IGS TC-H: Recent Advances in Geotextile Filtration Design: Pore Opening Size Measurement

Name: IGS TC-H: Recent Advances in Geotextile Filtration Design: Pore Opening Size Measurement
Uploaded: 2022-04-28T16:07:57.000Z
Duration: 3 h 26 min 51 s

Introduction to the Webinar

Welcome and Overview

Eric Blong, chairman of the technical committee on hydraulics of the IGS, introduces a 90-minute program focused on measuring the pore opening size of geotextiles.

Attendees are encouraged to use the Q&A button for questions, with ample time allocated for discussion at the end of the webinar.

Acknowledgments and Importance

Sam Allen, co-chairman, praises Eric Blong's leadership in addressing water preservation and filtration issues within engineering communities.

Sam invites attendees to engage with IGS technical committees post-webinar, emphasizing their significance in advancing geosynthetic technology.

Filtration Design Considerations

Geotextile Functionality

Eric begins discussing existing measurement techniques for pore opening sizes and their reliability based on experience.

The primary goal is to utilize geotextiles to retain particles while allowing water circulation, creating a filtering structure within soil rather than acting as a filter itself.

Retention Criteria

Effective filtration requires retaining larger soil particles while preventing clogging; certain materials like German drains cannot be used due to being watertight.

Discussion centers around determining relevant values for geotextile opening sizes and measurement challenges faced by professionals in this field.

Measurement Techniques Overview

ISO Guidelines

Reference is made to ISO 18283 which provides guidance on designing geotextiles for filtration; it covers installation impacts and performance metrics.

Common Measurement Methods

Various techniques are discussed:

ASTM D4751: Dry sieving using glass beads (O95 value).

ASTM D6767: Capillary flow test providing a complete spectrum of opening sizes.

ISO 12956: Utilizes well-graded granular material (O90 value).

Emerging Techniques

Introduction of hydrodynamic sieving tests popular in Canada (FOS), alongside newer optical measurement techniques based on image analysis that lack standardized protocols yet.

Challenges in Measurement Techniques

Historical Context

The development of dry sieving methods dates back to the 1980s when resources were limited; reliance was placed on existing laboratory equipment prevalent at that time.

Technical Challenges

Static Electricity and Testing Challenges

Overview of Static Electricity in Testing

The initial experiment involved creating static electricity by rubbing glass on fabrics like polypropylene or polyester, similar to the AOS test using glass beads.

Factors affecting D4751 results include impact energy, glass bead preparation, and humidity levels; the standard lacks precision regarding energy ranges.

Increasing humidity in the sieving area reduces static electricity but remains a persistent issue; anti-static sprays are suggested as a solution.

Glass Bead Preparation and Cost Implications

Preparing glass beads through sieving is impractical due to clogging; sedimentation processes yield better-defined beads but at higher costs (around $100 per pound).

Reusing glass beads poses challenges as they fracture over time, necessitating limited recycling to maintain testing viability and manage costs.

Contamination Risks in Testing

The reuse of previously tested specimens is allowed by standards but increases contamination risks from retained static electricity and bead sizes.

Observations indicate that contamination can skew results significantly, emphasizing the need for stringent testing protocols.

Accuracy of Test Results Across Laboratories

In 2014, a project involving DuPont revealed significant variability in AOS test results across eight laboratories for five different products.

Results showed a range from 75 micrometers to 250 micrometers for one product type, highlighting inconsistencies in testing methodologies.

Addressing Static Electricity Issues

One laboratory experienced extreme static issues leading to failed tests; excluding this data reveals some consistency among other labs' results.

Alternative ISO tests mitigate static problems by running tests under wet conditions with well-graded materials, improving accuracy.

Hydrodynamic Sieving Technique (FOS)

FOS employs hydrodynamic sieving with water immersion to simulate field conditions effectively; it reflects real-world scenarios more accurately than traditional methods.

Despite variations among labs, FOS provides a more reliable measure of geotextile performance compared to AOS tests.

Material Considerations in Testing

Geotextile Filtration Techniques

Overview of Filtration Methods

Discussion on interpreting the judexcel as a sieve, contrasting it with filtering soil mixtures.

Introduction to bubble point technique, highlighting its application in fine-grained products like stone ceramics and advancements since the 1990s for geotextiles.

Correlation Between Techniques

Presentation of a workflow involving dry flow and correlation between bubble point and historical data from CGS, emphasizing excellent correlation with hydrodynamic sealing (fos).

