The main objective of this research project is the development and launch of a seismic wave-based laboratory tool for the reliable determination of the damping characteristics of soils. The laboratory tool will make use of bender elements, installed in routine geotechnical testing apparatuses, especially in triaxial chambers. A specific software of acquisition, interpretation and analysis will be developed, as well as a set of implementation and testing guidelines. This tool will allow an integrated and advanced geotechnical characterisation, since it will enable the determination on a single specimen in the same test of: a) stress-strain response (currently routine); b) small-strain shear modulus (when BE are installed); c) damping ratio (to be provided by the new laboratory tool). Furthermore, the soil fabric and porosity of the specimen can also be assessed throughout the same single test. To this day, such characterisation requires separate tests, including expensive and complex apparatuses such as the resonant column or the torsional hollow cylinder. The innovative technological tools and procedures, based on seismic-wave measurements, to be developed and implemented in this project (in Tasks T2 and T5) will be capable of providing a reliable characterisation of the dynamic behaviour of a soil. A complete calibration, validation and performance analysis of the new tool will be made from comparisons with numerical simulations (Task T3) and with results obtained in the resonant-column (in Task T4).
For pursuing this challenge, this exploratory project is fundamentally technological, with a proof of concept supported by the validation using numerical simulations and by the calibration of results against resonant-column test, from which a set of implementation and testing protocols will be defined. The plan has been divided into 6 tasks (outlined in the attached flowchart), which involve extensive laboratory experimental work, complemented by numerical modelling for the production of a new soil characterisation tool, as follows:
T1: Characterisation of BE-system response by laser measurements
T2: Experimental measurement of soil damping using BE
T3: Calibration against resonant-column tests
T4: Method validation by numerical simulations
T5: Proposal of a new testing protocol for wave-based determination of soil damping
T6: Project management and dissemination
The main experimental work will be carried out at the Geotechnical Laboratory of FEUP (labGeo), one of the best equipped geotechnical laboratories in Portugal (www.fe.up.pt/sgwww/labgeo), where several standard and stress-path, as well as cyclic triaxial, cyclic simple shear, true triaxial and high pressure triaxial apparatuses are available, most of these equipped with bender elements for seismic wave measurements. Additionally, a set of BE transducers manufactured in-house at FEUP will be subjected to a series of high-precision laser measurements, at the Geotechnical Laboratory of the University of Waterloo (UOW), in Canada, as part of a long-standing collaboration with the project's consultant, Prof. Giovanni Cascante. The reason for the use of this specific laser vibrometer (which cost exceeded 100k EUR) resides on its high-quality and high-precision, complemented by the know-how of the research team and technical staff of UOW.
The research team members from FEUP research group CONSTRUCT, have been selected to provide the necessary know-how and expertise for the successful accomplishment of these tasks: Cristiana Ferreira (PI, CF) is an experienced soil mechanics and wave propagation experimentalist, working on soil characterisation for more than 20 years; Manuel de Matos Fernandes (co-PI, MMF) is a distinguished full professor in soil mechanics and geotechnical engineering, providing knowledge and expertise on the fundamentals of soil behaviour and applications to geotechnical design and practice; António Viana da Fonseca (AVF) is a well-known expert in field and laboratory experimental soil mechanics for decades and specifically on soil characterisation for geotechnical and earthquake engineering applications; Fausto Molina-Gomez (FMG) is a young researcher, who has already a remarkable experience in geotechnical laboratory testing, including resonant-column testing; Javier Camacho-Tauta (JCT), from the Universidad Militar Nueva Granada (UMNG) in Colombia, is an expert in the use of frequency-domain techniques in both resonant-column and BE testing. |
