Study On Laboratory Simulated Test And Mechanism Of Infiltration Clogging Effect Of Cohesionless Coarse-Grained Soil

There are several common clogging effects, for example it causes the geotextile and relief well to lose effectiveness,tailing dams destabilization and input well clogging which is mechanical blockage, also there exists bio-chemical clogging such as reproduction of micro-organisms,organic matter or the insoluble salts of various ions, while almost all of these types of clogging effect reduce porosity and permeability of rock and soil, and the above inflation is negative; At the same time, we studied on some seepage phenomena and preliminarily consider that some leakage problems may be resolved by using the feature of clogging effect of blocking pore, and achieve the purpose of reducing infiltration.At the first, the text analyzed and concluded the nature of cohesionless coarse-grained soil especially the factors of permeability, and provided the basis of selecting graduation,dividing the mixed grains and cohension;The subject is proposed by background of the view of leakage phenomenon which is built in the reservoir dam foundation of the alluvial and diluvial deposits with deep and thick layer,coarse particle and high permeability in mountains-gully rivers of Tibetan Plateau, and foundation of previous research experience,findings and deficiencies, and combines with the theories and results of the coarse-grained soil nature,the clogging of geotextile,natural filter layer, we also propose the problems that mechanical clogging verification,determination of factors and production conditions analysis in cohesionless coarse-grained soil as research contents.By study on the character of the foundation soil layers in Zhuo-Yu reservoir, and analysis the pre-test of gradation characteristics,clogging design,phenomenon, we consider that the core idea for the study is "necessarily continuous gradation of cohesionless coarse-grained soil occurs clogging through erosion under the action of seepage", which is more correct with issue background and achieve the desired purpose of verifying clogging, and select the Quaternary Alluvial layer of the foundation soil as test gradation; based on the fines content, uniformity coefficient and so on are the main affect factors of permeability of cohesionless coarse-grained soil, we set on the more reasonable choice from the super-size treatment,sample preparation,loading,saturation and other important details, and taking into account the type of soil pores large,strong permeability we analysis the flow state,infiltration and permeability in theory and determine the low constant head as infiltration cycle test.To judge the clogging produce and its impact on the permeability, we combined with "gradient ratio test " of geotextile and protected-soil in determination clogging, and consider the basic flow parameters,conditions and trend of seepage,hydraulic gradient and the gradient ratio,gradation and turbidity are reasonable judgment of clogging at the macro level unprotected cohesionless coarse-grained soil. It exists the clogging effect which lower the soil permeability by statistical analysis of test data, and indicate that the designs and theoretical analysis are feasible; Using the theory of average pore diameter,pore models and gradation properties of soil, we definite"clogging particle"which blocks the corresponding pore, and find out the theoretical calculation of average pore diameter is coincide with the change interval of gradation, and consider the three forms of clogging separately is single particle,particle arch and similar to nature filtering layer.We conclude that the basic conditions of clogging effect are soil gradation,loading effect and seepage effect, but it is because of restriction each of them, the clogging effect is more difficult produced in uneven soil than the uniform soil by eroding itself under the infiltration, and the latter one especially the extremely uneven (cohesionless) coarse-grained soil is not easy to produce the effect in nature condition or difficult to be found out; We analysis the pre-test and find that the infiltration parameter,the changing of specimen gradation and so on are not in accord with clogging effect by using the above results, and consider that it did not exist the clogging effect which can change the soil permeability effectively, but there may occur "false clogging" which is caused by gas. And we preliminary view that the mechanical of clogging laboratory simulated test ought to select the (cohesionless) coarse-grained soil which leak fine fractions relatively is more reasonability, and comparing the piping soil which lose many grains by fluid erosion in the low hydraulic gradient and the flowing soil which could sustain high hydraulic gradient, the type of soil which has enough pore space and portability grain(clogging grain) and sustain some degree hydraulic gradient is more adapt to the kind of comparison verification tests.Finally, combining the clogging effect of development process and achievement in Geological Engineering currently, we consider that there are many more works to be done if the mechanical of clogging effect will be applied in water conservancy projects of reducing seepage, so our subject provide initial feasible ideas and research direction for further studying on clogging effect.