Milan’s Teatro alla Scala or La Scala is one of the world’s most famous opera houses. It is halfway into a major and controversial restoration in which the theatre house will be left intact but the backstage space will be gutted and rebuilt. (see page 4).
One aspect, indubitably beyond controversy, was the need for additional storage space. This is being provided by a new deep-level basement – 24m by 34m in plan area – that is being constructed in the stage area. This is linked to a second, smaller 15m by 6m basement area stage right.
As a result the stage has been removed and – at the cost of Euro 2.5M – temporarily transformed into an 18.6m-deep pit. The site looks much like any deep foundation box, other than the fact that the heavily protected stage opening can be clearly seen supported by a new piled retaining wall immediately above the face of the excavation box.
Thick permeable sand and gravel deposits underlie Milan and with the water table at around 17m below site level – ie 1.6m higher than the maximum excavation depth – control of groundwater has had a governing effect on the foundation solution.
In addition the foundations had to account for long-term regional groundwater rise, which prompted foundation contractor ELSE to use an innovative combination of jet grouting and micropiling.
Structurally the most sensitive walls are the front stage wall and a wall that runs alongside the appropriately named Via Verdi.