Doctoral defence in Civil Engineering - Elín Ásta Ólafsdóttir

Ph.D. student: Elín Ásta Ólafsdóttir

Dissertation title: Multichannel Analysis of Surface Waves for Soil Site Characterization

Opponents: 
Dr. Steinar Nordal, Professor at the Geotechnical Division, Norwegian University of Science and Technology (NTNU), Norway
Dr. Sebastiano Foti, Vice-Rector for Education and Professor of Geotechnical Engineering at Politechnico Di Torino, Italy

Advisor: Dr. Bjarni Bessason and dr. Sigurður Erlingsson, both Professors at the Faculty of Civil and Environmental Engineering at the University of Iceland.

Also member of the doctoral committee: 
Dr. Amir M. Kaynia, Technical expert in vibrations and earthquake engineering at Norwegian Geotechnical Institute, and Adjunct Professor at Norwegian University of Science and Technology (NTNU), Norway.

Chair of Ceremony: Dr. Rajesh Rupakhety, Professor and Vice Head of the Faculty of Civil and Environmental Engineering at the University of Iceland.

Abstract:
Shear wave velocity is a fundamental parameter in soil dynamics and geotechnical earthquake engineering. Multichannel Analysis of Surface Waves (MASW) is a relatively new non-invasive technique to evaluate the near-surface shear wave velocity profile by utilizing the dispersive properties of surface waves in a heterogeneous medium. The method is both time and cost efficient and can be applied at a wide variety of soil sites, including locations where conventional invasive techniques are difficult to apply.
The main objectives of the project were (i) to develop an open software to acquire, process and analyse MASW field data, (ii) to validate and calibrate field observations by comparison with results obtained by other measurement techniques and alternative software packages, and (iii) to implement and adapt MASW for analysis of the stiffness properties of Icelandic soil sites and man-made fillings.
Alongside software development, an effort has been made to develop methods for combining dispersion curves from a number of records gathered at a given site, with the aim of increasing the range in investigated depths, get more reliable results, and assess experimental uncertainties. Furthermore, a simple but effective Monte Carlo-based technique has been developed for use in the MASW inversion analysis.
To date, MASW has been applied at over twenty natural locations in Iceland, ranging from sites characterized by peat and loosely compacted sand to cemented soil materials and soft rock. Where available, the results were compared to existing measurements. The method has also been successively applied for analysis of earth dams. In order to benchmark results obtained by the new software, field measurements were carried out at Norway’s National GeoTest Sites. The shear wave velocity profiles obtained by the new software (MASWaves) agreed well with results of existing measurements, thus verifying the performance of the set of data acquisition and analysis tools.

About the doctoral candidate:

Elín Ásta received a B.Sc. degree in Civil and Environmental Engineering from the University of Iceland in 2013 and a M.Sc. degree in Civil Engineering in 2016. Alongside her studies, Elín Ásta has worked as a assistant teacher at the University of Iceland and taught at the Commercial College of Iceland.