Evaluation of Microscale Behavior and Structural Deformation for Yeonji Wall in Gongsanseong Fortress of the Sixth Century in Korea

The Gongsanseong Fortress is a fortress built to defend the capital of Baekje Kingdom, and has been inscribed on the World Cultural Heritage for its outstanding historical value as a cultural site that allows one to see Baekje culture and construction techniques. In 2013, part of the rampart collapsed due to localized heavy rainfall, and since then, scientific and engineering studies have been conducted for its stable conservation. Based on these studies, a maintenance system has been established, and is still in operation currently. Automatic measurement equipment was installed on structurally unstable ramparts to measure the microscopic movements, and it was found that the walls in the pond site (Yeonji) on the north side of the Gongsanseong Fortress moved the fastest. The movement of the wall is concentrated from winter to thawing season, and it is repeated every year. It was interpreted that the movement is caused by the freeze-thaw action of water. To visually confirm these movements, we compared 3D scan data taken in 2014 and 2021. From the analysis, the largest deformation occurred in the central part of the wall in the horizontal direction of the wall, while in the vertical direction, the deformation was more concentrated in the lower part of the wall than in the upper part. Deformation outside the tolerance range was observed in more than 70% of the ramparts, where the walls were pushed and protruded towards the frontal direction. The movement of the wall, as measured by some measurement sensors, takes the form of a reversible deformation that returns to the original movement after structural deformation. However, the 3D scan data shows that this movement is irreversible, which is different data from the measurement sensors. These results indicate that the application of a two-dimensional measurement technique to capture the spatial movement in a 3D space may distort the reflection of an actual movement, so the possibility of such distortion must be considered in the interpretation of the two-dimensional measurement results.