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According to local villagers, the main Beiguo landslide on the Heyang Loess Tableland in China occurred several decades ago (the specific time is unknown). After the initial occurrence of the main landslide, there was no major activity for several decades until December 17–22, 2017 (2 months after the rainy season), when the main landslide was completely reactivated. One of the interesting findings of our field survey is that there are two erosion gullies and numerous loess caves (groups) developed at the top of the Beiguo landslide, which are generally considered to be the dominant channels by which rainwater or surface runoff enters the deep underground space. In order to better understand the process and triggering factors of the main landslide's reactivation, a multidisciplinary investigation including satellite remote sensing, interferometric synthetic aperture radar (InSAR), an unmanned aerial vehicle (UAV) survey, a terrestrial laser scanning (TLS) survey, an electrical resistivity tomography (ERT) survey, laboratory experiments, real-time monitoring using an inclinometer, and field investigations of the Beiguo landslide was conducted. We believe that the reactivation of the main Beiguo landslide may have been occurring for more than 10 years, or perhaps even longer. Since 2011, there have been several signs of local activity in the main landslide body, and the last accelerated stage of the entire deformation process occurred in 2017. The development and existence of loess caves directly destroyed the stability of the slope, and the rainfall and surface runoff quickly entered the interior of the main landslide. The influence of the loess caves on the landslide's reactivation was long-term and continuous. The results of this study suggest that the several days of abundant and continuous rainfall in the rainy season in 2017 were the last direct trigger of the final reactivation of the main landslide. The secondary landslide significantly changed the original slope, including the aspect of the slope profile's morphology, the slope gradient, relief, erosion, and accumulation, which accelerated the evolution of the tableland landform. This study enhances our understanding of the reactivation behavior of loess landslides, and also provides important support for the monitoring and prevention of reactivated landslides in the future. [ABSTRACT FROM AUTHOR]

This paper assesses potential slope movement in a landslide area using a grouted cable of time domain reflectometry (TDR) technology compared with data from an inclinometer and bore logs. The paper quantifies the magnitude of a TDR coaxial cable by laboratory shear and extension tests. The maximum and average magnitudes of cable deformation by laboratory shear failure were 60 mm and 47 mm, respectively. Then, in the paper, the results of the laboratory testing were applied to a case study where there were two inclinometers and two TDR monitoring stations. Based on laboratory shear and extension testing, differences in TDR-reflected waveforms can be regarded as locations of cable deformations. Meanwhile, the magnitude of cable deformations can be measured by the regression equation of the relation between reflection coefficients and shear displacements. Finally, the working limit of the cable for potential slope movement can be determined at 210-mρ reflection coefficient in laboratory and field testing. When a grouted cable ruptured, the TDR technology can detect a reflection coefficient at 210 mρ corresponding to the potential shear displacement at approximately 47 mm, which means that a localized slope deformation significantly occurred at the location of the cable rupture. [ABSTRACT FROM AUTHOR]