The Study On Collapsible Mechanism Of Loess Between Zhengzhou With Luoyang Of Henan Region

Collapsibility of loess is the comprehensive embodiment of the internal characteristics, enormously impacted by the cause, geologic forces, water into effect and the influence of the artificial factor. Collapsibility of the collapsible loess in certain part has its unique characteristics, and the controlled factors and mechanism of collapsible loess have regional differences in different part. This paper chooses the Henan loess as the research object, where have less collapsible mechanism researches. We research fist control factors of loess collapsibility, on this basis to sum up the loess collapsible mechanism of the area.Through researching the influence factors of collapsibility by the collapsible test and conventional test, we found that physical indicators of strong collapsible loess must meet water content<12%or saturation<40%, void ratio>0.95or low dry density<1.39, clay content<17%and liquid limit about28%, otherwise the loess don’t have strong collapsibility; The relationship between pressure and collapsibility coefficient is affected by void ratio and water content, under low water content(<10%) collapsibility coefficient increase with the increase in pressure, under high water content(>20%) collapsibility coefficient changes gradually until tends to a certain value, the soil in different load pressures only has a collapsible degree; high compacting soil has no collapsibility under low pressure, but which will have a slight collapsibility with the increase of the pressure, under low pressure low compacting soil has certain collapsible, but there only have slight variations with the pressure increasing; Through spectrum analysis, coefficient of collapsibility increases along with the increase of soluble anion content, and CO32-(or HCO3-) has the largest contribution to the degree of collapsibility; There is a monotone decreasing linear relationship between collapsibility coefficient and some soluble cationic(Na+, K+, Mg2+), and Ca2+accounts for the largest component of soluble cationic of loess; Through the analysis of the natural conditions and pressured conditions under different level of loess soil using scanning electron microscopy, it found that microstructure has a very obvious correlation with collapsible coefficient, if the particles conglomerate looser and the big pore is more, loess collapsible coefficient is significantly higher, or on the contrary, particle pattern and trend, particles and tiny pore distribution are similar between strong collapsible loess with the non-collapsible loess at high magnification, so soil tiny pore and the particle conglomerate’s direction have basically no contribution to the collapsibility, and the fractal dimension of strongly collapsible loess are2,2.3by fractal geometry principle.Based on the grey correlation and hierarchical analysis method this article determine contribution to collapsibility of various factors, we found that contribution of soluble salt content is the biggest and achieves45%above, and porosity is secondary master control factor, the contribution of30%,followed by modulus of compression, clay content and water content. At the same time on the basis of porosity ratio and moisture content, soluble salt content and clay content, we make the contour trend surface of collapsibility of loess by using MATLAB software, and there has been clear about the relationship between collapsible characteristics with the two kinds of index.The main cementation of loess in Henan region is calcareous cementation, in which calcium bicarbonate and part calcareous cementation influence on the collapsibility of loess largest, and that is the main control factor affecting the collapsibility. Porosity is secondary main control factor of loess collapsibility in this region, and the big pore skeleton structure is the main structure of strong collapsible loess; Natural water content and pressure also have certain contribution, affecting the loess collapsibility as condition parameters. According to the above conclusion, the author summarizes the collapsible loess mechanism of Henan region:under-compacted loess with low moisture content occur that cementing soluble salt is gradually dissolved after inundation, corresponding the soil shear strength weaken, then big pore skeleton structure lead to the "collapse" and crumb or set grain slip into pore of soil, structure occur secondary restructuring process.