THE SPECIALTY 

FS JETGROUT

FS JETGROUT , in a “nutshell” is a technology utilizing high speed water-jetting to substitute cement to soil with low mechanical strength , moving soil particles upward from a previously executed borehole,  and simultaneously replacing it in a continuous motion with the same volumes of cement grout, thus creating, in the treated soil, cylindrically shaped columns [usually 800mm in diameter] of high strength grouted conglomerate.  

FS JETGROUT,  FS JET GROUTING   are  technologies that Foundation Specialists had started developing in the late 1970s and   has applied   extensively  from the early 1980s.

As the name itself says, " jetgrouting " is executed in a process that utilizes powerful “ jets ”, using high pressure large capacity water pumps to deliver through the drilling rods  high speed, powerful water jets designed to "disintegrate" into fine particles the ground formations targeted for improvement, float the particles placed into water suspension and remove the fine mud thus produced by the soil particles in water suspension from the borehole. Simultaneously, the soil volumes removed by the high speed  water  jetting have to be replaced with cement jet grouted into the borehole through the same drilling rods  at a rate sufficient to back fill the volumes vacated by the soil removed by the water jetting.  The cement grout is pumped in the borehole by large capacity grout pumps capable of delivering the necessary volumes of grout at the fast rate required by the jetgrout process.                    

The name of this particular technology is often misused to designate other types of grouting operations that do not utilize the correct jet-grout equipment and procedures.                The “ JetGrout ”   technology requires the use of high pressure [ 700 bars ] water pumps able to deliver very large volumes of water at extremely high speed,  large capacity cement injectors working at about 70 bars pressure, capable of delivering  cement grout at the rate necessary to immediately replace with continuity the volumes of fine soil removed [floated] by the water-jetting. Essential part of the set-up for jetgrout execution is a coaxial  nozzle system necessary to deliver simultaneously, at different elevations  within the borehole, the binary [water, cement grout] fluid flow.     JETGROUT technology and the skills necessary for its correct application are up to present only possessed by a limited number of specialists, due to the level of expertise needed and the complexity of correctly predicting the behaviour of the soil to be treated, when subjected to the extremely high speed of water jets and the necessity of immediately backfilling with cement the entire volumes vacated by the floated fine soil, in a perfectly continuous motion in order to avoid destabilizing the surrounding soil.
The basic working procedure for the execution of JETGROUT,  or JET GROUTING   or JET GROUTING CEMENT, is to drill a hole in the ground formation to be "jetgrouted", or "jet  grouted".  Once the hole has reached the target depth,  the JETGROUT or JET  GROUTING operation begins,   right from the borehole bottom, proceeding upwards.
The Jet  Grouting  tool used for the  JETGROUT  or JET  GROUTING is a combination of (2) two [binary fluid system]  or (3) three nozzles [for ternary fluid system]. The nozzles are placed at an angle of 90 degrees with the drilling pipes on which are mounted.   The nozzles are placed at a distance (measured on the vertical) of about (1) one meter from each other [as shown in the sketches].
The upper " nozzle ", while being rotated is jetting water at extremely high speed against the wall of the borehole, with the effect of "disintegrating" the matrix of the surrounding formation, within a radius of 0.4 to 0.9 meters from the center of the borehole. 
The water jetting, provided by water-pumps pumping relatively  large volumes of water with a prevalence in excess of  700 kg/sq.cm  [700 bars], produce not only the  "disintegration” of the surrounding ground matrix, but also provides the necessary environment for the fine particles placed in suspension by the water jetting, to float upwards and  out of the hole, and create the condition for the cement  introduced through the lower nozzle, to fill the volumes originally occupied by the soil particles removed by floatation.
Ideal fields of application  for JETGROUT [ JET  GROUTING ]  are,  underpinning of large footing, underpinning and consolidation of bridge foundations, formation of diaphragms, seepage control under cofferdams in alluvium, ground consolidation in preparation  for deep excavation      in unstable bouldery ground or alluvium, formation of            “ Bottom Plug ” to prevent seepage from  bottom of deep excavation in high water-table conditions, general applications in  " alluvium formations ", bouldery ground, mountain slopes rocky  detritus,    or generically soil  in need of consolidation,  riverbeds to be used for foundations, landslide prone slopes in ground formations with abundant boulders, and any formation made of boulders in a soft groundmass or in lose, water-saturated soil formations in shallow water table.
The use of  jetgrout   [ JET  GROUTING ] for areas of applications as described, works particularly well, because it leaves in place the  pebbles, boulders, gravel and solid hard material while it eliminates  the soft soil groundmass  and replace  it with cement , thus eventually generating as a final product  vertical columnar elements made of a of well cemented_conglomerate.
Jetgrout  ( JET  GROUTING ) done in fine soil formations is causing  the whole volume of fine soil within the reach of the high speed water jetting, to float, consequently  the whole  volume vacated by the floated fine soil, has to be filled back in its entirety with cement.