Thomas WOLF

UMAT implementation of a hypoplastic constitutive law for numerical simulation of dynamic soil compaction (in German)

Dynamic soil compaction is a common soil compaction measure in civil engineering. Technical progress in recent decades has been accompanied by increasing automation. Work-integrated and continuous control of the compaction effect is required for soil compaction methods. In order to verify the experimentally developed control procedures with regard to the proposed compaction parameter, numerical simulations are used. For the theoretical research, the behavior of the soil must be described with a suitable constitutive model and implemented in the used software package.

In this Master thesis, a basic and extended (intergranular strains) hypoplastic constitutive model in the form of a UMAT is implemented in the FEM software ABAQUS. Two variants are coded for the numerical solution of the material tangent (consistent tangent and continuum tangent). The implementation is verified by element tests in the form of the oedometer and the triaxial test as well as by comparison with experimental and simulation results from published literature. The parameter studies performed show the large influence of the compression exponent on the behavior of the soil, which is already known from previous studies. Furthermore, the comparison of the simulation results of the oedometer test with those of the triaxial test shows a different sensitivity with respect to the critical friction angle. Practical applicability and numerical stability are verified by numerical simulation of dynamic soil compaction with the vibratory compactor on a simplified, three-dimensional vibrator-soil interaction model. The displacement controlled simulations with the hypoplastic constitutive model can qualitatively represent the propagation of the pressure wave and the increasing range of compaction over time. The selected parameter studies (vibrator amplitude, initial soil density) are numerically stable up to 100 cycles


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