Experimental Study On The Structure Stability In Soil-geotextile Filtration

Geotextile is widely used as filters in the hydraulic, civil and environmentalengineering. Application of geotextile as filters is badly limited due to the ambiguityof mechanism of soil-geotextile filtration, the limitation of current filter designcriteria and the faultiness of function of the filter products. The geotextile filtermechanism needs to be proved up and new filter geosynthetics need to be developed.In the dissertation, the concept of the state of fully-soil-eroding-away is developed;the structure stability of the soil-geotextile filtration system is studied by tests.Based on the conception of the state of fully-soil-eroding-away, thethree-dimensional simulation test apparatus of soil particle bridge formation isdeveloped, such as the structure stability test apparatus of fine particle soil and thereverse flow apparatus. The simulated bridge formation tests and the structurestability filtration tests of fine particle soil are presented.The results show that the bridge formation of the soil particles is related theshape and the coarseness degree of the granule, the shape of filtration opening, therelative open area. In the state of fully-soil-eroding-away, the maximal stable openingsize of filtration is obtained by the simulated structure stability test of the filtrationsystem. It is related to uniformity coefficient Cu and coefficient of curvature Cc of thesoil. The filtration opening size should be smaller as the Cu increases.The structure stability filtration tests of fine particle soil are presented. Theresults show that the structure of the soil sample will keep stable enough with biggerfiltration opening size, and clogging is avoided. In current filter design criteria, one ofthe significant causes of clogging is choosing filters of too small opening size. Filterswith the most possible big opening size should be chosen to avoid clogging in thefilter design.As the gradient increases, there will be more particles removing. In internallystable soil, particle-removing would not influence the structure stability of thesoil-geotextile filtration obviously;in internally unstable soil, particles probably loseexcessively and the structure would lose stability.The character of the unstable flow has significant influence on the structurestability of the filtration system. When the frequency or the biggest height of water ofthe reverse flow increases, there will be more particles removing in the soil and thestructure will lose stability more possibly.The dissertation will explain the filtration mechanism of soil-geotextile filter anddevelop the experimental apparatus and test technology of soil-geotextile filter. It willalso propose the filter design criteria applied to engineering and help to develop newfilter geosynthetics.