Critical State Characterization of New Zealand East Coast Sand for Numerical Modeling

Abstract

This paper outlines the findings of a laboratory-based and numerical study to investigate the undrained flow failure behavior of East Coast Sand (ECS). ECS is a commonly encountered coastal deposit from the upper North Island of New Zealand. The study focused on establishing the undrained strength characteristics of ECS under static, triaxial compressive loading conditions, and at confining pressures in the range of typical engineering interest and for a range of soil densities considered in loosely deposited sands. The research objectives of establishing the basic soil properties and the intrinsic advanced geomechanical properties specific to ECS from Auckland were achieved through laboratory experiments and matching numerical simulations with an advanced critical-state compatible soil constitutive model (Norsand). The current work examined five different aspects of the ECS undrained behavior under static loads. It was shown that loosely deposited ECS within mean effective stresses ranging between 50 and 200 kPa was highly susceptible to expensive flow failures of structures built on or with them. The obtained approximate peak undrained shear strengths before failure and critical states were 29 kPa, 84 kPa, 130 kPa, and 200 kPa for test confining stresses of 50 kPa, 100 kPa, 200 kPa, and 300 kPa, respectively. Similarly, the corresponding excess pore water pressures were 48 kPa, 98 kPa, 200 kPa, and 240 kPa, respectively. The above results proved that the soil’s effective and confining stress are key determinants of the soil’s undrained shear strength characteristics which was consistent with the existing literature.