Acta Scientiarum Polonorum

The shear modulus (G) is one of the key parameters for seismic ground response
analysis and it can be usually determined by means of dynamic tests (DT), such as resonant
column test (RCT), or cyclic static test (CST), e.g. torsional shear (TST). The RC and TS
tests are widely used laboratory methods to fi nd stiffness of soil at small to medium strain
range (0.0001–0.5%). The purpose of this paper is to present the experimental results from
RC and CS laboratory tests on silty-sandy clay from the western part of Warsaw, Poland.
The study aims to compare the shear modulus values obtained from two different research
techniques. The infl uence of, in particular, the applied effective pressure, associated shear
strain and experimental method (i.e. loading frequency and output amplitude) on the shear
modulus at small strains (Gmax) and secant shear modulus (G) are investigated and proved.
Generally, the results reveal that the examined soils stiffness calculated from TS tests is
lower than from RC tests.