عنوان مقاله [English]
Since field researches for evaluating drain envelopes are costly and time consuming, laboratory evaluation of these envelopes is a suitable approach. The main goal of this study was obtaining a set of empirical equations in order to estimate the hydraulical and clogging parameters using hydraulic head and drain outflow (which are easy to measure) and removing the effect of piezometers installed in the permeameter body. To conduct this research, a permeameter was designed and made according to ASTM-5101 standard. Then, three types of commonly used geotextile filters, e.g. PP-450, PP-700 and PP-900 were used. The required soil for this experiment was collected from a drainage project in the north of Khorramshahr at 1.65 m depth. The test was conducted in the laboratory using Permeameter by producing 4 different hydraulic pressure heads (25, 50, 75, 100 cm). Special parameters (envelope hydraulic conductivity, soil hydraulic conductivity, soil-envelope hydraulic conductivity, gradient ratio) were calculated by measurement of hydraulic head, outflow and piezometers installed in the permeameter body. Results showed that these models gave accurate estimation of the assessed parameters. High correlation coefficient values of these equations (for three synthetic envelopes PP450, PP700 and PP900) indicated that they provided an accurate estimation for soil-envelope hydraulic conductivity, soil hydraulic conductivity, envelope hydraulic conductivity and gradient ratio. Using the suggested equations clogging and hydraulic performance of drainage envelopes in different conditions can be simulated.