Jet Grouting Calculator

By soil and purpose. Regular cut-off and ground improvement use 300-350 kg/m³; soft soil or high strength takes 400 kg/m³ or more. Larger diameter and softer soil mean less complete replacement, so content goes up. Run a trial column first, measure the actual diameter and strength, then set parameters - do not commit volume on a rule of thumb.

Yes, but they must interlock - adjacent columns need 150-250 mm overlap to seal, or the gaps leak. Column diameter varies strongly with soil (sand and gravel especially), so when using jet grouting for a cut-off wall the overlap and trial-column verification matter most; never assume the theoretical diameter.

Judge by soil, depth and site access. Deep mixing (including the SMW method) gives uniform columns cheaply in mud, silty clay and clay, and is most economical to about 15 m; in sand, gravel, cobbles or obstructions, or beyond roughly 15-20 m, the mixing head cannot cut properly and both diameter and overlap become unreliable, which is where jet grouting takes over. Jet grouting costs clearly more and produces heavy return spoil needing a settlement pond and disposal, so use deep mixing for large cut-off walls and jet grouting for local strengthening, tight sites, congested services or restricted headroom. Pick wrong and the column either cannot be formed or the money is wasted.

Three things decide it: whether the rig can get in, how big a column you need, and what the ground is. Soil mixing (triple-axis) gives a more uniform column at a lower unit rate, but the rig is tall, needs a wide working platform and will not penetrate hard layers or cobbles. A jet grout rig is compact, works in confined space, hard against existing structures and inside basements, and will cut hard layers - but the unit rate is much higher and the return flow is heavy. So: soil mixing for bulk cut-off, jet grouting for local repair, tight corners and hard ground.

It can, and it is the most commonly missed item. Jet grouting replaces soil: the high-pressure grout cuts the ground and a soil-grout mix comes back out of the hole. The volume is broadly the same order as the column volume, though it varies widely with ground and method, so measure it on site rather than assuming. It costs twice: haulage and disposal of the return flow, plus the grout lost with it. If you price grout as column volume times cement content and forget disposal, disposal comes straight out of your margin.

The drawing gives the required column diameter. What you actually achieve depends on the ground, the pressure, the withdrawal rate and the nozzle. The same nozzle can differ by more than 30% between soils: sand over-cuts, clay and dense silt under-cut. So the order is: trial column first, measure the real diameter, then fix the cement content and the count. Taking the drawing diameter straight into a cement calculation normally comes out short.

Three reasons. Cement content is higher - 300-400 kg/m³ of column is normal, against the equivalent of 15-20% by soil weight for soil mixing. The return flow has to be hauled and disposed of, which is pure additional cost. And output is low: the withdrawal is slow, so fewer cubic metres per shift. That is why jet grouting is used where soil mixing cannot go - confined space, hard layers, hard against existing structures, local leak repair. Using it across a whole site puts the cost a tier above soil mixing.