Influence of Pile Rows on Tunneling-Induced Displacements in Sand

Tunneling in urban areas typically leads to ground displacements that pose risks to nearby structures. To mitigate these displacements, protective measures like pile rows are commonly employed. This paper presents a numerical investigation into the effects of pile rows on tunneling-induced displacements in sand. The study primarily assesses how pile spacing influences the effectiveness of pile rows in reducing surface and subsurface deformations resulting from tunnel excavation. A series of three-dimensional finite-element models are developed to simulate the interactions among the soil, piles, and tunnel, considering varying pile spacing and locations. The behavior of the sand is modeled using a hypoplastic constitutive model calibrated with data from element tests and centrifuge modeling. The results indicate that pile rows can significantly diminish displacements, with their effectiveness closely linked to the spacing between the piles. Smaller pile spacing improves the mitigation of displacements and reduces the bending moment in the piles, whereas excessive spacing reduces the protective effect. Notably, the role of pile spacing in reducing surface horizontal displacements differs from that in mitigating settlements and varies significantly based on the location of pile rows, highlighting the complexity of the interactions between the tunnel and the pile rows. A comparison of the presented numerical results with findings from existing studies highlights a significant drop in the efficiency of pile rows in sandy soil compared with undrained soil. These findings provide valuable insights for optimizing pile row designs in sandy environments, contributing to safer and more efficient urban tunneling practices.