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چکیده
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One of the major problems in using subsurface drain is pipe and envelope clogging by mineral materials. Such a process is the result of disturbances of soil structure during drain installation. Drain filter selection follows definite rules and neglecting them can result in project failure. Current study is based on evaluation of three kinds of synthetic filters in comparison with mineral filters. Two soil samples of northern Khorram Shahr (1.65m deep) were obtained for the study. Physical and chemical analysis on samples showed they do not have major differences in texture and particle size distribution (PSD). Original recommendations based on previous studies on synthetic filters in terms of PSD curve and soil texture was to use PP700 type. Two other types were also chosen as the upper and lower boundaries of the main choice. The performance of three types of filters (PP450, PP700 and PP900) was assessed in terms of clogging potential using ASTM-5101standard test. In addition, mineral blanket was designed according to the USBR criteria. Experiment was conducted in three treatments and completely on random. The test was conducted in laboratory, using physical model for infiltration (according to the ASTM D-5101 standard) and by creating four different hydraulic pressure head (25, 50, 75 and 100cm). In the study, changes in outflow from soil-geotextile system, hydraulic conductivity, gradient ratio and hydraulic conductivity ratio were analyzed for four filters. The results showed that 1) in terms of the gradient ratio, none of the filters were found sensitive to clogging, 2) outflow from mineral filter was 2 to 3 times greater than for geotextiles, 3) the hydraulic conductivity ratio of mineral filter for PP450, PP700 and PP900 geotextile filters were 3.47, 4.17 and 5.57 respectively, and 4) comparing outflow and hydraulic conductivity variations, geotextile filter of PP450 type was found the best. According to the optimization results, for PP450, optimum values for
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