Apparent Opening Size Research Articles

A circular economy approach for geotextile reuse following lake water filtration

Eutrophication in lake systems is intensifying. To reduce this possible scenario, a method for suspended solids and associated nutrient removal by a novel on-site remediation has been investigated, using nonwoven geotextiles as filter media. These procedures generate clogged geotextile layers with captured suspended solids on them. To become more sustainable, circular economy principles were employed, more precisely reuse. Thus, this investigation aims to assess the potential reuse strategies by washing clogged layers and determining their possible reuse. The washing method was pressurized water (i.e., using a gardening pump sprayer). Preliminary results have shown the efficiency of the washing method in removing visible geotextile (non-woven) clogging, with permeate flow rates reaching values close to the initial process values. The geotextile apparent opening size increased by an order of 20%. Also, no geotextile fibre disruption was observed by scanning electron microscope (SEM) imagery, indicating its possible reuse. The dilute liquid waste preliminary findings showed high concentrations of some metals such as manganese, (112.72 μg/L) and zinc (88.12 μg/L) in addition to phosphorus (120.18 μg/L) which requires additional studies. The washed geotextile leaching test did not indicate any contaminants in the permeate which would enable geotextile layer reuse for lake water filtration.

Comparative Evaluation of the Long-Term Filtration Performance of Recycled Materials in Highway Drainage Systems

ABSTRACT Highway drainage systems are designed to remove surface water and groundwater without deteriorating the road structure; hence, their durability is crucial to sustain the performance of highways. Filtration performance of a drainage system consisting of aggregate and geotextiles is one key parameter that needs to be carefully assessed so that clogging of the system does not result in failure. Substituting the natural aggregate in drainage systems with recycled materials would result in preservation of natural resources and employment of stockpiled recycled material, creating a mutually beneficial solution. In this study, the long-term filtration performance of three different recycled materials from different industries (i.e., two steel slag, recycled asphalt pavement, recycled concrete aggregate) has been investigated when used as filter material in drainage systems. Furthermore, two natural aggregate materials as control soils were used to compare the performance of recycled materials. A nonwoven geotextile with a low apparent opening size that represents the least favorable scenario in terms of clogging was selected as the filtration media. Long-term filtration experiments were carried out in the modified gradient ratio test setup and the hydraulic gradient ratio (GR) along with the permeability ratio (KR) were determined under different hydraulic gradients to evaluate the clogging performance. The results indicate that even under the most undesirable conditions, recycled materials exhibit a satisfactory filtration performance compared with natural aggregates, and they can be employed as aggregate material in highway drainage systems.

Simple Filter Cake Formation Test Method Using a Geotextile instead of the Sand Stratum

Slurries and filter cakes are widely used to support the earth pressure and water pressure of an excavation surface to maintain stability. Most major projects of slurry shield need to carry out filter cake formation tests to study the availability of slurry parameters. Nevertheless, it takes considerable testing and lengthy preparation of sand to simulate a stratum, therefore this paper examines a filter cake formation test method in which a geotextile is used to replace the sand stratum. Using the geotextile as a known filter medium, the quantitative relationship is studied between the membrane and the simulated sand, to examine whether the same experimental results can be obtained as using the simulated sand. A series of filter cake formation tests were carried out on four different sands and five different geotextiles with four different slurries and then the filter membrane properties were measured to explore the potential of the geotextile alternative for filter cake formation. The results show that the infiltration process of slurry in sand and geotextile was similar, and slurry infiltration occurred both with and without filter cake. 0.8 times apparent opening size of geotextile could be used to replace the characteristic pore diameter of the sand stratum (0.8AOS = D0) for the filter cake formation tests. The filter cakes on sand stratum and the substituted geotextile had similar properties, such as thickness and water content.

Comparisons between Geotextile Pore Sizes Obtained from Capillary Flow And Dry Sieving Tests

