Weiwei Zhan

Weiwei Zhan

Assistant Professor at University of Central Florida

Geomorphological Precursors for Landslide Early Detection

1 minute read

Early detection of rockslides at high-elevation and well-vegetated slopes remains challenging. This study used satellite and unmanned aerial vehicle (UAV) optical remote-sensing (ORS) images to track evidence of slope deformation and examine potential geomorphological precursors of five large rockslides in China. All the surveyed landslides had cracks or scarps and rockfalls within the landslide source area before the onset of rapid sliding. These precursors can be identified in ORS images taken several years or decades before the rapid slope failure, which provides sufficient time for the landslide early detection in practice. Local topography affects the spatial locations of cracks or scarps. Rockfalls within the landslide source area tend to locate at “key blocks” where slope mass provides forces resisting sliding. The rockfall area ratio, defined as the accumulated area of rockfalls over the landslide source area, ranged from 0.33 to 0.92 before rapid slope failure. The landslides developed on anti-dip and igneous rock slopes show a more significant rise of rockfall area ratio before the slope failure than the landslides on dip slopes. Given the broad availability of ORS data, this study could shed light on the ORS- based landslide early detection and landslide kinematics study.


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Numerical Modeling of Landslide Dynamic Processes

To further investigate the extraordinary mobility of rock avalanches, I employed the discrete element method to simulate the entire process of an earthquake-induced landslide (landslide initiation, propagation, and deposition). Through the case study, I observed that the progressive rock fragmentations and violent interparticle collisions significantly contributed to the extraordinary high mobility.

Geomorphological Surveys of Successive Landslide Dams

Earthquakes can not only cause immediate slope failure but also affect slope stability and landscape evolution in the short and long terms. Through the extensive field surveys in the earthquake-impacted area, I found an interesting near-fault slope unit where at least three landslide events occurred and dammed the river in the past. From the hazard assessment and prevention perspective, it is important to explore landslide hazard management at such successive sliding and dam sites. I collected multi-temporal remote sensing images and terrain data through unmanned aerial vehicle (UAV) surveys and conducted geomorphological and geological surveys. I concluded that this site is a good example of multiple reactivations of a prehistorical giant landslide under different triggering conditions: a reactivation of an older landslide during a strong earthquake, and a second reactivation during a rainfall event several years later. Meanwhile, I proposed a generalized framework for assessing landslide dam cascading hazards, including landslide volume estimation, empirical landslide dam stability evaluation, GIS-based barrier lake volume estimation, and dam-breach flooding parameter estimation.

Geological and Geotechnical Surveys of a Deep-Seated Rockslide

The 2008 Ms 8.0 Wenchuan earthquake triggered more than 200 thousand landslides, including hundreds of catastrophic deep-seated rockslides. The Among these catastrophic rockslides, the Daguangbao (DGB) landslide is the largest landslide triggered by the Wenchuan earthquake (28°38′16.93′′ E, 104°06′02.35′′ N). The DGB landslide moved the slope mass with volume of 1.2 billion cubic meters to covered an area of 7.8 km2, and formed a landslide dam nearly 600 m high. We had done detailed geological, geophysical, and geotechnical surveys to study the failure mechanism of this giant landslide. I observed that a 3-meter-thick fault gouge was well extended along the sliding bed and with a maximum burial depth of ~400 m. Geotechnical laboratory experiment results suggested that the weakest sublayer within the fault gouge consists of silt soils with strain hardening and liquefaction behaviors. I concluded that slippery fault gouge and strong earthquake-induced shaking led to the giant landslide.