Numerical modeling of object penetration in geotechnical engineering

Abstract

The finite element method (FEM) has been widely adopted in the analysis of geotechnical engineering problems, for instance, to evaluate the soil-structure interactions in tunnels, earth-retaining systems and foundations, etc. However, for object penetration problems in which large deformation of the ground is involved, the finite element mesh may distort excessively, resulting in an immature termination of the analysis. It is clear that advanced techniques must be applied.

In this study, the remeshing and interpolation technique with small strain (RITSS) is adopted to overcome the problem of excessive mesh distortion. The numerical analysis is carried out using the FEM package ABAQUS and the RITSS approach is implemented by developing a script written in the programming language Python. Two different mapping algorithms, namely the superconvergent patch recovery (SPR) and the mesh-to-mesh solution mapping (MSM), have been studied, implemented and evaluated. The limitations in the early attempts of the RITSS approach have also been stated and the corresponding improving techniques have been proposed in this thesis: firstly, the deformation of the ground surface has been unrealistically neglected in some previous studies. A technique of extraction of the deformed geometry is given in this study so the settlement/heave at the ground surface can be correctly recorded and simulated. Secondly, it was found in previous studies that a gap will be generated at the soil-structural object contact interface during the RITSS approach, leading to an underestimation of the contact normal stress. In this thesis, an element node-tracing technique has been developed to eliminate this gap so that the contact interface can be correctly modeled. Lastly, it was found that there will be a loss of contact normal stress when applying the RITSS approach. A technique called ‘dummy step’ is proposed in this thesis to properly recover the contact normal stress.

With all the techniques proposed, an application example has been carried out to model the penetration process of a concrete pile. The results, including the development of stress and the heave/settlement at different stages of the penetration process have been presented and discussed. Overall, it is envisaged that the techniques proposed in this thesis can generate results to provide a deeper insight into the numerical modeling of the object penetration problems in geotechnical engineering.