| With the rapid development of water resources and hydropower construction, thestability of bank slopes of large or medium hydropower station has been paid moreand more attention. Because of its special boundary condition, material composition,deformation characteristics and water sensitivity, it is difficult to master its stabilityand deformation development trend. Therefore, this thesis chooses left bank slope ofHeihui river in Xiaowan Hydropower Station as the research background. Accordingto the engineering geology anslysis principle systematically and the site investigatedand monitoring data, the shore slope structure features, water-rock interaction androck mass physical and mechanical properties were studied. And by the means ofqualitative and quantitative analysis, the deformation mechanism and stability wereanalyzed through two dimension and three dimension numerical modelling. The mainresearch contents and achievements are shown below.(1)According to field investigation, The rock mass of bank slope weatheredstrongly. The rock mass is mainly composed of Triassic weathered or strongweathered sandstone and mudstone, Jurassic strong weathered sandstone and siltstone,and fault fracture zone substance. Through the test of the particle analysis, thecomposition of the weathering bed is known. Triassic totally-strongly weathered layeris divided into two parts. Between0to30meters in depth is named gravel soil, whichhas13percent of clay. Lower Triassic and the Jurassic weathered layer and faultfracture zone substance are named clayey sand, which has17percent of clay of theTriassic and the Jurassic clayey sand and20percent of fault clay.(2)According to the investigation of shore slope deformation, we know that thedeformation scope and direction overall slope is controlled by fault. On the basis ofthe monitoring data analysis of the bank slope deformation, two conclusions aredrawn. Fist, where the slope deformation object occured the maximal displacement isweathered mudstone. Because the weathered mudstone was deformed, then the slipband was formed. Second, on the basis of the deformation time, after reservoir thebank slope had no deformation. However, in the process of the reservoir water levelfall, deformation was continuous. Comprehensive the above two points, the two main factors lead to bank slope deformation can be concluded that water softening onsliding zone and the change of pore water pressure when resevior water drops.(3)According to the monitoring data of drilling in different period, analysis of therelationship between deformation law and the water level change, the slopedeformation can be divided into three phases, which is bank slope rock softening andwater erosion phase, Creep-cracking-local instability phase, temporarily stable phase.(4)Permeability and mechanical strength of the weathered layer had been studiedby physical and mechanical tests, physical and mechanical properties of soil wereobtained. Penetration test results showed that the sand clayey was aquitard andweathered soil of sliding zone is almostimpermeable. Weathered mudstone of slidingzone is clayey soil after saturation. According to shearing test of different saturationdays, regression analysis slip soil showed the change law about its mechanicalproperty after long time saturating and softening.(5)According to the numerical modeling results of slope deformation mechanism,because of dynamic water pressure and excess pore water pressure, bank slopestability coefficient decreases first at the beginning, in the case of only considering thefluctuation of water level. After about30days of water level fall, the undergroundwater level began to rebound and the slope stability coefficient also graduallyincreased.The stability coefficient had small extent variation but the value is high duringthe reservoir water level was dropping. So the main factor of large deformation iswater’s degradation on the mechanical properties of sliding zone weatheredmudstone.(6)Apply numerical simulation of two-dimensional fluid and solid couplingmethod, the calculated result of seepage was imported into two-dimensionaldeformation calculation model. And use the long time saturating and softeningmechanical parameter of sliding zone and fault rock and soil mass. The calculatedresults showed that the deformation was in accordance with oblique hole monitoringvalue.(7)Reservoir response and stability were analyzed by flac3d numericalsimulation method. The results showed that bank slope had no big deformation, butthe underground water level was to rise. In the process of water levels fall,deformation of bank slope leading edge on the right side was great. Deformation wasgreater than1meterbelow elevation1270meters, which made surface sliding possible.The deformation speed changed slowly first and fast afterwards, at last stably. Water level was at1190meter for a period of time and then saturated rock above theunderground water level into unsaturated, rock mass matrix suction increased andmechanical strength parameters rebounded. From the results of numerical simulation,there were no regionsto continue the deformation and bank slope trended to stable.The numerical deformation behavior of reservoir process had a accordance with thesite monitoring data.(8)Based on two-dimensional limit equilibrium method, considering bank slopestability of profile A-A’ and B-B＇, the main sliding surfaces would be instable locallyafter water storage. The profile A-A’ would be instable when earthquake and waterstorage occurred and profile B-B’ would be local failure. The reservoir slope overallunstable is barely possible to occur once time. However, the right bank slope wouldbe local failure. Because of the influence of water on rock strength and reservoirwater erosion, the front and right of slope deformation body gradually formed thelocal instability. Local deformation would generate retrogressive failure slowly andthen influence on the stability of whole bank slope. |
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