The geology of the Nam Ngiep 1 Hydropower Project (NNP1) in Lao PDR (hereinafter “Laos”) consists of alternating layers of sandstone and mudstone with a gentle downward gradient and has an anticline on the right bank due to fold movement. Furthermore, during excavation of the dam foundation rock, weak layers, which are relatively thin and low-angled, appeared in the riverbed.
In order to efficiently implement curtain grouting for the dam foundation with complicated geology without any delay and cost overrun from the originally planned construction schedule and budget, a new grouting method named Hybrid Method was developed, which is incorporating the advantages of the Grout Intensity Number (GIN) Method advantageous in simplicity itself and the Conventional Method advantageous in quality assurance regarding impermeability. As a result of implementation of the Hybrid Method, the curtain grouting work was completed with keeping the original construction schedule and satisfying the necessary criteria regarding impermeability. The grout performance was verified by the image analysis using X-ray computed tomography (CT). Since it is expected that the number of dam constructions with complicated geological conditions will increase all over the world, it is anticipated that further sophistication of the Hybrid Method will improve its qualitative and economical attractiveness.
This article is the summary for the paper (Zhang et al. 2019) receiving the best research paper award from the Japanese Society for Rock Mechanics (JSRM) in the fiscal year of 2020. An integrated system including data acquisition using airborne LiDAR (light detection and ranging) system, ground deformation detection, and investigation of the seismic damages of mountain tunnel was proposed in this study. A pair of Digital Elevation Model (DEM) datasets were captured from the high-density airborne light detection and ranging (LiDAR) data before and after the 2016 Kumamoto earthquake. A new variant of Iteratively Closest Point (ICP) algorithm named Combination and Classification ICP (CCICP) was introduced to detect the three-dimensional (3-D) ground deformation field. The seismic damages of Tawarayama tunnel caused by the earthquake were studied via site investigation. The results indicated that the strong ground deformation can reflect the seismic performance of the tunnel to some extent. Furthermore, the results of the ground deformation direction validated the assumption of seismic wave propagation along the tunnel. It gives a clear explanation for the mechanism of the seismic damages under the earthquake force, especially lining cracks, pavement damage, and construction joint damage.
Understanding the mechanism of fracturing process in rocks is important in civil and mining engineering, as well as several other fields where rock fractures play an important role, such as geothermal, hydraulic, and oil and gas engineering. The combined finite-discrete element method (FDEM) is one of the attractive hybrid methods for numerical simulations of complex fracturing and fragmentation processes of rocks from quasi-static to dynamic loading cases. Through international collaboration between Australia, Japan and Korea, 3D FDEM simulator have been actively self-developed. This study aims to briefly addresses the characteristics of the developed FDEM code as well as its advantages and disadvantages. Finally, some of the featured outcomes obtained through the development are introduced, such as the advanced 3D modelling of extremely complex and fast fracture process of rocks observed in dynamic rock testing by including the incorporation of elastic anisotropy.