Hypoplastic particle finite element model for cutting tool-soil interaction simulations:Numerical analysis and experimental validation

This study presents numerical and experimental models for the analysis of the excavation of soft soils by means of a cutting tool.The computational model is constructed using an Updated Lagrangean(UL)velocity-based Finite Element approach.A hypoplastic formu-lation is employed to describe the constitutive behavior of soft soils.Large displacements and deformations of the ground resulting from the cutting tool-soil interaction are handled by means of the Particle Finite Element method,characterized by a global re-meshing strat-egy and a boundary identification procedure called a-shape technique.The capabilities and performance of the proposed model are demonstrated through comparative analyses between experiments and simulations of cutting tool-soft soil interactions.The experiments are performed using an excavation device at Ruhr-Universita¨t Bochum(RUB),Germany.The main details concerning the setup and calibration and evolution of the measured draft forces are discussed.Selected computational results characterizing the cutting tool-soft soil interaction including the topology of the free surface,void ratio distribution ahead of the tool,spatio-temporal evolution of the reaction forces and abrasive wear behavior are evaluated.

Acoustic waveform inversion in frequency domain:Application to a tunnel environment

Waveform inversion is an approach used to find an optimal model for the velocity field of a ground structure such that the dynamic response is close enough to the given seismic data.First,a suitable numerical approach is employed to establish a realistic forward computer model.The forward problem is solved in the frequency domain using higher-order finite elements.The velocity field is inverted over a specific number of discrete frequencies,thereby reducing the computational cost of the forward calculation and the nonlinearity of the inverse problem.The results are presented for different frequency sets and with different source and receiver locations for a twodimensional model.The influence of attenuation effects is also investigated.The results of two blind tests are presented where only the seismic records of an unknown synthetic model with an inhomogeneous material parameter distribution are provided to mimic a more realistic case.Finally,the result of the inversion in a three-dimensional space is illustrated.