Study On The Mechanism And Controlling Measures Of Loess Landslides In Tongchuan Area

Taking loess landslides in Tongchuan area as research subjects, the mechanism of loess landslides is studied in the thesis with the beginning of sliding zone research. Firstly, based on detailed analysis of engineering geology, environmental condition and combined with plenty of loess landside examples and data of sliding soil in Tongchuan, direct shear test and dynamic triaxial test in minor amplitude and long-term vibration are carried out on sliding soil of Jiaoping loess landslide in Tongchuan, so the residual shear strength and dynamic strength can be studied. Direct shear test shows that shear strength index (residual cohesion and internal friction angle) deceases while natural water content and natural void ratio increases and they have good exponential relevance. Triaxial test shows that sliding soil strength under load in minor amplitude and long-term vibration is distinctly lower than that under static load and dynamic shear strength decreases while continuous cycle index increases, in addition the descent rate of dynamic shear strength is quicker while cycle index is low and as cycle index rises, the changing rate defers and gradually tends to be stable. Secondly, microstructure of sliding soil is studied. Through fractal and quantizing, the study shows that void configurations of microstructure of sliding soil have statistic self-similarity and as the number of void increases, the number of fractal dimensions increases. Microstructure of sliding soil changes distinctively after sliding with macropores little space frame and more micropores. Also the structure of sliding zone changes from granular space and hapt-cementation texture to the more stable clotted and mosaic texture; After sliding the number of micropores increases about 1 time, however the overall void area increases less than 1 time and the number of space void in addition to average diameter decreases 2-3times, deuterogenic macropores almost diminish, total number of voids increases more than 1time, yet the overall void area and average diameter decreases almost 1 time. Thirdly, mechanism of loess landslide in Tongchuan is studied. Through studying, 2 types of mechanism are proposed. One is "collapsible-creeping-sliding" mechanism of loess landslides induced mainly by water and the other is "dynamic settlement-disaggregation-failure by shear" mechanism under load in minor amplitude and long-term vibration. Under certain fundamental assumption, the moving track of gliding mass which belongs to popping type on sliding bed of homogeneous loess landslide is deduced with variation principle. Moreover, moving track equation velocity equation of movement and solution formula of sliding distance are deduced from particle motion after gliding mass separates from sliding bed. Finally, a set of economical and practical control measures are summarized for loess landslide which are mainly induced by water in Tongchuan. Moreover, numerical simulation is used to analyze stability of Jiaoping landslide in Tongchuan and integrated controlling methods are proposed.