A macroblock 2D finite element model for assessing the roots of failure of Huaca de la Luna’s main pyramid (Peru) under seismic action

Abstract

This study contributes to the seismic structural failure analysis of the main pyramid of the archaeological complex Huaca de la Luna, Peru. Built with millions of adobe bricks by the Moche civilization (200–850C.E.), the monument is one of the largest adobe structures in the world. The monument shows signs of severe natural and anthropogenic damage due to its position along the Pacific Ring of Fire and extensive looting since Spanish colonial times. The pyramid was built as a succession of taller and larger platforms, each formed by erecting adjacent but disconnected vertical piers made of adobe masonry. A multiscale 2D nonlinear finite element (FE) model is introduced for assessing the contribution of this pier architecture to the structural response of the pyramid. The time-evolution of elastic strain and plastic dissipation energies is used to quantitatively track structural failure. The instant of structural collapse and attendant lateral capacity can be extracted from the point at which these energies match. Critical regions of a representative cross-section are modelled with individual piers represented by macroblocks and separated by frictional interfaces. A continuous description is adopted for the remaining part of the model. A nonlinear, two-dimensional (2D) plane strain analysis is conducted in Abaqus/CAE Explicit using concrete damaged plasticity and Mohr-Coulomb formulations for adobe construction and soft soil, respectively. A two-stage assessment procedure begins with a quasi-static analysis to predict the stress state due to gravitational load. A dynamic analysis follows to identify lateral capacity and failure mechanisms triggered by monotonically increasing ground acceleration. The development of local damage conditions up to structural collapse is visualized by the nucleation and propagation of maximum principal plastic strains throughout the model. A sensitivity analysis was conducted to evaluate the effect on lateral capacity of the contact friction coefficient between macroblocks and the number of macroblocks used to discretize the critical area. Introducing macroblocks to the model produces lateral capacities that are lower than analogous, purely-continuum models. These results are shown to be critically affected by the frictional coefficient that governs contact between the macroblocks. The results of this study offer critical insights on the consolidation strategy for the northwest corner of the pyramid and may find application to similarly-built historical earthen structures in northern Peru.