The required depth for a frost-free foundation is 80 cm. The bottom layer of the foundation must consist of an antifrost layer, 30 cm – 50 cm thick. The concrete layer above that must be of grade C12/15 and have a thickness of 20 cm – 30 cm. The backfill must consist of a non-bound, frost-proof material (at least sand-gravel mix). The safety against ground failure can be increased with a deeper foundation.

Assumption for structural analysis (standard):

Inner friction angle	ψ = 35° (backfill with sand-gravel mix)
Weight of backfill	Υ = 19 kN/m³
Cohesion	c = 0
Foundation	A frost-free foundation with a blinding layer of concrete (C12/15) is required. For the soil below the retaining wall a ground pressure of min. 200 kN/m² must be permissible. The following parameters were assumed for the foundation: ψ = 45°; Υ = 25 kN/m³.

Watchpoint:

The assumptions for the structural analysis can be applied on site by adhering!

Between top level concrete foundation and bottom level precast unit a free space of 5 cm must be provided. For installation, the precast units must be placed on thin hardwood pads and raised until level. Leveling is achieved by adding hardwood pads until the unit is in vertical and flush alignment. The hollow space between foundation and precast unit that is created in this way must be completely filled with flow concrete of grade C20/25, grain size 0/8.

Watchpoint:

To achieve perfect vertical and flush alignment for the precast units, adherence to the installation instructions is mandatory!

The retaining wall units have a construction length of 4’. A joint of approx. 1/3’’ must be left between the units.

Due to the narrower bases, a gap of approx. 2’’ will result. The narrower bases facilitate the installation of the units (radialinstallation is also possible). The gaps below the bases can be easily closed with an in-situ concrete topping poured over the entire area.

Example: 3 x 4’ (construction length) + 2 x 1/3’’(joint width) = 12’ 2/3’’ (installation length)

After the precast units are in place, they must be anchored with round steel of 1/2’’ diameter, by pulling the steel through the upper row of eyelets. Hammering down the eyelets will provide extra support.

Watchpoint:  Do not use the upper anchor for suspending the units!

The joints are sealed with strips of insulation board (bitumen) of 10’’ width. The strips must be fixed in place attached before backfilling the units, on their rear side on the joints.

To ensure durable drainage and to prevent frost lens buildup, a drainage layer must be installed on the rear side.

Tip: The joints between the individual precast units must not be sealed watertight.In this way, surface water can also be drained through the joints.

The backfill should be installed layer by layer in 12’’ lifts and must be consolidated until stable.Backfilling and compaction should be carried out with care, using lightweight tamping equipment to prevent the units from tilting. Higher precast units can be installed in the embankment with an incline of about 1’’ for added safety.

Watchpoint:

A proper drainage is very important for the stability and durability of the retaining wall!

The stability of the corner units, whose bases are shorter for ease of installation, can be ensured by pouring a sufficientamount of concrete topping over the bases of the corner and connecting units.

The connecting units must have shorter bases, depending on the construction height and the construction length of the precast unit.

Anchorage takes place with round steel of 1/2’’ diameter or by screw connection using a 90° fishplate.

Watchpoint:

The stability of the corner area must be ensured with a generous amount of in-situ concrete topping!

Disclaimer:
These typical details are preliminary and conceptual in nature. Anyone making use of these details and related information does so at their own risk and assumes all liability for such use. Site specific design must be performed by a licensed Professional Engineer who is familiar with the actual site conditions, materials and local practices.