Analytical solutions for the restraint effect of isolation piles against tunneling-induced vertical ground displacements

This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement, which can consider not only the relative sliding of the pile‒soil interface but also the pile row–soil interaction. The proposed method is verified by comparisons with existing theoretical methods, including the boundary element method and the elastic foundation method. The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling, i.e. the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation. The results also indicate that the stiffness of the pile‒soil interface, including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface, describes the strength of the pile‒soil interaction. The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.