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Taking the weakly cemented sandstone of Ordos, China, as the research object, the evolution law between the relative stress of weakly cemented sandstone and the multiparameters of the acoustic emission under different dry-wet cycles was explored, and the critical failure identification mode of weakly cemented sandstone under dry-wet cycle was established. The results show that as the number of dry-wet cycles increases, the wave velocity loss rate gradually increases. Overall, the longitudinal wave loss rate is larger than the shear wave loss rate, indicating that the longitudinal wave is more sensitive to the degradation of weakly cemented sandstone. With an increase in the number of dry-wet cycles, the crack is mainly caused by the main crack penetration failure, and the secondary crack is significantly reduced. The fractal dimension decreases with an increase in the dry-wet cycles and reaches its maximum at 0 dry-wet cycles, which means that 0 dry-wet cycles witness the most complex morphology of fractures within the weakly cemented sandstone. This finding indicates that the dry-wet cycle inhibits the generation and expansion of fractures. The event rate appears to be close to 0 before the rupture, and then the platform oscillates, followed by a sudden increase. The acoustic emission b value is relatively high during the initial stage and then decreases, which is the initial damage process. The elastoplastic phase rises again, the peak stage decreases rapidly, and the weakly cemented sandstone undergoes unstable damage. The change in the acoustic emission entropy value is exactly the opposite of the b value change law. When the weakly cemented sandstone reaches the critical failure state under different dry-wet cycles, the relative stress value is 95%. The test results provide new methods and a basis for the damage evolution mechanism and fracture prediction of weakly cemented sandstone under dry-wet cycles. [ABSTRACT FROM AUTHOR]

The political history of medieval China is written primarily on the basis of official records produced at centers of political power by victors in the preceding trans-dynastic war. With the help of alternative sources, one can hope to challenge the triumphalist and teleological narrative imbedded in these records. In this article, I use documents preserved in the Dunhuang "library cave" to uncover a failed attempt to establish a regional state with imperial pretensions in Dunhuang immediately after the fall of the Tang. This kind of political regionalism seen in Dunhuang is also found in several other post-Tang states in Sichuan and Guangdong. My investigation of their similarities exposes the teleological nature of the conventional framework of "Five Dynasties and Ten Kingdoms," and demands that we rethink the political history of China after the fall of the Tang. [ABSTRACT FROM AUTHOR]

In the vast inland areas of China, more than 3 million bridges have been built to connect the remote mountainous areas and also to make up the urban transportation networks. For these bridges, reinforced concrete is the most widely adopted material in construction. Unlike the offshore bridges subjected to chloride-induced corrosion, the inland bridges have been constantly threatened by atmospheric carbonation-induced corrosion. The inland areas of China are earthquake-prone regions where several major seismic events occurred in recent years. To investigate the seismic vulnerability of inland bridges subjected to atmospheric carbonation-induced corrosion, the time-dependent characteristics of carbonation were analyzed based on an illustrative cable-stayed bridge, and the time-dependent damage states of bridge components during earthquakes were identified through the material strains of reinforcing steel and concrete. A life-cycle fragility assessment method was proposed and was used to establish the time-dependent seismic fragility curves of the illustrative cable-stayed bridge at the component and system levels. Based on the time-dependent fragility analysis, the macro identification for the seismic damage to bridge system under each damage state and its influence on traffic and repair levels were discussed, the damage sequences of bridge components for different damage states were predicted, and the application strategies of the prediction for components' damage sequences at various service periods were introduced. The research shows that the stirrups tend to be corroded first, leading to rapid decreases of the characteristic strain values of the confined core concrete; and the longitudinal reinforcement experiences very slight corrosion during the bridge's service life. The atmospheric carbonation-induced corrosion increases significantly the damage probabilities of the various bridge components, and consequently change their damage sequences at different damage states. However, the carbonation-induced corrosion does not change the CDPs (complete damage points) and MDPs (maximum damage points) of various bridge components. The bridge system is vulnerable during earthquakes and significantly affected by material degradation. Within the design service life, the damage probabilities of the bridge system can be increased by 0.5620 by the carbonation-induced corrosion, the PGAs (peak ground accelerations) corresponding to CDPs can be decreased by 0.1 g, and the MDPs of the failure state can gradually convert to the CDPs. It is possible to predict the damage sequences of the bridge components during earthquakes on the basis of seismic fragility analysis for different service periods of the bridge, based on which the corresponding maintenance and retrofit strategies can then be determined to protect the bridge against possible earthquakes, and the costs can be reduced. [ABSTRACT FROM AUTHOR]

The Zhouqu County of Gansu Province in northwestern China is a geological hazard-prone area with frequent landslide and debris flow events. As a recent example, the Jiangdingya landslide, a smaller landslide within the larger ancient Nanyu landslide, was reactivated and partially collapsed to block the Bailong River near the Nanyu Township on 12 July 2018. Previous studies have shown that heavy rainfall is the major triggering factor of the failure event, but the spatio-temporal pattern of surface displacements of the landslide remains unknown due to a lack of in-situ measurements on the slope. In this study, we retrieved the surface displacements of the Nanyu landslide before the slope failure event using time-series Synthetic Aperture Radar Interferometry (InSAR) analysis of Sentinel-1 and ALOS-2 PALSAR-2 data. Our results show that the ancient Nanyu landslide has been in an unstable state prior to the failure event. To investigate the spatial patterns in displacement, we inverted a quasi three-dimensional (3D) surface displacement field using multi-orbit InSAR measurements combined with the surface parallel flow model, which showed a significant spatial heterogeneity in displacement patterns across the ancient landslide. In particular, a sign of local reactivation was observed on the upper slopes, which might be related to recent road construction activities. Furthermore, the detectability of unstable slopes near the Nanyu landslide with Sentinel-1 and ALOS-2 PALSAR-2 observations was analyzed to deepen our knowledge on the optimal choice of SAR data for geohazards detection and monitoring. • Historic displacements of the Nanyu landslide measured by time-series InSAR. • Multi-track InSAR combined with surface parallel flow model to retrieve 3D motions. • A complex spatial pattern of landslide movement revealed by 3D displacement field. • Slope-facing geometry found to be more suitable to detect active deforming landslides. • Rainfall and human activity inferred as major driving factors for slope deformation. [ABSTRACT FROM AUTHOR]