A document by Fanyu Zhang. Click on the document to view its contents.

How to reveal the physical mechanism affecting the contact and friction behavior of geomaterials is still a challenging problem in predicting geological disasters, such as landslides and earthquakes. We develop a multiscale friction model that describes the microscopic creep behavior of asperities and the macroscopic sliding friction behavior of geomaterial. The theoretical asperities contact creep model can characterize the random contact process of the interface friction through porosity which can successfully capture the transition from the mechanical properties of microscopic asperities to the macroscopic interface friction-slip behavior. The theoretical model also verifies that the friction behavior of the geomaterials is closely related to their temperature, activation energy, and saturation. Thus, the developed mode offers a theoretical basis for better understanding the mechanical mechanism affecting the contact and friction behavior of the geomaterials. Meanwhile, it would considerably help to predict future geological disasters quantitatively.

A flowslide overriding liquefied substrate can vastly enhance its disaster after failure initiation, due to rapid velocity and long-runout distance during landslides mobilized into flows. It is crucial to provide improved understanding to the mechanism of these catastrophic flowslides for hazard mitigation and risk assessment. This study focuses on the Saleshan landslide of Gansu in China, which is a typically catastrophic flowslide overrode a liquefied sand substrate. Geomorphologic and topographic maps along with analysis of seismic signals confirm its dynamic features and mobilized behaviors. ERT surveying detected abundant groundwater in the landslide, which is fundamental to its rapid long-runout distance. Particle size distributions and triaxial shear behaviors affirmed more readily liquefied behavior of superficial loess and underlying alluvial sand than red soil sandwiched them. We also examined the liquefaction susceptibility of the alluvial sand under loading impact at undrained and drained conditions. The alluvial sand is readily liquefied in the undrained condition while it is difficult at drained condition due to rapid water pore pressure dissipation. The results showed that the landslide experienced a sudden transformation from slide on the steep slope where it originated to flow on a nearly flat terrace with abundant groundwater that it overrode. This transformation can be attributed to the liquefied alluvial sand substrate enhancing the whole landslide body mobility. Along with recent, similar findings from landslides worldwide, substrate liquefaction may present a widespread, significant increase in landslide hazard and consequent mobility and our study reveals conditions necessary for this phenomenon to occur.

The Heifangtai area is commonly known as the museum of loess landslides in China. Irrigation-induced loess flowslides frequently recur along the margin cliffs of the Hefaingtai terrace, causing 42 fatalities and significant economic losses, as well as major ecological and environmental problems, such as increased soil erosion rate. The initiation and mobility of these irrigation-induced loess flowslide recurrences remain undetermined. On three typical recurrences of the loess flowslides, we performed joint geophysical detection using electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW), and also tested loess basic properties by field profile sampling. In addition, we examined the shear behaviors of saturated loess utilizing an undrained ring shear apparatus. The geophysical signatures and in-situ loess property profiles showed that hydrogeological conditions are key to the initiation of recurring loess flowslides. The results also demonstrated that liquefaction shear behaviors of saturated loess control the mobility of after-failure of the loess flowslides. Rapid criteria of liquefaction susceptibility evaluation are suggested to provide a better understanding of the dynamic mechanisms of loess flowslides. These findings shed substantial light on long-runout flowslides that occur in fine-grain soil and their implications for landslide hazard mitigation.