Horizontal soil injections

Horizontal soil injections are used if the groundwater regulations plays a key role in and around the building pit to be created. Obtaining a pumping permit may be difficult, particularly in built-up environments, with a view to settlement of the surrounding area or other groundwater regulations for the area. Filling the pores in a soil layer with an injection fluid creates a horizontal water-inhibiting layer, allowing excavation of the building pit under shallow drainage. The injection is applied at the right depth to create sufficient equilibrium between soil layers to prevent bursting of the pit. Horizontal soil injection is a temporary measure that often is a commercially attractive alternative (in terms of money, time and regulation) to underwater concrete.

Application

A horizontal soil injection is used in permeable soil, such as sand. Application must be assessed in advance by carrying out extensive soil investigations.

This technology is often used to create a water-inhibiting layer in building pits for railway tunnels, underground car parks, tunnels and cellars.

The principle is as follows: First, the soil-retaining walls are installed, such as sheet piling. Next, injection poins are created at pre-determined depths across a regular grid over the surface of the building pit. This depth is selected such that the weight of the soil above the injection layer is sufficient to prevent bursting of the building pit floor.

After this, injection liquid is pumped into the pores of the soil from each injection site.

This injection fluid hardens after some time to create a impermeable layer.

Building pits can then be dewatered under shallow drainage without impacting on the surrounding area.

Pros and Cons

The technique is vibration-free and low-noise
No soil produced during installation of injection points and during the injection proces
Limited footprint for the installation equipment
Dry earthworks
Depth of the wall/sheet piling is determined in part by the depth of the right injection layer and the equilibium of he soil floor and the waterpressure underneath the injected layer

Quality assurance

Quality assurance is essential for guaranteeing proper water inhibition. The injection fluids from a large number of injection points must form a solid, unbroken layer and holes must be avoided.
The following aspects are important:

Proper positioning of all injection points, including vertical positioning. The injection quantity may have to be adjusted according to the depth and the reached pressures.

VSF has a large quantity of measuring data and advanced calculation methods to make this adjustment possible. The mixing and dispensing process of the injection fluids is completely automated. The injection process is monitored by a large number of sensors and digitally registered.

This serves to guarantee that the design is fully implemented and irregularities can be identified and checked.

Applicated

Name of project	Client
Nunspeet, Building pit Nestle GOOPL	Visser & Smit Bouw Regio Noord
Tennet Mastenlijn fundatie, Nederland	Van Hattum en Blankevoort Regio Noord
Delft, motorway A4	Construction consortium A4All
Vijfhuizen, Reinforcement powerline mast	Tennet
Muiden, Construction pit Aquaduct motorway A1-A6	Construction consortium Saa-one
Waddinxveen, Underpass Bredeweg	Prorail
Rijssen, Railroad underpass Veenenslagen	Prorail
Bilthoven, Railroad underpass	Prorail
Amsterdam, Noord-Zuid subwayline Rokin	Projectbureau Noord-Zuidlijn