| Loess is distributed extensively in northwest and north area of our country, which has been used as groundwork in all kinds of architecture engineering during a lengthy history. Collapsible loess has high strength and low compressibility in natural low humidity, but this character will change upon when wetting and loading, that is the soil will develop a large and suddenly settlement and its strength will also reduce obviously. It is common occurance that the buildings ,which were constructed on collapsible loess ground, take place a large settlement even destructive, as a result of ground weltered during construction or use course. With the development of construction career in the collapsible loess area, it has a very important sense to understand the engineering properties of collapsible loess, to estimate the collapsibility of loess rightly, and to control the collapsible distortion of loess.In this thesis, the collapsible loess from different areas of our country were studied, odemeter tests and the routine soil tests were carried out not only on the undisturbed samples, but also on the samples whose water contents were changed either increasing or decreasing. Through these tests, the collapsibility of loess was studied from the angle of initial saturation. Under different initial saturation, the connections of compressive deformation, collapsible coefficient and pressure are analyzed. Under different pressures, the connections of compressive deformation, collapsible coefficient,collapsible deformation and initial saturation were analyzed too. The study indicates that the sensitive pressure (200～400kPa) and sensitive saturation (40%～50%) are existed in collapsibility of loess. With the increase of the saturation, the ability of deformation is minish of the collapsible loess as the water content of loess is increasing; when the value of the pressure is in 200～400kPa and initial saturation is in 40%～50%, the potential deformation is the maximal when the water content of loess is increasing. It is pointed out that the additional deformation in sensitive pressure segment and sensitive saturation ought to be taken into attention especially.In this thesis, scan electron microscope and the computer technology of image analyzing were used. Through the manipulation and analyse on the microgram of collapsible loess in different areas, the micro structure characteristic of collapsible loess is described qualitatively, the framework grain,microcosmic hole and connect fashion of grain are classified, and their influence on the collapsibility of loess is studied. The connection between the percentage of each kinds of microcosmic hole and depth, saturation, collapsible coefficient are quantitative analyzed. The concurrence of big hole and tiny hole is the primary causation of loess collapsibility. Moreover, the mechanism of the collapsibility of loess is explained from the angle of microstructure characteristic.The result of macroscopical and microcosmic experiment on collapsible loess which took from Shaanxi and Shanxi province is contrasted and analyzed in this thesis. The study indicate that the collapsibility of Shaanxi sample is bigger than Shanxi loess; the collectivity trend that the collapsibility of loess is wear off from northwest to southeast was exist; the characteristic of microstructure, such as the form of framework grain, the form of grain connection, the form of grain array and microcosmic hole, have obvious region change rule. The characteristic of loess microstructure is the basic reason which caused regional differences on the collapsible characteristics. |
