On August 20, 2019, at 2 a.m., a disastrous debris flow occurred in Chediguan gully in Yinxing town, China. The debris flow destroyed the drainage groove and the bridge at the exit of the gully. In ...addition, the debris flow temporarily blocked the Minjiang River during the flood peak, flooding the Taipingyi hydropower station 200 m upstream and leaving two plant workers missing. To further understand the activity of the debris flow after the Wenchuan earthquake, the characteristics of this debris flow event were studied. Eleven years after the Wenchuan earthquake, a disastrous debris flow still occurred in the Chediguan catchment, causing more severe losses than those of earlier debris flows. In this paper, the formation mechanism and dynamic characteristics of this debris flow event are analysed based on a drone survey, high-definition remote sensing interpretations and other means. The catastrophic debris flow event indicates that debris flows in the Wenchuan earthquake area are still active. A large amount of dredging work in the main gully could effectively reduce the debris flow risk in the gully. In addition, it is also important to repair or rebuild damaged mitigation measures and to establish a real-time monitoring and early warning system for the high-risk gully.
In recent decades, there have been several extreme earthquakes around the world, with the 2008 Wenchuan earthquake resulting in the highest number of landslides and substantial deposition of loose ...material on steep terrain and deep gullies, thereby promoting post-earthquake debris flows. Our monitoring indicates that debris flows have become long-term threats for over a decade after the earthquake, and it is crucial to determine the long-term spatial and temporal changes of debris flows and the evolving influence of condition factors in the earthquake-affected area. Thus, we established a database of 1628 debris flow events occurring between 2000 and 2020 within the 31,627 km2 area affected by the Wenchuan earthquake. The database included information on the date of occurrence, GNSS (Global Navigation Satellite System) coordinate at the gully outlet, event washout volume, and scale level obtained from various sources. Post-seismic debris flow activity witnessed a significant increase, followed by oscillation with rainfall and gradual weakening. Using the average washout volume for each scale in different periods, we applied a grid calculation method to characterize the debris flow intensity (DFI) using the total debris flow volume of cells in different epochs to study the spatial and temporal evolution of debris flow activity. Thus, based on the DFI calculation, we introduced the certainty factor and Geodetector to determine the dynamic evolution of condition factors. Our results indicate that lithology, rainfall, and slope degree primarily controlled debris flows before the earthquake. However, coseismic landslides became the main promoting factor after the earthquake. As loose materials were consumed, hydrodynamic and topographic factors began to play a more significant role in controlling debris flows. During this process, the requirements for rainfall, slope degree, and terrain relief amplitude increased over time. Based on the annual volume of debris flows from 2000 to 2020, we developed a preliminary conceptual model, which indicated that post-earthquake debris flow activity can be categorized into three phases: active (2008–2013), unstable (2014–2033), and recession (2034–2045), with the debris flow activity anticipated to return to pre-earthquake levels by 2045.
•Database of debris flow events that occurred in the Wenchuan earthquake affected area from 2000 to 2020 was established.•We use a grid calculation method to track the spatial and temporal evolution of debris flow activity.•The certainty factor and Geodetector were used to evaluate the dynamic evolution of the condition factors.•Debris flow activity increased sharply early after the earthquake, then oscillated with rainfall and gradually weakened.•Hydrodynamic and topographic factors began to influence debris flow activity more in 2014 than loose materials.
Ultra high voltage (UHV) transmission tower-line coupling system consists of transmission lines (conductors and ground wires) supported by a series of lattice towers. However, in the current seismic ...design code, the transmission lines are just simplified as additional mass while the effect of nonlinear vibration of transmission lines on the seismic responses of transmission towers is not taken into consideration. To analyze the influence of the ignorance of the coupling effect between towers and transmission lines, two types of model structures, i.e. tower-line coupling system model and single tower model with lumped masses, should be tested for comparison. But normal reduced-scale model design method cannot complete the shaking table test by a uniform geometric similarity ratio for the coupling system in the limit of table size, hence this paper proposed to rescale the geometric similarity ratio for the model design of transmission lines and meanwhile satisfied the requirement in dynamic properties similitude and inertia force similitude separately, which successfully solved the problem that the span of transmission lines in the test was too large to fit within the shaking table. This method may offer reference to experimental studies for other large-span structures and the experimental results show that the nonlinear vibration of transmission lines plays a role as seismic reduction by dissipating some seismic energy to towers under earthquake.
As the support carrier of transmission lines, transmission towers are of great importance to the safe operation of the power grid. Geological changes and disasters often lead to the displacement of ...transmission towers, which eventually cause them to tilt or even collapse and fail, seriously threatening grid security. In order to accurately evaluate the stability of the mast and ensure the safe operation of the power grid, this paper investigates the historical occurrence of disasters at the site and the distribution of hazardous areas in China, and simulates the influence of geological changes on the transmission mast to obtain the weight of the influence of geological disasters on the stability of the transmission mast, which provides a reliable standard for evaluating the stability of the mast.
