Analysis of ground volume loss for EPB shield tunneling in thick silty clay layer

Ground volume loss is an important parameter for settlement control and prediction in shield tunneling. This parameter is usually determined empirically, while its variation along the tunnel is not predictable. In this study, an analytical formula for ground volume loss is obtained based on physical derivation. The ground volume loss is divided into two components. Key operational parameters, i.e. face pressure, grouting pressure and grouting volume, are used to calculate the two components. The proposed formula is then validated against the field data collected from Changzhou Metro in thick silty clay layer. The validation shows that the new formula gives reasonable prediction of ground volume loss. Furthermore, the three model coefficients derived from physical calculation are very close to the regression coefficients based on statistical method. For EPB tunnels excavated in silty clay layer, the ground volume loss along a specific tunnel can be predicted by the new formula. The analysis also indicates that the surface settlement of EPB tunnel should be controlled by a balanced combination of varied operational parameters.