Study On The Forming Mechanism And Maintenance Methods Of Longitudinal Embankment Crack In Permafrost Region

The Qinghai-Tibet Highway amounts to 1100km from Germod to Lasha. It plays important roles for Tibet in political stabilization, economic development and defense construction. At the same time, it is an important line that makes sure the lives, work, and safety of more than 2 million local people.The Qinghai-Tibet Highway lies in the areas of Tibet Plateau with the 4500 average attitude. The weather is so bad with longer winter, colder and drier, fewer air, and stronger solar radiation that there is big temperature difference in slopes of subgrade. In addition, there are very complex geology conditions, especially permafrost along line.Due to the above reasons, there are many longitudinal cracks occurring in the line. These cracks are too huge to be maintained with ordinary methods. As a result the performance of road is very low. In recent years, these cracks become more severe and have a threat to the riding safety.Therefore, the paper, depending on the Qinghai-Tibet Highway, begin to study. The paper has two main parts; the first part has analyzed the forming mechanics of longitudinal cracks through FEM, and the other part has studied the treating structures according to the different types and classes.First of all, the paper has investigated the longitudinal cracks in the fields, and analyzed the characteristic and distributing laws of the crack. At any more, the paper also tests the reasons of crack through Reiligh Wave Instruction.In the mechanism analysis part, the paper has established the model through analyzing the changing laws of permafrost upper limit, temperature field characteristic and the longitudinal crack traits, and solved through FEM. The results has revealed that the forming process of crack have three different phases: the initial deforming phase, the strength destroying phase and deforming destroying phase; and there are three different area in mechanics aspects: development area, restrict area and urging area. At the same time, a lot of factors, including thawing zone of permafrost, seasonal active layer and subgrade, are considered to study forming course of the longitudinal cracks.On the basis of the above analysis, the paper has put forward the protectingprinciples and classifying and grading methods of the longitudinal cracks. According to the protecting principles, three protecting methods are suggested to use; and according to the classifying and grading methods of cracks, the longitudinal crack is divided into two types: the linear crack and the slope arc crack. In addition, the linear crack is further divided into three grades: light, severe and much severe. Though studying, there are three basic maintain methods on the linear crack, including single layer geogrid, the flexible beam and the composite structure of geogrid and flexible beam, and the geogrid of many layers to used to treat the slope arc crack.The paper has studied the design parameters of the treating structures and mechanics characteristic after treating through FEM, analyzed the feasibility and adaptability of these structures, and brought forward the corresponding design methods. Among these, the flexible beam is firstly introduced and studied.In the end, combined with the field test project, the paper has studied the construction techniques.