Microstructure Of Loess In Heifangtai And Its Indication Of The Landslide Cause

Heifangtai is a typical area of loess landslides. Because of the special stratigraphic structure and the perennial water diversion irrigation, Heifangtai developed different types of landslides. Jiaojia area of the Heifangtai, mainly developed the homogeneous loess landslides, which not only made a serious threat to lives and properties of local people, but also restricted the local economic development. This article took the sections of Jiaojia region and back-edge of Huangci landslide which located in north and south of eastern Heitai respectively as the research objects, studied the basic physical and mechanical properties of soils and the change rules of soil microstructure on the profiles by the basic physical mechanics experiment, the laser particle size test, specific surface area test and scanning electron microscopy (SEM) test, then discussed the climate environment and engineering geological significance and analyzed the change trend of internal microstructure of soils when slope deformation and failure. The main results are as followed:(1) Named the different types of soils on the profiles in detail. Soils’ basic properties are shown as:the water content of red clay was about3times of loess and silty soil, and its specific surface area was about2times of loess, in addition, its permeability coefficient was far below the loess, just was about loess’s1/11～1/9times. For the red clay, as the deposition time was shorter, the clay content and fine silt content was lesser, the coarse silt content was more, but eolian loess changes relatively homogeneous.(2) In-depth studied the change rules of soil microstructure on the sections by SEM. The different types of soil had different phenomenon in the particle structure, contact relationship and the surface morphology etc., which reflected the difference of macro and micro stress. The content of easily dissolved salts not only influenced the soil granular structure, but also affected the formation of landslide development indirectly.(3) The mechanical and chemical effect of soils were not obvious in silty sand layer and the stability was poor; The climate when red clay formatted was wetter, physical and chemical influences were strong, it had small permeability, and the stability was best in the soils of the section; The silty clay layer’s formatted climate was drier than the red clay, its pedogenesis was weak and the stability was poor, however, because of the waterproof effect of adjacent red clay layer, lead to this part of soil’s stability was good; For bottom loess, the formatted climate was arid and the leaching effect was relatively weaker, granular structure just experienced the carbonation effect. The upper loess may be formed in a dry and cold to semi-arid environment, which the stability is poorer than bottom loess.(4) From the viewpoint of soil microstructure, we discussed the forming process of landslide slip surface and the weak belt. When the cut export of landslide occured at the bottom of the loess, with the infiltration of irrigation water, particles near the joint surface would go through the process of "particles spined by water effection big pores were filled into small pore by vertical pressure-particle breaked to little particle-grain orientation arranged", the loess at the bottom was softened, the sliding surface formed from top to bottom; When the cut export of landslide occured in the silty sand layer, irrigation water infiltrated along the construction joint surface of the red clay, particles near the joint surface generated heat by friction, which made the clay mineral particles be similar to the slices, and increased the lubrication on the joint surface, the sliding surface developed from both sides to middle.