A possible device that can utilize the Advanced Permittivity Testing Method for geotextile purposes is shown in Figure 6.1a, where the flat specimen, mounted in the specimen holder, is first inserted into the device. By means of the thrust shaft, the drive motor moves the pistons at the same rate, forcing the fluid through the specimen fabric at a controlled rate.  A motor controller will hold a variety of constant motor speeds to determine geotextile permittivity.

Figure 6.2a illustrates possible specimen holder configurations. Of course, the effective area of the specimen A=pd²/4.  Silting experiments and sedimentation flow can be conducted, as shown in Figure 6.2b, using graded silts, here shown of thickness t.   Flow reversal will indicate the blocking effect of the silt.

Figure 6.2 Possible flat Specimen Holder Design

The permittivity testing procedure is fully automated, as shown in Figure 6.3, using the electric valve for fluid control. Automatic motor sequencing permits a full series of tests to be run by a specially programmed central processing unit. In this manner, reproducible permittivity determinations can be made for geotextiles.

Figure 6.4a represents an example of the initiation stage of a fully automated testing procedure using the Advanced Permittivity Testing Method. After the specimen holder has been inserted, the fluid chambers are evacuated to remove air bubbles from the fabric. The electric valve then connects the test chamber to the fluid source, as shown in Figure 6.4b, and a previously de-aerated fluid is then automatically injected into the test chamber.

Figure 6.4 Initial Valve Sequencing

Piston motion at a fixed specified speed is initiated, forcing the fluid through the flat specimen, with the pressure difference across the fabric recorded.  Piston motion is then reversed. This process is repeated at different motor speeds to obtain the information required to calculate the permittivity, as shown in Figure 2.2. If any deviation from linearity appears, this can be readily discerned.

Test completion is represented by Figure 6.5a. The fluid is evacuated from the chambers, as represented by Figure 6.5b, and air is then bled into the chambers. The specimen holder can then be removed. Figure 6.6 shows a possible design of a commercial geotextile testing device using the Advanced Permittivity Testing Method. The passage of particulate matter into and out of the fabric can be directly observed. Operation is fully automated.

For example, to determine the pore-size distribution of a geotextile fabric, a soil or silt sample is washed through the geotextile and the distribution of the soil particles passing though the fabric is determined. The sample is vibrated vertically to cause fluid surges in the soil. The tested geotextile can then be used to classify various soils according to particle size distribution.

The advanced geotextile permittivity tester can readily emulate a granulometric device. Fluid surging is provided simply by programing the piston drive to pulse. The soil passing though the geotextile would be collected, for example, in a device, shown in Figure 6.8.