De-Aired Geotextile Permeability Tester – QualiGTX™ GPT D
The QualiGTX™ GPT D de-aired geotextile permeability tester evaluates the vertical water flow properties of geotextiles and related materials under zero-load conditions. Developed by Qualitest North America, this system features a de-aired, temperature-regulated water supply that minimizes measurement errors caused by entrained air in conventional permeability testing. An industrial touchscreen computer automates specimen clamping, hydraulic head positioning, test timing, and calculations. The system directly determines the vertical permeability coefficient, eliminating manual stopwatch operation and calculations.
Designed for civil engineering laboratories, geosynthetic manufacturers, and infrastructure quality-control facilities, the QualiGTX™ GPT D helps verify filter fabric performance before installation in subgrades, embankments, and drainage structures. It accommodates 50 mm specimens, applies a user-defined head difference of up to 250 mm, and measures the water volume passing through the specimen over a specified period. An integrated dissolved oxygen analyzer verifies that the test water satisfies the deaeration requirement before testing begins. Completed results can be generated as reports and uploaded or printed directly from the control station.
The instrument features interchangeable water-supply configurations, allowing multiple vertical permeability testing protocols to be performed without changing hardware. Operators select the appropriate configuration through the touchscreen, and the system automatically directs water through the corresponding supply unit. Its 50 L stainless steel thermostatic tank uses PID temperature control to maintain water temperature within ±0.5 °C. This stability is essential because temperature affects water viscosity and consequently influences measured flow rates. These controlled conditions support consistent and repeatable results across different operators, work shifts, and seasonal conditions.
De-Aired Geotextile Permeability Tester – QualiGTX™ GPT D Applications
The QualiGTX™ GPT D is designed for testing geosynthetic filtration and drainage materials used in civil engineering, hydraulic infrastructure, and transportation projects.
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Geotextile Manufacturing Quality Control: Verifies production batches of woven and nonwoven geotextiles against specified permittivity and water flow-rate values before shipment.
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Highway and Roadway Construction: Evaluates separation and filtration fabrics installed between subgrade soils and aggregate base layers for construction acceptance.
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Dam, Levee, and Canal Engineering: Assesses filter materials designed to allow seepage water to pass while preventing fine soil particles from escaping through the fabric.
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Railway Subgrade Engineering: Qualifies geotextiles used to minimize mud pumping and maintain effective drainage beneath railway ballast.
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Port, Coastal, and Reclamation Works: Tests geotextiles used in revetments, breakwater cores, and dredged-material containment applications subject to continuous hydraulic loading.
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Landfill and Environmental Containment: Checks the performance of leachate collection and drainage materials positioned above liner systems.
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Erosion Control and Land Drainage: Evaluates filtration fabrics used in French drains, trench drainage systems, and slope protection installations.
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Third-Party and Certification Laboratories: Provides independent verification of supplier test data for project acceptance and tender documentation.
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Materials Research and Product Development: Compares fiber compositions, pore structures, and manufacturing methods based on measured cross-plane water flow performance.
De-Aired Geotextile Permeability Tester – QualiGTX™ GPT D Key Features
The QualiGTX™ GPT D integrates water conditioning, automated specimen handling, and automatic result processing into a single floor-standing testing system.
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Integrated De-Aeration and Thermostatic Water System: Conditions test water within an integrated circuit, eliminating the need for separate vacuum deaeration equipment and additional transfer procedures that could introduce air back into the water.
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Dissolved Oxygen Measurement System: Displays oxygen concentration in mg/L, percentage saturation, and partial pressure to document compliance with the required water deaeration conditions.
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Industrial Touchscreen Computer Control: Provides guided test setup, automated run recording, and parameter storage to maintain consistent operating procedures between technicians.
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Automatic Specimen Clamping: Positions and seals specimens automatically without manual tightening, reducing edge leakage and variations caused by operator handling.
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Automatic Head Positioning: Moves the testing assembly to the specified hydraulic head difference and establishes the required position without manual leveling or shimming.
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Constant Water Level Device: Maintains a stable driving head throughout the test to prevent changes in the hydraulic gradient.
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Two-Unit Lateral Supply Stabilization: Quickly establishes the target hydraulic head and reduces surface fluctuations, minimizing the stabilization time required before measurements begin.
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Switchable Supply Configurations: Allows operators to select different testing protocols through the control panel, enabling one instrument to perform the work of multiple dedicated permeameters.
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Automatic Flow Collection and Timing: Records collected water volume against elapsed time with 1 s resolution, removing timing inconsistencies associated with manual stopwatch operation.
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Automatic Permeability Calculation and Reporting: Processes measured flow data to determine the vertical permeability coefficient and prepares reports for direct uploading or printing.
