Researches In The Influence Of Foundation Excavation On Engineering Properties Of Riverbed Foundation Rock Of A High Areh Dam In Jinsha River River

The engineering geological characteristics of the foundation rock are very high in the foundation of the high arch dam.The slope of the natural river valley is mostly developed with a certain thickness of weathering and unloading rock.It is obvious that the deformation and strength of this part of the rock can not meet the requirements of the construction.Therefore,large-scale excavation of rock mass is unavoidable,which will affect the engineering properties of rock mass within a certain range of excavation face.In this paper,based on a large number of field geological survey,acoustic detection,in situ test and preliminary exploration research results,the deformation and failure phenomena of disturbed rock mass,disturbed area characteristics,rock mass disturbance deformation and failure mechanism,quality of foundation rock mass and its mechanical parameters are analyzed through two-dimensional and three-dimensional numerical simulation methods.Based on this,the influence of dam foundation excavation on the engineering properties of the riverbed foundation rock is studied.The main results are as follows:(1)The disturbance and deformation of the foundation rock mass of the dam foundation is mainly manifested in the opening of the cracks,the generation of new cracks,the dense fracture zone and so on,which leads to the reduction of the rock mass engineering characteristics.(2)Using the characteristics of blasting hole and the change of wave velocity attenuation rate before and after excavation,combined with the numerical simulation of stress changes after excavation,the scope of the excavation disturbance area is within the range of 15 m below the base surface,in which 0～3m is the blasting damage zone;3-15 m is the stress adjustment area;15m below the normal rock mass area.(3)On the basis of the mechanism analysis of the deformation and failure of rock mass caused by blasting and stress adjustment,the FLAC3 D software is used to simulate the stress field,displacement field and the distribution characteristics of the plastic zone after the excavation of the dam foundation,and it is found that the influence range of the excavation of the rock mass is basically consistent with the determination of the influence depth of the field acoustic wave.(4)According to the evaluation standard of rock mass quality in the construction stage,the quality of the foundation rock mass of the river bed foundation is classified by a large number of wave velocity results.The results show that the comprehensive rock grade in the blasting area is III 2,the proportion of class II and III 1 accounts for50.34%,and the comprehensive rock grade in the stress adjustment area is III 1,class II and III 1 account for 62.42%;In the normal rock mass,the proportion of class II,class II and III of the comprehensive rock class accounts for 80.47%.(5)Based on a large number of in-situ deformation experiments,the correlation formula of deformation modulus-wave velocity,strength parameter-deformation modulus is established,and the mechanical parameters of the foundation rock of river bed dam foundation are evaluated.(6)Based on the quality classification of the foundation rock mass of the river bed dam foundation and the evaluation of the mechanical parameters,the influence of the excavation disturbance on the quality of the rock mass and the mechanical parameters of the riverbed foundation is analyzed.