Job Reports
ALUMINIUM OF GREECE S.A.

Technical description:

The project involves the construction of a new well at this company’s plant in Agios Nikolaos, which will be used for casting 8.50m long aluminium columns. The works to be carried out necessitate the prior construction of a provisional outside lateral support shaft, wherein to place the permanent aluminium column casting shaft, at the bottom of which a watertight hole will be constructed for the placement of the piston.

The technical survey of the soil in the project’s area showed that down to a depth of 30m the subsoil consists of a very soft formation with poor mechanical properties, while the underground water level lies at a depth of only 3.50m from the working surface. In addition, the construction area of the new well was already occupied by an older underground armoured concrete shaft cased in 15m deep steel sheet piles.

The erection of the provisional lateral support shaft required the construction of an in-situ cast armoured concrete diaphragm wall, 80cm thick and running 21m deep on the outside of the existing sheet piles. The purpose of the diaphragm wall is both to laterally support the excavation trench and to ensure waterproof conditions at the project’s area.

For the construction of the shaft for the installation of the hydraulic piston, first a 1.80m wide hole was drilled at a depth of 23m, and then a 1.40m wide steel pipe was placed, closed at the bottom end. Grout was injected all around the pipe to ensure on the one hand the pipe’s firmness inside the hole and on the other hand its protection against erosion.

At the same time, 2 pumping shafts were constructed inside the diaphragm wall to facilitate keeping the underground water level below the working surface at all times. Subsequently, stone columns were constructed and arranged on a grid inside the diaphragm wall by the jet grouting method. This improved the foundation conditions for the permanent casting well and reduced the soil’s permeability underneath the excavation bed, thus reducing the pumping required.

Upon completion of the stone column construction works, excavation works started inside the diaphragm wall and, when the final depth was reached, a metal box was placed to ensure absolutely watertight conditions before commencing with the construction of the permanent well.