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Use of walls

Retaining walls are used to contain earth in a given area when building underground car parks, supporting on-site groundwork, laying foundations, protecting sites from mudslides, etc.
Different techniques are used to build structures in a range of shapes and sizes and down to very significant depths:
- Retaining walls for underground car park side walls, and platform walls.
- Round walls to build stormwater basins or tunnel ventilation shafts.
- Major ground works on urban sites.
- Open-air or covered trenches on urban sites.
- Deep and load-bearing foundations.
- Rainwater retention basins.
- Motorways or railway lines.

Adjoining buildings, the presence of water, or even non-cohesive soil can require the involvement of foundations experts, who can estimate the project’s specific soil pressure and choose the most appropriate technique.

Different types of walls are possible: the right technique is chosen based on the purpose of the structure and the soil characteristics.

Diaphragm wall

Diaphragm wall

When they are used as temporary structures, diaphragm walls simultaneously fulfil three functions:
- Supporting
- Load-bearing
- Waterproofing
Based on the soil’s mechanical characteristics and the structure’s geometric characteristics, diaphragm walls can be strutted or anchored as required. Boreholes are drilled using a cable-operated excavator, hydraulic excavator, or cutter. Drill mud provides support during the excavation process: a mixture of bentonite and water, i.e. a 100%-natural product. This mud is used to stabilise the groundwork and set up the rebars and concrete.
Cutters are required when building diaphragm walls or load-bearing elements in high-resistance ground (sandstone, rocks, blocks). This tool - the most sophisticated machine used for foundations - makes working down to significant depths (>50m) and with a variety of thicknesses (0.80 to 1.20m) possible. The rebar cage is then lowered into the borehole down to the required depth. Finally, the concrete is cast using either 1 or 2 tremies lowered down to the base of the borehole.
Soldier pile wall

Soldier pile wall

A soldier pile wall is a type of temporary or permanent retaining wall, commonly used for groundwork on urban sites.
This retention method consists of:
- Drilling regularly-spaced boreholes in which metal uprights are set up;
- Adding plating (wood, shotcrete, or metal plates) between the uprights as the earthworks advance;
The support structure is temporarily stabilised using struts or tie beams except in the case of shallow groundwork where the support structure can be free-standing.
Soil nail walls

Soil nail walls

Soil nail walls are THE standard light, flexible, soil-based support structure.
This support structure is mainly based on the stabilising capabilities of nails, combined with a shotcrete containment layer. The groundwork is excavated in successive top-down phases with the immediate addition of nails and shotcrete.
watertight curtains

watertight curtains

Different types of walls can be used to create watertight curtains:
- Grout walls: walls perforated with a conventional tool using mud mixed with cement that stabilises the trench during digging and sets in a few hours.
- Reinforced grout walls: setup in fresh grout of an H- or I-shaped upright to convert the “flexible” wall into a retaining wall.
- Thin walls: a high-inertia H-shaped upright is vibro-driven into the ground; when this is extracted, the empty imprint is injected with grout. The upright is moved along the wall and the process repeated.
- Composite walls: drainage and waterproofing techniques can be combined using a draining material and a watertight membrane in the same trench.
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