CHARACTERISTICS,PROCESS AND MECHANISM OF HEIDUO INTER-MITTENT SLOW-MOVING LANDSLIDES,UPSTREAM OF BAILONG RIV-ER,CHINA
Slow-moving accumulation landslides are common geological hazards in the middle and upper reaches of the Bailong River.Characterized by slow sliding speeds and long longevity,these landslides have often been over-looked due to their small instantaneous disasters.The long-term continuous sliding of slow-moving landslides pro-vides a rare opportunity to study their process and mechanism.In this paper,we take the slow-moving landslide in Heiduo Village,Diebu County,in the upper reaches of the Bailong River as the research object.Through field in-vestigation and interviews,interpretation of multi-phase high-resolution remote sensing images,analysis of rainfall data,and laboratory physical and mechanical tests,we describe the geological environmental conditions,deforma-tion,and failure characteristics of the slow-moving landslide.Additionally,we study the process of movement and evolution,and discuss the formation mechanism,driving factors,and future development trend of the Heiduo slow-moving landslide.The study reveals that:(1)The Heiduo slow-moving landslide is a shallow accumulation landslide developed in a narrow and long channel with a volume of approximately 36.6×104 m3.Before its initiation,it al-ready had a three-layer structure consisting of the sliding body,sliding zone,and sliding bed.The soil in the slid-ing zone has a high fine particle content,rich clay minerals,and high plasticity.(2)The Heiduo slow-moving land-slide has recently experienced at least three significant movements induced by continuous rainfall in the 1990 s and July-August 2020,as well as continuous movement induced by the 2008 Wenchuan earthquake combined with rain-fall from 2008 to 2010.(3)The sliding body in the upper gentle channel is driven by rainfall seepage to produce a retrogressive slide,while the sliding body in the lower gentle channel is driven by the loading of the middle and up-per sliding body and combined rainfall to produce a push-type slide.(4)The Heiduo slow-moving landslide exhibits intermittent movement characteristics of start-movement-stagnation cycles.The weak rock soil mass and sliding zone rich in shale and slate weathered materials are the internal basis for the development of the slow-moving landslide.Continuous rainfall softens the sliding zone,earthquakes coupled with rainfall reduce the stiffness of the landslide,and the load of the landslide body is the main external driving force for the acceleration of the slow-moving land-slide.The geomorphologic characteristics of low gravity,gentle sliding surface,and distal blocking are possible mechanisms of the slow-moving and temporary stagnation of the landslide.(5)In the future,the landslide body in the current channel will still undergo similar slow-moving movement.Furthermore,the adjacent secondary landslide body of approximately 10.5 × 104 m3 and deformation body of approximately 18.5 × 104 m3 might destabilize and block the main channel,causing large-scale,high-speed dam-breach debris flows,threatening downstream villages and roads.This study has important implications for understanding the process,mechanism,and disaster prevention of similar landslides in the middle and upper reaches of the Bailong River.
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