Effects of Clay Creep on Long-Term Load-Carrying Behaviors of Bored Piles: Aiming at Reusing Existing Bored Piles

Abstract

An analytical procedure is presented for assessing the long-term load-carrying behavior of bored piles in clay, where the plastic volumetric strain of surrounding clay caused by creep is estimated by an advanced elasto-viscoplastic constitutive model. Two key soil parameters, the undrained shear strength and the shear modulus, which govern the load-carrying behavior of bored piles in clay, are determined from the definition of the quasi-overconsolidation ratio and the concept of the critical state theory-based Cam-clay model. The long-term load-carrying capacity of bored piles is evaluated based on the total stress method. Hyperbolic load-transfer models are developed with proper incorporation of the two developed soil parameters to predict the long-term load–settlement behaviors of the bored pile. The proposed framework is validated by predicting a pile field test on an existing bored pile (about 30 years) in clay, which was recently performed by the authors in Pudong New Area, Shanghai, and field static load tests on two single bored piles conducted by other researchers. Comprehensive parametric studies are conducted to explore the effects of secondary compression index and in situ soil properties on long-term load-carrying behavior of bored piles. The proposed procedure is expected to provide useful guidance for estimating the load-carrying behavior of existing bored piles in clay and take the ultimate aim of reusing them in practice.