| More than 100km of red clay was discovered along Wuhan-Guangzhou high-speed railway, for the lack of awareness on this kind of special soil with obvious regionality, as well as stability of slopes built up by red clay, it is hard for engineers to evaluate slope stability of red clay reasonably and to adopt proper reinforcement. Consequently, it is of practical significance to conduct all-round research on red clay slope.Based on the program of "study on the dynamic stability and deformation properties of the red clay foundation under ballastless track of passenger line" (50778180) founded by the national science foundation and "experimental study on subgrade deformation and slope stability of red clay eluvium formed by limestone along Wuhan-Guangzhou passenger line" (2005K002-B-2-1) founded by the ministry of railways, some issues of red clay slope stability were studied by means of lab tests, filed survey, theoretical analysis, as well as numerical simulation. Some main conclusions are drawn as follows:1. Through large amount of lab tests, main physical and mechanical properties of red clay of representative sites (Xianning, Quankou, Leiyang, Chenzhou) were obtained. Combined with field investigation, failure features and mechanism of red clay slopes were concluded.2. On the basis of direct shearing tests of undisturbed red clay samples under dry-wet cycling, correlation curves between shear strength indexes and water content were plotted and fitted. Subsequently, selection principle of shear strength parameters in slope stability analysis was suggested.3. Using strength reduction as back-calculation method, equilibrium equations of "similar profiles" were set up based on control condition "Pn=0" (Pn is the imbalanced thrust of the last slice). Combined with multidimensional chart, shear strength parameters (c and (?)) could be determined through trial calculation, interpolation and curve fitting.4. Improved Imbalanced Thrust Force Method (ITFM) was put forward, taking both force and moment equilibrium into account. Improved ITFM has better precision and faster convergence rate. It needs merely one more postulation than Conventional ITFM, which is "normal stress at the slice bottom acting on the midpoint of the slip surface". When proportion coefficient equals to zero, Improved ITFM is equivalent to Conventional ITFM. So it could be regarded as an extension and supplement of the conventional method.5. By introducing variation factor, upper-bound limit analysis of slope stability was conducted while cohesion varies linearly as depth increases; stability of slope with different layer distributions was discussed. Moreover, different evaluation indexes, adopted in limit analysis and limit equilibrium method respectively, were compared.6. Numerical simulation was performed with Flac3D to study on strengthening effect of red clay bedding slope reinforced by cables. For specified site, optimized spatial factors (such as cable length, inclination, spacing, layout, etc.) were suggested.7. Numerical simulation of reinforcement effect of high red clay cutting slope was put forward with Flac3D in which construction process was followed and layers with different material properties, as well as several retaining structures were taken into account. Some useful conclusions were obtained, which provide reference to reinforcement of red clay slope along Wuhan-Guangzhou passenger line or other similar engineering entities.8. Preliminary evaluation of slope stability within wide range was performed by combining 3D mechanical model with Geographic Information System (GIS). Study area was divided into many slope units, and slip surface was regarded to be the lower part of an ellipsoid. Location and posture of the potential sliding surface could be determined by Monte-Carlo simulation. Finally, a GIS-based 3D limit equilibrium model was adopted to calculate safety factor or failure probability for each slope unit to assess the sliding risk quantitatively. By plotting regional stability assessment map partitioned by safety factor or reliability index, preliminary understanding of slope stability in studied area would be available.9. By theoretical analysis, explicit solution of infiltration depth under heavy rainfall was proposed in which infiltration depth could be calculated conveniently with given infiltration duration. Furthermore, on the basis of Green-Ampt infiltration model and infinite slope model, a limit equilibrium model was proposed with the consideration of seepage force. Comparative study on the influence of several parameters was performed, such as slope inclination, infiltration depth and matric suction. Considering the difference between sliding direction of each column and main inclination direction of corresponding slope unit, an improved model was proposed for 3D slope stability analysis. |
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