ABSTRACT
Foam, an instrumental soil conditioner in Earth Pressure Balance (EPB) shield tunneling, serves to reduce soil permeability. This study employs a simplified one-dimensional foam penetration model to predict the penetration behavior of foams with distinct rheological properties in saturated sand. The rheological behavior of various foams is described using power-law fluid model. The foam penetration characteristics are represented through the temporal curves depicting foam penetration distance. Results indicate that the flow behavior index of foam governs its penetration characteristic. A smaller flow behavior index facilitates rapid injection of foam into the sand, forming a low-permeability layer. Moreover, while maintaining a constant flow behavior index of foam, increased foam flow consistency index decreases the foam penetration distance. From an engineering perspective with anti-permeability, foams characterized by lower flow behavior indices and higher flow consistency indices exhibit pronounced advantages in EPB shield tunneling. The outcomes of this study provide valuable insights for the selection of foams in facilitating EPB shield tunneling.