Optical Measurement Techniques

Historical context of optical measurements used since the 1980s by the U.S. Army Corps of Engineers to measure percent open area in geotextiles.

Current opportunities for measuring opening sizes in thin geotextiles using optical sources; limitations noted for thick non-woven materials.

Testing Standards and Challenges

Summary of various testing standards: ASTM's poor repeatability may lead to challenges in acceptance testing due to tight specifications.

ISO 1296 presents fewer challenges but still shows high result dispersion; CGSB standard believed to best reflect salt filtration mechanisms despite limited laboratory participation.

Future Opportunities in Testing

Bubble point and image analysis techniques are highlighted as offering promising future opportunities for improved filtration testing methods.

Innovative Use of Barometers in Filtration Testing

Introduction to Barometer Use

Transitioning to Sam Allen’s presentation on barometers, focusing on their growing use within the geosynthetics community.

Challenges with Traditional Testing Methods

Emphasis on traditional filtration design challenges where products must balance maximizing water passage while limiting soil particle movement through controlled opening sizes.

Variability Among Geotextile Specimens

Understanding Geotextile Testing Challenges

Historical Challenges in Testing Practices

Eric highlights the historical challenges associated with high-quality testing practices, particularly in AOS tests that require washing geotextile samples to remove machining oils and lubricants which can interfere with glass bead movement.

The glass beads used in testing must be sieved or washed for size determination; they can change during testing due to collisions and fracturing, impacting test results.

Equipment stress during tests necessitates regular maintenance to ensure accurate operation, emphasizing the importance of how labs control these variables.

Permittivity and Water Quality

The sister filtration test measures permittivity based on water travel through the material plane, requiring a soaked specimen and removal of trapped air from the test water.

Clean de-aired water is crucial for this test's accuracy, as water quality significantly affects results. Temperature corrections are also necessary due to variations in permittivity related to test water temperature.

Everyday Filtration Systems

The discussion shifts to everyday filtration systems like HVAC filters that manage dust and biological media, highlighting their design considerations amid global health concerns such as pandemics.

Masks serve dual purposes: breathability while acting as barriers against viral loads. Both products undergo rigorous testing beyond just measuring their largest opening sizes.

Testing Equipment for Filtration Performance

A parameter is described as a benchtop piece of equipment measuring airflow through materials under varying pressures to determine filter resistance.

The dynamics of hydraulic flow are illustrated using a cartoon representation where inflow velocity and pressure differentials are key components in understanding permeate fluid behavior.

Constants in Fluid Flow Testing

Constants identified by Mr. Lacey's 2016 paper leverage physical variables derived from Darcy's law and energy conservation principles applied to flow through constrictions.

This methodology allows conversion of data obtained from one fluid type to another if densities are known, enhancing the versatility of testing procedures standardized under ASTM D4491.

Correlation Between Air and Water Permeability

Constant head permittivity at 20°C is calculated using standardized methods involving specific velocities at defined pressures (490 Pa).

Mr. Lacey’s research established correlations between needle punched and heat bonded geotextiles tested with both air and water, aiding laboratories in qualifying parameters for hydraulic property assessments.

Engineering Parameters for Geotextile Testing

It’s noted that parameters engineered for HVAC filters may not be suitable for geotextiles; appropriate sensors and flow meters must be utilized for accurate measurements.

Innovative Techniques in Determining Opening Sizes

An analogy is drawn with soap bubbles; knowing surface tension allows determination of ring diameter when blowing bubbles—this principle applies similarly when coating geotextiles with solutions under pressure.

Understanding Geotextile Testing and Permeability

Overview of Wet Testing Procedures

The pressure in pascals is measured during wet testing at flow rates of 1%, 2%, or 5% of the dry flow rate, which is established during permittivity testing.

Specimens are coated with mineral oil or other media to determine pore openings; as air pressure increases slowly, the largest openings release their oil coating first.

Two geotextile specimens with similar apparent opening sizes (AOS) are characterized for gradation and distribution of opening sizes, highlighting important variances in samples.

Importance of AOS Testing

Previous work by Tencate revealed that smaller AOS can lead to greater soil loss when tested under hydraulic wave action, challenging assumptions about geotextile performance.

The use of a perometer allows for better understanding and informed choices regarding product design by defining average pore size openings effectively.

Transition to New Testing Methods

Melissa Medlin introduces herself and discusses her involvement in the perimeter project aimed at improving AOS testing methods since 2008.

