Experimental Study On Seepage Characteristics Of Rockfill Ecological Submerged Dam

Rockfill is widely used in water conservancy projects due to its low cost and easy access to materials,such as rockfill cofferdam,rockfill dam and filter dam.The ecological stone cage submerged dam rockfill for stone cage structure,which can smooth over the water in the flood season and in the dry season can impoundment,the formation of puddles of water in the upstream,suitable for fish and waterfowl habitat,has good ecological benefits,which belongs to a building model of ecological harnessing.But for a long time,because lack of knowledge about rockfill,the characteristics of both surface overflow and internal seepage,but also by the constraints of various conditions,rockfill structure need more theoretical basis.The characteristics of seepage in rockfill are more complex(generally random flow),and no longer follow Darcy’s law.Instead,they will tend to two times as the flow pattern is partial to turbulence.If we continue to use Darcy’s law,there may be danger.In order to promote the application of the ecological caged submersible dam,it is necessary to do experimental and theoretical research on the seepage characteristics of the rockfill body.Because there are two periods of dry period and flood period in the operation of rockfill dams,this study discusses the permeate flow problems from two situations: non-overflow state and overflow state.The relationship between pressure gradient and flow velocity inside the rockfill,the relationship between Reynolds number and friction factor,the relationship between Reynolds number and Manning coefficient,and the ratio of seepage to the state of overflow are provided,which provide the basis for the application of ecological dam of rockfill.The main conclusions of this paper are:(1)By plotting the relationship between pressure gradient and flow rate,it is found that the seepage flow regime of rockfill dams is no longer subject to linear law,but is more in line with Forchheimer’s formula.Continuing to fit the test data with Forchheimer equation and Izbash equation,according to the magnitude of their correlation,it is found that the Forchheimer equation has better physical meaning and better correlation under rectangular channel conditions.(2)Calculate the Reynolds number and friction factor through the flow velocity,pressure gradient,etc.,and fit the Reynolds number with the friction factor to obtain the fitting equation of Reynolds number and friction factor.Then derive the Forchheimer equation coefficient through the formula.(3)By plotting the correlation between Reynolds number and Manning coefficient,the variation law of Manning coefficient in seepage of rockfill is studied.It is found that with the increase of the particle size of the pebbles,the Manning Coefficient gradually approaches a constant,which indicates that the Manning Coefficient is likely to be used in the calculation of the non-overflow rockfill.(4)By using the relationship between the pressure gradient and the flow rate,the test converts the measured total pressure value into a percolation flow rate,and uses the product of the flow rate and area to calculate the seepage flow,and calculates the ratio of the percolation rate to the total flow rate for analysis.It was found that when the difference in the water level difference is small,the seepage flow rate accounts for more than or equal to 9.58% except d=7.13 mm.It provides the basis for the design of rockfill dams.