Yange Li

The slope modeling method with GIS support for rockfall analysis using 3D DDA

Rockfall is the most frequent major hazard in mountainous areas. For hazard assessment and further countermeasure design, realistic and accurate prediction of rockfall trajectory is an important requirement. Thus, a modeling method to represent both geometrical parameters of slope and falling rock mass is required. This study, suggests taking the advantages of discontinues deformation analysis (DDA) and geographical information system (GIS). In this study, after developing a three dimensional (3D) DDA program, firstly a special element named contact face element (CFE) was introduced into 3D DDA; secondly, effectively modeling tools with GIS support were developed. The implementation of CFE also improves the efficiency of both the contact searching and solution process. Then a simple impact model was devised to compare the 3D DDA implemented directly with a sliding model with theoretical analysis to verify the reliability of the modified 3D DDA program and investigate the parameter settings. Finally, simulations concerning rock shapes and multi-rocks were carried out to show the applicable functions and advantages of the newly developed rockfall analysis code. It has been shown that the newly developed 3D DDA program with GIS support is applicable and effective.

A new approach of combining aerial photography with satellite imagery for landslide detection

Subsequent rainfall after a strong earthquake can easily trigger landslides. Aerial photography is always available after a strong earthquake but not always available in a timely manner after a subsequent rainfall following the earthquake. Sometimes, only panchromatic imagery is available because of its relatively low cost and large cover capacity. To detect multi-temporal landslides induced by earthquake and its post long-term effect, in company of other factors such as subsequent rainfall, traditionally, it needs to carry out image classification multi-times to calculate the variance information. Therefore, the accuracy will be affected by accumulated errors from multi-classification, and the process is very time-consuming. In this paper, a new semi-automatic approach combing aerial photograph with satellite imagery was proposed for rapid mapping of multi-temporal landslides. The approach can enhance the change information of each landslide event in one detection process. In addition, slope units were introduced to separate the detected conjoint landslides. Chenjiaba area, which located in the highest seismic intensity zone of Wenchuan earthquake in Beichuan, China, and had a strong rainfall 4xa0months later, was selected as a case study to demonstrate the usefulness of this methodology. Accuracy assessment was carried out by comparing those extracted ones with a manually prepared landslide inventory map. Correctly detected were 90.1 and 94.2xa0% for earthquake-induced landslides and new landslides, respectively. Results show that this approach is capable of mapping different temporal landslides efficiently and quickly.

Numerical Analysis of the Largest Landslide Induced by the Wenchuan Earthquake, May 12, 2008 Using DDA

The Daguangbao landslide, with an estimated affected area of about 7.3–10 million m2 and a volume of 750–840 million m3, is the largest landslide induced by the 2008 Wenchuan earthquake. The sliding mass travelled about 4.5 km and blocked the Huangdongzi valley, forming a landslide dam nearly 600 m high. In order to investigate the landslide progression and reproduce the post-failure configuration, the kinematic behavior of sliding mass was simulated by a dynamic discrete numerical analysis method called DDA that has been widely applied for geotechnical engineering problems due to its superiority in modeling the discontinuous material. In this simulation, based on the shape of failure surface and the character of slope topography, the whole slope was divided into three parts: base block, upper sliding mass, and lower sliding mass. Then two sliding masses were divided into the smaller discrete deformable blocks based on pre-existing discontinuities. Corrected real horizontal and vertical ground motion records were applied as volume forces act to the base block. The simulation results of landslide progression, sliding distance, and shape of post-failure were in good agreement with those obtained from post-earthquake investigation, description from the survivors. Therefore, the methodology applied in this paper is able to capture essential characteristics of the landslide and give a post-failure configuration.

Hazard Mapping for Earthquake-Induced Geo-disaster Chain

Dammed lakes are considered as the most subsequently dangerous post-earthquake geo-hazard because the lakes not only flooded human habitats in upstream areas but also posed threats to potentially inundated downstream areas with large populations. Therefore, it is necessary and important to pay attention on prediction of earthquake-induced landslides and landslide dams in order to mitigate or avoid the secondary disasters occurrence. This study proposes a landslide dam prediction system over a regional scale. The prediction procedure is carried out in slope unit-based mapping unit, and utilizing four filters to remove steady slopes to obtain landslides dam prone slopes. A practical application is presented to show the usefulness of the hazard mapping system.

The Disaster Chain of Earthquake Induced Landslides

A strong earthquake can cause a large number of landslides and avalanches, which can initiate causal disaster chains. A representative disaster chain is that a coseismic landslide can block a river and form a landslide dam, which may burst and cause a catastrophic flood. In order to disclose the serious impacts of the disaster chain induced by earthquake, this paper presented the form process of disaster chain and proposed some cutting measures. According to the developmenting process, the disaster chain from the 2008 Wenchuan earthquake was discussed. Firstly, the characteristics of both earthquake induced landslides and landslide dams are summarized in this paper. Secondly, four characteristics of debris flow also presented. Thirdly, two measures for cutting the chain are proposed, one is the landslide hazard map constructing on susceptibility analysis and the other is numerical simulation of debris flows for assessment of dangerous zone. The results of this study can help the authority make the right decision rapidly to take appropriate counter measures to reduce the risk of the disaster chain or cut it directly.