Geotechnical and geophysical exploration in archaeological heritage: initial assessment at Huaca de la Luna

This paper presents results of geotechnical and geophysical tests carried out at Huaca de la Luna, which is one of the most important adobe archaeological complexes in Perú. This complex is located at the north coast of Perú just south of the city of Trujillo. This huaca is a massive earthen structure in the form of a stepped pyramid, occupying an area of approximately 8200 m2and with an approximate height of 21 m, built by the Moche civilization from 100 AD to 650 AD. Archaeological and conservation works are being carried out at this site since the beginning of the 90s. An ongoing research project led by the last two authors has revealed some fissures and cracks in adobe walls and columns in some areas of the huaca particularly close to the northern façade of the structure. This identified damage has motivated the geotechnical and geophysical investigation summarized in this paper. To characterize the foundation soils of the areas of interest of the huaca a series of Multichannel Analyses of Surface Waves (MASW) and seismic cone penetration tests (SCPTu) have been carried out. These tests were performed primarily to develop a generalized geotechnical profile and estimate engineering properties. The results of SCPTu tests showed that near the North façade practical cone refusals occurred at depths ranging between 6 and 12 m which provides evidence of a sloping competent foundation layer which seems consistent with the observed slope of the granite outcrops of the adjacent granite rock Cerro Blanco hill which is located just to the east of the Huaca. The paper discusses the shear wave velocity profiles from the MASW and SCPTu tests which in general were found to be in good agreement. The analyses of the results of these tests indicate that the sloping bedrock layer is shallower as we move to the east from the NW corner. Further structural and geotechnical studies are being carried out for assessing the pattern and magnitude of foundation settlements near the NW corner of this monument which is where most of the structural damage has been observed.