Research On Mechanism And Stability Of A Large Accumulation In A Hydropower Station Area

Southwestern China is relatively rich in water resources, which mainly distribute inJinsha river, Yalong river, Dadu river, Lancang river and Nujiang River. Because of the urgentdemand of the social economy rapid development for energy, hydropower exploitation of eachbig basin in Southwest China is increasing. During the process of hydropower exploitation,however, associated engineering geological and environmental problems are very prominent.The special case is the large deposit slope in the dam site area and the reservoir area. Due tocomplex composition, remarkable deformation and poor stability, these large deposit slopesbecame the major hidden trouble that threatening the safety of engineering construction andhuman beings. For the important hydroelectric project, it is thus a major engineering geologicalproblem to recognise the scope and morphological characteristics of the deposit slope, to analyzeits formation mechanism and to obtain its deformation and stability.In this paper, a large-scale deposit slope located in the reservoir region of a hydropowerstation in the upper middle Nujiang river is presented for study. At first, by means of fieldgeological investigation, engineering geological conditions of the reservoir area such as regionalgeology, landform, stratum lithology, geological structure, weathering unloading, hydrogeologyare deeply studied. The engineering geological conditions of the deposit slope are thenindentified clearly. On base of engineering geological mapping and surveying, the structurecharacteristics of the deposit slope are fully understood according to the drilling holes andgeological profiles. The strength parameters are also studied and determined by means ofexperimental analysis, parameter inversion and engineering analogy.The evolution processes and mechanism of the deposit slope is discussed according to theanalysis of previous survey, field investigation and deposit characteristics and the research ofterrain conditions, stratum lithology, geological structure and climate factors. And deformationcharacteristics and failure modes of the slope are conducted by enginering geological analysis ofthe slope present deformation. After the previous analysis, SEEP/W and SLOPE/W module of GeoStudio software isadopted to study the limit equilibrium stability of the deposit slope. Firstly, the seepage fieldunder different water level boundary conditions is simulated to determine the head change of theaccumulation under different working conditions. The results from the analysis of theaccumulation seepage simulation reveal that the impact mainly concentrated in the range ofaccumulation leading edge water level fluctuation under the conditions of water level fluctuation.Meanwhile, the overall stability and local stability under different working conditions iscalculated, and the calculation results reveal that the front edge of the deposit will be in dangerand local buckling easily occurs when the region I-1of the accumulation suffer from adverseeffect such as water level fluctuation, rainfall and earthquake.Lastly, three-dimensional deformation stability analysis of the slope is carried out by usingsoftware FLAC-3D.The three dimensional numerical model is established according to theengineering geological plan, profiles and drilling holes data, and the parameters is determinedaccording to the physical and mechanical properties of rock and soil mass experiment data andparameters recommended value offered in the geological exploration report. The stress anddeformation of the slope under the conditions of natural and1925m are caculated. The threedimensional numerical simulation analysis show that the stabilities of the slope decrease with thereservoir waterlevel and its local deformation of the front I-1region increase. Tension-shearsliding failure will occur because of the bank slope softening.A deep understanding of the formation and deformation characteristics of the deposit slopelocated in a large-scale hydropower station reservoir region is achieved according to fieldinvestigation, geological mechanism analysis, stability assessment and three dimensionalnumerical simulation analysis. The deformation monitoring method and corresponding controlmeasures are thus proposed. The study results in this paper can provide guidance for the latersafety management and control engineering design.