Shaft resistance loss of piles due to excavation beneath existing basements

The excavation beneath the existing high-rise buildings, which changes the ground stress field, will result in changes of the stresses at the pile-soil surface and the pile end so as to reduce the bearing capacity of piles. Considering the field conditions, the bearing capacity of piles can not be obtained by field tests after excavation, so it is particularly necessary to evaluate the resistance loss using the theoretical analysis and the finite element simulation. The classical theory is used to calculate the ultimate shaft resistance of the piles. The Mindlin’s stress solution and a simplified method are adopted to consider the additional stress caused by excavation. Subsequently, the results of theoretical analysis are compared with those of the finite element analysis. The relationship among loss ratio of the ultimate shaft resistance, excavation width and depth is also analyzed. The results show that the loss ratio increases with the increase of excavation width and exhibits an initial linear increase followed by a more nonlinear increase until a constant value. Moreover, the loss ratio increases with the increasing excavation depth in a linear manner and decreases along the shaft from top to bottom.