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304 Stainless Steel Wetted Parts: Uses corrosion-resistant 304 stainless steel for the specimen clamp and water tank, supporting long-term durability under continuous water contact.
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Electrostatic Powder-Coated Working Vessel: Provides a durable protective coating over the stainless steel surface for reliable operation in humid laboratory environments.
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Corrosion-Resistant Silicone Sealing Rings: Maintain an effective specimen seal through repeated clamping cycles while resisting hardening and leakage.
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Adjustable PID Control with Auto-Tuning: Enables users to adjust the temperature control loop to suit laboratory operating conditions rather than relying exclusively on fixed factory settings.
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Temperature Deviation Correction: Allows temperature readings to be adjusted in 0.1 °C increments to support accurate viscosity-related corrections.
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Internal and External Circulation Modes: Supports internal circulation during testing and external circulation for transferring conditioned liquid to other vessels for heating or cooling, expanding the system's laboratory applications.
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Outdoor Condenser Unit Cooling: Transfers compressor heat outside the laboratory, helping reduce indoor heat accumulation and energy consumption during extended temperature-holding periods.
Theory and Method
Geotextile permeability testing is based on Darcy's law, which describes the relationship between fluid flow through a porous material and the hydraulic gradient across it. The QualiGTX™ GPT D maintains a constant hydraulic head difference across a secured specimen and measures the volume of water passing through a defined area during a controlled time interval. Dividing the volumetric flow rate by the specimen area and hydraulic head difference determines permittivity, representing water flow per unit area and unit head. Multiplying the permittivity by the specimen thickness provides the vertical permeability coefficient used in drainage and filtration engineering design.
Dissolved air is a significant potential source of measurement error during permeability testing. Tap water contains dissolved oxygen and nitrogen, which can separate from the water when pressure conditions change, forming microscopic bubbles within the fine pore structure of nonwoven geotextiles. These bubbles obstruct water flow paths, reduce the measured flow rate, and produce permeability results lower than the material's actual performance. To minimize this problem, the QualiGTX™ GPT D removes dissolved gases from the test water before measurement and verifies the deaeration level using its integrated dissolved oxygen analyzer.
Water viscosity decreases as temperature increases, allowing a geotextile specimen to pass more water at 30 °C than at 15 °C under otherwise identical conditions. Standard testing methods account for this temperature-related variation by correcting measurements to a reference temperature. However, accurate correction requires the water temperature to remain known and stable throughout testing. The QualiGTX™ GPT D uses a PID-controlled thermostatic tank and circulating water system to maintain temperature within ±0.5 °C while providing temperature measurement correction to ±0.1 °C. Its two-unit lateral water supply rapidly stabilizes the hydraulic head and minimizes water surface fluctuations, maintaining a consistent driving gradient throughout the measurement process.
De-Aired Geotextile Permeability Tester - QualiGTX™ GPT D Technical Specifications
| Parameter |
Specification |
| Maximum Head Differential |
250 mm |
| Specimen Clamp Inner Diameter |
Ø50 ± 0.5 mm |
| Maximum Specimen Thickness |
20 mm |
| Timing Range |
0 to 9,999 s |
| Temperature Measurement Range |
0 °C to 110 °C |
| Temperature Control Range |
5 °C to 100 °C |
| Temperature Accuracy |
±0.5 °C |
| Temperature Correction Accuracy |
±0.1 °C |
| Dissolved Oxygen Range |
0 to 20 mg/L; 0 to 200 %; 0 to 400 hPa |
| Dissolved Oxygen Accuracy |
±1.5 % FS |
| Dissolved Oxygen Repeatability |
±0.5 % FS |
| Dissolved Oxygen Resolution |
0.01 mg/L; 0.1 %; 1 hPa |
| Water Supply Tank Capacity |
50 L |
| Cooling Capacity |
13,000 W |
| Circulation Modes |
Internal and external |
| Temperature Control Modes |
Cooling and heating |
| Cooling Method |
Outdoor condenser unit |
| Compressor Power |
1.5 hp (approx. 1.1 kW) |
| Internal Circulation Pump Power |
100 W |
| External Circulation Pump |
100 W, adjustable flow |
| Circulation Pump Flow Rate |
45 L/min |
| Temperature Control |
PID with auto-tuning |
| Heating Time |
Room temperature to boiling, approx. 30 min |
| Cooling Time |
Boiling to 20 °C, approx. 90 min |
| Water Conditioning System Power Supply |
380 V, 50 Hz, 12 kW |
| Test Operation Power |
1 kW |
| Dimensions (W × D × H) |
1,380 × 780 × 1,870 mm |
| Weight |
160 kg |
