Abstract: Collapse accidents of tied-back excavations caused by over-excavation or overloading occasionally occur. However, studies on the mechanism of progressive collapse under these conditions are still lacking, which limits the targeted prevention and control of such accidents. Based on two cases of excavation collapse, Model tests of the progressive failure of tied-back excavations were designed to investigate the influence of partial over-excavation or overloading on the deformation, soil pressure, and internal forces of the anchors, piles and capping beam. The results show that after partial over-excavation, the soil arching effect generated outside the excavation and the load transfer effect of the capping beam will cause a significant increase in the internal forces of the adjacent piles and anchors. Under this condition, the two effects will be exacerbated by partial failure of anchors in the over-excavation area, leading to the progressive failure of adjacent anchors. If the embedment depth of piles is small, the bending moment of piles will decrease after the failure of anchors, and finally the overturning failure will occur due to the lack of constraint on the pile top. On the contrary, the maximum bending moments will increase and eventually leading to bending failure and collapse. The deeper the normal excavation depth is, the stronger the soil arching effect caused by over-excavation and anchor failure becomes, and the worse the ability to resist progressive failure of excavations is. Therefore, the reinforcement of anchors should be given priority to prevent progressive failure in the partial component strengthening method. Excessive surcharge load will cause progressive failure of anchors from the center of the overloading area, leading to the collapse of the excavation. Different anchor placement heights lead to different surcharge loads required to trigger the progressive failure of anchors, the progressive failure path and the components that need to be specially checked against potential surcharge loading risks may also vary. When the anchors are set on the waler beam, the load transfer coefficient of anchors is greater than that of piles under surcharge loading, priority needs to be given to the design of local reinforcement of anchors; when the anchors are set on the capping beam, a greater surcharge load is needed to trigger the progressive failure, and the load transfer coefficient of piles is greater than that of anchors, priority should be given to the design of piles considering the surcharge load .