Digital Documentation and Short-term Monitoring on Original Rampart Wall of the Gyejoksanseong Fortress in Daejeon, Korea

대전 계족산성 원형성벽의 디지털기록화 및 단기모니터링 연구

Abstract

This study was carried out unmanned aerial photography and terrestrial laser scanning to establish digital database on original wall of Gyejoksanseong fortress, and measured ground control points for continuity of the monitoring. It also performed precise examination with the naked eye, unmanned aerial photogrammetry, endoscopy, total station and handy measurement to examine the structural stability of the original walls. The ground control points were considered as a point where visual field can be secured, 3 points were selected around each of the south and north walls. For the right side of the south original wall, aerial photogrammetry was conducted using drones and a deviation analysis of 3-dimensional digital models was performed for short-term monitoring. As a result, the two original walls were almost matched in range within 5mm, and no difference indicating displacement of stones was found, except for partial deviation. Regular monitoring of the areas with structural deformation such as bulging, weak and fracture zone by precisely examining with the naked eye and using high-resolution photo data revealed no distinct change. The inner foundation observed through endoscopy found out that filling stones of the original walls were still remained, while most filling soil was lost. As a result of measuring the total station focusing around the points with structural deformation on the original walls, the maximum displacements of the north and south walls were somewhat high with 6.6mm and 3.8mm, respectively, while the final displacements were relatively stable at below 2.9mm and 1.4mm, respectively. Handy measurement also did not reveal clear structural deformation with displacements below 0.82mm at all points. Even though the results of displacement monitoring on the original walls are stable, it is hard to secure structural stability due to the characteristics of ramparts where sudden brittle fracture occurs. Therefore, it is necessary to conduct conservational scientific diagnosis, precise monitoring, and structural analysis based on the 3-dimensional figuration information obtained in this research.

이 연구에서는 계족산성 원형성벽의 디지털 데이터베이스 구축을 위해 무인항공사진촬영 및 지상레이저스캐닝을 수행하였고, 모니터링의 연속성을 위해 지상기준점을 측량하였다. 또한 원형성벽의 구조적 안정성 검토를 위해 육안 정밀조사, 무인항공사진측량, 내시경 촬영, 토털스테이션 및 수동 계측을 진행하였다. 남쪽 원형성벽의 우측구간은 드론으로 항공사진측량하고 3차원 디지털모델의 편차분석을 통해 단기간 모니터링하였다. 이 결과, 두 성벽은 5mm 이내의 범위에서 거의 일치하였고 부분적 편차는 있으나 성돌의 변위와 변형을 지시할만한 차이는 없었다. 정밀 육안조사와 고해상도 영상자료를 이용하여 배부름, 약선대, 균열대 등 구조적 변형이 발생한 지점을 주기적으로 모니터링한 결과, 뚜렷한 변화는 관찰되지 않았다. 내시경을 통해 본 내부의 적심상태는 원형성벽의 채움석이 잘 남아 있었으나, 채움토는 대부분 유실되었다. 원형성벽에서 구조적 변형이 발생한 지점을 중심으로 토털스테이션 측정 결과, 북쪽 원형성벽의 최대 변위량은 6.6mm, 남쪽 원형성벽의 최대 변위량은 3.8mm로 다소 높았으나, 최종 변위량은 각각 2.9mm와 1.4mm 이하로 나타났다. 간이계측 역시 모든 지점에서 0.82mm 이하의 변위가 발생하여 뚜렷한 구조적 변형은 확인되지 않았다. 원형성벽의 변위 모니터링 결과가 양호하게 나타났다 하더라도 갑작스런 취성파괴가 발생하는 성벽의 특성상 구조적 안정성을 담보하기 어렵다. 따라서 이 연구에서 취득한 3차원 형상정보를 바탕으로 보존과학적 진단과 정밀 모니터링 및 구조해석이 요구된다.

Fig. 1. Original wall and ground control points for survey in Gyejoksanseong fortress. (1 and 2) Original wall of north and south area, respectively.

Fig. 2. Original walls of Gyejoksanseong fortress. (A) Original wall of north side. (B) Supporting terrace of north original wall. (C) Temporary treatments for unstable area in north wall. (D) Reconstructed walls in left side and original walls in right side of south area. (E) General view if original wall in south area. (F) Enlarged photo for original wall in right side of photo E.

Fig. 3. Three dimensional laser reflection mapping and point clouds data for original walls. (A) Plane of reflection point clouds data for north original wall. (B) Scanning point for north original wall. (C) Measurements of RGB point clouds data for north original wall. (D) Plane view of reflection point clouds data for south original wall. (E) Scanning point for south original wall. (F) Measurements of RGB point clouds data for south original wall.

Fig. 4. Unmanned aerial vehicle (UAV) photogrammetry showing the original wall in south area. (A) Stereoscopic view of texture mapping modeling. (B) Stereoscopic view of polygon mesh modeling (C) Result of the first photogrammetry in September, 2017. (D) Result of the second photogrammetry in March, 2018.

Fig. 5. Configuration processes showing the first and second modeling result of original wall in south area.

Fig. 7. Representative damages showing stone properties of original wall. (A) Cracks and fractures in stones. (B) Loss and dehiscence of stones. (C) Deformation and weak zone of the wall. (D) Protuberant zone of the wall. (E) Slackened and protuberant zone of the wall by plant roots. (F) Highly weathered zone of the wall.

Fig. 9. Endoscope monitoring points and images showing north and south original walls. Numbers are the same as in those of upper and lower photographs, respectively

Fig. 10. Measurement points showing light wave total station for north and south original walls. Numbers are the same as in those of Table 4 to 6 and 7 to 9.

Fig. 11. Points showing handy displacement measurements of north and south original walls. Numbers are the same as in those of Table 10 and 11.

Fig. 12. Diagrams showing handy displacement measurements of north original walls.

Fig. 13. Diagrams showing handy displacement measurements of south original walls.

Fig. 6. Deviation analysis for short term monitering of original wall in south area.

Fig. 8. Points for check list and recorded zones for damage monitering of original walls. Numbers are the same as in those of Table 3.

Table 1. Methods of digital documentation and monitoring for Gyejoksanseong

Table 2. Measurement result for ground control points of Gyejoksanseong fortress. Numbers are the same as in those of Figure 1

Table 3. Damage types and zones of original walls. Numbers are the same as in those of Figure 8

Table 4. Result of light wave total station for north original walls. Numbers are the same as in those of Figure 10

Table 5. Differences between each measurement for north original walls. Numbers are the same as in those of Figure 10

Table 6. Result of displacement analysis for north original walls. Numbers are the same as in those of Figure 10

Table 7. Result of light wave total station for south original walls. Numbers are the same as in those of Figure 10

Table 8. Differences between second and third measurement for south original walls. Numbers are the same as in those of Figure 10

Table 9. Result of displacement analysis for south original walls. Numbers are the same as in those of Figure 10

Table 10. Result of handy displacement measurements for north original walls. Numbers are the same as in those of Figure 11

Table 11. Result of handy displacement measurements for south original walls. Numbers are the same as in those of Figure 11