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Sealing walls

Sealing walls are a special kind of slurry walls, cast in-situ, and depending ion the value of permeability lined with almost impermeable HDP lining. They prevent horizontal groundwater movements and, as such, isolate the site hydrologically from its surroundings. Typical wall thicknesses are 0.40-0.60 and 0.80 metres, and large depths up to 60m can be attained. Sealing walls are liquid-retaining and have no bending moment capacity. To enable moment capacity, the walls can be fitted with prefab concrete elements,which also enable the transfer of vertical loads to the subsoil. The trenches are dug using a special grab. The stability of the trench during excavation is guaranteed by introducing cement, bentonite and water or Dämmer. When the trench has reached the desired depth, the supporting liquid stays behind and the mixture hardens. Excavation can also be performed with bentonite and replacing it with the sealing mixture at a later stage (two-phase system). However, the single-phase system described first is more common. The degree of impermeability greatly depends on the additive chosen.vThis typically is a mixture of bentonite and cement, which can easily attain a permeability of 1 x 10-8 m/s. The quality of the sealing wall mass is assessed during construction in a field laboratory set up for the purpose.

Applications

Sealing walls can be applied for e.q.:

  • to enclose building pits to allow open draining and prevent impacting the groundwater level in the area; 
  • to create green slopes for the entrances of tunnels for sunken motorways; 
  • to isolate landfills and soil pollution to prevent groundwater pollution in the area;
  • to enclose building pits in inner-city areas..

Ambient factors

  • The equipment used for sealing walls is large-scale and requires a fairly large surface area for the bentonite plant.
  • Storage and set-up space for the bentonite basins, silos and mixing installations must also be taken into account.
  • Guide walls for the grab and for the stability of the top of the wall must be constructed prior to production.

Pros and Cons

  • Sealing walls can be realised with little noise and vibrations.
  • Hard layers of soil can be penetrated without problems.
  • The system is not sensitive to small obstacles in the soil.

Applicated

 

Name of project

Client

Delft, Motorway A4

Construction consortium A4All

Nijmegen, Ruimte voor de Waal project

Dura Vermeer

Tollebeek, Extension wastewater plant

Aan de Stegge

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