Evidence of a unique critical fabric surface for granular soils

Abstract

The critical state of granular soils needs to make proper reference to the fabric that develops at critical state. This study substantialises the concept of critical fabric surface (CFS), which attracts the fabric state of granular soils upon continuous shearing. Numerical experiments using discrete-element method (DEM) modelling are conducted under drained and undrained conditions with varying Lode angles. Fabric tensors are defined based on the normals of all contacts and of the strong force contacts only. Both tensors have their spherical component preserved such that the information of coordination number can be carried. A separate series of low-confining-pressure undrained tests is conducted to probe the fabric states of soils in the post-liquefaction regime. Finally, a single CFS spanning across a wide range of coordination numbers is established based on the DEM results. The CFS concept provides an important reference state for soils sheared to large strains, complementary to the traditionally defined critical state. This provides a new perspective to interpret and model the mechanics of granular soils in both pre- and post-liquefied regimes. The evolution of fabric shows that the normalised strong-contact fabric evolves linearly with the stress ratio even for liquefied or anisotropically consolidated soils.