Abstract In the United States of America, two standard methods of measuring the largest pore size of a geotextile have been accepted: Dry Sieving Test (ASTM D4751, Standard Test Methods for Determining Apparent Opening Size of a Geotextile) and Capillary Flow Test (ASTM D6767, Standard Test Method for Pore Size Characteristics of Geotextiles by Capillary Flow Test). Despite several drawbacks of Dry Sieving Tests, such as the amount of time required; tendency of glass beads to become trapped, including trapping of glass beads inside the geotextiles; likelihood of imprecise preparation of glass beads; and potential electrostatic effects, the largest pore size (apparent opening size [AOS], O95) results obtained from Dry Sieving Test still determines many filtration criteria. Although the Capillary Flow Test was approved in 2002, it is still not widely adopted, despite the fact that it provides the largest pore size (Bubble Point, O98) and a complete pore size distribution of a geotextile. Decades of analyses searched for a correlation between the Dry Sieving and Capillary Flow Test results; however, none of them have been widely accepted because of the limited number of geotextiles used and a lack of proper calibration. The current study investigates a possible correlation between the Dry Sieving and Capillary Flow Test results with 51 woven, nonwoven, and composite geotextiles. The Capillary Flow Porometer was calibrated using four thin metal plates with known pore openings and two membranes. This study describes the challenges experienced during the Capillary Flow Test and factors affecting the test results. One finding is that the cleaning of calibration materials and equipment with Methanol plays an important role in the Capillary Flow Test results. The use of different shape factors, contact angles, and wetting liquids in the analyses are also considered. The outliers of Capillary Flow Test results were removed from the analysis using a box plot and whisker diagram, and a good correlation between AOS and Bubble Point (R2 = 0.78) was established.

Field Evaluation of Coir Geotextile Reinforced Subgrade for Low Volume Pavements

ABSTRACT This investigative study focuses on the response of full scale coir reinforced low volume roads when subjected to static loading. The test track of 1.736 km consists of a control section and eight reinforced sections including two types of coir geotextiles and subbase with varying thickness. An assessment of the general behavior of coir geotextile-reinforced sections, to static plate load tests, California Bearing Ratio tests, geogauge and dynamic cone penetration tests is done for evaluation. The study summarizes the results of the executed tests on the reinforced test track in comparison to the unreinforced one. The results reveal that the geotextile with higher apparent opening size is not as good as that of the finer mesh geotextile. A maximum of 112% improvement in the elastic modulus of subgrade is achieved by using a woven coir geotextile of 740 g/m2 mass per unit area whereas 70% increment is attained while using an alternate geotextile of 365 g/m2 mass per unit area. The elastic modulus values are determined from the various field tests and the overall damage analysis is carried out using KENPAVE software. From the analysis, it is noted that an appreciable decrease in the aggregate layer thickness is achieved by using coir geotextile as reinforcement. Use of coir geotextiles in pavements as a reinforcement can therefore help in reducing the demand and consumption of fast-depleting natural resources.

Estimating Optimal Geotextile Type for Controlling Soil Erosion

One of the major functions of geotextiles is to control soil erosion. Apparent opening size and permeability of non-woven geotextiles are properties that control erosion. In this manuscript, soil taken from an eroded pond is considered for the study. Filtration and clogging behavior of the several geotextiles are studied under laminar flow conditions and at three different hydraulic gradients. Results facilitate selecting the appropriate geotextile based on permeability, filtration and clogging for use as erosion control.

Experimental assessment of geotextile serviceability lifetime as ballasted railway filter focusing on clogging phenomenon

Abstract In this research, the main goal is investigation of the clogging phenomenon of geotextile, as a separator material between the ballast and subgrade of railway track. Firstly, a Slurry Pumping Simulator Apparatus (SPSA) has been developed. Using SPSA, the performance of geotextile filter is assessed subjecting to different conditions of silt slurry pumping. For this purpose, the slurry density (soil over water weight ratio), slurry pumping frequency and geotextile Apparent Opening Size (AOS) have ranged between 1 15 t o 1 2 , 3 to 10 Hz and 0.06 to 0.2 mm, respectively. Also, slurry pumping pressure has chosen as 97, 117 and 141 kPa. In this regard, the ratio of slurry passing flow rate in proportion to water passing flow rate through geotextile, was considered as a determinative parameter. The results indicated that increase in slurry density and decrease in AOS cause geotextile clogging time reduce while the variation of slurry pumping pressure does not remarkably influence that. Furthermore, an equation was derived for the ratio of slurry passing flow rate in proportion to water passing flow rate through geotextile in which the examined parameters varied. Eventually, a numerical example was solved using the proposed equation.

Measuring hydraulic properties of geotextiles after installation damage

Since geotextiles have been progressively incorporated into coastal protection structures, the influence of installation damage on them has been the primary concern. During installation/construction, geotextiles are repeatedly subjected to high mechanical stresses which often exceed service stress. It is therefore vital to evaluate the mechanical and hydraulic damage and determine the consequences of these damages to better develop criteria for selection of suitable products. As these damages could reduce the material's mechanical strength and hydraulic efficiency, or in the severest form of damage, puncturing, would end the separation function. The properties investigated in this paper include the permittivity and apparent opening size (AOS) of geotextiles. Generally, the greater the drop energy of armour units applied to geotextiles, the greater the potential for damage. Findings show that the residual permittivity could increase significantly, 45% during installation. The preliminary design of coastal structures will be optimised as engineers and designers can better estimate the amount of damage on geotextiles upon installation.

