Mechanism and control of progressive collapse caused by failure of local anchors in multiple-level anchored pile excavation

Collapse of tied-back excavations occurs frequently. In this study, the finite difference method is used to simulate failure of anchors. In a multi-level anchored pile excavation, the failure of the first-level anchors has a great impact on the adjacent anchors and causes the bending moments of piles to decrease, while the failure of the lowest-level anchors has the opposite effects. The impact of failure of column anchors in a multi-level anchored-pile system is significantly greater than that of a single-level anchored-pile system, which easily leads to progressive collapse. Therefore, the construction or design methods, such as interval-level anchor strengthening, should be adopted to limit the failure at a certain level. When the failure of anchors causes the most affected adjacent anchors to fail progressively and even many anchors to fail, the failure position of the initial anchors does not affect the transmission path development of failure of anchors. Accordingly, the progressive failure of anchors is close to the failure of column anchors, and shows an inverted trapezoidal horizontal expansion. The failure of column anchors in a multi-level anchored pile system easily leads to damage to the beam. Then it will cause pile failure and accelerate the process of excavation collapse. Therefore, the capping (waler) beams should be designed under the failure of column anchors to improve the overall safety performance of the retaining system.