# Exploring the Macroscopic Behavior and Microstructure Evolution of Lightly Cemented Sand in the Post-Liquefaction Process Using DEM

## TL;DR

This paper uses simulations to study how cemented sand behaves after liquefaction, linking macroscopic properties to microscopic changes.

## Contribution

The study introduces a DEM-based approach to analyze post-liquefaction behavior of cemented sand at both macro- and microscales.

## Key findings

- DEM simulations capture the influence of cement content on shear strength and stiffness.
- Liquefaction reduces initial stiffness regardless of cement content.
- Microstructure evolution significantly affects macroscopic post-liquefaction behavior.

## Abstract

This study investigates the post-liquefaction monotonic undrained shearing behavior of cemented sand at the macro- and microscales, using the discrete element method. A series of cyclic undrained triaxial tests with different stress amplitudes and post-liquefaction monotonic undrained triaxial tests were simulated on cemented sand with diverse cement contents (CCs). For comparison, a series of monotonic undrained triaxial tests on cemented sand without liquefaction (virgin cemented sand) were also modeled. The macroscopic behavior was analyzed in conjunction with the microscopic characteristics of the assembly, such as the deviator fabric of contact normal orientation, mechanical coordination number, energy components, and bond breakage. The results show that the DEM model can capture the effect of CC and cyclic stress ratio (CSR) on the undrained shear strength, stiffness, and pore pressure observed in laboratory experiments. Referring to the virgin specimen, with an increase in CC, the mechanical coordination number and the input work increment increase, while the deviator fabric for total contacts changes irregularly, leading to a greater initial stiffness and shear strength. In the case of the liquefied specimen, the smaller initial mechanical coordination number results in a very low initial stiffness regardless of CC. Contrary to the uncemented sand, both the mechanical coordination number and the input work increment decrease with an increasing CSR for the cemented sand. The microstructure evolution governs the effect of cementation level and liquefaction history on the macroscopic post-liquefaction behavior.