Thomas Barciaga

Quantitative Interpretation of Tracks for Determination of Body Mass

To better understand the biology of extinct animals, experimentation with extant animals and innovative numerical approaches have grown in recent years. This research project uses principles of soil mechanics and a neoichnological field experiment with an African elephant to derive a novel concept for calculating the mass (i.e., the weight) of an animal from its footprints. We used the elephants footprint geometry (i.e., vertical displacements, diameter) in combination with soil mechanical analyses (i.e., soil classification, soil parameter determination in the laboratory, Finite Element Analysis (FEA) and gait analysis) for the back analysis of the elephants weight from a single footprint. In doing so we validated the first component of a methodology for calculating the weight of extinct dinosaurs. The field experiment was conducted under known boundary conditions at the Zoological Gardens Wuppertal with a female African elephant. The weight of the elephant was measured and the walking area was prepared with sediment in advance. Then the elephant was walked across the test area, leaving a trackway behind. Footprint geometry was obtained by laser scanning. To estimate the dynamic component involved in footprint formation, the velocity the foot reaches when touching the subsoil was determined by the Digital Image Correlation (DIC) technique. Soil parameters were identified by performing experiments on the soil in the laboratory. FEA was then used for the backcalculation of the elephants weight. With this study, we demonstrate the adaptability of using footprint geometry in combination with theoretical considerations of loading of the subsoil during a walk and soil mechanical methods for prediction of trackmakers weight.

Constitutive Parameter Adjustment for Mechanized Tunneling with Reference to Sub-system Effects

In this research, the effect of sub-system on model response for mechanized tunneling process has been taken into consideration. The main aim of this study is to modify the constitutive parameters in a way that the best agreement between numerical results and measurements is obtained. The sub-system includes supporting pressure at the face of the TBM, contraction along the TBM-shield and grouting pressure in the annular gap. The commercially available finite element code, PLAXIS is adopted to simulate the construction process. The soil behavior during the excavation is numerically reproduced by utilizing Hardening Soil model with small strain stiffness (HSsmall). The constitutive parameters are obtained via sensitivity and back analyses while they have been calibrated based on the real measurement of Western Scheldt tunnel in the Netherlands. Both local and global sensitivity analyses are used to distinguish which parameters are most influencing the soil deformation. Thereafter, the model validation is accomplished by applying different scenarios for face pressure distributions with respect to the slope of the tunnel. In addition, the effect of contraction factor is modified individually or coupled with the variation of grouting pressure. Evaluating the influence of the sub-system is conducted to assess its effects on the model responses and to seek the possibility to decrease the disagreement between the calculated displacement and real measured data.

On the Use of Isotropic Hardening Plasticity to Model Cyclic Consolidation of Fine Grained Soils

Cyclic soil behavior plays an important role in geotechnical engineering, both in the installation phase as over the life span of constructions. Relevant application examples which find increasing attention nowadays are the dimensioning of on- and offshore foundation systems, the analysis of soil behavior due to mechanized tunneling processes as well as analyses of loading histories related to deep excavation walls. Thus, in the present paper fundamentals of cyclic soil behavior under partially drained, oedometric conditions are analyzed. Excess pore water pressure evolution and accumulated deformations are studied by both numerical and experimental approach. For this purpose, a new oedometer device is introduced which allows to measure complete stress state under transient loading. Additionally, by numerical experiments using FEM the influence of soil stiffness and permeability on the evolution of excess pore water pressures and accumulated deformations is studied. By comparison of numerical and laboratory experiments the ability of classical isotropic hardening plasticity to model cyclic consolidation phenomena is validated.

Cyclic Response of Natural Onsøy Clay

In geotechnical applications cyclic loading occurs frequently caused by earthquake shaking, traffic or wind and wave loading. The consideration of cyclic loading effects finds increasing attention nowadays. This particularly holds true for structures, which are of civil importance and involve high investment costs. Sophisticated calculation approaches are applied within the design process of these boundary value problems. However, many of the calculation models assume undrained stress paths, where cyclic loading leads to a continuous generation of excess pore water pressure. When soft, marine clays under slower loading are involved, the dissipation of excess pore water pressure becomes relevant. The transient consolidation process needs to be considered. Thus, in the present paper the consolidation behaviour of Norwegian Onsoy clay as a typical representative of natural, marine clay under cyclic loading is analysed. Part I of this paper presents the experimental study. Testing results from monotonic and cyclic oedometer tests on natural as well as remoulded clay are introduced. The differences in the compression behaviour and pore water pressure dissipation of structured and remoulded clay are illuminated. Furthermore, the effect of cyclic loading characteristics, as e.g. the load amplitude, on consolidation is analysed. Part II of the paper comprises a numerical study. Modelling the cyclic consolidation processes by use of FEM, the focus of the analysis is set on the necessity of different features of a hierarchical model to analyse this type of boundary value problems.