Development of a Mixing Index for Cutter Soil Mixing-Paper

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The paper proposes a practical quality-control index for Cutter Soil Mixing (CSM), which lacks an established counterpart to the Blade Rotation Number (BRN) used in conventional auger mixing. Unlike an earlier energy-based proposal, the authors argue that energy spent cutting and disaggregating soil should generally be excluded: in two-phase CSM, binder is added during withdrawal, when the soil is already disaggregated and mixing occurs.<br /><br />The authors reviewed production data from 261 panels across 11 sites in British Columbia. Neither total mixing energy nor mixing-phase energy showed a clear relationship with 28-day unconfined compressive strength (UCS). The authors attribute UCS variability mainly to binder content, water-cement ratio, and natural soil properties. Evidence from prior research suggests mixing energy has a threshold, beyond which additional mixing does not improve strength; observed CSM operations typically exceeded this threshold by three to five times.<br /><br />The paper introduces the Cutter Wheel Rotation Number (CWRN), a measure based on cutter-wheel rotations during withdrawal, normalized for panel thickness. It is intended as an accessible field indicator of mixing effort and energy input. Preliminary recommended CWRN values are 200 for sand, 250 for silt, and 300 for clay; recommendations for organic clay and peat require further data. These guidelines should be verified through project-specific field trials.<br /><br />The findings suggest CSM achieves thorough mixing at lower index values than conventional auger mixing and that mixing time may be reduced without compromising quality. However, the recommendations are preliminary and based on a limited range of soils and current Canadian construction practices.

Keywords

Cutter Soil Mixing

CSM quality control

Cutter Wheel Rotation Number

CWRN

unconfined compressive strength

binder content

water-cement ratio

mixing energy

panel thickness normalization

soil mixing efficiency