The external and internal measurement impact on shear modulus distribution within cyclic small strains in triaxal studies into cohesive soil
Silesian University of Technology, 44-100 Gliwice, ul. Akademicka 5/214,
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The paper deals with comparison of tangent shear moduli Gs of kaolin from Tułowice obtained from cyclic triaxial tests on the basis of external and internal reading in the small strains range (10-5÷10-3). The tests were carried out on a modernised test bed, enabling full saturation of specimens using the back pressure method as well as a precise internal measurement of strains by means of contactless microdisplacements sensors. The value of linearity factor L is one of adopted quality criteria for two measuring methods. Maintaining a constant deformation rate the influence of various cyclic process parameters (deviator stress amplitude – constant or variable; high or low; initial level of stress and strain, at which the unloading and reloading cycles were started; overconsolidation ratio OCR as well as cycles’ number and arrangement) on the "shear modulus – axial strain" characteristic was studied. The obtained values of Gint and Gext (or Lint and Lext) clearly show an underestimation (even 5 times) of Gs value within the range 10-5÷10-3 when using an external measurement. In addition, the differences between Gint and Gext, which develop differently depending on specified cyclic process parameters, gradually decrease with increasing axial strains.
© Owned by the authors, published by EDP Sciences, 2010