Soil Conditioning for EPB Shield Tunneling in Argillaceous Siltstone with High Content of Clay Minerals: Case Study

Soil clogging occurred in the early construction stage of Nanchang Metro Line 1, China, when an earth balance pressure (EPB) shield passed through the argillaceous siltstone with a total content of clay minerals of 40.5%. This paper presents a new scheme for determining soil conditioning parameters to avoid the occurrence of soil clogging, taking both the slump value and the liquidity index of the soil into account. As indicated by the results of slump tests, the optimum slump value for the soil conditioning ranged from 17 to 20 cm, and a fitting function of slump value against foam injection ratio (FIR) and water content (w) was obtained. Considering the requirement for a liquidity index equal to ∼0.4–0.75 to ensure the stability of the excavation face, a chart was proposed for the soil conditioning. Based on the chart, the optimum FIR and w for the soil conditioning for tunneling in argillaceous siltstone were determined to be ∼19.2–23.2% and ∼14.2–36.6%, respectively. Taking shield parameters, tunnel design, and soil parameters into account, the soil conditioning techniques were implemented in field conditions. The field implementation indicated that soil clogging was effectively avoided in the later section of Nanchang Metro Line 1, and the thrust and torque of the shield were reduced significantly.