Soil Conditioning for EPB Shield Tunneling in Silty Clay and Weathered Mudstone

Abstract

Soil conditioning technology is commonly applied to prevent mud caking and soil clogging in earth pressure balance (EPB) shield tunneling and to ensure continuous and efficient construction in highly viscous clay and weathered mudstone strata. In the note, the properties of soil conditioning agents and their interactions are investigated through a series of experimental tests and field construction applications in Changchun Metro Line 2, China. Tangential adhesion tests are carried out to learn the adhesion strength and the torque change relationship between the soil and the metal disk, by which the soil conditioning effect is evaluated. The results indicate that there is a certain interaction between the commercial foam agent and the customized anticlay agent and that the foam agent solution’s concentration and anticlay agent amount play an important role in determining the foam expansion ratio (FER) and the half-life time (HT). When the foam agent solution’s concentration is low, the anticlay agent can increase the FER and decrease the HT. When the foam agent solution’s concentration exceeds 4%, an opposite pattern is observed. It is also found that the composite application of an anticlay agent and a foam agent can significantly decrease the torque and adhesion strength of the weathered mudstone. Torque and adhesion strength can reflect the adhesion of chemically conditioned soil better than the consistency index, which has a good effect on the evaluation of unconditioned soil. Finally, field implementation indicates that mud caking and soil clogging were avoided by the application of the two conditioning agents in the EPB shield tunneling construction of Changchun Metro Line 2, China, and the thrust and torque of the shield were reduced.