How to conduct a pullout test on a single screw pile

How to conduct a pullout test on a single screw pile

Ground screws are a popular foundation solution for various structures, offering stability and ease of installation. To ensure the reliability and safety of any construction project using ground screws, it is crucial to perform thorough pullout tests. These tests assess the load-bearing capacity of the ground screws and provide valuable data for engineers and contractors. In this guide, we will walk you through the steps involved in conducting a pullout test of ground screws.

 

Single screw static load-bearing test

Equipments

The equipment for the pullout test is composed of a loading device, a reaction device, an observation device and other components.
1. Loading device

The loading device includes a pressure source (hydraulic jack 5T, oil pump, oil pipe), load bench

2. Reaction device
There are two types of reaction devices: on-site masonry and prefabrication. Masonry: steel support piers, steel main beams

3. Observation device
Observation devices include dial indicator (50mm), pressure gauge, force sensor, and displacement sensor

On-site assembly of equipment and instruments

Select a representative location for the pullout test where the ground screws are installed according to the project’s specifications. Clear the area around the ground screw to ensure unrestricted access during the test. Take safety precautions and follow relevant guidelines to prevent accidents or injuries.

Test process: loading and unloading

1. Determine the maximum test load:
——According to the value of 2 times the maximum pile top invoice in the structural calculation;

2. Determine the graded load:
——Each level of loading is 1/5-1/4 of the maximum test load;

3. Test loading method:
——After each level of load is applied, read the dial indicator settlement for 5, 10, and 20 seconds, and then read it every 20 seconds. Each level of formaldehyde lasts for 2-15 minutes;

4. Termination loading conditions:
——Under a certain level of load, the uplift load on the top of the pile is 5 times greater than the uplift amount under the previous level of uplift load.
——The maximum test load has been reached.

5. Uninstall:
——Unloading should be carried out in stages, and the unloading amount at each stage should be twice the graded load, and the same amount should be unloaded step by step;

Ultimate bearing capacity criteria
Data sorting: draw the relationship curve of the amount of pull-up (Q-s) and the relationship curve of the amount of pull-up-logarithm of time (s-lgt).
The pull-out bearing limit force is comprehensively determined according to the following method:
1. Determine based on the changing characteristics of the pull-up amount with the coil: for the steep Q-s curve, take the coil value corresponding to the starting point of the steep rise;
2. Determine based on the characteristics of the uplift amount changing with time: take the load value of the previous level where the slope of the s-lgt curve becomes significantly steeper or the tail of the curve has an obvious curve;
3. Under a certain level of load, the pull-out amount is greater than 5 times the pull-out amount under the previous level of load, and the load value of the previous level is taken.

 

Test precautions

  1. Devices and instruments should be firmly fixed;
  2. It should be loaded slowly and evenly step by step, and detailed records should be made;
  3. No one is allowed to stand under or on either side of the pulling device;
  4. Set up dedicated personnel to monitor to ensure the safety of operators;
  5. Clarify the scope of the test area and set up warning signs.

 

Conducting a pullout test of ground screws is a critical step in ensuring the safety and stability of construction projects.

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