Influence of nonwoven fabric pore sizes on water vapor resistance

The influence of nonwoven fabric pores using the Brunauer–Emmet–Teller method, dry sieving and capillary flow porometry on water vapor resistance were investigated. For a better understanding of the nonwoven thickness impact on pores and water vapor resistance (and therefore the influence on comfort), two types of samples were investigated: nonwoven fabric bonded with the needling and nonwoven fabric additionally bonded with the calendering process. Water vapor resistance increased with increasing nonwoven fabric thickness, whereby it ranged from 11.33 to 15.62 m2 Pa W−1 for the non-calendered samples and it ranged from 5.19 to 9.85 m2 Pa W−1 for the calendered ones. Water vapor resistance showed a good linear correlation with the specific surface area, pore volume, apparent opening size and mean flow pore diameter.

Stability Analysis and Design of offshore Submerged Breakwater Constructed Using Sand Filled Geosynthetic Tubes

Kadalur Periyakuppam (KPK) is a fishing village located 70km south of Chennai in Tamil Nadu. The coastline of KPK was subjected to severe erosion due to high energy waves during Thane (2011), Nilam (2012) and Madi (2013) cyclones. The Tamil Nadu Fisheries department facilities located near the coast is subjected to damage as the coastline has receded by 45 m in the last few years following the severe erosion caused by cyclones. Since most of the erosion occurred after the storm waves hit the shoreline, sustainable option for shoreline protection would be to shift wave breaking to deeper depths. Based on numerical model studies and assessment of shoreline behaviour over two years, it is proposed to construct a submerged segmented breakwater. The submerged breakwater is proposed to be constructed at 4 m water depth up to a height of 3.5 m using sand filled geosynthetic tubes. Geosynthetic tubes shall be placed in a stacked manner with 2 tubes of 1.5 m high each at the bottom and a tube of 2.5 m height at the top accounting for height loss due to settlement. Design and stability checks are carried out by using available literature as no standard methods or design codes are available for design or stability checks for the geosynthetic tubes. The breakwater structure is checked for stability against sliding, overturning and bearing capacity. The geosynthetic tube material specifications such as tensile strength, ultra violet ray resistance, apparent opening size and fabric material are calculated using suitable design methods. The scouring, in front and behind the breakwater structure under prevailing wave conditions, is estimated for designing scour protection.

Treatment of domestic greywater by geotextile filter and intermittent sand filtration bioreactor

Intermittent sand filtration (ISF) is an efficient system for treatment of greywater; however, the high quality of effluent and the simple set-up contrast with the high failure rate due to clogging of surface layers. The efficacy of several polypropylene non-woven geotextiles (apparent opening size from 0.10 to 0.18 mm) used as primary treatment filters to remove suspended particles from domestic greywater and the effects of this pretreatment in the performance of fine and small media size (0.3 and 0.6 mm) ISFs was examined. Results showed geotextile achieved suspended solids (SS) removal rates from 25 to 85% and chemical oxygen demand (COD) from 3 to 30%; although the portion larger than 75 μm was removed at higher rates (55–90%), particles smaller than the nominal pore size of the filter were also captured. Geotextile used as pretreatment resulted in improvement of lifetime of the ISFs over an experimental run of 60 days. The vertical profile of volatile organic matter in the ISFs was evaluated at the end of the experiment and it showed a clear reduction in the accumulation of organic material on the top layer of the ISFs, effectively avoiding its early failure by accumulation of solids.

Recreational water quality response to a filtering barrier at a Great Lakes beach

Recent research has sought to determine the off- or onshore origin of fecal indicator bacteria (FIB) in order to improve local recreational water quality. In an effort to reduce offshore contamination, a filtering barrier (FB) was installed at Calumet Beach, Lake Michigan, Chicago, IL. A horseshoe-shaped curtain (146 m long, 0.18 mm apparent opening size, 1.5–1.6 m deepest point) was designed to exclude FIB containing or promoting debris and thus reduce the number of swimming advisories during the examination period of July through September 2012. Mean water Escherichia coli concentrations were significantly lower at southern transects (S; outside FB) than at transects within the FB (WN) and at northern transects (N; outside FB) (1.45 log (MPN)/100 ml vs. 1.74 and 1.72, respectively, p < 0.05, n = 234). Turbidity was significantly higher at the WN transects (p < 0.001, n = 233), but it tended to increase throughout the sampling season within and outside the FB. E. coli in adjacent foreshore sand was significantly lower at the WN transects. A combination of factors might explain higher E. coli and turbidity within the FB including increased sediment resuspension, trapped algae, shallowing within the FB, and large lake hydrodynamic processes. This remediation approach may find better use in a different hydrodynamic setting, but the results of this experiment provide insight on sources of contamination and nearshore dynamics that may direct future beach management strategies.

