| Ci Ha Xia Hydropower Station,located in Qinghai Province,is the biggest staved hydropower station on Yellow River from Long Yang Xia to the altitude below3000m.The maximum height of the station’s dam is 254m.And the main purpose of the large comprehensive water conservancy infrastructure is electricity generation.Meanwhile,the project can intercept sand,control flood.The 4~#toppling slope is situated on the left bank of the dam site area,at the upstream of the dam axis478m-Duozonglongwa ditch,which is large and near the dam.Once the slope is damaged,it will directly threaten the dam’s safety.According to the engineering geological study on region and dam site area of Ci Ha Xia Hydropower Station,the basic characteristics,deformation and failure characteristics,formation mechanism,failure modes and stability of the 4~#toppling was analyzed in detail.The major achievement and knowledge are as follows:(1)The main stratum of 4~#toppling slope is belong to the third rock group of middle Triassic,and its main lithology is the interbed of the thin layer grey slate and gray-green sandstone.Some rock is medium~thin sandstones with slates,so the whole stratum is thin layer~interbedded antidip laminate structure.Normal attitude of stratum is NE50°~65°NW∠69°~77°,after toppling deformation,the dip angle of rock is 40~60°,some location rock even less than 30°.The toppling body is large which distributes as a band,and its slope angle is steep,terrace is undeveloped.According to the deformation and failure characteristics and structure of the 4~#toppling slope,the slope can be divided into two regions,located in upstream and downstream,andⅠa rea toppling deformation depth is slightly larger thanⅡarea.(2)According to the statistics of engineering projects,based on previous researches,the classification index of toppling deformation was proposed,such as rock inclination,rock weathering and unloading characteristic and wave velocity of rock mass.And then the 4~#toppling body is divided into four different typical deformation zone(area):Surface toppling loose broken area,strong toppling deformation zone,moderate toppling deformation zone and slight toppling deformation zone.(3)Combined with the studies on the influencing factors of the toppling deformation and destruction,such as topography,lithology,rock mass structure and stress conditions,the formation mechanism of 4~#toppling body is studied by the analysis of geologic processes mechanism,physical simulation and numerical simulation.That is:at the slope unloading rebound premise,firstly,the rock at the toe was bent and toppled under the force of gravity,then continues to expand upward,so that the rock fracture under constant moment.(4)Based on the formation mechanism and deformation and damage characteristics of toppling body,synthesized with the geological analysis,numerical simulation and physical simulation methods,the instability modes of 4~#toppling body was studied.It overall believes that the failure mode of slope is mainly based on toppling-fracture,some steep zone happened toppling–collapsing and along the interfaces of different toppling deformation classification occurred creep-crack.(5)Evaluation of 4~#toppling slope with qualitative and quantitative analysis of the stability evaluation shows that it is stable in the natural and excavation conditions,and excavation can help to improve the stability of slope.However,as the slope may occur avalanching and slump at local small scale,so under the construction,the local loose slope is need to clean up,or it can be temporary controlled by shotcrete method.So these methods can ensure the safety of construction. |
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