Experimental Study On Riverbed Boulder And Sandy Gravel Media Permeability Characteristic

The serious short of water resources in our country, especially in the northern regions, the groundwater overdraft has become the common problems of the northern regions. The limited exploitation of groundwater has also become the main measures for protection of groundwater resources. Therefore, in recent years, the water intake project near the river has gradually increase in the northern china in order to meet the water demand of human daily life and social development. The technological problem is the large difference between theoretical calculated result and practical engineering water intake quantity in the exploitation riverbed underground water project construction actually. It was considered through the detailed reconnaissance in the field analysis that it have a direct relationship with boulder of accumulation sand pebble layer in the river trough. The paper researches permeability characteristics of the boulder and sandy gravel media the river trough, which possesses important significance for taking underground water project construction near the river and improving water intake efficiency.Taking the original state natural accumulation sandy pebble and boulders at Liulin County Yellow River bottomland as the research object, using the method of experimental study, from the aspect of the influence of boulders shape, scale, gradation, profile structure, sediment deposit to osmotic coefficient and osmotic flus of sandy pebble carrying out systematically study. The following main conclusions were drawn: (1) The characteristic diameter index of boulder and sandy gravel media on natural riverbed contributed significantly to the permeability coefficient. The characteristic diameter indexes are different, and the numbers and size of pore space of sandy gravel media, the discharge area of seepage flow and the percentage filling of fine particle are different too, that is characteristic diameter indexes have influences on the permeability coefficient. There are the close correlation among permeability coefficient of sandy gravel media and its effective diameter (d10), limit diameter (d60) and Non-uniform coefficient (Cu). The permeability coefficient (K) increases with the increase of the d10, the same as with the increase of the d60, while the permeability coefficient decreases with the increase of the Cu, there is a logarithmic relationship between permeability and Non-uniform coefficient (Cu), while a quadratic equation can be fitted to the correlation between permeability coefficient and effective diameter (d10) the same as with Non-uniform (Cu). There are the close correlation among permeability coefficient of sandy gravel media and the size of boulder and hydraulic gradient.(2)When the depth of water in the river course is kept constant and the content of sullage occurs in small amounts, a majority of sullage will be taken away by water through pore way in the cobblestone medium. Therefore, the effect of sullage on the seepage flux is less visible. But when the depth of sullage increases to certain extent, a part pore of cobblestone medium will be jammed by the increasing sullage. And at the same time, seepage flux decreases gradually. Covered by the sullage with the same depth, the seepage flux of cobblestone in the river course increases with the increase of water depth. But in the context of lager depth of sullage on the surface of cobblestone, alone with the progress of the experiment, the influence of the increasing depth of water on the seepage flux is weaken little by little.(3)The coating which consists by large size cobble, fine particle and geotextile has the best mud resist and keep infiltrating function. The best composite structure of fine particle and geotextile compound coating which to resist mud and keep seepage is geotextile+fine particle+geotextile. After overall consideration to osmotic coefficient and water quality, the top to bottom best sand gravel profile structure of artificial percolating filter is1～0.25mm pine particle14cm+geotextile+3～1mm sand gravel20cm+6～3mm sand gravel20cm+10～ 6mm sand gravel20cm+30～10mm sand gravel20cm+50～30mm sand gravel20cm+90～50mm sand gravel15cm.The research on artificial percolating filter profile structure of different particle size matching sandy gravel media in this paper,which only belongs to preliminary analysis according to the test structure, the best profile structure eventually got need the future project practice verification.