Document Type : Research Article
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Abstract
Conventional graded granular filters which are commonly used in subsurface drainage projects in Iran, encounter various difficulties such as huge costs and long distances from source of gravels and led to use of other materials as envelopes. Synthetic products can be justified over granular filters due to their comparable performance, improved economy and ease of placement. Considering that, it’s essential to assess selected synthetic envelopes performance before setting them in the field. The objective of this study is assessment of permeameter test proccessing (based on ASTM D-5101 standard), using 3 different PLM synthetic envelopes (PP450, PP700 and PP900) in application of water with different salinity (EC= 22.2 dS/m and 0.78 dS/m) and saline-sodic soil (EC= 169.3 dS/m and SAR= 45.18 (meq/lit)0.5), prepared from north Khoram-Shahr drainage project located in Khuzestan Provience. This study deal with evaluation of permeability tests results by applying saline water and soil which is not common in permeameter standard tests. So, a distinctive point of this research is using drainage water with high salinity, in comparison with applying normal water and also saline soil. For this purpose, two physical models of permeameter used to do a series of permeability tests by varying synthetic envelope types and saline and normal water. Permeability tests were done at 5 different hydraulic gradients (1, 2.5, 5, 7.5 and 10). Variations of discharge, hydraulic conductivity and gradient ratio (GR) were measured and investigated statically as factorial experiments in the form of randomized complete design. The results demonstrated that the more salinity the lower the hydraulic conductivity in all synthetic envelopes. The average hydraulic conductivity by applying normal water were 1.29, 1.36 and 1.26 times more than the average hydraulic conductivity by applying saline water for PP450, PP700 and PP900 samples respectively. Based on all tests of gradient ratios, it can be concluded that none of the envelope samples were susceptible to clogging, even in application of saline soil and water, even though the probability of clogging by applying saline water was higher. Also, it should be noticed that water quality is essential to encounter in permeability tests.
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