Abstract:

The Zhanjiang clay is a typical structured soil with high strength and sensitivity, and its mechanical properties are easily affected by sampling disturbance. Based on the self-boring pressuremeter tests (SBPT) and seismic dilatometer tests (SDMT) in the typical structured clay stratum, the in-situ stiffness decay curves are obtained. Furthermore, the Stokoe model is used to describe the normalized stiffness decay behaviors. Results show that the in-situ stiffness decay curve can be obtained by combining the tangential shear modulus G_t from SBPT with the small-strain shear modulus G₀ from seismic wave velocity V_s calculated by SDMT. The in-situ stiffness decay curves of structured clays at different depths have a declined trend with a hyperbolic type with the increasing strain levels, which proves that the mechanical properties of structured clays exhibit nonlinear characteristics. With the increase of depth, the in-situ stiffness parameters tend to increase under the condition of shear strain less than 10⁻³%, while they almost remain unchanged when the shear strain is larger than 1%. The normalized G-g decay curves obtained from the in-situ tests are in good agreement with the fitting curves from the Stokoe model, indicating that the numerical model could accurately describe the in-situ stiffness decay characteristics of structured clays. This study provides the design parameters for geotechnical engineering constructions of structured clays in Zhanjiang and an important reference for similar formations.

Key words: structured clay, stiffness decay characteristics, shear modulus, in-situ test, Stokoe model