Taking Sichuan electric power system as an example, landslide hazards in this region are often widespread and insidious, so traditional investigation methods are not sufficient in identifying large ...scope of landslide hazards and producing accurate landslide deformation analysisin the mountainous regions. The paper proposes torely on satellite remote sensing, UAV remote sensing and field investigation, and leverage the advantages of multi-domain technologies, including satellite remote sensing with wide coverage and strong repetitive observationcapacity and airborne remote sensing with strong maneuverability and high resolution.Through space-air-ground investigation system,this paper provides a solution to the early detection of landslide hazards, and conducts anearly detection of potentiallandslide hazards of a 500kV overhead transmission line.
The Grain-size distribution and structural dimension analysis of the accumulation zone of the debris flow was accomplished with the graphic method and fractal theory. Results show that the giant ...debris flow deposits in Hou gully, Xiongjia gully and Majingzi gully are bad sorting, very bad sorting, and very bad sorting, and the components mainly consist of deposit coarse grain. According to fractal theory, it can be known that those three giant debris flow gullies are viscous, and their grain sizes are non-uni-form. Results show that comprehensive utilization of grain-size distribution and structural dimension analysis could understand sorting, grain-size distribution and type of "7·4" giant debris-flow deposits very well. It also can provide reference data to formation, movement, accumulation characteristics,numerical simulation, etc.
To study the force of foundation of the transmission tower-line system under wind load, refined finite element models of the transmission tower-line system and the foundation were established. First, ...the wind load time history of the transmission tower-line system was simulated. The response of the structure was calculated by the dynamic analysis method and a comprehensive assessment of the ultimate wind-resistant bearing capacity of the transmission line was conducted. The force of the foundation of the transmission tower line system under the action of wind load was obtained. The force was applied to the foundation and the dynamic analysis of the pile foundation was conducted based on the reaction time history of the dangerous foundation, then the crack form of the foundation was predicted through the index of main tensile stress of the concrete foundation. The results show that the first 228 modes of the three-tower and two-line system are all vibrations of the ground line, and then the tower body will vibrate in the vertical direction; under wind loads, the tower legs on the windward side of the transmission tower are weaker; under the wind speed of 40m/s, the maximum main tensile stress of the pile foundation concrete is at the edge of the anchor bolt, which is close to the cracking strength of the concrete; when the pile foundation is tensioned, the stress distribution of the local concrete around a single anchor bolt forms a cone shape. After the stress is superimposed, a large stress ring area is formed on the surface of the foundation. When the concrete is tensioned and cracked, it will be damaged in the form of a cone. The force analysis results of the transmission tower foundation under wind load show the more dangerous parts of the foundation and provide theoretical guidance for the design and reinforcement of the foundation in the project.
In this paper, Persistent scatterer interferometric synthetic aperture radar (PS-InSAR) is employed to extract the deformation of the transmission tower foundations. The extracted results are ...compared with the measured results to verify the correctness of the extracted results. 26 SAR images from January to December 2021 are selected for the deformation extraction of the high voltage transmission tower foundations near the landslide area in Guangyuan City, Sichuan, China. Time sequence analysis was performed using the StaMPS software, and GACOS products were used for atmospheric correction. The final deformation results are compared with the monitoring results of the sensors installed on the foundations of the transmission tower. The comparison shows the effectiveness of the method. The conclusions obtained from the experiment provide scientific guidance and suggestions for the power maintenance personnel.
This paper proposes a landslide detection method combining gray level co-occurrence matrix (GLCM) and polarization decomposition technique. The proposed method makes full use of the characteristics ...of the SAR image and combines the polarization information with the texture feature. Landslide candidate areas were identified using GLCM and final landslide areas were determined using polarization decomposition techniques. The data used for evaluation is taken from Guangyuan City, Sichuan, China. The proposed method successfully detects the changes of two SLC sentinel-1A C-band VV and VH dual polarization SAR images before and after the landslide, which proves the effectiveness of this method.
In this paper, a remote monitoring system of transmission towers and foundation deformation based on Beidou technology is built. By using Beidou multi-frequency high-precision carrier phase ...differential processing technology and short message technology, the positioning and solving platform of the system is checked by ground base station and the data transmission network adopts wireless private network.It realizes all-weather automatic acquisition, analysis, calculation and storage of millimeter accuracy monitoring data of transmission towers and foundation deformation, and effectively monitors transmission towers and foundation deformation in depopulated areas and weak signal areas.This paper also verifies the reliability of the system through an application example of tower slope, which provides a reference for monitoring and implementation of tower slope.
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