Mechanism of conditioning EPB shield soil

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4. Mechanism of conditioning EPB shield soil

Large internal friction angle and small cohesion for sand result in engineering problems such as difficulty in soil dumping and excessive torque during Earth Pressure Balance (EPB) shield tunneling in sandy strata. Therefore, it is necessary to change the mechanical characteristics of the excavated shield soil by adding conditioning agents. However, the conditioned soil containing a variety of the agents could cause environmental contamination. In order to make a workable conditioning scheme to ensure the shield construction and to reduce environmental risk, it is necessary to understand the mechanism of soil conditioning. This study investigated the influence of the addition and combinations of conditioning agents on the workability of sand, and analyzed the rheology and mechanical properties of sands with adequate workability by using workable agent combinations to condition sands, in order to analyze the influence of the agent combinations on the properties of sand. The results show that the addition and combination of conditioning agents have a significant influence on the workability of sand. The combination of bentonite slurry, foam and Na-CMC can effectively improve the workability of sand, and reduce the addition of bentonite slurry and foam to reduce costs and mitigate environmental contamination. The sand conditioned by the combination of bentonite slurry, foam and Na-CMC has workable rheology, shear strength and compressibility. The results will provide theoretical guidance for making the workable conditioning scheme and green treatment scheme of the shield soil.

9th International Congress on Environmental Geotechnics (ICEG2023)

Characterisation, Remediation and Management of Contaminated Sites and Wastes