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Interpretation of shear modulus degradation tests

Srokosz P., Dyka I., Bujko M.

Studia Geotechnica et Mechanica

2018

Vol. 40, nr 2

125--132

The problem is a continuation of the research conducted at the University of Warmia and Mazury in Olsztyn, Institute of Building Engineering. It concerns the development of methods for the interpretation of the shear modulus measurements based on the tests conducted on a torsional shear (TS) apparatus. The issue has significant importance in determining the deformation parameters, essential to perform numerical simulations of the interaction between a geotechnical structure and the subsoil. The purpose of this study was to conduct a comparative analysis of the various methods of interpretation of research results based on direct and reverse analysis, as well as automated classification of the first cycle of the relationship between the shear stress and the shear strain components obtained from the TS test. The methodology for verification of the presented interpretative methods consists in carrying out a series of laboratory tests on non-cohesive and cohesive samples of different granulation and state parameters. The course of the research includes the following steps: elaboration of the granulometric composition of several samples of soil, determination of soil index properties and execution of TS tests. Various methods of interpretation of obtained results were taken into account, in addition to conducting a comparative analysis. The study used a non-standard interpretation approach consisting of analysing onefourth of the hysteresis loop of the first load-unload cycle of the tested samples. The obtained results confirmed the hypothesis that it is possible to estimate the degradation value of the shear modulus based on a part of the TS test results carried out under quasi-monotonic load conditions. The proposed methods of interpreting test results have confirmed their high usefulness, which is devoid of the uncertainty associated with standardised resonant column/TS testing.

Constitutive model of nonlinear elasticity in the frame of small strains theory

Szwed A., Jemioło S.

Logistyka

2009

nr 6

CD-CD

A constitutive relationship of nonlinear isotropic material is proposed in the paper. Model is thermodynamically consistent with the requirements for reversible processes in the frame of small strain theory. Using the isotropic strain tensor decomposition, the Green type constitutive strain potential is proposed. The specific strain energy functions are scalar valued, isotropic, non-negative and convex satisfying the natural state of material. Model is dependent on the two strain or stress invariants and four material constants. Proposed constitutive model predicts locking behaviour for the volumetric straining and yielding for shear loading. Dual model equations are given in the closed explicit mathematical form.

Proponujemy relacje konstytutywne nieliniowej spręzystości materiału izotropowego, które zgodne są z prawami termodynamiki procesów odwracalnych. Opis ten mieści się w ramach nieliniowej teorii sprężystości małych odkształceń. Postulujemy potencjał Greena w postaci funkcji jednostkowej energii odkształcenia objętościowego i postaciowego. Funkcje energii sprężystości spełniają wymaganie stanu naturalnego oraz są izotropowymi, nieujemnymi i wypukłymi funkcjami skalarnymi tensora odkształcenia. Są one zależne od niezmienników tensora odkształcenia i jego dewiatora oraz czterech stałych materiałowych. Proponowany model przewiduje zakleszczanie i mięknięcie materiału odpowiednio części kulistej i części dewiatorowej relacji konstytutywnej. Dualne relacje konstytutywne są podane w postaci jawnych wzorów.