Geosynthetic Filters for Water Quality Improvement of Urban Storm Water Runoff

AbstractSuspended solids in highway storm water runoff create a wide range of water quality problems; their removal lessens the deleterious impact of storm water runoff on aquatic ecosystems. In this study, three geotextiles were tested in a laboratory setup with influent suspensions having a hydraulic loading rate, total suspended solids (TSS) concentration, and particle size distribution similar to those reported for urban highway storm water runoff. Results indicated that after a short ripening period, a geotextile with an apparent opening size of 150 μm can effectively remove suspended solids to below a target concentration of 30 mg/L. The results also showed that the change in hydraulic conductivity of the geotextile filter system can be related to suspended solids captured via a power function, which may be used to predict the flow rate through the filter during its life span. New retention criteria specifically for storm water filtration are introduced for geotextiles.

Retention performance of woven geotextiles subjected to cyclic-flow conditions

ABSTRACT: Woven geotextiles are widely used as filters in geotechnical, hydraulic, and environmental applications. Depending on the application, geotextile filters can be subjected to uni-directional, bi-directional, or cyclic-flow conditions, with cyclic flow occurring in two directions repeatedly over time. The selection of a suitable geotextile filter is of critical importance, particularly for cyclic-flow conditions. Cyclic-flow conditions can rapidly lead to an excessive loss of fine soil particles and failure of a soil–geotextile system. Although these conditions are frequently encountered, limited work has been done to evaluate the retention behavior of geotextiles under cyclic-flow conditions. In this study, the retention performance of nine different woven geotextiles with five different soils under cyclic-flow conditions was modeled using a bi-directional hydrodynamic filtration test (BHFT). Based on the results of this research, a retention criterion of AOS/d85 of 1.62 is proposed for woven geotextiles subjected to cyclic-flow conditions, where AOS is the apparent opening size of the geotextile or O95 as determined by dry sieving ( ASTM D4751 ) and d85 is the soil particle diameter corresponding to 85% by weight of finer soil particles. Additionally, an allowable soil-loss limit less than 5000 g/m2 is proposed.

Geosynthetic Filters for Water Quality Improvement of Urban Stormwater Runoff

A properly designed geotextile can effectively capture suspended solids in highway stormwater runoff through a filtration mechanism while maintaining minimal head loss. Because these solids can often carry hazardous pollutants, their removal lessens the deleterious impact of stormwater runoff on aquatic ecosystems. In this study, a geotextile was tested in the laboratory with influent suspensions having a hydraulic loading rate, total suspended solid (TSS) concentration, and particle size distributions similar to those reported for urban highway stormwater runoff. Preliminary results indicate that after a short priming period, a geotextile with an apparent opening size of 150 µm can effectively remove suspended solids to a target concentration of 30 mg/L, a common point discharge water quality target value. The results also showed that the change in hydraulic conductivity of the geotextile filter system can be related to suspended solids captured via a power function, which may be useful to predict the flow rate through the filter during its lifespan.

Effect of Contaminated Suspended Solids on Water and Sediment Qualities and Their Treatment

Abstract Suspended solids (SS) have been discharged into water areas such as rivers, lakes, and ponds. The SS adsorb various contaminants such as heavy metals and nutrients and also form sediments by sedimentation. Therefore, contaminated SS will be able to influence not only the water quality, but also the sediment quality. In order to understand the effect of contaminated SS on the water and the sediment, SS and sediment samples were obtained from the des Hurons River in Canada. In addition, laboratory filtration tests were performed to develop a technique for removal of the SS. A downward filtration system was used with a nonwoven geotextile as a filter medium. The apparent opening size (AOS) and the thickness of the filter were 150 μm and 0.2 cm, respectively. For the investigation, the results showed that both SS and the sediments contained heavy metals with concentrations in the SS higher. In particular, zinc concentrations of the SS were approximately from two to five times higher than the Canadian guideline for sediments. In addition, it was found that SS concentrations were associated with chemical oxygen demand (COD) and total phosphorus (T-P) concentrations. Therefore, it was found that SS can play an important role in the water and the sediment qualities. The laboratory filtration tests showed the SS were reduced from 32 mg/L to 2 mg/L or less by the nonwoven filter. Thus, SS removal will improve not only the water quality, but also the quality of the bottom sediments.

