Execution process

The execution of the diaphragm walls is preceded by the construction of low guide walls of the dimensions, section and qualities described for the corresponding wall. The bivalve excavation grab, due to its weight and mode of use, needs guides that allow a straight, aligned excavation, to ensure that along the length of the diaphragm wall there are no deviations or curves. The grab also needs a resistive element, capable of resisting the impact produced when it is dropped.

Once in place and adjusted, the grab will start the excavation to the projected depth, normally with the help of bentonite slurries. These liquids, of variable density (and whose principle component is bentonite) allow the excavation to be completed cleanly and do not trigger landslides from the surrounding walls. The bentonite can be introduced into the excavation cavity by pumps from storage tanks.

Once the foundation trench is excavated (the name given to the hole from the depth and maximum aperture of the hydraulic grab, cable or rotary to the hole to be filled with thixotropic cement) the steel support indicated in the framework and cutting plans is introduced, then the concrete is poured through an elephant trunk system, consisting of a bell type tongue and grove system (tremie pipe). With the help of excavation or other auxiliary equipment the framework is introduced and concreted whilst the excavation begins on the next trench. These steps are repeated successively until the completion of the diaphragm wall around the perimeter of the site.

Once the wall is constructed a length of no less than 20-30cm is removed to ensure that the top part of the trench remains clean and uncontaminated with earth, which can remain mixed with the concrete. At this moment the interior guide walls are removed and demolished, leaving a view of the top of the diaphragm wall.

Finally, the beam is joined, levelled and crowned, prior to the excavation and emptying of the cavities. This beam, as its name indicates, has the job of working together with all of the trenches completed consecutively. It also provides a surface above the section of wall with a perfectly levelled elevation, which may form part of the top floor beam. The beam is the highest element of the diaphragm wall, due to which it is given the name, coronation beam.