An investigation into subgrade fluidisation in transport infrastructure under cyclic loading

Fluidisation in saturated subgrades of transport infrastructure is a huge problem in many countries around the world caused by dynamic cyclic loads due to heavy haul trains on railways and heavy trucks on highways. The mechanism of subgrade fluidisation has been experimentally studied to a significant extent. However, numerical studies that have been carried out for studying fluidisation are limited. The first part of the paper includes a critical review of previous studies on the mechanism and the effect of cyclic loading factors on fluidisation. It is vital to conduct a comprehensive study with numerical modelling to simulate the actual field conditions of transport infrastructure to find reliable and cost-effective solutions to mitigate subgrade fluidisation. This goal can be achieved only by choosing a soil constitutive model that can capture the changes to the soil stiffness and strength due to excess pore pressure generation and dissipation, along with accumulated deformations in clay soil subjected to cyclic loading. Therefore, in this study, the SANICLAY constitutive model is selected as the suitable candidate to fulfil those requirements. It is implemented in the ABAQUS/Standard finite element program using the user-developed material subroutine UMAT. In the second part of the paper, the validation of the SANICLAY model that accounts for the anisotropy and structure of natural clay was presented using triaxial test data found in the literature for undisturbed clay. Application of the model to simulate cyclic loading shows that the version of SANICLAY used in the simulations needs modifications to capture the stiffness and strength degradation during cyclic loading.