Revealing the liquefaction mechanism and anisotropy behaviour of root-reinforced soils: an energy-based approach

Revealing the liquefaction mechanism and anisotropy behaviour of root-reinforced soils: an energy-based approach

 

Ali Akbar Karimzadeh, Anthony Kwan Leung

Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Kowloon, Hong Kong SAR

 

Abstract:

Recent physical modelling work has demonstrated that plant roots provide seismic resistance to geotechnical infrastructure such as slopes and pipelines against liquefaction. Indeed, there is evidence from published triaxial data that the presence of roots increased the liquefaction resistance of soil and changed the liquefaction failure mode from limited flow failure to cyclic mobility, depending on the amount of cyclic stress ratio applied and the available root volume. However, effects of root orientation on soil anisotropy and energy dissipation during the process of liquefaction, have not been adequately addressed in the literature. In this presentation, we will present a new energy-based framework and its application to reinterpret a set of published triaxial data concerning on the undrained strain-controlled cyclic behaviour of root-reinforced soils. Based on the framework, the changes in the amount of dissipated energy required to reach the liquefaction criteria (i.e. 5% double-amplitude axial strain) of the soil due to the presence of roots of different volume ratio will be determined. We will use this energy term and the strain values at the compressive and extensive sides of a cyclic loading at the liquefaction state to explore how root orientations would affect the soil anisotropy. A new correlation between normalised cumulative dissipated energy (∑ΔW/σ_c’, where σ_c’ is the effective confining pressure) and the cyclic resistance ratio at the cycle number of 15 (CRR₁₅) will be established. We will also present the correlation between the ∑ΔW/σ_c’ with the normalised cumulative strain energy (∑4W/σ_c’) which is representative to the the demand energy of an earthquake event. Finally, we will discuss any effects of the recycling and recovering of strain energy upon cyclic loading, and their importance in the energy interpretation to root-reinforced soils.

Keywords: Energy-based approach, Root-reinforced soil, Anisotropy, Liquefaction, Triaxial cyclic tests