Slope monitoring using combined optical and drone survey tools

The Nam Theun 1 hydropower project is currently under construction in central Laos, on the Nam Kading river. To create a platform for the construction of the two shaft powerhouses, significant surface excavations were carried out. The final steep slope with intermediate berms has a height of ca. 110 m. A monitoring programme was established consisting of optical survey with fix prisms and regular drone flights for photogrammetrical evaluation. A pattern of large colour markers was installed for large area interpretation of displacements based on the concept of PIV methodology using drone photos. As a result of variable illumination, dust, humidity and obstacles, the application of standard PIV methods was not successful. With the introduction of AI pattern recognition techniques, reliable marker recognition could be achieved, while reducing the amount of manual interaction to a minimum. The originally low accuracy could be raised to a level comparable with the optical survey.