Research On Formation Mechanism Of Kaka Landslide And Its Engineering Effects In The Dadu River

Danba hydropower station adopts hybrid method development, as the 8th cascade hydropower stations of Dadu river levels 22 cascade planed in the lancang river, The dam site is located on the main river of dadu river(the Dajinchuan river)where distanced the Shuikazi ditch 400 m in water upstream, and the underground powerhouse is located on the the right bank of the Xiajinchuan river, a tributary of Dadu river 450 m from its mouth. Danba hydropower station hub buildings is mainly composed of dam and sluice gate structure, water diversion system, power plant and switching station, etc, with the total installed capacity of 1176.6MW and a total investment of 10.333 billion yuan, which belong to the second class type(2)engineering. The dam of Danba hydropower station is gravel soil core wall rockfill dam and it’s maximum height is 36 m, and the normal storage level 1997 m, dead water level of 1991 m.Kaka landslide is an ancient one, which is located adjacently to the dam in the upstream direction, on the right bank of the Dadu river. The landslide boundary is clear with a bedrock slope in the trailing edge, and it’s front insert at the bottom of the Dadu river modern riverbed, both upstream and downstream edge is contact with a mountain ridge bedrock exposed. The shape of Kaka landslide is like a fan on the plane with an arc in the front, the length distribution along the dadu river is 820 m,vertical river is 380~624m; the central of the landslide raised slightly in the longitudinal, the upper is a bit slow, and the lower is steep, with a whole slope angle35~40°; the plane distribution area of the landslide is 29.09×104m2, the average thick68 m, and the total volume is about 2000 × 104m3 。 According to the topography,material composition and the structure characteristics, deformation characteristics,formation mechanism, Kaka landslide can be divided into I, II and III of three parts,among them, the II partition is landslide, with a volume of about 1250×104m3, the I and III partition are colluvial deposit body, with a volume of about 500 × 104m3 and250×104m3。And the II partition is the main body of the landslide.The landslide development in thin~medium thick grain of clip schist rock slope belongs to Maoxian county group, generation anddistribution, the towards of bedrocklevel is N25~40°W, and parallel to the river, tended to NE, with a angle of 50 ~ 75°,locally 80~90°, the structure belongs to the typical bedding slope steep slope. There is a series of oversize, giant landslide developmented along the banks of the Dadu river in this area, It is interesting that these landslides are all located on the right bank where the bedrock belongs to steeply dumped outside layered structure, however, The other bank where the bedrock belongs to steeply dumped inside layered structure, has none typical landslide. Therefore, What is the relationship between Kaka ancient landslide and steeply dumped outside layered structure of the slope,and what kind of the formation mechanism it is? Kaka landslide tightly close to the dam with a large scale, its stability makes a great significance to engineering’s construction and operation.therefore, what is the landslide stability in the current conditions and water storage conditions? Will it be instability and failure wholily or partially? These problems are particularly important. If partial failure occurs, what influence on the dam and reservoir, would it causes surge and how would surge disasters? How to scientifically predict the surge harm? These problems not only relate to the security of construction and operation of the project, but also the plant could achieve it’s expected benefit, What is more important is it poses a threat to the people’s life and property safety along the river and the local natural environment conditions. Therefore, find out the basic characteristics of the landslide and the landslide mechanism of the ancient landslide, give out a reasonable evaluate of the stability, through studying the influence on engineering. Thereby, give out a scientifically forecast of landslide hazard are especially necessary.The paper is based on "Dadu river feasibility study stage danba hydropower station right bank landslide stability research project", a program of my mentor’s,which makes Kaka landslide as the research object, paper through field investigation,survey and indoor study, basis of the in-depth study on the basic features of the landslide. This paper is a systematic study on the landslide formation mechanism, the stability of the landslide and deformation failure mode, engineering effects of partial failure, especially the impact of landslide surge.Paper uses the geological process mechanism analysis method, on the basis of the analysis of all kinds of forming conditions for Kaka ancient landslide, Its formation mechanism is analyzed and discussed, put forward the original slope deformation failure mode is “Dump deformation-Cracking–Sliding”,and reproduce landslide formation process through UDEC, a discrete element software. At the same time, the thesis analyzes the deposit formation on both sides, thought it’s formedearlier than middle landslide.Thesis calculates stability of Kaka landslide and two side colluvial deposit on various operating conditions though GEO–SLOPE, a software based on limit equilibrium analysis methods, on the basis of qualitative evaluation. It analyze the stress field and the deformation though FLAC3 D, a finite element analysis software.And research suggests that Kaka landslide stability is good with certain safety stock. Accidental conditions exist in the landslide part local buckling failure,the volume of 81.7×104m3.The effects of Kaka landslide on reservoir sedimentation is little, with the part of the landslide instability only small amount, for this reason that landslide sites near the dam, surge harm caused by landslide instability partly is more significant. To forecast landslide surge scientifically, paper uses three empirical formulas(the methods of iwhr empirical formula, Panjiazheng methods, the American society of civil engineering recommended formula) and physical model simulation method, to study the surge height of Kaka landslide instability block, thesis think method water conservancy academy of sciences calculate the results of the physical simulation results most close, so more suitable for the Danba reservoir. In order to further reveal the relationship of landslide surge and landslide characteristics, the paper select landslide entry speed, scale, the angle of slip surface into the water, the water level four factors in orthogonal experiments and single factor experiment, the measured landslide initial surge height, and sensitivity to each factor is analyzed, according to four factors is highly sensitive to the initial surge biggest order as: entry speed >landslide scale > landslide slip surface Angle > enter the water depth. On this basis,this paper puts forward an experiential formula of the initial surge which applies to danba reservoir. In addition, the paper discusses the influence of degree of landslide collapse to the initial surge maximum height, found that initial surge height as the largest landslide collapse degree increases.