Study on the control theory and design method of progressive collapse in excavations retained by cantilever piles

The progressive collapse problems in excavation engineering have attracted the attention of engineers and academic scholars. However, the relevant control theory has not been established. Based on the progressive collapse mechanism of excavations retained by cantilever piles, a method for alternately setting progressive failure blocking units (abbreviated as blocking unit method) to control the development of progressive failure is proposed. The effects of blocking units under different excavation depths, soil conditions and stiffnesses of reinforced piles are analyzed by the finite difference method. Furthermore, based on the load transfer coefficient curve, the design principles of blocking units under different stiffnesses of the reinforced piles are summarized. The results show that the reasonable design of blocking units can effectively control the progressive failure caused by the partial failure within the setting range. However, when the number of the reinforced piles in the blocking unit is insufficient, the progressive failure has crossover effect, which means the progressive failure continues to develop across the blocking unit and in turn leads to the failure of the blocking unit. For the bending-failure type progressive collapse of retaining piles, the failure of the capping beam or actively cutting off the capping beam cannot block the development of the progressive collapse. On the contrary, it may aggravate the progressive collapse.