Study On Shallow Layer Failure Mechanism And Ecological Protection Of Red Bed Slope

Red bed has special geomechanics properties, which strength is low, deformation is easy, weathering resistance is poor, and which is easy to be softened and disintegrated after absorbing water, and so on. Therefore, the excavated slope without slope protection in red bed often occur soil erosion and geological hazards of shallow layer, such as weathering spalling, collapse, rockfall, and shallow landslide etc. Red bed is widely distributed in China. A lot of high-grade highway and railway have been built or will be built in the red bed with infrastructure construction. So it is very essential to study failure mechanism and protection measures of shallow layer of red bed slope. In view of this, combined with the west region communication construction technology project, 'Technology Study on Highway Construction in Red-Bed Soft Rock Area", by the methods of field investigation, field test, laboratory test and theoretical analysis, etc, the contents, such as failure types and failure mechanism of shallow layer, parameters and evaluation method correlated to difficult degree of planting, ecological protection and its effects, are studied and analyzed systematically on red-bed soft rock slope.The main contents and conclusions of the article are summarized as follows.1. The failure types of shallow layer of red bed slope are summarized and the influence factors leading to shallow layer failure are analyzed to provide a basis for failure mechanism study.Based on the widely literature and field investigation, the failure types of shallow layer of red bed slope are divided into six categories, including weathering, spalling, rockfall, collapse, topsoil slip, slump, shallow landslide, and 14 sub-categories. By analyzing the occurrence condition and characteristics of various failure types, the conclusion is drawn that the structure and the special physical and mechanical properties of red bed, especially the properties related to water and weathering are the main factors leading to the shallow layer instability of red bed slope. It provides a basis for failure mechanism study.2. Through in-situ monitoring of weathering, a main factor causing slope instability, instability mechanism and fast weathering range of shallow layer of red bed slope are revealed.The influences of temperature and moisture content change on red bed fast weathering are studied by in-situ monitoring the weathering of red bed slope, the monitoring results show that only the change of water environment or temperature can not causes rapid weathering and collapse, the condition that red bed suddenly meets strong rainfall when it is in high temperature is a main cause of red bed fast weathering.3. Theoretical study on shallow layer instability mechanism and the range of fast weathering of shallow layer of red bed slope are carried on deeply with "Mathematical Physics Equation" and the software MATHEMATICA.Heat conduction equation of red bed slope with high temperature exposed to strong rainfall are presented by "Mathematical Physics Equation", further, the temperature field of rapid decreasing temperature when the red bed slope with high temperature are exposed to strong rainfall suddenly and the slow daily temperature change are solved by the software MATHEMATICA, A comparative analysis of the two kinds of temperature field further proved the conclusion of the weathering in-situ monitoring of red bed slope, the former condition is the main external cause leading to red bed fast weathering.4. The erosion properties of bare red bed slope are studied by rainfall simulation experiment.Rainfall is import to weathering of red bed slope, it not only slow down the temperature of rock significantly, but also erosion the weathered material of red bed therefore, the unaltered rocks are exposed to further weathering.5. On the basis of the parameters study correlated to ecological protection for red bed slope, the method of fuzzy comprehensive evaluation on topsoil and foreign soil correlated to difficult degree of planting are put forward, which provide guidance for slope ecological protection design in red bed.By investigating ecological protection for red bed slope, analyzing and summarying the problems existed in it, evaluation indexes of top soil and foreign soil correlated to difficult degree of planting are proposed. Furthermore, the indexes are tested and their membership grades are studied. Based on the results, the method of fuzzy comprehensive evaluation on topsoil and foreign soil correlated to difficult degree of planting are put forward. These indexes and fuzzy comprehensive evaluation results provide reference for soil improvement and plant choice; moreover, combined with stability state of slope, they provide guidance for slope vegetation protections design in red bed.6. By the systematic study on ecological protection effect to shallow layer stability of red bed slope, it is proved that ecological protection can effectively keep red bed slope from weathering and erosion and can improving stability of red bed slope.The influence of ecological protection to shallow layer stability of red bed slope are systematically studied by the field rainfall tests with the ecological protection and without it, the long-term monitoring tests on the temperature field and the moisture content of the shallow layer of red bed slope and the mechanics experiments on red bed with and without plant roots. It is concluded that the ecological protection can not only slow down significantly the weathering process of red bed slope and basically eliminate the fast weathering of the shallow layer caused by high temperature and rainfall together by eliminating the weathering material erosion and changing the temperature field and the moisture content of the shallow layer of red bed slope, but also increase the shear strength of shallow layer (including guest soil) in the range of plant root. So, the shallow layer stability of slope is improved.