| The loess’ area is very large in China. With the increasingly development of engineering construction in the loess region, the loess collapsibility has evolved into a kind of geological disasters. It’s usually caused catastrophic economic losses for engineering construction, and threatening people’s lives and property as well. In order to exactly know the reason of loess collapsibility, reducing and preventing the occurrence of collapsibility disasters, which is not only has important research significance but also has a deep practical significance. Therefore, this dissertation deeply research the collapsible mechanism of the loess on the basis of predecessors’ research results.In this dissertation, Q3 and Q2 loess as the research object of Luliang, jingyang and longdong region. Firstly, Comparing the level of collapsibility loess of different region and different age, analyzing the rule of collapsibility with depth, studying the collapse characteristics under different water content of changing with pressure, and analyzing the relationship between every physical and mechanical indexes and collapsibility. Secondly, in order to discuss the effecting of dissolute soluble salt to the collapsibility, we considerating the dissolution of soluble salt into the collapsibility and studied the relationship among easy soluble salt, soluble salt, undissolved salt and that. Thirdly, analyzing the collapsibility in different type microstructure of loess, and the relationship between the particle contacting, connecting, pore types and the collapsibility. We quantitatively studied the characteristics of microstructure change before and after collapsible loess, it’s mainly including the area, diameter, perimeter, radius ratio and roundness of particle and pore. Finally, Based on the principle of fast lagrangian analysis or continuum, using the FLAC3D soft simulating the stability of structure consisted of different sphericity particles. Comprehensive analyzing the influence of all factors effecting on the collapsible loess, Explains the collapsible mechanism of collapsibility loess. The main research results are as follows:(1) The level of Collapsibility is very weak or hardly no collapsibility Q2 loess in the study area. The level of collapsibility of Q2 loess is stronger than Q3 loess, but them has the same change rule with the increase of pressure, which is first increased and then reduced. Under the different moisture content, the maximum collapsibility of Q3 loess is basic in 200-400 kPa pressure, and Q2 loess is about at the 1200 kPa pressure.(2)Water content one of influence factors has an important impacting on collapsibility coefficient (8S).δs decreases with the increase of water content and is little in the condition of saturated.δs decreases with increasing density, severe and depth that is different microstructure type manifest on macro.δs increases with the increase of salinity because of the dissolution of salt destroyed part of the important cohesion between particles, accelerated the trend of intergranular slip and move among particles, and it benefits the particle sliding each other.(3) The loess microstructure types has overhead structure, overhead-mosaic structure and cementation structure. The overhead structure has an important contribution to collapsible loess, the overhead-mosaic structure has a little contribution on it, and cementation structure without contribution on loess collapsibility. The big and medium porosity in loess (especially medium porosity) providing a space for loess collapsibility. The big particles is overhead contacting, contacting connection each other of contact relationship and connection form which are provides convenient for sliding and moving of particles. This is mainly due to the proportion large (about 60%) of loess particles sphericity small. |