The impetus for this project arose from challenges faced around 2004–2005 regarding fabric performance discrepancies compared to expected data.

Collaboration and Research Development

Extensive research was conducted in collaboration with Syracuse University experts to enhance manufacturing-level testing based on over 30 years of prior research.

Presentations at ASTM sparked interest in developing better testing methodologies for AOS, leading to advancements in laboratory practices.

Features of the New Perimeter Instrument

The tri parameter instrument is compact and user-friendly, designed for easy operation on benchtops without the hazards associated with traditional methods.

Utilizes commercial-grade mineral oil as a wetting fluid due to its proven effectiveness across various materials while maintaining manageable surface tension properties.

Equipment Limitations and Testing Improvements

Flow Meter Challenges and Solutions

The equipment's performance is significantly influenced by flow meters, necessitating a dual-station approach for testing materials with varying flow characteristics.

A chart was developed to categorize different material styles, simplifying the training process for technicians, allowing them to perform tests accurately within days.

Issues with Static Electricity and Material Drying

Static electricity poses challenges during washing and drying processes, particularly in cooler months; smaller beads are especially susceptible to static attraction.

Non-woven samples can take an extensive time to dry, leading to potential loss of costly beads during testing phases.

Time Efficiency in Testing Procedures

Over the past decade, it has been determined that specimen preparation can be streamlined by die-cutting instead of washing and drying, reducing test run times to 30-45 minutes.

This efficiency is crucial for quality control in manufacturing as it allows quicker feedback on fabric quality.

Permittivity Testing Insights

The permittivity test also requires significant preparation time; however, simultaneous testing of pore size distribution can save time.

Variability introduced by different apparatuses and technicians can affect test outcomes; thus consistency is key.

Advancements in Laboratory Practices

Utilizing parameter C from D4491 eliminates soaking time, enabling concurrent tests which enhance overall efficiency.

Two independent laboratories are currently conducting round-robin tests using the perimeter method; this method is widely adopted among manufacturers for its ease of use.

Educational Use and Future Opportunities

Many universities have engaged in research utilizing the perimeter method over the last few decades, indicating its growing acceptance in academic settings.

While there are still challenges with very low pore sizes (e.g., 15 or 30), ongoing efforts aim to refine testing methods further.

Conclusion on Current Testing Methods

Filtration Design and Parameter Testing

Overview of Mineral Oil Utilization in Filtration Tests

The use of mineral oil has been successfully integrated into filtration evaluations, maintaining the primary tests as governing standards.

There is a correlation exercise necessary for users of parameter tests to ensure they align with primary test results, particularly for ASTM 40 44.91 and 47.51.

Ongoing efforts are being made to incorporate parameter test results into filtration design, driven by increasing demand from engineers focusing on dewatering applications.

Transitioning to New Standards in Geotextile Testing

Eric introduces the topic of assessing pore opening sizes in knitted geotextiles, emphasizing the need for new standards despite existing ones.

The specific properties of circular knit geotextiles necessitate a tailored approach due to their regular manufacturing process and low elastic modulus.

Challenges in Current Testing Methods

The ability to control yarn distance during production allows precise design of opening sizes; however, stretching during testing can affect measurements significantly.

ASTM D4751 attempts to standardize measurement but faces challenges due to human error when transferring specimens from pipes to holders.

Innovations and Improvements in Testing Procedures

Issues arise with small diameter pipes where traditional specimen sizes cannot be accommodated; innovative solutions are required for effective testing.

A new method involving a stiff plastic ring has been introduced to facilitate specimen handling, although it complicates the testing process and increases costs.

Future Directions and Considerations

Understanding the Challenges of Measuring Geotextiles

Limitations of Current Measurement Techniques

The discussion highlights limitations in measuring parameters for knitted circular knit geotextiles, particularly with lightweight non-woven structures, which complicate the measurement process.

High flow products pose challenges in controlling flow and pressure, making it difficult to accurately measure openings based on established equations.

Solutions for Improved Measurement

To address measurement difficulties, a solution was proposed to enhance stretching techniques for better control over specimen handling and opening measurements.

An optical measurement technique was developed to allow direct observation of pore dimensions without transferring specimens, minimizing manipulation.

Development of Optical Measurement Techniques

A dedicated stretching ring was introduced to control stress during measurements while avoiding the use of glass beads; this innovation aims for precision in capturing physical dimensions.

