Evaluation of jet grout column diameters by acoustic monitoring

To evaluate the diameter of jet grout columns actually formed under the ground, several methods had been developed over the past years. Nevertheless, uncertainty still exists in different methods mostly due to the variations of ground and grouting conditions. This study proposes an acoustic monitoring system capable of directly recording the jet grouting sounds detected at different distances from the jet nozzle. To correlate the actual diameter of the jet grout column with the monitored sound prints, a field test was conducted in an interlayered sandy and gravelly soil and the jet grout column was excavated for dimension measurement. The recorded sounds show that the distribution of the threshold peak amplitudes at different distances can be represented by the curve of the normal distribution function. In addition, the standard deviation and mean of the normally distributed threshold peak amplitudes can be used as indicators to determine the effective diameter of the jet grout column for a specific jet grouting project. Although this acoustic monitoring method would be costly and time-consuming if used to examine all jet grout columns, it is suitable for frequent use in trial tests for finding reasonable grouting parameters when forming jet grout columns with design diameters.