Experimental Study of the Effect of Excavation on Existing Loaded Piles

AbstractExcavation beneath an existing building to add a new basement is an effective mean to expand underground space that caters to the increased need of space in urban areas. Because piles serve as load-bearing structures in high-rise buildings, excavation inevitably changes the bearing capacity of the existing piles and affects the safety of aboveground structures. This paper presents a series of experimental tests in a calibration chamber designed to clarify the effect of excavation on the performance of existing loaded piles. Excavation tests as well as pile load tests at the ground level and at the formation level of excavation were involved in capturing the effect of excavation on the capacity, stiffness, and load transfer of loaded piles. Test results showed that the reduction of pile capacity due to excavation is proportional to the magnitude of confinement of the area to be excavated. Constructing a new basement beneath an existing basement may result in a larger reduction of pile capacity when comparing that conducted at the ground surface. Unlike the nonloaded pile subjected to excavation, tensile force is not observed along the loaded pile shaft in the present test series. The results also indicated that the stress relief induced by excavation may be instrumental in the stiffness efficiency of the pile group.