Anchor plays an important role in construction projects, especially in tunnel and slope engineering. It stabilizes the surrounding rock or soil. Therefore, for the anchors to perform better, various tests are evaluated with two main indicators of Anchor pullout force.
Anchor Force and Pullout Force
Even though these terms look similar, they refer to different aspects of the anchor’s performance.
We will explore the differences between these forces, and the purpose of the pullout force test. Also, let’s look at the key precautions to ensure reliable results.
Anchoring Force and Pullout Force – The Difference
- Anchor Force
During the anchoring process, the anchor force helps indicate the strength of the anchor. The higher the anchoring force, the more reliable the anchor’s performance, and the better the anchoring effect. It represents the maximum force the anchor can hold without failing.
- Pullout Force
Pullout force is a testing index that is used during the process of anchor production. Simply, it measures the force that is required to pull the anchor out of its position. It deals with resistance that is caused by the deformation of the metal as well as the friction between the metal and the mold wall.
The pullout force reflects the anchor’s initial pullout resistance before it fails, therefore the pullout force should be less than the anchoring force.
Anchor Pullout Force Test – The Purpose
The main purpose of the anchor pullout force test is to assess the effectiveness of the anchoring system. This secures the surrounding rock of a roadway or tunnel. This test confirms the ability of anchors to hold them under stress and ensures that the anchors provide the support that’s required to prevent accidents like rockfalls and collapses.
Also, it evaluates the performance of,
- Anchor rods
- Resin
- Anchorage system
Inspection of Anchoring Force of Anchor Rods
The anchoring force of anchor rods is typically tested underground using an anchor rod pulling test. Here are some important aspects of the testing procedure:
- Sampling Rate: The sampling rate for anchor rod anchoring force testing should not be less than 3%. For every 300 top and gang anchors, nine samples are selected for testing. If fewer than 300 anchors are used, the test will be conducted as if there were 300 anchors.
- Qualification Criteria: The anchoring force is considered qualified if it is at least 90% of the design anchoring force. If any anchor falls below this threshold, a re-sampling test is required and if the re-sampling test passes, the anchor is deemed qualified. However, if the test results remain unqualified, the construction quality is considered subpar, and further investigation into the reasons for failure is necessary.
Hazards of Anchor Failure
Failure of the anchor can have severe consequences. Inadequate anchoring can lead to the collapse of tunnel roofs, gang sheets, and the surrounding rock, posing risks to both the project and the workers involved. Ensuring that anchors pass the required strength tests is essential for the safety of the entire construction operation.
Precautions for Anchor Pulling Tests
It is important to consider several precautions. These precautions will ensure that the pullout test is smoothly carried out while preventing the results from interfering with the progress of the project. Below are a few guidelines that are essential for a successful anchor pullout test:
- Construction Quality: Anchors must be constructed according to design specifications, with special attention paid to the length and grouting fullness.
- Anchor Length Control: For the pullout test, the exposed length of the anchor should be between 40 to 45 cm.
- Test Setup: To facilitate accurate testing, the anchor should be tested in a concrete base (or steel plate for good rock layers) with a thickness of 10 cm and a 5-6 cm hole in the center. The base should be positioned perpendicular to the anchor.
- Pre-Test Preparation: Technicians must provide key information before the test, such as the pile number, anchor type, quantity, specification, and design pullout force.
- Sampling Frequency: A sample group should consist of three anchors, with one group tested for every 300 anchors. If fewer than 300 anchors are installed, tests should be conducted for at least one group of three.
- Anchor Availability: The construction team must ensure that a sufficient number of anchors are reserved for testing, particularly in tunnels where anchors may not be exposed.
- Pullout Force Determination: In each test group, the average pullout force of the three anchors should be equal to or greater than the value of the design. Make sure that the minimum value is not less than 90% of the design value.
By following these precautions, you can successfully complete the pullout test, ensuring that the anchors are performing as expected and the construction quality meets safety standards.
Conclusion
When assessing the stability and safety of construction projects that involve anchoring systems, the anchor pullout force test plays a crucial role. It is important to understand the difference between anchoring force and pullout force and follow proper testing procedures and precautions. This will guarantee that the anchors perform reliably even under stress.
By conducting thorough tests and maintaining the standards, engineers can significantly reduce the risks of structural failures and enhance the overall quality of the project.
Visit Langry to get more details on the anchor pullout tests.
