| The stability of bank slopes in Three Gorges Reservoir area is significantly affected by the periodic rise and fall of reservoir water level.As for high slopes interbedded by soft and hard rocks in the reservoir area,a long-term effect of reservoir water fluctuation on erosion of the soft rock in slope and a softening of the rock strength make the deformation and failure mechanism of this kind of slope very complicated.Taking high slopes with soft and hard interbedded of Dulong section in the Three Gorges Reservoir Area as examples,based on field investigation,monitoring analysis and numerical simulation,the deformation mechanism of thin layer and medium thick layer of soft and hard interbedded slope is studied from rock mass structure,failure mode,deformation failure mechanism and reservoir water mechanism.(1)Through analysis of investigation data,field investigation,UAV aerial image analysis and data extraction,slopes and rock mass structure characteristics of Dulong section in wuxia gorge are identified.It reveals that slopes of the Dulong area are oblique counter-tilt layered slopes.And there are mainly three groups of joints(rock layer J1,interlayer leaning fracture J2 and longitudinal joint J3).The thickness of soft and hard rock strata and the law of rock fracture in the anti dip high slope of the study area are statistically analyzed.It is found that the main rock stratum is 20-50 cm thick limestone and 10-20 cm thick muddy ash.The ratio of fault to layer thickness(S/T)is mainly between 0.9-1.5.(2)Based on the field investigation,deformation and failure characteristics of the slopes in the study area,the deformation and failure mode of the slopes in the study area is generalized.The local failure modes including:erosion damage,bending and toppling failure,block toppling failure,interlayer shear failure and local flexural failure.The whole failure mode includes:the toppling-slip failure of the overlying soft and hard interbedded slope(D3 slope)and the flexible bending-slip failure mode of the soft and hard interbedded slope within a hard rock beam(D7 slope).(3)Based on analysis of existing monitoring data,a long-term surface deformation response of slopes and its influence on reservoir water are clarified.From 2012,the slope displacement of the study area is obviously fluctuating.Displacement of slope increases obviously with the decline of reservoir water,and keep stable in the reservoir water rising section.It shows a regularity of the periodic change with the reservoir water.(4)Through numerical simulation by UDEC,reveales failure mechanism of the slope and the influence of reservoir water on the soft and hard interbedded slope.Taking the D3 slope as an example,the bending deformation of the slope at the foot is aggravated by the erosion and softening with reservoir water.The interlayer shear zone is formed through fracture,which eventually passes through the split gap in the upper part of the slope and causes the collapse slip failure.When the reservoir water falls,slope forms the seepage force pointing to the foot of the slope,which is the main reason for the deformation of the slope.(5)Through numerical simulation by UDEC,reveales failure mechanism and the influence of reservoir water on soft and hard interbedded counter-tilt slope within a hard rock beam.Taking the D7 slope as an example,the bending deformation of the lower slope is aggravated by erosion and softening of reservoir water.At this time,the hard rock beam plays a hindrance to deformation in the slope,and the "rock arch" locking zone is formed in the curved rock stratum.When the action of the rock beam is broken,the shear stress concentration zone is formed in the locking region,and "S" appears,slope eventually slips along the shear band.When the reservoir water falls,the seepage force of the foot pointing to the slope is dominant,with reservoir water rises,it forms the seepage force pointing to the slope,which is favorable for the stability of the slope. |
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