In order to examine the mechanism of shear deformation by absorbing due to rainfall infiltration, behavior of seepage water and deformation in the model slope were measured under artificial rainfall. As results, deformation of slope increases remarkably after rainfall under unsaturated condition of slope. And a dependency of shear strain increment during absorbing process on volumetric water content increase (hereafter VWCI)or suction decrease is greater at deeper soil layer. This seems to be due to smaller VWCI rate or suction decrease rate at deeper soil layer.
It is necessary to evaluate the relative risk of seismic sliding collapse to estimate damage effectively on the extensive land reclamation fills, and it is desirable to be evaluated from only common geographical information in all fills through the primary screening in accordance with the guideline for movement estimation investigation in extensive residential fill sites published by Ministry of Land, Infrastructure and Transport. Therefore, the authors conducted development and verification of the support system to be able to measure fill shape and evaluate relative stability for seismic sliding collapse.
The Global Positioning System (GPS) began to be used for displacement monitoring in the mid-1980s. Although it had the potential to continuously monitor the displacements of the ground surface over an extensive area, it was not applied much in practice. The reasons were uncertain accuracy, troublesome handling, and high costs at that time. In order to overcome these problems, the authors have developed a new type of GPS displacement monitoring system and used the trend model for improving the accuracy of the measurement. In this research, the authors have developed a web-based GPS-automatic displacement monitoring system combining the above monitoring system with the trend model. The system can automatically measure the three-dimensional displacements with the high accuracy, and provide the monitoring results in real-time on a home page through the internet. In order to verify the system, field experiments were conducted and a practical application for a cut slope is illustrated.
During the 2008 Sichuan earthquake (M8.0), more than 60, 000 landslides were triggered and 800 landslide dams formed. Those dams with high risk of collapse threatened the rescue activities, and almost all the large ones were treated by digging sluiceway immediately after the quake. Although the risk of collapse of the landslide dams was moved, not all of the countermeasures were based on ideal methods. To analyze the formation of landslide dams and then perform reliable countermeasures, we investigated some of them, and here a landslide dam occurring on Tianchi area is described. The grain size analysis revealed that the displaced landslide materials experienced fragmentation and segregation during the movement with long travel distance. The S-wave velocity profile of the dam revealed that the dam site has higher S-wave velocity, compared to those landside dams that had suffered collapse failure during the construction of drainage work, showing that the structure of the dam is consisting of densely deposited materials. This kind of dam body has lower permeability capable of retarding the seepage force to trigger collapse failure of the dam body due to piping. Big blocks on the surface will also enable the dam body to have stronger resistance to overflow and then to avoid the possible collapse failure immediately after the occurrence of overtopping.