Landslide-dammed lake is a typical geological hazard induced by earthquakes in mountainous river areas that pose a great threat to human lives and property for reservoirs and downstream areas. In this paper, the 3 August 2014, Hongshiyan landslide-dammed lake induced by the Ludian earthquake (Mw 6.5) was taken as an example to study the dam-break risk and flood routing process. The fuzzy mathematics method was used to evaluate the risk level of the Hongshiyan landslide-dammed lake, and six main indicators were developed to classify its risk level. The assessment results indicated that the Hongshiyan landslide-dammed lake had an extremely high risk and very serious possible disaster consequences. Then, we analyzed the possible dam-break flood routing process by numerical simulation. The simulated results showed that a dam-break flood would pose a great threat to the downstream Tianhuaban Hydropower Station. Therefore, some effective artificial measures must be taken to control the scale of the disaster. The artificial measures included upstream interception, middle grooming, downstream emissions and subsequent treatments. Some emergency measures were implemented and prevented the failure of the landslide-dammed lake through 19:00, October 4 2014, and subsequent treatment even turned the potential harm into a benefit.

The water-softening property of soft rocks is a key problem in geotechnical engineering. A typical red-bed soft rock (the Zigong argillaceous siltstones) with different weathering degree is selected as an example to study the water-softening property and the influence of degree of weathering. A series of mechanical and microstructure tests are carried out to analyze the weathering characteristics and mechanism of the Zigong argillaceous siltstones. The results of mechanical experiments reveal that the water content and the weathering degree of rock specimens both have a weakening effect on the compressive and shear strengths. According to the results of present microstructure tests, the mechanical properties of the Zigong argillaceous siltstones are closely correlated with their physical properties, including internal microstructure and material composition for highly weathered rocks or moderately weathered rocks (in both natural and saturation conditions). Finally, experimental results indicate that the changes of microstructure and internal materials are two main factors that influence rock strength parameters after contacting with water and that these properties reflect the rock weathering degree. In a word, when red-bed soft rocks are encountered in geotechnical engineering, special attention should be paid to presence of water.