Weiwei Zhan

Weiwei Zhan

Assistant Professor at University of Central Florida

Geotechnical Site Characterization of Deep Sediment Soils

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The dynamic penetration test (DPT) and the Menard pressuremeter test (PMT) have been widely used in geotechnical survey of deep soils for megadam foundations in western China. The DPT measures are not well utilized due to the lack of correction factors and of empirical relationships for deep soils. I developed a method for DPT correction and empirical relationships between the corrected DPT blow counts with deformation modulus and bearing capacity of deep soils.


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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.

Empirical Modeling of Landslide Mobility

Landslide-impacted area is another crucial element for individual landslide hazard assessment for slope units close to infrastructure and community. Rock avalanche is a high-mobility type of landslide that can travel a few to tens of kilometers and move a mass of a million to billion cubic meters.

Geomorphological Precursors for Landslide Early Detection

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.