Mechanical Behavior of Bitumen: In the Context of Bitumen Coated Piles

Abstract

Bitumen has long been used in geotechnical applications as a coating on piles to modify the interaction between the pile surface and the surrounding soil. Relative ground settlements induce negative skin friction, increasing axial loads and reducing structural capacity. A well-established method to mitigate this effect is to apply a thin layer of bitumen. However, despite bitumen’s long-standing use in practice, the mechanisms governing the behavior of bitumen and its effectiveness in reducing pile–soil interaction remain insufficiently understood. In this thesis, the fundamental mechanical behavior of bitumen is investigated to establish a basis for the numerical evaluation of adhesion strength in bitumen-coated pile design. A literature review is combined with the implementation of suitable constitutive material models, which are subsequently calibrated using available experimental data. The results suggest significantly lower adhesion values than those commonly adopted in design. However, the essential viscoelastic behavior of bitumen can be adequately described within the calibrated range of the model. Nevertheless, due to limited experimental data for realistic loading conditions, significant extrapolation in both strain magnitude and strain rate was required, increasing uncertainty in the predicted response. Consequently, further experimental studies are required to characterize bitumen’s behavior when subjected to the large deformations and low strain rates observed in practice. This will enable more reliable calibration of the material model for practical design applications.