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prof. Ing. Jana Frankovská, PhD.
Identification number: 3849
University e-mail: jana.frankovska [at] stuba.sk
 
Profesorka CSc.,PhD. - Department of Geotechnics (FCE)
Institute chief official - Department of Geotechnics (FCE)

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Basic information

Basic information about a final thesis

Type of thesis: Dissertation thesis
Thesis title:Elastic properties of natural sands with fines measured by bender / extender elements
Written by (author): Ing. Jakub Panuška, PhD.
Department: Department of Geotechnics (FCE)
Thesis supervisor: prof. Ing. Jana Frankovská, PhD.
Opponent 1:prof. Ing. Ivan Vaníček, DrSc.
Opponent 2:doc. RNDr. Eva Hrubešová, PhD.
Opponent 3:doc. András Mahler, PhD.
Final thesis progress:Final thesis was successfully defended.


Additional information

Additional information about the final thesis follows. Click on the language link to display the information in the desired language.

Language of final thesis:English

Slovak        English

Title of the thesis:Elastic properties of natural sands with fines measured by bender / extender elements
Summary:Presented dissertation „Elastic properties of natural sands with fines measured by bender / extender elements“ is focused on laboratory measurement of elastic properties of coarse grained soils with different content of fines. Stiffness of soils is discussed in the beginning along with isotropy and anisotropy of stiffness. Degradation of stiffness with increasing strains is introduced and laboratory and in-situ methods used to measure soil stiffness under various range of strains are described. Different factors influencing very small strain stiffness as grain shape, grain size distribution properties, effective stress, void ratio, time effects/ageing/cementation are reviewed. Present stiffness degradation models and empirical equations for evaluation of very small strain stiffness are described. Finally, application of very small and small strain stiffness and reduction of stiffness with increasing strain in geotechnical engineering is described. Fifteen different natural soils from five different sites (three in Hungary, two in Slovakia) with different content of fines are studied. Bender Extender / Element test in triaxial cell, as the method based on measurement of wave velocities (shear wave velocity vs, compressional wave velocity vp), is used to measure very small strain stiffness (shear modulus Gmax and constrained modulus Mmax) and subsequently estimate Poisson´s ratio. The Bender / Extender Element test is widely used in geotechnical engineering since 1978 (benders) and 1981 (extenders) to measure very small strain stiffness of soils under a variety of stress and void ratio conditions. Test execution and methods of evaluation are still discussed by professionals and the test is not fully standardized yet. Bender Element test and methods of results evaluation were verified through the set of measurements at Széchenyi István University on Resonant Column test, comparison of field and laboratory measurements on clayey soils and with numerical and analytical models. Effects of soil sample preparation and effect of measurement equipment was studied. Sample preparation, evaluation methods, and parasitical effects in measurements were studied and systematic method of preparation, testing procedure and evaluation of results were established through these extensive analyses. Effect of overconsolidation, anisotropic state of stress and gravel content is discussed on set of tested samples. Matlab codes including evaluation and analytical models are attached in the Annexes. Unique regression procedure, employed in evaluation of the results and in order to set regression constants of empirical equations used for prediction of small strain stiffness, is introduced in this study and the procedure was verified on datasets of independent researcher (Wichtmann, et al., 2015). Finally, correlations for elastic soil properties Gmax and Mmax using grain size properties and fines content were developed. These correlations were specially developed for sands with plastic fines as these were already tested by variety of researchers but no systematic correlations have been provided until now. Furthermore, simple correlations for estimation of Poisson´s ratio max based on Gmax and Mmax are provided in the thesis. The independent tests on set of measurements not included in regression were done to verify the applicability of developed correlations. Minor observations on overconsolidation, anisotropic state of stress, and gravel content made during testing are discussed and applicability and restrictions of the developed correlations are presented.
Key words:soil stiffness, small strains, bender / extender elements

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