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 to directly record the jet grouting sounds picked up 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 sound show that the distribution of the threshold peak amplitudes at different distances can be represented by the curve of normal distribution function. In addition, the standard deviation and the 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 to examine all jet grout columns, it is suitable for frequent use in trial tests for finding reasonable grouting parameters to form jet gout columns with design diameter.

The major focus of this study was determining the effectiveness of new construction specifications regarding the method of cement grout injection for the jet grouting system (high-pressure injection stirring method), with the objective of developing a sustainable ground improvement method. The recent innovative jet grouting techniques allow for improvement at middle pressure, but the mud discharge amount is drastically increased. This produces a serious environmental and financial burden during the disposal of mud discharge. This study attempts to develop a sustainable jet grouting method. The simulation model was prepared by the 3D AutoCAD software, and the analysis was conducted using the moving particle semi-implicit method (MPS method). The study focused on the changes that occurred in the mixing ratio of cement slurry and soil due to the changes made in cement milk spraying during the construction phase and compared it with the traditional method of cement milk spraying. All other construction parameters were kept the same for both cases, and the comparison result shows that the modified construction specification provides a denser and larger improved soil body than the traditional method. Furthermore, the density of the number of particles was determined at the upper, middle, and lower portions of the improved body for comparison.

This paper provides a summary report on measures taken to remove embedded steel ‘H' pile obstacles from the cutter head of an advancing tunnel-boring machine. The piles were part of the soil-mixing retaining wall built for the cut-and-cover tunnel construction of a Taiwan high-speed rail tunnel and a Taiwan railways administration tunnel, which were directly above the mass rapid transit tunnel that was to be constructed. The collision zone between the boring machine and piles was below groundwater level and was approximately 23 m below the ground surface in a silty sand layer. To remove the piles safely from the cutter head, horizontal grouting from two adjacent work pits was conducted for waterproofing and solidification purposes. By controlling the amount of soil being flushed out during the grout hole drilling first, and also the pressure used for grouting later, the measured tunnel settlement resulting from grouting was negligible. Because of the favourable watertightness of the grouted zone and the dewatering influence of a nearby construction site, pile removal was conducted under particularly dry working conditions. In total, 12 piles were identified in the collision zone and were successfully removed from the cutter head by hand tools.

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