Analytical solutions for soil flushing through geotextiles considering filter cake and clogging
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Abstract:
Prefabricated vertical drains (PVDs) have been used in finegrained soils remediation system to provide a higher flow rate.However, the migration and accumulation of the fine particles inthe soil result in the filter cake adjacent to the geotextile and thepore clogging in the geotextile. An analytical solution for soilflushing through a clogged geotextile with a filter cake isdeveloped. The results obtained by the proposed analyticalsolution agree well with those obtained from the finite differencemethod. Results from an illustrative example indicate that theformation of a filter cake at the surface of a geotextile is far moredisadvantageous to soil flushing than pore clogging within ageotextile. The 5-hour base concentration at the depth of z = 50mm for the case just considering the pore clogging in thegeotextile is just 1.06 times more than that assuming no filtercake and no pore clogging in the geotextile. When the poreclogging combined with a filter cake are considered, the 5-hourbase concentration at the depth of z = 50 mm increases by afactor of approximately 4.94.Keywords:
Clogging
Geotextile
Flushing
Filter cake
Abstract Lateral flushing is expected to become an important means of controlling emitter clogging in drip irrigation systems. This research investigated the effect of different flushing frequencies (once every 32, 64, 96 and 128 h) and flushing velocities (0.2, 0.4 and 0. m s −1 ) on emitter clogging. The experimental results showed that the substances that clogged the emitters mainly come from the cast of internal laterals, and could be effectively controlled by lateral flushing. And emitter clogging was most effectively relieved for the frequency of once per 64 h, and the velocity of 0.4 m s −1 . The discharge ratio variation (Dra) and the coefficient of uniformity (CU) of the drip irrigation system, increased from 7.7 to 21.9% and 11.6 to 67.4%, respectively, compared with non‐flushed laterals. Also, as the frequency increased, Dra and CU first decreased and then increased. Similarly, with the increase of flushing velocity, Dra and CU also decreased then increased. In conclusion, for the drip irrigation system with YRW, the suitable lateral flushing velocity was found to be 0.4 m s −1 at a frequency of once per 64 h. Copyright © 2017 John Wiley & Sons, Ltd.
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Prefabricated vertical drains (PVDs) have been used in finegrained soils remediation system to provide a higher flow rate.However, the migration and accumulation of the fine particles inthe soil result in the filter cake adjacent to the geotextile and thepore clogging in the geotextile. An analytical solution for soilflushing through a clogged geotextile with a filter cake isdeveloped. The results obtained by the proposed analyticalsolution agree well with those obtained from the finite differencemethod. Results from an illustrative example indicate that theformation of a filter cake at the surface of a geotextile is far moredisadvantageous to soil flushing than pore clogging within ageotextile. The 5-hour base concentration at the depth of z = 50mm for the case just considering the pore clogging in thegeotextile is just 1.06 times more than that assuming no filtercake and no pore clogging in the geotextile. When the poreclogging combined with a filter cake are considered, the 5-hourbase concentration at the depth of z = 50 mm increases by afactor of approximately 4.94.
Clogging
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Flushing
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Drainage through pipes plays an important role in tailings pond projects. Reductions in drainage capacity and even clogging of drainage pipes are common issues, especially in tailings projects. To address these clogging issues, a drainage pipe with a replaceable porous-foam filter core (referred to as DPRF) is proposed. This paper studied the drainage characteristics of DPRF wrapped with a woven geotextile and traditional drainage pipes wrapped with a nonwoven geotextile (referred to as DPNG) in fine tailings sands with a reduced scale model test. The results showed that the woven and nonwoven geotextiles could successfully retain fine tailings sand; however, the woven geotextile easily clogged as the experiment progressed. For the DPRF wrapped with a woven geotextile, the larger the aperture of the woven geotextile, the higher the drainage rate of the pipe. The average drainage rate of the DPNG was larger than that of the DPRF wrapped with the woven geotextile. It can thus be inferred that the DPRF wrapped with the woven geotextile is not a good solution to prevent physical clogging. Alternatively, it is suggested that the DPRF wrapped with the nonwoven geotextile can be used to alleviate chemical clogging problems.
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The use of nonwoven geotextile filters is common in geoenvironmental and geotechnical engineering applications. The main requirements for successful performance of drainage and geotextile filters are soil retention, permeability and clogging resistance. In case of anti-clogging capabilities, the most popular method to evaluate the filtration behaviour of nonwoven geotextile in contact with soils is gradient ratio test. Also the number of constrictions of nonwoven geotextile should be determined on the basis of fibre diameter, thickness and porosity. The number of constrictions has been found to explain the different filtration behaviours of nonwoven geotextiles with similar or even the same opening sizes but different structures for various soil conditions. This paper presents the gradient ratio test program for internally unstable soil and nonwoven geotextiles with different structures. Test results show a significant impact of the number of constrictions on the filtration characteristics of geotextile. What is more some modifications to the filter design criteria are proposed based on interpretation of the experimental results.
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Geotextile
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Filtration (mathematics)
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Nonwoven geotextiles have been used as filters for over four decades in geotechnical and geoenvironmental works. These products have a complex fibre matrix and their behaviour as filters depends on how this matrix interacts with fluids and soil particles. Therefore, uncertainties still exist regarding prediction of geotextile filter performance under severe and critical situations. This paper investigates how confinement and partial clogging influence the dimensions of openings in nonwoven geotextiles. Bubble point (BBP) tests were carried out on six nonwoven geotextiles under unconfined and confined (equivalent vertical stresses of up to 1000 kPa) conditions with and without partial clogging of the geotextile. The results obtained show significant influences of confinement and partial clogging on geotextile opening dimensions and retention capacity. The results of O 95 from bubble point tests on unconfined and virgin specimens compared well with results from hydrodynamic tests. Comparisons between BBP results and data from filtration tests under confinement are also presented and discussed. The repercussions of reductions in opening size caused by confinement and partial clogging on geotextile clogging potential and filter criteria are discussed.
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Filtration (mathematics)
Hydraulic head
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When the geotextiles are used in drainage applications, the relationship between the opening size of geotextile and soil particle size becomes a essential factor. In this paper there methods have been used to measure the opening size of geotextiles. The results indicate that the method which water drains out and washes soil particles through the geotextile is suitable for needle-punch nonwoven whose opening size is finer than 50μm.Next, the clogging tests on five geotexile samples with silty sand were carried out, and the test results were compared with the typical filter criteria already formulated by some reseachers.
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