Direct Shear and Pull-Out Friction Testing Methods
The geosynthetic direct shear and pull-out friction testing system offers comprehensive functionality for both types of tests. It's designed to be easily reconfigured when switching between direct shear and pull-out methods. In this article, we will walk you through the direct shear friction test method and the pull-out friction test procedure.
Direct Shear Friction Test Method
1. Place the sample flat on a rigid horizontal base located in the lower part of the shear box, with the front end clamped within the shear zone. If bonding is used, ensure that the sample adheres properly to the base (e.g., using alumina standard friction base, which can be unbonded). After bonding, the specimen should remain flat without any folds or wrinkles. No relative slippage between the sample and the base is allowed during the test.
2. Install the upper shear box by filling it with standard sand of pre-determined quality. The thickness of the sand should be uniform and approximately 50 mm. After compaction, the dry density should be around 1750 kg/m³.
3. Mount the horizontal loading device and apply a normal pressure of 50 kPa. This can be achieved by hanging a benchmark weight equivalent to 50 kPa, along with three additional standard weights. Each additional weight increases the normal pressure by 50 kPa.
4. Apply a horizontal load at a rate of 1 mm/min ± 0.2 mm/min. Record the shear force (T) and corresponding displacement (ΔL) at intervals of 12 seconds. The test continues until the cut surface reaches 16.5% of the total contact area, at which point the test ends automatically.
5. Steps to operate the system:
- 1) Turn on the power switch.
- 2) Enter the password "600" to access the system.
- 3) Select the desired test speed and press Enter.
- 4) Start the test. The system will automatically proceed through the normal stresses of 50 kPa, 100 kPa, 150 kPa, and 200 kPa.
- 5) Once the test is completed, the machine will stop, and the data will be displayed on the screen.
- 6) Confirm the results and view the test data.
- 7) Press OK to print the report.
Pull-Out Friction Test Method
1. Cut the specimen according to specifications. The width should be slightly less than the test chamber’s width, while the length should be sufficient to prevent breakage during the test.
2. Ensure that each test group includes at least 3 samples.
3. Reinforce the ends of the specimen to prevent excessive deformation during the test.
4. Carefully fill the lower part of the test box with soil based on the design requirements. Ensure the soil level is flush with the seam and the surface is smooth.
5. Place the specimen on the soil surface, aligning the pulling end with the seam. Ensure symmetry and gently cover the specimen with a thin layer of soil to secure its position.
6. Fill the upper half of the box with soil following the required density and conditions.
7. Secure the specimen in the tension clamp, ensuring even clamping at the center.
8. Place the top cover and apply the normal pressure. Allow time for consolidation as per the relevant test procedures.
9. Adjust the horizontal loading device and follow the test parameters. Use the up/down arrows to adjust the fixture position. Begin the test when the tension clamp starts to engage. Press start to record displacement and pull force. For sandy soils, the pulling rate is typically 5 mm/min.
10. Continue pulling until the peak pull-out force stabilizes, then stop the test.
11. Replace the specimen and apply a new normal pressure. Repeat the process for all required tests.
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