Research On Effect And Mechanism Of Clogging Process On Permeability Of Coarse Grained Soil Dam Foundation In Shannan Prefecture Of Tibet

Mountains-gully rivers area of the Tibetan plateau is important to the local agriculture，and its deep thick alluvium foundation with strong permeability is a big problem forreservoir construction project decision-making，design and construction. Anti-seepageengineering of dam foundation is cost much，but its effect is poor，and it is difficult tomeet the design requirement. Through the preliminary study of this kind of problem，it is found that clogging phenomenon in infiltration process has important influenceon the permeability of soil of dam foundation，so it is of great significance to studyinfiltration-clogging rule and its mechanism.This paper takes the south of Brahmaputra River in Shannan region of Tibet toKong-Shan Rail Rafah as the study area, and selects Jiangxiong reservoir in andproposed Zhuoyu reservoir as the research objects, then mainly conducts the field testinvestigation in Zhuoyu reservoir, and selects test points to carry on weight test,bicyclo method infiltration-clogging permeability test and test pit methodinfiltration-clogging permeability test in the channel of Zhuoyu reservoir. Throughthese tests the weight and related infiltration parameters of soil are got, and thediameter interval of soil causing clogging is studied preliminarily, then it provides thebasis for laboratory test.Improved infiltration-clogging equipment is designed and developed, and it has agreat improvement than before. The feeding device designed innovatively canguarantee continued water flooding when feeding fine particles. The improved porewater pressure monitoring device includes two parts which are pore water pressuresensor and computer data acquisition and processing system, which can continuouslymonitor the relationship between the pore water pressure and the seepage flow indifferent conditions, and its data can be read continuously then before, then it can reduces the reading error.Through indoor test analysis of soil, the approximate particle grading curve ofsoil is got. According to coarse grain soil size partition theory, combining the testscreening criteria, P=4mm is selected for the cut size of soil. Considering the sizeeffect of test instrument, the particles above64mm are processing,at the same timethe natural state of soil should be kept as intact as possible.Through laboratory tests, study the influence and regularity ofinfiltration-clogging on permeability of coarse grained soil dam foundation. At first,study the best clogging diameter interval of single size uniform soil and get thecorrespondence between clogging particle size and uniform soil grain diameterthrough many experiments. Then through simulating natural soils, study cloggingeffect of different size particles on average pore diameter in different water level andget the best clogging diameter interval with0.063-0.125mm and0.125-0.25mm, thensummarizes the correspondence between diameter interval and water level.Through observing fabrics of soil before and after clogging and building soilparticle model and pore model, study particles arrangement, pore characteristics andparticles force of test soil, and combine with experimental results and related theoriesconclude the correspondence between clogging particle size dyand average porediameter D0is d0.25~0.5D by combining with experimental results andrelated theories, then study mechanism of clogging on the microcosmic, and get theclogging interval of soil is0.063-0.125mm，which agrees well with the experimentalresults and proves the rationality of the two.