A generalized elastoplastic load-transfer model for axially loaded piles in clay: Incorporation of modulus degradation and skin friction softening

The softening behavior of skin friction is commonly observed from load-displacement responses of axially loaded piles in stiff clay, sensitive clay, and dense sands at a large loading level. This paper presents a generalized and novel elastoplastic load-transfer model to predict the load-displacement response of axially loaded piles in clay considering the degradation of skin friction. In this model, the soil around piles is divided into the shear band immediately adjacent to piles and the soil outside shear bands. An elastoplastic model in terms of the critical state theory-based modified Cam-clay model is developed to describe the mechanical behavior of shear bands. The elastoplastic model can explicitly consider both hardening and softening behaviors of skin friction. The elastic behavior of the soil outside shear bands is represented by a modulus degradation model, which captures the shear modulus degradation with the shear strain. Subsequently, an elastoplastic load-transfer model possessing generalized ability to describe both hardening and softening behaviors is developed by combining these two theoretical models. Predictions of the load-settlement curves are compared with the measured values from three well-documented cases to verify the proposed model. Good agreements demonstrate that the proposed load-transfer model provides reasonable and effective prediction for bearing performance of piles.