Semi-analytical approach for the load-settlement response of a pile considering excavation effects

Piles are often installed before tunnel excavation to support the tunnel structure. However, excavation inevitably causes disturbance to the soil below the excavation surface, significantly changing the soil mechanical behavior. Hence, it is necessary to evaluate the excavation effects on pile load-settlement behavior. This study proposes a semi-analytical approach for estimating the load-settlement behavior of a pile beneath the excavation surface, that considers the excavation effects. Piezocone tests are performed in the Taihu tunnel region to evaluate the excavation effects on the soil mechanical properties. The results show that after excavation, the undrained shear strength of the soil decreases, while the soil effective friction angle remains unchanged. Thus, this study proposes using the soil effective friction angle before excavation to predict the pile load-settlement behavior after excavation. Then, the load-transfer method is employed to simulate the pile settlement behavior. Hyperbolic functions are used to describe the nonlinear loading and unloading pile-soil interface behavior. The proposed semi-analytical approach also considers the shear-induced elastic deformation of the surrounding soil. The predictions of the load-settlement behavior are compared to the results of pile load tests in the Taihu tunnel region, centrifuge model tests, and numerical investigations to validate this approach. The excellent agreement indicates that the proposed approach can reasonably predict the pile load-settlement behavior after excavation. As a case study, it is predicted that the ultimate capacity of a pile in the Taihu tunnel region is 4388 kN, reflecting a 10% loss of pile capacity due to excavation.