## 6 Conclusions  
Based on the shield tunnel project of Guangzhou Metro Line 12 in China, the applicability of a slurry-earth pressure balance dual-mode shield was investigated in a composed stratum with medium-coarse sand and argillaceous siltstone. Then, the soil conditioning was studied for the high-adhesion stratum to prevent shield clogging. The main conclusions are described as follows:  
1. The slurry mode of the slurry-earth pressure balance dual-mode shield was not applicable to the composed stratum with medium-coarse sand and argillaceous siltstone. It was difficult to transport the adhesive soil from the chamber only by the slurry circulation. The excavated soil accumulated in the slurry chamber. The accumulated soil prevented the excavated soil from entering the slurry chamber. Finally, the excavated soil accumulated in the cutterhead, and the opening of the cutterhead was clogged.
2. The total thrust force of the shield increased significantly, the tunneling speed gradually decreased to 0, and the torque of the cutterhead increased slightly after the slurry-earth pressure dual-mode balance shield machine in the slurry mode was clogged. The fluctuations in the total thrust force, cutterhead torque, and tunneling speed also increased significantly.
3. The EPB mode is recommended for the composed strata with medium-coarse sand and argillaceous siltstone. The dispersible foam agent and water can be used to condition the soil. The type of dispersible foam agent was determined by measuring the effect of the soil conditioner on the liquid limit of the particles with sizes less than 0.15 mm in the soil. The concentration of the foam agent was determined by measuring the half-life and foam expansion ratio of the foam. The injection amount of the foam and water was determined according to the status of the mud discharged by the screw conveyor.
4. Water absorption can be used to characterize the water absorption capacity of particles larger than 0.15 mm. The ideal soil state was that the consistency index of the particles smaller than 0.15 mm was less than 0.5 to prevent the EPB shield from clogging. The water absorption of soil with a particle larger than 0.15 mm should be removed when calculating the consistency index.  
Conceptualization, Z.Y. and P.L.; methodology, Z.Y.; software, P.C.; validation, P.L. and S.L.; formal analysis, P.C.; investigation, P.C.; resources, F.J.; data curation, F.J.; writing--original draft preparation, P.L.; writing--review and editing, S.L.; visualization, F.J.; supervision, P.C.; project administration, F.J.; funding acquisition, P.L. All authors have read and agreed to the published version of the manuscript.  
The financial support from the China Postdoctoral Science Foundation (Grant No. 2022M723536) is acknowledged and appreciated.  
Not applicable.  
Figure 15: Variation in the tunneling speed.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** The authors are also grateful to the help from [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] in the CCCC Second Harbor Engineering Company Ltd.  
**Conflicts of Interest:** The authors declare no conflict of interest.