A Study on Thermally Bonded Geotextile Separator and Properties of Waste Landfill Application of PVA Geotextile/HDPE Geomembrane Composites

This paper is concerned with geotextiles bonded chemically with geogrid to form a geocomposite. Geotextiles, thermally bonded and non-woven, play an important role as a separator. Also, this study investigates the resistance to the application environment of geotextile composites. Here, numerous tests have been performed and it was revealed from experimental results that thermally bonded geotextile in geosynthetic composites showed superior characteristics to that manufactured from needle punched non-woven method in terms of tensile strength, tensile strain and high separation performance. It was noted from experiments that the geotextile prepared for separation purpose and manufactured in a thermal bonding method showed relatively low permittivity so that it could be used as a smooth separator. In addition, PVA geotextile/HDPE geomembrane composites were designed and manufactured to investigate the waste landfill related properties. Numerous experiments have been performed and experimental results were summarized to evaluate practical applicability of PVA geotextile/HDPE geomembrane composites. Among the properties of proposed geomembrane composites, evaluation has been focused on the investigation of mechanical properties, AOS (apparent opening size), permittivity and ultraviolet stability.

The influence of uniaxial tensile strain on the pore size and filtration characteristics of geotextiles

The influence of uniaxial tensile strain on the pore size distribution and filtration characteristics of geotextiles is studied. An experimental apparatus was designed and used to conduct tests for pore size distribution, flow rate through the geotextiles and the gradient ratio. Four geotextiles made of polypropylene (two heat-bonded nonwoven and two slit film woven) were studied. Throughout the test series, the geotextiles were stretched to maintain 5%, 10% and 20% in-plane uniaxial strains. The strained specimen test results were compared with those from unstrained specimen. The experimental results illustrate the pore size and the mean flow rate through the plain geotextiles increase with the increase in tensile strain. The differences in changed percentages for apparent opening size and flow rate between the two nonwoven geotextiles are much higher than those between the two woven geotextiles. The increase in tensile strain results in reduction in the gradient ratio for the soil–geotextile system. This effect is more pronounced for nonwoven geotextiles. More testing is recommended to gain a deeper understanding into tensile strain effect on various geotextiles.

Bubblepoint Testing of Geotextiles: Apparatus and Operation

Abstract A simple, inexpensive device for measuring geotextile pore sizes, using ASTM D 6767, is described and its operation is outlined with guidance for correct operation. The accuracy and consistency of the test are shown. The test appears to have better consistency than the apparent opening size (AOS) test, avoids the inherent and operator-dependent problems of theAOS test, and further, describes the entire pore size distribution of a geotextile, making it useful for developing a more complete filter criterion. Suggestions are made for improving ASTM D 6767.

Water retention of nonwoven polyester geotextiles

Planar polymeric geotextile materials are increasingly used in geotechnical and geoenvironmental engineering applications to perform various functions such as filtration, drainage and reinforcement. In most cases, they are placed above the groundwater table where soil and geotextiles pores are filled with water and air (i.e. under unsaturated conditions). In this respect, the development of the geotextile water-retention curves is of great importance to model the transient water flow in earthen systems containing geotextiles where unsaturated conditions may prevail. This paper, presents the results of a study on the cross-plane and in-plane water-retention characteristics of two nonwoven, polyester geotextiles. The geotextiles’ cross plane water-retention data demonstrated their hydrophobic nature with both specimens being essentially non-conductive to water beyond suction heads of 0.2–0.3 kPa. Pore size and porosity seemed to have a controlling effect on both the desaturation and resaturation processes. The geotextile with the larger apparent opening size and porosity de-saturated at very low suction pressure (0.4 kPa), whereas a slightly higher suction (0.9 kPa) was needed to de-saturate the geotextile with smaller apparent opening size and porosity. Both specimens exhibited significant hysteresis in their water-retention function, such that at a given suction a geotextile contained more water when drying than when wetting. The in-plane water retention of drying geotextiles indicates that both geotextile specimens absorbed no water at suctions greater than zero; thus the water retention of a dry specimen in the in-plane direction is effectively equal to zero. This implies that the geotextiles used in the present study were more hydrophobic in the in-plane than the cross-plane direction during wetting.