Three-dimensional geological modeling of Longyou grotto No. 3 with terrestrial laser scanning

Terrestrial laser scanning is a Three-Dimensional (3D) measuring technology that rapidly developed in recent years. By this measuring technology users can generate a 3D point cloud, derive the size and geometry of objects rapidly and accurately and build a high resolution 3D surface model. The technology is widely used in many fields, such as geotechnical engineering, surveying and mapping and preservation of cultural relics. The Longyou grottoes, a group of ancient underground caverns, are a famous sightseeing place in China. Establishing a realistic geological model for stability assessment is important in order to develop and protect Longyou grottoes in terms of preserving the cultural relics and safety of the visiting tourists. Point cloud data for Longyou grottoes No. 1 to 5 have been acquired by a Leica ScanStation 2 and each of the point cloud datasets were joined together with the help of targets organized before scanning. The point cloud data was transformed to another coordinate system to be merged with contour line data of the local elevation. According to a geological survey and the point cloud data, several points in the same bedding planes were extracted in the entrance of cavern No. 3, which were used to reconstruct the bedding planes by least square regression method. A detailed model of cavern No. 3 was built and a numerical analysis to calculate the tensile stress in the roof was carried out. Finally a comparison was made about whether or not taking the bedding planes into the models of the tensile stress in the roof. The numerical results show that weak mudstone interlayers have a significant influence on the stress state in the roof of cavern No. 3. With decreasing strength of the interlayers, the trend of tensile stress areas enlarging is consistent with the expansion cracks.