Forming Mechanism Of Loess Vertical Joints

The vertical fissure of loess is an integral problem in the engineering practice in loess region. The distritive feature, developing characteristics and fomation mechanism of vertical fissures are foundations of study on loess geohazard mitigation, loess engineering properties, and relavent geotechnical problems. Hence, it is vital in both scientific and realistic terms to get the solutions of mechanisms of vertical fissures. On this basis, this study stems from the realistic situation of distribution of loess vertical fissures, takes the loess of Heimugou, Luochuan, Shaanxi as study object, and utilizes technical solutions including site insvestigation, laboratory tests of soils in microscopic scale, transient retention and imbibition test (TRIM), theoretical deduction and analytical simulation. It focuses on the formation mechanism of vertical fissures of loess and the developing mechanism in the vertical direction.The main achievements are as follows:(1) Through to understanding and analysing the loess vertical joints from the macroscopic Angle, On the basis of comprehensive classificaiton of loess vertical fissures, this thesis summarized the developing features of loess vertical fissures and concluded that vertical fissures in different scales are interchangeable. And results obtained loess sedimentation in the historical process of the formation process from the Angle of vertical joints growth space and time, put forward the structure of the loess structure unit of forming vertical joints;(2) This thesis studied the structural features of loess in both microscopic and mesoscopic scales. It raised a structural elemental system existing in loess structure which can form vertical fissures, that is, the vertical pipelike passages or pore concentration zones, which were formed in the history of sedimentation of loess. They are the products of stratification process. And pointing out that the vertical pipelike passages under the mesoscopic scales of structure of loess is the bridge of transformation between the macroscopic scale and microscopic scale for vertical joints;(3) Based on unsaturated one-dimentional flow equation established the matrix suction, moisture content and suction stress with the relational expression of head, and simulated the distribution characteristic of water sensitivity of soil parameters. Coefficient of earth pressure of the generalized expression was obtained expanded Hook's law from suction stress. Respectively, the moving laws of zero point of earth pressure coefficient were calculated for different infiltration and evaporization rates. Effects on the zero point by wetting-drying cycles and self weight were also considered, so that the formation and receding mechanisms of vertical fissure of loess were set up. The depth of unstable zone was found to be 2.2m.(4)Via the analysis of formation mechanism of suction-stress-based vertical fissures, this thesis set up the developing mechanism of vertical fissure of loess in the vertical direction, which further verified the conclusion of the existence of vertical pipelike passage in loess.(5) Based on correction of the development mechanism of horizontal holes and inner crack expansion mechanism and combined with based on the suction stress of vertical joints, from the angle of historical sedimentation, the thesis unified the formation mechanism of vertical fissures on the basis of analyzing multiple factors.