Study On Engineering Characteristic Of Similar Soft Soil Slope And Steel-Tube Bored Grouting Anti-Sliding Retaining Wall

Recent years have seen one sort of slopes consisting of special soft soil during montanic railway and highway construction in China. This special soft soil is significantly different from sedimentary soft soil in its formation, distribution, physical components, but remains similar properties of mechanics. Therefore it is called "similar soft soil". Similar soft soil means the special eluvial-declivous, colluvial-declivous and diluvial-declivous soft soil which comes from the series of carbonaceous soft rock such as carbonaceous shale, carbonaceous limestone, carbonaceous mudstone and its weathering products under specific conditions determined by engineering geology, meteorology, hydrogeology, long-term saturation and microbial reactions etc.Taking the case of similar soft clay landslide located in south K108 of Guangdong segment of Beijing-Zhuhai highway, engineering characteristic of similar soft soil is systematically investigated by field monitoring, indoor test, theoretical calculation and numerical simulation. Some work is also done for the designingtheory and constructing technics of new pattern retaining structure------steel-tubebored grouting anti-sliding retaining wall. Main results and conclusions achieved are presented as follows.1. Important engineering characteristics of similar soft soil landslide are systematically summarized. Analysis is given to the strata lithology, geologic structure, hydrogeologic properties, the cause and process of the K108 landslide.2. Physical and mechanics properties of similar soft soil are studied by indoor test. The parameters of physics and mechanics and their range are obtained, among which natural water content, void ratio, coefficient of compressibility and natural shear strength are almost the same as those of the sedimentary soft soil, just water content a little less than liquid limit. The thixotropy and dilatability of similar soft soil are studied and the thixotropy-testing curve is drawn.3. By SEM observation of the dominant mineral component, lamellar kaolinite, and landslide thrust, the micro-structure of similar soft soil are categorized into four types: flocculent structure, turbulence structure, direction-array structure and complex structure.4. Creep properties are studied on basis of simple-shear creep test. The curves of shear stress-strain-time are drawn with different water content. The creep behavior of similar soft soil is described based on the Burgers visco-elastic model. The shear rheological parameters and long-term strength of natural and recomposed samples ofsimilar soft soil are obtained. It's shown that the long-term strength drops rapidly with water content increasing.5. The chemical thermodynamics theory applies to analyze the cause of formation and soil-forming action of similar soft soil. Formation and evolvement of clay minerals in similar soft soil are discussed. Soil-forming mode of similar soft soil is that mother rock goes through the procedure of weathering, grain-grouping and soil-forming.6. The strength reduction technique of FEM applies to the stability of K108 similar soft soil landslide. A brief introduction of this technique is given and slope failure, constitutive model and yield criterion of soil are defined. The numerical simulation of K108 similar soft soil roadcut slope is conducted, which proves to be consistent with limit equilibrium analysis. Also the stability of K108 similar soft soil landslide is analyzed by soft soil creep model. The factor of safety drops 20% due to creep properties. In addition, the process of excavation is simulated which keeps consistent with creep situations in practice.7. Theoretical investigation of the new pattern of retaining structure, steel-tube bored grouting anti-sliding retaining wall, is conducted. Its properties and advantages are introduced and the designing methods are proposed. From the perspective of single pile, FEM applies to steel-tube bored grouting micropiles based on Winkler foundation model. Also the stability of slope reinforced by steel-tube bored grouting micropiles is analyzed and the design method is presented. The equivalent bending-resistant stiffness method is taken to explore the situation of decomposition of mechanics between micropiles row. Internal forces of the retaining structure are passed on to micropiles row through cross-section area or lateral bending-resistant stiffness. FEM is used to simulate the soil arching effect between micropiles. The influence of different micropiles array on soil arching and load assignment between micropiles row is studied.The steel-tube bored grouting anti-sliding retaining wall composed of one or several rows of steel-tube bored grouting micropiles is considered as underground continuous wall. Internal forces of retaining wall are calculated by foundation counterforce method ("m" method). The design method, strength check and calculation of overturn and sliding instability of retaining wall are presented.8. Taking the example of K108 similar soft clay landslide in Beijing-Zhuhai highway, the whole technics of construction of steel-tube bored grouting anti-sliding retaining wall is proposed by the way of flow chart.9. The effect of steel-tube bored grouting anti-sliding retaining wall applied to reinforce similar soil slopes is checked by means of field excavation, indoor test, dynamic probe, permeability test, PS wave test and pressuremeter test. The K108...