The horizontal soil sealing theory:
A water retaining injection layer can be applied within a pre-built soil and water retaining structure (sheet piling, diaphragm wall, pile wall). The injection layer is formed by placing injection tubes at depth in a pre-determined grid and then injecting one at a time.
As the pressure and flow are monitored and controlled by injection computers, the injection bodies can be built-up simultaneously. The ground water present during the injection process is forced out of the voids and replaced with the desired injection fluid. This technique is known as ‘permeation grouting’. The injected fluid reacts at the desired location thereby forming the water retaining layer.
The injection layer is applied below the excavation level to avoid ruptures in the floor of the excavation pit. Tension elements are not needed because of the ballast layer. It could occur that the required structural sheet piling length is not sufficient to maintain adequate ballast on the injection layer. In this case we can specify the sheet piling length that is needed for the injection.
Benefits / Considirations:
Many current construction projects use underground construction layers. Pump drainage or a combination of sheet piling and underwater concrete is used for much of these cofferdams.
Horizontal soil sealing using injection is an alternative to the above methods. There is no rule-of-thumb to determine which option will be the most profitable in a project or with regard to execution is technically the best option.
Thus, every cofferdam is customized work. The following have to be taken account of, the present subsoil, the width and depth of the cofferdam, the structural length of the sheet piling, the permeability of the subsoil, the regulations in respect of pump drainage, the anchor blocks needed for the underwater concrete, etc. In order to select the right option, it is best to look at all alternatives for every project.
The following are some of the benefits of horizontal soil sealing using soil injection:
- Little or no groundwater abstraction;
- A clean and dry construction pit;
- Excavation can take place from within the construction pit within one week after the injection process is completed;
- Possibility for dry excavation, thus no wet transport;
- There is no need for a sludge deposit;
- During excavation any warping in the sheet piling construction will not result in
additional horizontal pressures to the injection layer, thus no leaks in the
sheet piling housings;
- The top layer of soil creates sufficient downward pressure to prevent any ruptures
occurring. This means no anchor blocks or piles are needed with soil sealing.