# Real-Time Behaviour of Dredged Slurry Treated by Air-Booster Vacuum Consolidation
## 9 Conclusions  
A laboratory test was used to investigate the real-time behaviour of the air-boosted vacuum consolidation of dredged slurry. A measuring system incorporating the PIV technique, a vortex flowmeter, pore water/air pressure gauges and an electronic balance allowed real-time monitoring of the soil and pressurised air during the air-boosting process. The PIV technique obtained the displacement field of the test slurry, which provided direct observations of crack initiation and propagation. The pressure/flux of the pressurised air and PWP read from the gauges and vortex flowmeter help understand the undrained soil behaviours under pressurised air based on which the air-boosting process can be divided into different stages. The total water discharge read from the balance confirms that the air-booster vacuum preloading promoted consolidation of the dredged slurry. The crack initiation pressure observed from the model test was compared with theoretical predictions. The following conclusions can be drawn:  
1. When subjected to pressurised air, the soil surrounding the booster plate undergoes four stages of deformation: cavity expansion, crack initiation, crack propagation and crack stabilisation.
2. Both vertical and oblique soil fractures can be induced by pressurised air and connected to form a Y-shaped crack. The vertical crack occurs parallel to the booster plate, and its position basically overlaps the booster plate axis. Oblique cracks only emerge in soils above the head of the booster plate.
3. A sudden drop and increase in the air/pore water pressure and air flux indicate the initiation of soil cracks. Crack initiation is due to the fact of either the tensile or shear failure of the soil under undrained conditions.
4. The air-booster system can induce cracks in treated soil, which promote the drainage consolidation of the dredged slurry.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Source** & **Mechanism** & **Value (kPa)** \\ \hline Equation (1) & Tensile failure & 13.2 \\ Equation (2) & Shear failure & _7.6_ \\ Equation (3) & Tensile/shear failure & 8.8 \\ Equation (4) & Cavity expansion & 10.9 \\ Equation (5) & Limit cavity expansion & 12.6 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Estimations on crack initial pressure of slurry soil.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Symbol** & **Value** \\ \hline Internal pressure (kPa) & \(p\) & 8 \\ Hydrostatic stress (kPa) & \(p_{0}\) & 6.3 \\ Limit value of internal expansion pressure (kPa) & \(p_{L}\) & 12.6 \\ \hline \hline \end{tabular}
\end{table}
Table 5: _Cont._  
**Author Contributions:** Conceptualisation, L.S., J.S. and D.C.; methodology K.Y., D.C. and L.S.; formal analysis L.S., J.S. and L.H.; writing--original draft preparation, J.S., Y.Y., D.C. and L.H.; data curation, J.S., K.Y. and L.H.; writing--review and editing, L.S., K.Y. and Y.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Natural Science Foundation of Zhejiang Province (grant no. LZ22E080009) and the National Natural Science Foundation of China (no. 52278377) is acknowledged. The Ph.D. candidate [PERSON] helped to prepare the PIV equipment.  
The data is unavailable due to the further research.  
The authors declare no conflict of interest.