# Potential of Computer-Aided Engineering in the Design of Ground-Improvement Technologies
## 5 Results and Discussion
### Reproduction of Development Situation of Columnar Soil-Improved Body  
Figure 8 shows the development progress of a columnar soil-improved body. The ground particles are shown in transparent yellow, the water particles in light blue, and the slurry particles in red. Water starts spraying at about 2 s and continues until it reaches the maximum depth of 1 m within 20 s.  
Figure 6: CAE-MPS simulation results compared to known data.  
Figure 7: Comparison of simulation results for different soil sizes.  
Blue particles can be confirmed to be moving to the surface and scattered into open space as mud discharge. Cement-grout-spraying starts when the jet-grouting string reaches the desired maximum depth of 1 m and is pulled upward, rotating in a counter-clockwise direction. It can be confirmed that water particles scoured below the 1 m depth, although soil-improvement body formation at this depth is not intended. At 78 s, when the rod reaches the desired height of 0.5 m below the surface, the construction simulation is completed. Cement grout was sprayed for 0.5 m height only, but it can be confirmed to have spread beyond with uneven distribution.  
The main objective of creating a realistic jet-grouting construction simulation was successful, as this study was able to recreate the realistic phenomenon of mud discharge and the formation of the soil-improved body. Generally, mud discharge observation and soil-improvement diameter measurement are conducted as a verification method for a jet-grouting method in real situations. As for the content of mud discharge, it should be a mixture of water, soil particles, and a certain amount of cement grout. In this simulation, water particles and a few cement particles were ejected as mud discharge. The soil particle ejection might have not been visually confirmed because of its visuality setting in the simulation. As for the soil-improvement body diameter, the target design shape is shown by the blue rectangular frame in Figure 8. A maximum diameter of 0.9 m and minimum diameter of 0.6 m were observed within the target zone, whereas a total height of 0.86 m soil-improved body was formed with 0.1 m height and 0.5 m average diameter above the target zone and 0.26 m height and 0.5 m average diameter below the target zone. It is expected that more accurately controlled soil-improved body shape and size can be formed by amending the construction specifications.  
The probable reasons for forming the soil-improved body below the target area might be the permeation of the cement slurry particles and heavy accumulation of the cement slurry at the lower portion. Since water particles had already scoured the ground below the lowest point of drilling, they simply percolated to the soil below when the cement slurry was sprayed. Next is the accumulation of sprayed cement slurry particles, which percolated in a downward direction due to the influence of gravity rather than moving in the radial direction. Meanwhile, the probable reasons for forming the soil-improved body above the target might be the vertical movement of the mud discharge and the presence of a higher amount of cement particles at the center. The mud discharge phenomenon likely stimulated loose particles to move in upward directions but cement particles being comparatively heavier, settled along the midway, resulting in soil-improvement body formation beyond the target zone. Further, since there was a heavy accumulation of cement particles at the center because of the longer spraying time, the number of cement particles carried in the upward direction might have increased proportionately, resulting in the formation of a soil-improved body above the target area. However, it is expected that soil-improved body  
Figure 8: Reproduction of development condition of the soil-improved body.  
formation range can be effectively controlled by changing the specifications for the cement slurry spraying, such as changing the total time of the spraying, the velocity of the rod pulling in an upward direction, etc.