Damage assessment via time history analysis of the massive earthen pyramid of Huaca de la Luna (Huacas de Moche, Perú)

Huaca de la Luna is a monumental religious complex located in the north coast of Perú built in different stages from 100 to 650 CE by the Moche civilization using millions of adobe blocks. The specific focus of this study is the main stepped pyramid at the centre of the complex, and the present objective is to use time history analyses simulating an actual earthquake to investigate how an accumulation of seismic damage affects its structural response. Built on the slopes of Cerro Blanco Mountain, this monument consists of superimposed horizontal platforms added on top of each other during historical renovations. On the east side, the pyramid is supported on sloping bedrock while the west side is built directly on layers of soft soil. The pyramid presents severe structural damage near the northwest corner. Previous work has focused on 2-and 3D continuum models, with the goal of determining a lateral capacity limit. These models of the structure and its foundation are derived from a detailed evaluation of available archaeological, material, and geotechnical data. Nonlinear analysis is performed in Abaqus/CAE Explicit 2022. The foundation of soft soil is modelled with a Mohr-Coulomb formulation. Using a macro-modelling approach, the adobe masonry is represented as a continuum of concrete damaged plasticity (CDP) material with damage parameters. In this material model, plastic strains represent fractures. This artefact of the material formulation allows us to follow the development of local damage conditions up to structural collapse by separation of the adobe structure into discrete sections by observing the time-evolution of elastic strain, kinetic, and plastic dissipation energies. A 2D FE plane strain model selected from previous research as the most critical case is used to perform and correlate dynamic pushover and time history analyses. The present study supports the conclusions that a) current damage to the pyramid’s northwest corner is unlikely due to gravitational loading, b) horizontal accelerations cause damage similar to that which is extant at the northwest corner of the pyramid, and c) seismic acceleration of considerably higher magnitude than the highest recorded may have occurred to produce such damage.