Experimental study on mechanism of progressive collapse along length of excavation retained by cantilever contiguous piles

Progressive collapse of deep excavations along the longitudinal direction induced by partial failure may extend to tens of meters or even more than one hundred meters. However, the researches on the initiation and termination mechanism of progressive collapse are limited. The model tests on partial collapse caused by the breakage of some retaining piles are designed. The changing rules of earth pressures and internal forces of adjacent piles are analyzed. Furthermore, the model tests on progressive collapse induced by partial collapse are conducted. The test results show that the partial collapse can cause sudden increase of earth pressures and structural internal forces of adjacent piles. Afterwards, the soil outside the excavation flows into the excavation, which is an unloading effect for the adjacent piles. However, the unloading effect lags behind the loading effect. If the load transfer coefficient of partial collapse is larger than the safety factor of bearing capacity of the adjacent piles, the progressive collapse will occur. During the process of progressive collapse, when the soil arching effect is mitigated by the unloading effect and cannot cause further breakage of the retaining structures, the progressive collapse ceases naturally. Within a certain extent, the larger the partial collapse is, the larger the load transfer coefficient and the influenced area are. Additionally, when the lateral stiffness of piles is low, the load transfer coefficient will be small, but the influenced area will be large.