Monitoring through replication: Design and evaluation of the monitoring reburial at the Laetoli trackway site

Abstract How is it possible to monitor the condition of a site or artefact after it has been reburied? In the case of the reburial of the extremely fragile and remote site of Laetoli in Tanzania this problem was addressed by creating a replica reburial close to the site in 1995. The method and materials used to rebury the trackway are replicated in the monitoring trench, which thus provides a ‘window’ on the condition of the trackway. A series of samples and indicator objects of different materials placed in the trench are intended to provide an understanding of the burial environment over the long term. Additionally, triangular recesses with sharply defined edges were cut into the floor of the trench to allow determination of the mechanical stability of the tuff to deformation under the reburial overburden. The trench was lined with root-inhibiting Biobarrier® geotextile and then reburied in the same manner as the trackway; existing acacia trees at the edge of the trench were allowed to remain. In 1997 excavation of part of the trench was undertaken. Of particular interest was the fine detail of the topography of the floor of the trench and the effectiveness of the Biobarrier®. Geosynthetics showed no evidence of deterioration, but severe degradation of all wood samples without preservative chemical treatment and of indicator objects indicated a very aggressive environment. Many of the findings, such as survival or deterioration of the indicator objects, use of geosynthetics and the efficacy of Biobarrier®, have relevance to a broader understanding of buried environments.