Lin Wang

Validation and Interpretation of Monitored Behavior of Slopes Vulnerable to Failure

Monitoring and early warning is one of the most promising ways toward reduction of disasters induced by landslides and slope instabilities. Although less costly than construction of retaining walls and other mechanical measures, early warning has several problems to be overcome. First, it is often the case that the exact location of an unstable soil mass is not defined and hence the location of monitoring sensors cannot be decided. This problem can be solved by installing many low-cost sensors within a possibly unstable slope. The second problem concerns what information of slope should be monitored. The present study has developed a low-cost MEM sensor unit that can monitor slope deformation during heavy rainfall. A wireless network collects signals from the sensors periodically and helps the local government issuing an alert signal or emergency evacuation order, depending upon the progress of tilting. It is further important that the low cost of the sensors allow individuals to purchase personally and installs them in order to protect themselves from slope disasters. The developed equipments have been deployed in several slopes in the recent times for validation of their field performances. The present text reviews the obtained records and discusses their use for practice.

Explore on Hydro-Mechanical Threshold for Early Warning of Rainfall induced Shallow Landslides

After the Wenchuan earthquake on May 12th, co-seismic landslides and fractured slopes were more susceptible to rainfall-induced shallow mass re-mobilization and post-earthquake disasters were gained widespread significance for the disaster mitigation. However, despite the rainfall thresholds, the hydrological parameters of rainfall induced mass re-mobilization in natural environment of Wenchuan earthquake regions is not well understood and widely used for disaster early warning. In this study, shallow rainfall triggered slope failures under partially saturated conditions in the hollows of the gully was proved by instrumental evidence of in situ experimental tests in a natural co-seismic landslide for simulating the rainfall triggered erosion process of shallow failures in debris flow catchment. In addition, the results revealed the transient process and unsaturated condition for mass movement in response to rainfall, and demonstrated the importance of hydrological parameters includes soil matrix suction and moisture content for shallow slope failure in the hollows, and the stability analysis suggested a hydro-mechanical thresholds including water contents and matrix suction based on the mechanism of slope failure for early warning of the mass-remobilization in hollows of debris flows. These findings were expecting for contribution effectively on improvement of early warning accuracy for rainfall induced shallow landslides and debris flows in earthquake hit region.

Experimental Identification on Thresholds for Early Warning of Rainfall-induced Failure on Fractured Slopes after Giant Earthquake

Prevention and mitigation of rainfall induced geological hazards after the Ms=8 Wenchuan earthquake on May 12th, 2008 were significant for rebuild of earthquake hit regions. After the Wenchuan earthquake, there were tens of thousands of fractured slopes which were broken and loosened by the ground shaking, they were very susceptible to heavy rainfall and change forms into potential debris flows. In order to carry out this disaster reduction and prediction effectively in Longmenshan region, careful real-time monitoring and pre-warning of mountain hazards in both regional and site-specific scales is reasonable as alternatives in Wenchuan earthquake regions. For pre-warning the failure of fractured slopes induced by rainfall, the threshold value or the critical value of the precipitation of hazards should be proposed. However, the identification of critical criterion and parameters to pre-warning is the most difficult issue in mountainous hazards monitoring and pre-warning system especially in the elusive and massive fractured slopes widespread in Wenchuan earthquake regions. In this study, a natural coseismic fractured landslide in the Taziping village, Hongkou County, Dujianyan City, was selected to conduct the field experimental test, in order to identify the threshold parameters and critical criterion of the fractured slopes of Taziping. After the field experimental test, the correlation of rainfall intensity, rainfall duration and accumulative rainfall was investigated. The field experimental test was capable of identifying the threshold factors for failure of rainfall-induced fractured slopes after the giant earthquake.