Theory and Method
Geosynthetic thickness changes with the load placed on it. Nonwoven geotextiles, geonets, and drainage cores compress as pressure rises, so a reported figure means nothing unless the contact area, the applied pressure, and the dwell time are all defined. Test methods pin those variables down, then take the thickness as the perpendicular distance between the reference plate and the presser foot once the specified load has been held. The QualiGTX™ TG D fixes each of those conditions in software rather than leaving them to the technician.
Pressure at the specimen follows from force divided by presser foot area, which is why the two feet carry different weights for the same starting pressure. The 25 cm² foot at 5 N and the 100 cm² foot at 20 N both produce 2 kPa. Above that seating load the frame adds motor-driven force, and the 500 N capacity reaches 200 kPa on the 25 cm² foot, covering the upper pressure step that multi-pressure test methods call for.
Closed-loop control keeps the applied force on target throughout. The load cell feeds a measured value back to the controller, which corrects motor position rather than assuming the commanded travel produced the commanded load. Resolution stays at one part in 300,000 of full capacity across the whole range with no internal range switching, so a 5 N seating load resolves as finely as a 400 N compression step. Force reads within ±1% of indication and displacement within ±0.5%.
