Resumo em Inglês:

Abstract In order to move towards discrete analyses of soil behaviour, we need to develop a new range of apparatus and testing techniques. The lecture describes attempts to develop these new apparatus and presents data for a range of coarse-grained geomaterials at the single particle scale. The roles of the particle morphology and hence geological origin are discussed and are shown to influence both the contact mechanics and particle breakage behaviour. The mechanics of single particles are shown to be more complex than generally assumed and will require new means of modelling to account for the significant plasticity that occurs at particle contacts and patterns of breakage that are strongly influenced by the origins of particles and their effect on their morphology.

Resumo em Inglês:

Abstract This keynote lecture discusses the results of a long lasting experimental research, devoted to the investigation of clay microstructure and its evolution upon loading. Micro-scale analyses, involving scanning electron microscopy, image processing, mercury intrusion porosimetry and swelling paths to test the clay bonding, are presented on clays subjected to different loading paths, with the purpose of providing experimental evidence of the processes at the micro-scale which underlie the clay response at the macro-scale. Data from the literature on clays of different classes, either soft or stiff, are compared to original results on two stiff clays, Pappadai and Lucera clay, both in their natural state and after reconstitution in the laboratory. The results presented herein allow building a conceptual model of the evolution of clay microstructure upon different loading paths, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics. For editorial purposes, the research results are presented in two parts. The first part, presented in this paper, concerns the results for reconstituted clays, whereas a second part, concerning the corresponding natural clays, is discussed in a second companion paper.

Resumo em Inglês:

Abstract The in-situ small-strain shear modulus of soil and rock materials is a parameter of paramount importance in geotechnical modeling. It can be derived from non-invasive geophysical surveys, which provide the possibility of testing the subsurface in its natural and undisturbed condition by inferring the velocity of propagation of shear waves. In addition, for soil dynamics and earthquake engineering applications, the small-strain damping ratio plays a relevant role, yet its estimation is still challenging, lacking consolidated approaches for its in-situ evaluation. Recent advancements in instrumentation, such as distributed acoustic sensing (DAS), combined with advanced analysis methodologies for the interpretation of seismic wave propagation (e.g., machine learning and full waveform inversion), open new frontiers in site characterization. This paper presents and compares some advanced applications of measuring 1D and 2D variations in shear wave velocity and attenuation in-situ with reference to a specific case history.

Resumo em Inglês:

Abstract The InSight mission is a geophysical mission aimed at better understanding the structure of Mars and of the other rocky planets of the solar system. To do so, a lander accommodating two cameras, a very sensitive seismometer, and a dynamic self-penetrating heat probe nicknamed the mole were placed on the Mars surface by the Instrument Deployment Arm (IDA). Besides geophysical data (which definitely enriched the existing knowledge on the structure of Mars), the InSight instruments significantly increased the knowledge of the geological and geotechnical characteristics of the surface material at the InSight site. Small strain (elastic) parameters were derived from wave velocity measurements during the hammering sessions between the self-penetrating probe and the seismometer. A detailed observation of the soil profile along a depth of 37 cm was made possible thanks to the photos taken by the cameras, and to a detailed analysis of the mole penetration process. Further information was provided by an intense campaign of scraping and piling conducted by the IDA on the surface sand/dust layer. It was shown that the soil profile was composed of a surface 1 cm thick sand/dust layer, overlaying an around 20 cm thick loose duricrust made up of a cohesive matrix containing some pebbles, located above a 12 cm layer of sand overlaying a gravel/sand deposit. It is believed that the geology and soil mechanics data provided by the InSight mission will help for further robotic exploration of Mars.