Efficiency for jet grouting consists in forming cemented soil columns with the largest diameter and the highest mechanical strength. Experimental evidence supported by analytical models shows the two requirements being often contradictory. In fact, strength proportional to the amount of injected cement per unit column volume and higher values are achieved increasing the cement water ratio of the grout. However, the thicker grout obtained by this measure makes the cutting action of the jet less efficient. The paper proposes a solution based on the use of chemical additives to reduce the viscosity of the cement grout and enhance the penetration capacity of the submerged jet. After reporting the results of a field trial, the theory of submerged jets was recalled from previous studies to explain observation highlighting the role of grout rheological properties. Then, laboratory tests were performed varying the grout composition, namely cement-water ratios and fractions of chemical additive, to explore the effects on the grout viscosity. The effects of grout conditioning on the diameter of columns were finally quantified with predictive relations developed in this study.

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