Reference is made to an existing standard from Australia (2012) that outlines techniques for determining opening sizes in circular knit geotextiles, suggesting room for improvement.

Collaborative Research Efforts

The project involved collaboration between Carrick as a manufacturer and CGIO's CTD group at Western University, focusing on developing optical testing parameters.

Expertise from a specialized research group at Western University played a crucial role in setting up complex optical tests necessary for accurate measurements.

Practical Implementation and Results

Initial steps included stretching specimens similar to ASTM tests; adequate stress levels were identified (typically 2.5 pounds), followed by microscopic imaging for precise measurements.

Understanding Pore Measurement Techniques

Differentiating Solid Parts from Voids

The discussion begins with an image that distinguishes solid areas from voids, emphasizing the measurement of dimensions, particularly the pore open area. While this is less critical for knitted socks, it holds potential for other products.

Key Parameters in Pore Measurement

The Ferret diameter and the ellipse fitting within the pore are identified as crucial parameters. The Ferret diameter measures the distance between two parallel lines around a given shape, while the ellipse represents its maximum and minimum diameters.

Reference Values and Testing Reliability

A reference value was necessary to assess measurements accurately. Initial reliance on AOS (Apparent Opening Size) was deemed unreliable, leading to a preference for FOS (Fabric Opening Size), which offers better reliability and repeatability.

Correlation Between Different Test Methods

The decision to use FOS as a reference stemmed from its superior reliability compared to AOS. This correlation allows for understanding how information can be transferred between different testing methods despite their varying precision levels.

Results of Image Analysis

Image analysis results were compared with FOS data, revealing good trends across various measurements such as major/minor ellipse diameters and Ferret's diameter. Notably, correlations showed an R² value greater than 0.95, indicating strong relationships despite some variations.

Impact of Measurement Methodology

The methodology used in measuring openings significantly affects results; gravimetric measurements differ from counting openings based on surface or volume definitions. This distinction leads to notable differences in measured values at 300 micrometers versus volumetric approaches.

Observations on Diameter Measurements

Optical Measurements in Geotextile Quality Control

Importance of Mean Diameter in Testing

The mean diameter is crucial as it represents the most likely size of openings on the surface, ensuring a higher chance that larger soil particles will pass through during testing.

Using optical results provides extensive data for circular net geotextiles, surpassing traditional manufacturing quality control methods by accurately measuring opening sizes and structural characteristics.

Correlation Between Opening Size and Factor of Safety (FOS)

An excellent correlation exists between the opening size measured optically and the factor of safety (FOS), with a constant correction factor applied to maintain consistency across measurements.

Different correlations can be used to extrapolate image opening sizes to AOS or ISO standards, emphasizing that consistent products yield reliable design values based on optical measurements.

Advantages of Optical Measurement Methods

Optical measurement tests are simpler than AOS or FOS tests, requiring fewer controlled parameters and avoiding issues related to beads. They also allow for non-destructive testing.

Efforts are underway to standardize this optical measurement method, with a draft expected soon for member feedback aimed at improving quality control processes.

Transition to Next Speaker

The presentation concludes with an introduction to Anne Lor from DuPont Luxembourg, who will discuss applications of optical measurements in manufacturing quality control for heat-bonded textiles.

Application of Optical Methods in Production

Overview of Production Lab Practices

Anne Lor shares insights into how her lab controls opening sizes using optical methods immediately after production.

The product range includes non-woven geotextiles made from polypropylene, with unit weights varying significantly depending on application needs.

Challenges with Traditional Measurement Methods

Traditional O90 measurement methods are time-consuming; they require specimens to be submerged in water for 12 hours before weighing and analyzing particle size distribution.

Development of Optical Tools

Over 20 years ago, an external company developed a quick optical tool that measures O90 values within 20 minutes while also calculating open area ratios efficiently.

Principles Behind Optical Measurement Techniques

Analysis of Optical Methods in Product Measurement

Overview of Product Length and Image Analysis

The length of the mozzarella product ranges from 4 to 5.2 meters, with over 1,000 images analyzed per specimen and a total of 10,000 for comprehensive analysis.

Unlike knitted stocks, the product exhibits non-uniformity in pore size, which is crucial for understanding its properties.

Image Processing Techniques

Counting parameters are based on stress thresholds; this involves analyzing highlights, shadows, backgrounds, and objects using grayscale values ranging from 0 to 255.

A threshold is set at a grayscale value of 190; pixels below this value are not considered relevant for analysis.

