project in Oslo, which can be downloaded here. (Sorry: Dutch language only)
The basic methodology was often used in the past for the immersion of tunnel elements. Wikipedia contains a good description of immersing tunnels in The Netherlands (Dutch). In other languages several articles are available, mostly describing specific tunnels. Search on "Immersion tunnel".
The software, infrastructure and instrumentation as used in the past were much less advanced resulting in a much higher dependency on human factors for the evaluation of the ongoing process, which also translated in longer running operations. As the deployment of resources, both in terms of equipment and manpower, for these types of operations is quite sizable, a small saving in time can already result in significant financial savings.
Most important however is, that the techniques used must deliver accurate information and the commander always has the final judgement.