Assessing damage to archaeological artefacts in compacted soil using microcomputed tomography scanning

摘要

This laboratory study investigated the susceptibility of subsurface archaeological ecofacts/artefacts to incidental damage from utility construction activities, as it pertains to the cultural heritage aspects of environmental impact assessment and municipal planning. The research objective was to use X-ray microcomputed tomography (micro-CT) imaging to non-destructively determine the nature and extent of any damage inflicted on a range of ecofact and artefact types (authentic and replica) embedded in repacked, plastic clay soil by pure soil strain at variable levels of static load compactive effort up to 600kPa. Uniaxial soil compression testing and micro-CT imaging were combined procedurally to meet this objective. It was concluded that lithic artefacts were largely immune to damage from stresses up to 600kPa due to their high strength properties, while moderately fragile ecofacts (replica charred maize kernels) exhibited evidence of dimensional distortion, but not of breakage. Very fragile ecofacts (unionid freshwater clam shells) showed dimensional distortion and minor structural damage at lower stresses (50 and 100kPa), but significant breakage and fragmentation at higher stresses (300 and 600kPa). Overall, the micro-CT technique was shown to be useful in monitoring and describing any breakage or morphometric distortion in a wide range of test ecofacts/artefacts compressed in a clay-rich soil matrix. However, earthen artefacts, such as terra cotta pottery sherds, were found to be problematic using the micro-CT imaging technique for this application due to similarities in the densities of the ceramic sherds and the surrounding compressed soil matrix.