Calibration and Consistency Measures

Key parameters include light intensity and the size of pores defined by the small axis of an ellipse; these factors determine what granular materials can pass through the product.

Camera resolution is set at approximately 250 pixels with a minimum criteria established at 15 microns for exposure time.

Correlation and Validation Procedures

Light intensity is verified every shift (8 hours), ensuring consistency; monthly checks involve comparing reference symbols against defined values.

Quadratic correlation methods are employed four times a year to measure optical standards according to ISO guidelines.

Reporting Results and Limitations

Reports generated provide detailed information about product dimensions (e.g., width nearly four meters), open area data, and average optical scans conducted on over 900 images.

The optical method has been validated over two decades but is limited to thin products due to challenges with thicker materials like geotextiles.

Discussion on Filtration Design Proposals

A question raised regarding filtration design methods highlights diverging outcomes in literature; there’s a call for standardized procedures amidst varying design criteria.

Production and Quality Control of Geosynthetic Filters

Importance of Consistent Manufacturing

The production of geosynthetic filters emphasizes the need for a specific design porosity, which is crucial for manufacturing quality control.

A high-quality geosynthetic filter must be consistently manufactured to ensure efficiency in use and reliability in performance.

Variability in Filter Types

Different types of filters (knitted, needle punched, woven) require distinct manufacturing procedures tailored to their material properties.

This variability should not deter specifiers or researchers; instead, it allows for fine-tuning procedures that enhance filter consistency.

Evolution of Testing Procedures

The industry is transitioning from simple variable test procedures to more sophisticated measurement techniques aimed at ensuring consistent filter products.

Researchers are encouraged to stay informed about these advancements as they contribute significantly to product reliability.

Engineering Properties and Measurement Techniques

There isn't a one-size-fits-all procedure for measuring engineering properties like tensile strength; different materials necessitate tailored approaches.

For instance, testing methods vary between geogrids and geotextiles based on material type (polyester vs. polypropylene).

Standardization Challenges

The aspiration exists for a universal standard (like 4751), but currently, there are multiple testing options available (glass beads method vs. parameter test).

Future developments may introduce optical tests into the standard framework alongside existing methods.

Testing Efficiency and Methodology

Single Specimen Testing Approach

In parameter testing, specimens are tested individually rather than stacked; this enhances measurement speed without compromising accuracy.

Historical Context of Testing Methods

Previous methods involved stacking specimens to improve precision; however, modern techniques focus on individual specimen testing for efficiency.

Internal Challenges in Load Application

Applying load on geotextile specimens while maintaining flow measurement integrity remains an ongoing challenge within testing labs.

Ground Truth Considerations in Filtration

Reference Strategies in Filtration Testing

Establishing a reference point is essential due to the variability in filtration results across numerous tests.

General Filtration Concerns

In most scenarios, filtration issues are not critical if proper installation techniques are followed; thus, focusing on extreme cases is vital.

Risk Assessment in Specific Situations

Filtration Testing and Ground Truth in Geosynthetics

Understanding Ground Truth in Filtration Tests

The speaker emphasizes the importance of conducting filtration tests to establish a "ground truth," which includes understanding manufacturer specifications and product porosity.

They agree with Eric on the significance of proper procedures, highlighting that different measurement methods can yield varying results, particularly in applications like coal ash fines and geotube design.

A variety of performance-oriented filter tests are discussed, stressing that it's not just about the geotextile itself but also its relationship with other materials, which is crucial for accurate filtration performance assessments.

The speaker suggests that future webinars will focus on filtration performance tests as a necessary step for industry advancement.

Closing Remarks and IGS Overview

As the webinar nears its conclusion, the speaker invites final thoughts and shares information about the International Geosynthetic Society (IGS).

The IGS aims to promote understanding and appropriate use of geosynthetic technologies globally, striving for recognition as essential to sustainable development.

The organization comprises 44 chapters worldwide, including individual members and technical committees focused on various aspects of geosynthetics.

Upcoming conferences are highlighted, such as Eurogeo in Poland and Geo Asia in Taiwan, emphasizing opportunities for networking and knowledge sharing within the field.

International Geosynthetic Society Elections

Upcoming Council Elections

The speaker discusses the upcoming elections for the International Geosynthetic Society (IGS) council, indicating that now is an opportune time to join technical committees.

Sam is mentioned as a candidate running for the presidency of IGS, with the speaker humorously noting that he is likely to win since he is the only candidate.