Nonlinear viscoelastic wave propagation: an extension of Nearly Constant Attenuation (NCQ) models

TL;DR

This paper introduces a nonlinear viscoelastic model for seismic wave propagation in soils, incorporating nonlinear elasticity and damping to better simulate soil behavior under various excitation levels.

Contribution

It extends existing NCQ models by including nonlinear effects in both stiffness and damping for isotropic materials, validated through finite element simulations.

Findings

Model accurately reproduces low amplitude ground motion.

Larger excitations lead to lower amplitudes and increased time delays.

Higher frequency content observed at larger excitation levels.

Abstract

Hysteretic damping is often modeled by means of linear viscoelastic approaches such as "nearly constant Attenuation (NCQ)" models. These models do not take into account nonlinear effects either on the stiffness or on the damping, which are well known features of soil dynamic behavior. The aim of this paper is to propose a mechanical model involving nonlinear viscoelastic behavior for isotropic materials. This model simultaneously takes into account nonlinear elasticity and nonlinear damping. On the one hand, the shear modulus is a function of the excitation level; on the other, the description of viscosity is based on a generalized Maxwell body involving non-linearity. This formulation is implemented into a 1D finite element approach for a dry soil. The validation of the model shows its ability to retrieve low amplitude ground motion response. For larger excitation levels, the analysis of seismic wave propagation in a nonlinear soil layer over an elastic bedrock leads to results which are physically satisfactory (lower amplitudes, larger time delays, higher frequency content).