Deep mixing in underwater conditions: a laboratory and field investigation

The aim of the present paper is to discuss the laboratory and in situ behaviour of an artificially cemented dredged material. An extensive laboratory testing campaign carried out on soft soil specimens, mechanically mixed with different binders, demonstrated that blast furnace cement has a great potential for the stabilisation of such material. In the laboratory the ordinary practice of mechanical mixing by means of a dough mixer was used, whereas in the field a newly developed deep mixing method was implemented for the installation of trial columns (the soft soil improvement technique), making use of high pressure for injecting a cement slurry through nozzles at the mixing level. A column quality control revealed that the improvement level in the field was higher than on samples prepared in the laboratory. Scanning electron microscopic analysis employed to investigate the microstructure of a specimen mixed both in the laboratory and in the field demonstrated the premise that the technological details of the mixing procedure in the field are key parameters and possibly the main cause of the important beneficial differences in strength results