Experimental and numerical investigation of rate and softening effects on the undrained shear strength of Ballina Clay

Y. Ansari, J. Pineda, G. Kouretzis and D. Sheng

We present the basic components of a methodology to investigate two key aspects of the mechanical behaviour of some natural clays, namely the dependency of the undrained shear strength on the rate of shearing, and the softening response at large strains. For that, we will use a blend of novel experimental testing procedures and cutting-edge computational techniques, currently under development at the University of Newcastle. Measurements of the shear stress-strain response under undrained conditions will be obtained using a newly developed miniature vane shear apparatus, featuring automatic control of the blade rotation velocity. Laboratory tests will be complemented with large deformation numerical simulations of the vane test with the coupled Eulerian-Lagrangian method. For that, an appropriate constitutive model is implemented in ABAQUS/Explicit, able to simulate the visco-plastic strain-softening response of soft clays. Testing will be performed on the soft estuarine clay samples retrieved from the national geotechnical soft soil field testing facility, established in Ballina, NSW. With the focus being on Australian soft clays, the long-term goal of this study is to improve the procedures for performing and interpreting in situ tests included in Australian Standards.