Shearing Behaviors Of Interlayer Staggered Zones At Baihetan Hydropower Station

Interlayer staggered zones at Baihetan Hydropower Station has a series of bad features such as loose structure,poor water-physical properties,poor mechanical characteristics and large spatial distribution.These weak structural surfaces in the surrounding rock mass of underground space determine the deformation and destruction of the surrounding rock mass.Based on great geological exploration,experiments and numerical simulations,their macrostructural and microstructural features,shearing behaviors etc.are studied systemically.Generally,the main research work and conclusions are as follows:?1?The engineering geological characteristics of the C₂ and C₄ interlayer staggered zones in the Baihetan Hydropower Project are studied from the macroscopic and microscopic perspectives.The geological exploration and test results show that:?1?It is recommended to use the sampling method of slotting and then manually cutting the specimens;?2?The zones can be divided into three parts structurally:joint bands?cleavage zone and muddy zone;?3?The interlayer staggered zones contains a large amount of clay minerals,and the clay mineral content of different zones is obviously different;?4?Some physical,hydraulic and mechanical properties of the interlayer staggered zones are revealed from a microscopic perspective through SEM.?2?The direct shear test results of undisturbed specimens show that:?1?the shear displacement test curve mainly shows the ideal elastoplastic characteristics,but the influence of the interlayer thickness,the large particle content in the interlayer,the water content and the sample size are dramatical;?2?The test found that the shear strength and internal friction angle of the interlayer staggered zones have obvious scaling effects.?3?Analyzing some factors such as interlayer thickness,water content,normal force,large particle content and contact surface fluctuation on the shear strength of interlayer staggered zones by orthogonal test.It is found that:?1?With the thickness of the interlayer soil increases the shear strength has a decreasing trend;?2?The influence of large particle content and contact surface roughness on shear strength is not obvious by statistical method and shear displacement curve;?3?With the increase of interlayer soil thickness,the frictional barrier effect of the soil-rock contact surface roughness is weakened.When the thickness of the muddy interlayer in the site fault zone is greater than the undulation difference of the upper and lower contact surfaces,the shear strength is similar to the shear strength of the muddy interlayer.When the thickness of the muddy interlayer in the moving belt is smaller than the fluctuation of the contact surface,it is necessary to comprehensively consider the mechanical effects of the muddy interlayer itself and the muddy interlayer and the contact surface as a whole.?4?Based on the results of laboratory experiments,a direct shear test model was constructed by using discrete element software PFC2D.The meso-mechanical characteristics of the interior of the interlayer staggered zones were studied during shearing.The effects of interlayer thickness,large particle content and structural surface roughness on shear properties and scale effects of shear properties were further analyzed by comparing the results of indoor orthogonal test The numerical simulation results show that:?1?During the shearing,the variation of the porosity,coordination number and number of fractures in the shear box is generally consistent with the variation of the shear displacement curve;?2?The peak shear strength is related to the interlayer thickness;?3?Within the range of large particle content selected by the test,the effect of large particle content on the peak shear strength of the shift zone is not obvious.