Monitoring of dangerous rock mass in the Three Gorges Reservoir area based on the terrestrial laser scanning method

Changes in water level of the Three Gorges Reservoir are easy to induce the deformation and failure of the reservoir slope. Periodic impoundment changes in the groundwater seepage field and stress field in the reservoir slope reduce the shear strength of rock and soil mass, and have a great impact on the stability of the reservoir bank slope and rock mass. It is urgent for the deformation monitoring of bank slopes in the reservoir area. It is difficult to find out the overall change of rock mass by setting fixed observation points, and the terrestrial laser scanning method (TLS) can obtain the point cloud data of the overall rock mass surface with centimeter accuracy, which is very suitable for the monitoring of rock mass of characteristics of no contact with the target, fast acquisition speed and high precision. In this paper, the terrestrial laser scanning method is used to monitor the dangerous rock mass of Jianchuandong in Wuxia county for two years (2017—2018) and three periods data are acquired. The stable rock mass data around the observation target of the first period is selected as datum and the iterative closest point registration (ICP) is carried out with the overlapping point cloud. The registration accuracy of the point cloud is better than ± 2.7 cm, which realizes the accurate alignment of multi-period data. According to the change of dangerous rock mass in the observation period, the datum TIN model of dangerous rock body area is constructed, and the deformation of dangerous rock mass is analyzed with the nearest distance method from point to reference surface combined with the change range of dangerous rock mass. Through the comparative analysis of the 3 periods observation data of the Jianchuandong dangerous rock mass, it is found that the dangerous rock mass has the expansion trend in 2018 compared with the left rock mass in 2017. In the reservoir water storage stage, there are obvious sag changes in some parts of the dangerous rock body, and the local deformation is about 30-70 mm due to the influence of water storage. The experiment proves the correctness and validity of the proposed monitoring method, which provides reference for the monitoring of dangerous rock state and the prevention and control of geological disasters in the Three Gorges Reservoir area.