The Study On Formation Mechanism And The Stability Of The Geri Slope Near By The Emi Hydropower Station In Nujiang, Tibet

The Geri slope in Nujiang, Tibet is located downstream of the Emi hydropowerstation about1000m and its relatively elevation is very high, along the Nujiang riverlength of about2290m. The Geri slope is close to the dam site area in linear distance,if it slipped into the river and blocked the river, water line will be above the minimumelevation of underground plant, Thus cause damage.It is an oversize high and steeprock consequent slope. The study area exposed rock consists of C1g3Metamorphicfine-grained sandstone, phyllitic slate, ultrabasic magmatic rock and quaternarydeposits. The deformation failure mechanism and stability of the landslide in Gerislope plays an important influence on the safety of the hydropower projectconstruction, the solution of these problems have great significance for making thecorresponding protection countermeasures as early as possible.This paper studies mainly about mechanism and stability of the Geri slope, withits damage model, speed and the river blocking under poor working conditions. Baseon the analysis of geological background conditions, study with the developmentsituation, scale, partition feature and deformation characteristics of the deformationrocks and landslides in the study area. Combining with the basic characteristics of theGeri slope, analyze its Deformation Factors, Failure mechanism and Formationmechanism. By using two-dimensional finite element method, analyze the stress fieldof the Geri slope. Calculate and evaluate the stability of the slope by using imbalancethrust method and two-dimensional finite element method. By using the method ofPan Jiazheng reports，calculate the sliding speed of the Geri under poor workingconditions. Calculate and evaluate the river blocking up height.Base on the analysis of the basic characteristics, we can see that deformation andfailure is more obvious, most of the failure modes are dumping–bending, dumping–breaking. The development process of the deformation rock: stream trenching andstress concentration, then off-load, then dumping–bending, then dumping–cracking,finally through the surface. The landslide is further development from the deformationrock，its deformation mechanism is from bending-cracking to slipping-cracking.By2-Dimensional Finite Element Simulated Method, it shows that the stressdistribution in the Geri slope is uniform under the natural situation. Because of theinvading effect, the closer to the surface of the slope the smaller stress values will be, even negative. Because of the influence by rock lithology and structure, appeared thephenomenon of stress differentiation and concentration. It shows that the stressdistribution in the Geri slope is almost uniform under the rainstorm and earthquakesituation, but the stress values increase a lot from the natural situation, the increasephenomenon mainly in the toe and trailing edge of the Geri slope. We can see thatobvious changes have taken place in stress field of the Geri slope under the rainstormand earthquake situation, those changes will affect the stability of the Geri slope.By using imbalance thrust method and Geo-slope method, it shows that thedeformation rocks and landslides are all in stability condition under the naturalsituation; under the rainstorm situation that the deformation rocks are inunderstable~stable state, the landslides are in understable~almoststable state; underthe earthquake situation that the deformation rocks are in understable~stable state, thelandslides are in unstable~almoststable state.Choose the QDI deformation rock, the QDⅡ deformation rock, the HP01landslide and the HP02landslide, which are in unstable~understable state under therainstorm situation and close to the Emi hydropower station, to analyze the riverblocking. Base on the analysis of the river blocking conditions and slipping speed, itshow that the blocking modality is incompletely blocking. By the calculation of theriver blocking height, we can see that the maximum blocking height is63.88m, whenthe four areas slid at the same time. It shows that even though he blocking modality isincompletely blocking, the blocking height will affect the safety of underground plantof the Emi hydropower station.