| Covering an area of about 630,000 km2 of loess in China, it is one of the most widely distributed loess region in the world, of which about 60% with different degrees of collapsibility of loess. Loess under natural condition, high structural strength, and compressibility is rather low, but when immersion in water, soil strength is significantly reduced, collapsibility loess in water and under the combined effect of additional loads, the original structural will be destroyed, resulting in collapsible deformation. Loess collapsibility caused geological disasters such as landslide, collapse and land subsidence, causing huge losses to many regions of economic construction. Therefore, to reduce and prevent harm of collapsibility loess, clarify the collapsibility of loess causes is very important.Based on a lot of previous work, the paper further analysis and research the collapsibility of loess. First of all, through to Yan ’ an、Jingyang、Qingyang and Guyuan in four regions of loess field investigation, sampling and using the double line method for indoor collapsible compression tests, analysis of loess collapsibility coefficient and pressure and soil depth relationship. In the glue injection slice of loess sample preparation, by using specially preparation bonding material soaked gel, make the soil grains cemented together, avoid the loess particles scattered by the original structure was destroyed when in slices, making observation of pore structures closer to the actual pore morphology of loess. Secondly, by the optical digital microscope and scanning electron microscope respectively before and after collapsibility of soil samples for microstructure observation and analysis, analysis of characteristics of microstructure change before and after collapsibility. Then, form the characteristics of microstructure changes and microstructural mechanical mechanism of loess collapsibility origin made a microscopic explanation, in soaking conditions the loess has collapsibility is a result of multiple factors comprehensive action. The unique pore structure system in loess provides space for its collapsibility, loess under the natural state, cement mainly occurs in the contact parts of the skeleton particles, when the loess is immersed in water, change in the balance force of acting on the contact point, internal microstructure of loess will occur a series of complex physical and chemical effects, lead to inter-particle part cements are dissolved, some clay minerals are softened, the original skeleton particle has been disrupted, so that part of particles scattered into the pores and occurs redistribution, eventually leading to the occurrence deformation of collapsible loess.Finally, Using IPP image processing software for analysis loess slices samples of before and after collapsibility, the results show that, after the collapsible of loess than before the collapsible of loess micro-pores increased 31.18%, small pores increased 54.07%, pore decreased 30.49%, large pore decreased 90.14%. This shows that the combined effect of loess under pressure and water, pores of soil are compressed, lead to the number of large pores and pores gradually reduced, the number of small pores and micro-pores gradually increased, provided a space for collapsible deformation of loess. Combined with mineral energy spectrum analysis, the introduction of linear planning method to calculate the main content of clay minerals content in loess,analysis of different areas of collapsibility of loess and clay mineral content in the relationship. |
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