| In recent years,with the development of social economy and the increasing attention to environmental protection,the hydropower resources in Southwest China have been greatly developed and utilized.The stability problem of high-steep slope is one of the main engineering geological problems in the hydropower development,which plays the role of controlling to feasibility,economy and safety of the whole project and is related to the key factors of normal development and operation of hydropower station.RuMei hydropower is the fifth stage of the 7 steps of ChangDu's following river basin planning of Tibet section of LanCangjiang river,of which project scale is first class-big,maximum dam height of which is 315 m,installed capacity of which is2100 MW.The rock mass which develop many small fault and compression joint of the left bank abutment slope whose stability directly affects the safety of dam of RuMei hydropower is heavily weathered and unloaded,and the rock mass structure of slope is complex.With the backing of tutor's research project on“Study on Engineering characteristics and application of dam foundation rock mass“,which is the fourth sub topics on“Study on engineering characteristics and application of rock mass in complex geological environment of RuMei hydropower station on LangCangjiang river,I participated in the investigation of dam site and studied the stability of the left bank abutment slope in detail.The main conclusions are as follows:?1?The lithology is single,mainly for the Middle Triassic ZhuKa formation(T2z)Dacite.Within a certain range of slope surface,rock mass is heavily weathered and unloaded and slope of dam abutment multiple distributes huge scale fragmentation loosening rock mass,causing structure of rock mass is complicated.Faults,long cracks and fractures with middle and low angle have great amount of development among the slope of left bank abutment,which have affection on the stability of slope,especially there are four faults with low dip angle named L69L72,which play a controlling role in the stability of the slope of left bank abutment.?2?The joints with low to middle inclination angle in the left bank abutment slope are very developed,and its development characteristics are as follows:1)According to the difference of occurrence,the joints with low to middle inclination angle can be divided into 5 groups,of which the most developed is NNW-NNE groups.2)Statistics show that the distribution form of inclinaton,dip angle and trace length in each group are normal?or lognormal?,normal?or lognormal?and negative exponential distribution.3)Joints with low to middle inclination angle are mainly of wave-roughness,aperture is less than 0.5 mm?very close?,no filling,no cementation,drying and bonding well.4)According to the statistics of the whole tunnel,the continutity of joints with low to middle inclination angle of the three most developed groups is between 40 to 60 percent.The development degree of cracks with low to middle inclination angle is different in space,and the strong development section coincides with the unloading depth of rock mass,namely,the development degree of cracks with low to middle inclination angle is related to the unloading of rock mass.The connectivity rate of the unloading section is commonly 70 to 95 percent,and the no unloading section is 10 to 50 percent.?3?There are 3 groups of steep dipping fractures,of which the most developed is NEE group.The distribution form of inclination and dip angle are normal?or lognormal?and normal?or lognormal?distribution.Steep dipping angle fractures are mainly of wave-roughness,aperture is less than 0.5 mm?very close?,no filling,no cementation,drying and bonding well.The connectivity rate of steep dipping angle fractures is between 30 to 50 percent and trace length estimated between 0.7 to 1meter.?4?The structure of the rock mass of the left bank abutment slope are mainly mosaic structure,layered structure and sub blocky structure,while the local structure is fragmented.All kinds of rock mass structures appear alternately in space,which results in complicated rock mass structure.According to the structural characteristics of slope and phenomenon of deformation and failure of slope,deformation and instability mode of the left bank abutment slope mainly include 3 types,namely,sliding failure,toppling failure and local collapse.Sliding failure can be divided into four types:circular sliding,sliding-pulling,wedge failure and plane sliding.According to the characteristics of the slope structure,the main problems of left bank abutment slope after the excavation is the stability of sliding body composed of weak structural plane in low dip angle and and small fault in steep dip angle or unloading fissure.Among them,fault named L72 is the control boundary of slope stability.?5?FLAC3Dsoftware was used to simulate the evolution of slope in dam site.The mian conclusions are follows:1)By trial and error,when the 4 MPa normal stress and the tangential of 2MPa are applied to the boundary of the model,the simulation results are in good agreement with the measured borehole stress.2)When the valley cut to present surface,the bottom of the valley produced a high stress package,and the stress value is 40 MPa,and the distribution of elevation is between 2510 to 2610m.3)The development length of L72 has a great influence on unloading depth.The longer the extension length is,the deeper the unloading depth of the slope is.By trial calculation,when the extension length of L72 is increased by 50 meter,the unloading depth is close to the actual results.?6?Based on the finite element strength reduction method,the stability of the left bank abutment slope under natural and rainstorm conditions is calculated.The main conclusions are follows:1)The calculation results show that the overall instability of the natural slope of left bank is likely to occur along the bottom of the strong unloading.The stability coefficient of left bank slope is 1.77,which meets the stability requirements.The stability coefficient of left bank slope under the condition of heavy rain is 1.66,which meets the stability requirements.2)After excavation,the stability coefficient of the left bank slope is 1.74 and 1.63,respectively,under the natural and rainstorm conditions,which can meet the stability requirements.That is,the overall instability of left bank abutment slope under the condition of rainstorm is not possible?7?Based on the rigid limit equilibrium method,the stability coefficient of unstable combined sliding body?mainly sliding and fracturing?of left bank abutment slope in natural condition,the 1/4 saturation condition,the seismic condition and the1/4 saturation condition combined with seismic condition are calculated,concluding that the stability of all possible combinations of sliding body is 1.28?transfer coefficient method?under the most unfavorable condition of 1/4 saturation and seismic condition.Based on the block stability theory,the minimum stability coefficient of the three-dimensional movable block is 1.256 under the most unfavorable condition,which can meet the stability requirement.After the excavation of the left bank abutment slope,there is no possibility of sliding instability. |
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