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Study On Deformation Characteristics Of Slip Surface Of Loess-mudstone Interface Landslide

Posted on:2017-01-28Degree:MasterType:Thesis
Country:ChinaCandidate:W LiuFull Text:PDF
GTID:2180330503461858Subject:Geological Resources and Geological Engineering
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Tianshui is a city in typical mountain valley. As it is controled by the special landform, geological structure and lithologic characters so the mudstone is coated by the loess. As a result of the mudstone is coated by the loess, loess-mudstone interface landslide occurs frequently in Tianshui, Gansu province. The landslide has caused serious economic losses and casualties. The sliding zone soil of this kind of landslide is a mixture of weathered mudstone and the loess. So sliding zone soil is formed on the surface of the sliding bed in the process of landslide forming, which is a poor structural layer of soil. But it is an important part of the landslide.This paper utilizes GDS triaxial apparatus and direct shear apparatus to explore the mechanical property, consider the change of microcosmic structure and study soil deformation of slide surface on Huanancun landslide, Banshancun landslide and Zuitoucun landslide. The research shows that there are abundant big particles which are wrapped by clay particles. Those big particles suffer moving and slipping during the soil deformation, and then their further movement is limited by clay, which results in typical characters of strain hardening at macro level.This paper samples the slide surface soil in Huanancun loess-mudstone interface landslide, and mixes the upper loess and lower mudstone as 1:1 and 3:7. Then we carry out direct shear experiment under different compaction and water content on mixed specimens. The research result indicates that when the ratio is 1:1, the shear strength indexes of remolded soil show a significant decreasing trend, which means the landslide is easier to take place. The stress and strain turn out to be typical strain hardening when the water content is small, and it shows weak hardening when the water content increases. Meanwhile, we do the direct shear experiment on remolded mudstone under the same conditions, the same water content and dry density, and its shearing strength is higher than the mixed ones. This means that this kind of landslides happen in the upper part of the contact layer. Besides that, constitutive relation of mudstone shows significant strain softening, and the phenomenon weakens when the water content increases.Meanwhile, based on the triaxial test parameters, this paper simulates the deformation characteristic of loess-mudstone interface landslide via FLAC3 D. We make calculation on displacement and stress on slope shoulder, middle part and slope toe. Through the calculation, under the conditions wihout consideration of earthquake, rainfall and underground water activity, we find that the deformation of middle part is relatively big, and the deformation of slope shoulder and toe is small. It means that the middle part of slope should be monitored as key object. The calculation result is identical to the field investigation. The middle part and slope toe show partial antithetic phenomenon which is developed by depression in middle part and scarp in slope toe.Through the field investigation and indoor experiment, we find that loess-mudstone interface landslide has typical feature of low speed and gentle movement. This kind of landslides will reappear frequently, while the displacement is small every time. During the deformation, the displacement in trailing edge and slope toe is relatively big, which is closely connected with water seepage condition in landslide shear crack and advantageous empty face of slope.
Keywords/Search Tags:loess-mudstone interface landslide, triaxial test, direct shear test, microstructure, numerical modeling
PDF Full Text Request
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