Generalized Approach for Prediction of Jet Grout Column Diameter

This paper presents a generalized approach for predicting the diameter of jet grout columns based on the theoretical framework of turbulent kinematic flow and soil erosion. The proposed calculation method is applicable to all conventional jet-grouting systems and takes into account the full range of operational parameters, fluid properties, soil strength, and particle size distribution, including the effect of the injection time on erosion distance. It was demonstrated that the increase in the jet grout column diameter arising from the use of a compressed air shroud in the double and triple fluid systems is approximately 27-81% for the typical range of air pressure of 0.5-1.5 MPa. The proposed method was applied to four case histories involving four variants of jet-grouting systems, i.e., single fluid, double fluid, triple fluid, and an enhanced triple fluid system. Comparison between the calculated and the measured jet grout column diameters indicated that the proposed method can produce reasonable predictions for a variety of soil conditions. It was shown that jet grout columns formed by the enhanced triple fluid system are larger than those formed by the conventional triple fluid system by approximately 36% on average. The proposed generalized approach allows all the key variables to be considered and is a useful means for the design of ground improvement by jet grouting.