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A two-phase velocity-pressure stabilized formulation is proposed for the numerical analysis of mechanized excavations in partially saturated soft soils using the Particle Finite Element Method (PFEM). The fully coupled formulation is based on the theory of porous media in association with the Soil Water Characteristic Curve and the porosity-dependent Kozeni-Carman model for the realistic estimation of the soil permeability. The combination of the PFEM methodology, characterized by a global re-meshing strategy equipped with a new adaptive mesh refinement scheme for the resolution of strain localization zones in the ground, with a hypoplastic constitutive model for the description of the nonlinear behavior of the deformable soil skeleton, allows for the modeling of very large deformations, as required for excavation simulations. The PFEM model is validated based on selected geotechnical benchmark problems concerned with fully and partially saturated soil specimens. The model is further applied to computational re-analyses of excavation tests involving a single cutting tool moving in a sandbox. The reaction force-tool displacement curve for the excavation tool as well as the evolution of the deformed topology of the sand including the formation of shear zones obtained from the computational model are compared with respective experimental observations. Parametric investigations aimed at elucidating the influence of selected geotechnical parameters on the excavation process are also carried out. Finally, the suitability of the proposed PFEM-based numerical strategy for the modeling of 3D excavation problems is demonstrated by means of 3D PFEM simulations in fully saturated sand.

The mechanized tunnel construction is carried out by tunnel boring machines, in which the soil in front of the working face is removed, and the tunnel lining is carried out with shotcrete or the setting of segments and their back injection. Advancements in this field aim towards increase of the excavation efficiency and increase of the tool lifetime, especially in rock-dominated grounds. The latter is achieved by understanding the wear mechanisms abrasion and surface-fatigue, and by knowledge of the microstructure-property relation of the utilized materials. Improvements for tool concepts are derived, based on experiments and simulations. A key parameter towards efficient rock excavation is the shape of the cutting edge of the utilized disc cutters. Sharp cutting edges have proven to generate higher rock excavation rates compared to blunt ones. The compressive strength of the utilized steel has to be high, to inhibit plastic deformation and thereby to maintain sharp cutting edges. This requirement competes with the demand for toughness, which is necessary to avoid crack-growth in the case of cyclic loading. Solutions for this contradiction lie in specially designed multiphase microstructures, containing both hard particles and ductile microstructural constituents. Besides adapting the alloying concept, these required microstructures and the associated properties can be adjusted by specific heat-treatments.

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