Coarse-grained soil vertical permeability deformation apparatus

Technical Parameters of Coarse-grained Soil Vertical Permeability Deformation Apparatus:

1. Test cylinder specification: ф300mm*600mm

2. Test cylinder height: 600mm

3. Water supply tank specification: ф510mm, height 500mm

4. Measuring cylinder: 1000ML

5. Measuring cylinder: 100ML

6. Total weight: 300kg

Operating Method of Coarse-grained Soil Vertical Permeability Deformation Apparatus:

1. Connect the lower water inlet to the water supply pipe, fill the apparatus with water, and check if there is any blockage or water leakage in the components. After inspection, lower the water supply tank so that the water level in the apparatus is level with the lower edge of the lower permeable plate.

2. Remove the top cover, lay a filter screen on the lower permeable plate, and apply a ring of waterproof material along the contact gap between the cylinder wall and the filter screen.

3. Open all piezometric holes to allow air discharge.

4. The sample should be filled in 3 to 5 layers, with each layer having the same gradation. The filling layer thickness: for sandy soil, it can be 2cm to 3cm; for gravelly soil, it can be 1.5 to 2 times the maximum particle size of the sample. If necessary, add water equivalent to 1% to 2% of the sample mass, mix evenly, and then proceed with filling.

5. Evenly layer each weighed sample into the measuring cylinder, compact it with a compaction hammer to the required height. For weathered rock debris or crushed soil, the vibration compaction method can be used.

6. Saturate the sample in the apparatus using the capillary saturation method. Adjust the height of the water supply tank so that the water level is slightly above the bottom surface of the sample, then slowly raise the water supply tank. For every 1cm increase, stabilize for 10 minutes before raising further. As the water level in the sample rises, connect the corresponding piezometric tubes until water overflows from the outlet, ensuring the sample is fully saturated. At this point, the water levels in all piezometric tubes should be level with the outlet water level.

7. Based on the fine particle content in the sample, preliminarily determine the failure mode of the sample's permeability deformation: for piping failure, the initial hydraulic gradient should be 0.02 to 0.03, with increments of 0.05, 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.70, 1.00, 1.50, 2.00, and thereafter increments of 1.00 to 2.00. When approaching the critical gradient, the increment should be appropriately reduced; for soil flow failure, the values can be appropriately increased.

8. Gradually increase the water head as specified above. After each increase, allow water to flow out for 30 to 60 minutes until stable, then record the water levels in the piezometric tubes and measure the seepage volume with a measuring cylinder. For each water head, take readings at least three times, with intervals depending on the seepage volume, typically 10 to 20 minutes, while also measuring the temperature of the inlet and outlet water. When the water levels and seepage volumes are stable over three readings, proceed to the next water head. Take the average of three closely matching readings as the test value. For non-piping soils, the duration can be appropriately extended.

9. Observe various phenomena during the test, such as the turbidity of the outflow, bubble emergence, fine particle movement or being carried away by water flow, soil suspension, changes in seepage volume and piezometric tube water levels, and describe them in detail. When signs of critical or failure gradient appear, adjust the gradient increment promptly.

10. End the test when the sample fails or the water head can no longer be increased. For permeability tests only measuring the permeability coefficient, the test can end after applying 1 to 2 more water heads after the critical gradient appears.

11. After the test, close the water inlet, remove excess water from the sample, observe changes in the sample, and measure the post-test height if needed. For loaded samples, unload promptly and observe rebound, remove the top cover, extract excess water, and remove the upper permeable plate. Drain all remaining water from the apparatus and dismantle the sample. If necessary, test the post-test particle gradation.

12. During the test, it is advisable to plot the relationship curve between hydraulic gradient and seepage velocity. Use hydraulic gradient as the vertical coordinate and seepage velocity as the horizontal coordinate on double logarithmic graph paper. If necessary, also plot the relationship curve between seepage velocity and time. Adjust the duration of each water head and the head difference based on curve changes.

13. The organization of test results should comply with DL/T5356-2006 requirements.

14. Clean up after the test for next use.