Study On Seepage Mechanism And Stability Of Stone-soil Roadbed In The Three Gorges Reservoir Area

As for the highway roadbed in Chongqing region which consist of stone-soilwith different particle size and under the combined influence of ground water,landsliding and collapse are the two most widely types of geological disaster to themand could take a significant influence on the highway traffic of Chongqing. Thisthesis based on the study of regional geology and geological disaster investigationsof reservoir highways which locate on Chongqing region. In order to estimate soilbasic properties, rules of strength and deformation development and relatedhydraulic characteristics, this thesis taken some typical stone-soil samples withdifferent water contents and particle gradations to conduct field and laboratory tests.Based on these obtained parameters, we could take analysis for the liquid-solidcoupled effect and conduct our study for the stability of roadbed slope which isunder the condition of water level drawdown. These results could help us to have aninsight into this type of construction and build a series of methods to improvehighway capability that withstand more geological disasters, furthermore, to reducethe loss of society fortune and the negative influence on our normal life that inducedby geological disasters.According to these characteristics of highways which locate in reservoir region,this thesis focus on some fields as follow:As for these geological disasters we could meet in highway construction andmaintenance work and need to be solved urgently, some known research results abouthighway geological disaster have been collected and sorted, especially to theengineering geology history and regional stratum condition history of Chongqing regionand four typical cities which are the disaster easily to occur areas, namely, Fengjie,Wushan, Yunyang and Wanzhou. Based on these materials, we can estimate thesecharacteristics of engineering geology, hydrogeology, water level fluctuationdistribution and highway geological disaster of Chongqing region. Additionally, we alsopaid attention to the characteristics of highway construction, and spent a lot of time toseek the disaster source of arterial highway in Chongqing region. Combining these obtained results and historical disaster cases, we can estimate all the types of geologicaldisaster and corresponding impact factors. Meanwhile, based on these geologicalexploration and early designed data of65implemented cases of the second phaselandsliding management project which conducted by government, we taken statistic andanalysis for the rules of soil physical properties and distribution, and to use them as asolid principle for our following research work.Taken a typical reservoir highway roadbed in Chongqing region to conduct a seriesof tests, such as physical properties test, direct shear test, triaxial shear experiment andfield static load test, et al. Therefore, we can determine the corresponding characteristicsof soil physical properties, P-S curve, triaxial CD curve and other related data. Withthese above data, we can obtain a relationship among water content, particle percent ofthe d5size and maximum dry density of stone-soil, and estimate the influence of particlesize percent and water content on two typical shear strength parameters, C、φ, and thegradient change rule of stone-soil’s compressibility modulus with varied load anddifferent gradations. Finally, on the basis of field static load test, we start analysis forsoil samples with different water contents and gradations and try to seek thedevelopment law of soil’s strength and deformation, as well as the influence of wettingprocess on deformation parameters of soil.Taken the stone-soil of highway roadbed in Chongqing region as the object ofstudy, we can estimate the influence of finer particle on stone-soil permeability andobtain the function relationship between stone-soil permeability, K, and weight contentof a typical particle size, P5. Based on Darcy’s law, an analysis about the mechanism ofstone-soil stress and seepage field was finished, and with the condition of fluid-solidcoupling, a dynamic calculation equation which can be used to describe the relation ofsoil permeability and porosity has been built. Taken the influence of water levelfluctuation on roadbed stability into consideration, and with the Buossinesq functionthat applied in the condition of unsteady flow of phreatic water, we can find a method todetermine the phreatic line which was influenced by water drawdown. UsingLevenberg-Marquardt solution to conduct fitting work for λ and M (λ), by the way,this thesis also presents an exponential relational expression between them. In fact, theroadbed soil mass has almost the same slope degree with that of the under-lied bedrock, and the sliding mass always slide along the bedrock surface, on the other hand, thesliding surface is a common type of soil-rock contact surface, therefore, we present aniteration process which need to be involved in our whole calculation process when wetry to estimate the phreatic line of groundwater.A typical roadbed slope is selected for case study, this slope locates on Wushan cityand is affected by the influence of water level fluctuation (drawdown as usual),according to sliding mass’s configuration and its material components, we can start ananalytical work for these impact factors which will induce the slope to slide. Accordingto these obtained results from field shear test and laboratory shear test, some neededphysical parameters in sliding calculation can be determined. Select iterative calculationmethod to estimate the phreatic line within sliding mass which was influenced by waterlevel drawdown, and to have an insight into the evolutionary process of landslidingusing a commercial code to do simulation work for this slope. Calculating the factor ofsafety for a selected typical slope cross-section by employing the imbalance thrust forcemethod that suggest by the National Specification.