Uniaxial clay dispersibility pinhole tester accuracy ±0.5%

Dispersible clay refers to soil in which the cohesion between fine particles largely or completely disappears in low-salinity water (or pure water), causing the aggregated particles to disperse spontaneously into primary clay particles.

According to the theory of permeability, when water flows through soil pores, it transfers its kinetic energy to soil particles, thus dispersing them. The Pinhole test of dispersible clay simulates the flow rate, color, and pore size changes of water flowing through soil pores under a certain water pressure, reflecting the soil particles' ability to withstand water erosion and indicating the force required to separate the particles.

1. Place a filter screen (pore size <1 mm) and standard sand (particle size 1.25 mm–2.5 mm) at both ends of the sample for the pinhole test.

2. Add distilled water to the equipment to begin the test. Set the initial water head to 50 mm. If using a hose to connect the water tank and testing device, purge the air from the hose, water tank, and testing device before starting the test.

3. Record the time at the start of the test (or start a stopwatch), and measure the volume of water flowing through the sample using a graduated cylinder. If no water flows out at the start of the test, stop the test, open the testing device, and re-drill the hole.

4. Observe the color of the water in the graduated cylinder. The color can be divided into seven levels: very turbid, turbid, somewhat turbid, slightly turbid, visible to the naked eye, clear, and completely clear.

5. Conduct the test at a water head of 50 mm. If the water flowing out of the pinhole appears very turbid when viewed from above after 5 minutes, and the flow rate is 1.0 mL/s to 1.4 mL/s, the test is ended.

6. Open the pinhole testing device, remove the sample from the sample container, cut the sample along the direction of the pinhole, and measure the pinhole diameter.

7. If the final hole diameter is greater than 2 mm, the sample is classified as dispersible soil D1. If the flow rate and the final hole diameter are inconsistent, restart the test.

8. If after 5 minutes, the water flowing through the sample appears very turbid when viewed from above, and the flow rate is less than 1.0 mL/s, continue the test for another 5 minutes. After 10 minutes, if the water flowing through the pinhole appears turbid when viewed from above, stop the test and measure the aperture. If the flow rate is 1.0 mL/s to 1.4 mL/s and the aperture is greater than 1.5 mm, the sample is classified as dispersible soil (D2). If the water flowing through the pinhole appears relatively turbid when viewed from above, and the flow rate is 0.8 mL/s to 1.0 mL/s, and the aperture is no more than 1.5 mm, the soil is classified as transitional soil (ND4).

9. After 10 minutes, if the water flowing through the pinhole appears clear or slightly turbid when viewed from above, and the flow rate is approximately 0.4 mL/s to 0.8 mL/s, close the inlet valve and increase the water head to 180 mm at a rate of 50 mm/s to 60 mm/s. 10. At a water head of 180 mm, if the water flowing through the pinhole appears slightly turbid when viewed from above, and the flow rate is approximately 1.4 mL/s to 2.7 mL/s, stop the test and measure the hole diameter. If the hole diameter is greater than or equal to 1.5 mm, the soil sample is classified as transitional soil ND3.

10. At a water head of 180 mm for 5 minutes, if the water flowing through the pinhole is completely clear or contains barely visible particles, and the flow rate is approximately 0.8 mL/s to 1.4 mL/s, close the inlet valve and increase the water head to 380 mm at a rate of 50 mm/s to 60 mm/s. At a water head of 380 mm for 5 minutes, if the water flowing through the pinhole gradually becomes slightly turbid when viewed from above, or the flow rate is approximately 1.8 mL/s to 3.2 mL/s, stop the test; the soil sample is classified as transitional soil ND3.

11. After 5 minutes at a water head of 380 mm, if the water flowing through the pinhole is completely clear with a flow rate of approximately 1.0 mL/s to 1.8 mL/s, increase the water head to 1020 mm at a rate of 50 mm/s to 60 mm/s. After 5 minutes at a water head of 1020 mm, if particles are visible to the naked eye when viewed from above in the water flow through the pinhole, or if the flow rate exceeds 3.0 mL/s and the pinhole diameter is <1.5 mm, then the soil sample is classified as non-dispersed soil ND2; otherwise, the soil sample is classified as non-dispersed soil ND1.