The first step in constructing the buildings of Anse du Portier 1/3
The foundations ensure the stability of the structures
Foundations are the structural elements that support buildings on the surface and underground. They have two main functions:
- They transfer to the ground the forces of the structure, its weight and the loads and overloads applied to it. They ensure the resistance and stability of the structure. The larger and heavier it is, the larger the dimensions of the piles that support it;
- During rare events such as an earthquake, they play an essential part as they enable the building to respond to the seismic tremor uniformly over its entire surface, keeping it safe from damage. If the building sits on different types of soil (e.g. sand and rock), their different mechanical properties generate different shake responses, which in turn create imbalances.
In order to absorb all the forces to which the buildings are subjected, the foundations are anchored in the ground. Therefore they must be established on a stable and solid support.
Generally speaking, depending on the nature of the construction to be supported (taking into account its weight, dimensions and shape), and the geological composition of the soil, a homogeneous and hard ground must be found in the subsoil to support the foundations.
The deep foundations of Anse du Portier
At the construction site of the offshore extension, the foundations are deep:
The bedrock (the stable and hard layer of rock under the backfill1 and under the new land created) is not at the same depth under the entire surface of the district. The boreholes to reach it for pouring the reinforced concrete piles vary from 17 to 61 metres.
Schematically, the piles can be likened to huge stilts on which the constructions are placed.
The buildings of the Anse du Portier district are heavy and have particular shapes, especially the port building. It will have 17 floors and be 126 metres long, says Philippe Péchiné, in charge of the deep foundations for MODA2 “… consequently, the load distributions are significant3.
Philippe Péchiné, is in charge
of deep foundations for MODA. Photo © SAM L’Anse du Portier
The special design of the building includes large overhangs. These concentrate loads on particular points…” which must therefore be supported.
The layout map of the 1,100 piles that will support the buidlings and structures of the Anse du Portier district. Illustration © SAM L’Anse du Portier
In addition to the buildings above ground and their unique qualities, there are also underground levels:
- The level one basement holds the technical gallery that houses the various networks essential to the life of the district (water, electricity, gas, telephony, sewage disposal, etc.),
- The level two basement contains the inner service road allowing the circulation of vehicles and access to the car parks and technical premises.
The piles in figures
- A total of 1,100 piles will be installed under the entire six-hectare offshore extension. This is the largest operation of its kind in Europe.
- The average length of a pile is 38 metres.
- The shortest lot of piles is 17 metres long and the longest 61 metres.
- Placed end to end, all the piles would form a straight line 40 kilometres long.
- 40 000 m3 of concrete will be needed to build all the foundations.
- The area that includes the port building requires 160 piles laid out over 3000m2, i.e. 15% of the total foundations.
- For each of the four buildings of the “Jardins d’Eau” (Water Gardens), 70 piles will be needed, about 15 for each villa.