| In our country, loess area is continuously and widely distributed in the northwest arid and semi-arid region, which forms the unique landform of loess plateau. Because of the lack of water resources and social economy development, agricultural water conservancy projects are widening. This changes in different degree of loess original geological environment conditions and induces a large number of geological disasters. In Heifangtai area, the agricultural irrigation lastes 48 years, the ground has produced a large area of subsidence deformation and occurred many landslides, which has brought a huge loss of life and property safety for the local villagers.Based on the field investigation and predecessors research results, the paper thoroughly and systematically studies on the deformation characteristics and mechanism of loess landslide by the statistic analysis, mechanics test and physical model tests.(1) In Heifangtai area, it mainly distributes in loess and loess- rock landslide and the loess landslide accounts for more. As a whole, the landslide groups show the volatility and partition with the time and space. Orthogonal experiment results show that the number of landslide is associated with the characteristics of the landslide. The sequence of influential factors from big to small is that of landslide volume, landslide type, landslide shape, gradient of slope. Among of the selected influence factors, the volume and type of landslide have a significant effect on the number of landslide.(2) There is a lot of cracks along the landslide margin. Loess landslide development mainly linear cracks, but the loess-mud flow is arc cracks. Through observation of fracture pile spacing, the deformation of loess landslide has the freeze for a certain period of time. The deformation rate of loess-mud flow is twice of loess landslide. Using the regression analysis, it established one dimension and multi-dimension regression model and verified the regression model.(3) The loess of Hei Fangtai has strong water sensitivity, its strength will drastically decrease and shows timely softening after it soaks. The softening will decrease as the normal stress increasing. Meanwhile, shear strength grows in the logarithm form. Softening effect has depth effect and time effect in a certain extent. The cohesion of loess firstly increases and then decreases with the time of soaking, but the friction angle grows in the logarithm form.(4) The saturated loess of Hei Fangtai shows stable characteristic in the compression. The steady strength and effective stress approached to 0 and the samples were fully liquefied, below 300 kpa confining pressure. On the contrary, saturated loess had some steady strength. So it can be concluded that it occurres loess-mud flow as the thickness of the overlying soil is thinner, or it is loess landslide. By the interpolation calculation, the critical thickness is 20 m. The three-dimensional space of pss’-qss’-ec is a surface, the relation is logarithm between pss’ or qss’ and ec. The pss’-qss’ is linear relationship. It established critical state parameters and critical line of shear strength with steady surface in the three-dimensional space. It maked mechanical analysis about the flow slide of Jiao Jiaya.(5) The model test showed that slope produced evident vertical and horizontal displacements when water infiltrating into the loess, then produced cracks in the superficial and slope body. Finally, the model slope perforation failed. Before slope brittle collapsed, the displacement and pore pressure rapidly increased, but the moisture was not. The results could provide a theoretical basis for prevention engineering of landslide. |
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