Formation mechanism of large-scale red bed gently inclined strata landslide:Taking Duanqu landslide in north Sichuan as an example
Large-scale slow dip landslides are widely distributed in the red bed area,and it is difficult to prevent them early because the signs before sliding are not apparent.In order to study the potential risk of such landslides slope identification and early warning,the formation mechanism of the Duanqu landslide in northern Sichuan basin is analyzed in this study,with a focus on several key aspects including the sedimentary facies and lithological combination characteristics of the disaster-prone strata,the regional geological tectonic evolution,and the basic features of interlayer shear zones in bed rock around the landslide.The volume of the landslide is approximately 1 153 × 104 m3,with an main sliding direction of 170°.Duanqu landslide is a large-scale,thick-layer,gently inclined strata ancient landslide.The disaster-prone strata of the landslide are situated at the junction of the Middle Jurassic Upper Shaximiao Formation and Lower Shaximiao Formation,marking a lithological and lithofacies transition zone.The combination characteristics of sedimentary facies determine the slope's structure of hard on top and soft on the bottom.The Duanqu landslide is located on the northern margin of the Sichuan Basin,on the northwestern wing of the Xinhua syncline,and has been subjected to multiple phases of geological tectonic activity.The wedge thrust tectonic mode at the base of the foreland basin cover on the southern margin of the Micang Mountain has induced an in situ tilting effect on the upper layers,resulting in the regional occurrence of shallow monoclinal red beds.This deformation pattern is more prone to generate layer disturbances distributed throughout the entire layer along the stratigraphic tilting range,thereby increasing interlayer mechanical fragmentation to some extent,and the junction between the soft and hard strata is more prone to stress concentration,which make dozens of interlayer shear zones distributed surrounding the disaster-breeding strata within the thickness range about 80 meters.With significant groundwater involvement,these interlayer shear zones,characterized by high degrees of fragmentation and containing abundant clay minerals in the parent rock,gradually become mud,which providing mechanical conditions for sliding.
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