Jet grouting is one of the most popular techniques for strengthening soils. The principle relies on the use of a liquid jet with high kinetic energy to deconstruct the soil matrix and mix it in place with a binder brought by the jetted liquid itself (Morey – 1995). The device inside which the liquid jet is formed, called monitor, is usually slowly rotated while jetting to build columns.
This concept was originated in the seventies in Japan. During the past decades, developments around jet-grouting have led to three sub-techniques called single, double and triple jet; depending on the number of different fluids simultaneously operated to build columns: Single jet requires a cement grout with high hydrodynamic energy, while double jet operation adds a second jet of compressed air encapsulating the grout jet to increase its erosion capacity. For triple jet, erosion of soil is obtained by a high energy water jet encapsulated by air while grout is added at lower pressure on the toe of the monitor to incorporate the binder in the mixture.
For a given sub-technique and given soil conditions, the jetting energy – pressure, flow-rate and lifting rate – can be adjusted to reach a target column diameter. Jet-grouting is usually operated with small diameter drilling rigs, which can be operated from narrow platforms and/or low- headroom conditions.
More recently, some technical developments were undertaken to increase the erosive power of the jet, leading to the introduction of new jet-grouting equipment on the market amongst which Superjet monitor in Japan or Jetplus monitor in France (Morey et al – 2004), operated for the first time in Australia on Barangaroo site.