Excavation-Parallel Laser Scanning of a Medieval Cesspit in the Archaeological Zone Cologne, Germany

摘要

During the construction of an underground museum in the historic city center of Cologne, Germany, large parts of the Roman and medieval city are being excavated. The newly excavated remains as well as remains of the Roman city, which had already been excavated in 1954, exhibit structural damages. While at first deficiencies in the construction were assumed to be the cause of the damages, in 2003 a seismogenic origin was suggested. To further test this hypothesis of seismically induced slope movements and other possible causes, a multidisciplinary project was started. One step in this project is the documentation of the damages using a 3D laser scanner, followed by a quantitative damage analysis. This article presents the 3D documentation and the quantitative damage analysis of a recently excavated medieval cesspit. The 8.3m-deep cesspit was mapped during 11 campaigns using a phase-based 3D laser scanner. Due to the static conditions of the cesspit, the structure could not be excavated in its entirety. After the excavation of every 1-2m-section, restoration work had to be done to avoid a collapse of the construction. The laser scanning technique offered the possibility of working parallel to the excavation so the original conditions of each section could be documented before the restoration. The resulting models were used to identify, classify, and quantify the structural damages of the cesspit.