How bridges get built · Ground improvement · Deep cement mixing (DCM) and jet grouting
Also called: soil-cement columns, deep soil mixing, CDM, jet grout columns
How it is done
- DCM: a hollow-stem mixing tool descends injecting cement slurry or dry powder, and mixes on withdrawal; columns 0.8-2 m in diameter, up to 40 m deep, in grids or walls.
- Jet grouting: a small hole is drilled, then high-pressure grout (single, double or triple fluid) erodes and mixes the soil as the rod is rotated and withdrawn; columns 0.6-2.5 m.
- Cure 7-28 days; core and test the columns.
Where it fits
- Soft clay under abutments and approach fills when there is no time for PVDs.
- Cofferdam base plugs, cut-off walls, treatment around existing foundations, karst voids (jet grouting).
Where it does not
- Highly organic soils (cement does not set well).
- Cobbles and boulders for DCM; jet grouting handles them better.
Plant, pace and money
PlantDCM rig with single or multiple mixing shafts, slurry plant; jet grouting rig, high-pressure pump, grout plant.
ProductivityDCM: 100-300 m of column per rig per shift. Jet grouting: 30-80 m per shift.
CostDCM USD 60-120 per m3 of treated soil; jet grouting USD 300-800 per m3.
Risks and controls
What goes wrong
- Uneven mixing and low-strength zones; ground heave near structures under jet grouting; spoil disposal.
Quality assurance
Wet-grab samples during mixing, cores at 28 days, unconfined tests, column diameter checks by excavation in a trial.
Examples
Japanese CDM for port and bridge approaches; jet grouting to seal river cofferdam bases in Europe.
Related methods
Further reading
EN 14679 (deep mixing) · EN 12716 (jet grouting) · Kitazume and Terashi, The Deep Mixing Method