What is the pull out resistance of geogrid cast into a Interbloc or Stonebloc concrete block for Mechanically Stabalised Earth wall designs?
Envirocon casts lengths of geogrid into our blocks during the manufacturing process for mechanically stabilised earth wall designs. We undertook testing on the pull out resistance of cast in geogrid, and the results are outlined in this article.
Access a full copy of the report here.
Objective:
To determine the pull-out resistance of a Tensar RE580 geogrid embedded in a concrete block, comparing it to its short-term and long-term tensile strength.
Test Setup:
- A Hydrajaws Model 2008 device was used to apply a pull-out force.
- A steel pipe with a welded threaded rod transferred the load to the geogrid, simulating a bodkin.
- An extra piece of geogrid was stitched to the embedded geogrid for the test.
- The loading device was mounted and elevated behind the concrete block.
Loading Procedure:
- The test aimed to reach and exceed the ultimate long-term load (42.4 kN) and approach the short-term load (89.3kN).
- Load was applied in 10 equal intervals to the ultimate long-term load, with each interval held for 5 minutes.
- The ultimate long-term load was held for 15 minutes.
- The load was then increased in 10 kN intervals, each held for 5 minutes, until the loading device's maximum capacity (145 kN) was reached.
Key Results and Observations:
- Ultimate Limit State (42.4 kN):
- Up to 21.2 kN, no visible signs of geogrid failure or stretching.
- At 21.2 kN, concrete cracking began near the geogrid edges.
- From 25.44 kN to 42.4 kN, slight propagation of the existing cracks was observed, but no new cracks or geogrid stretching.
- Failure Test (Up to 145 kN):
- At 80 kN, visible stretching of the geogrid occurred in the middle.
- At 130 kN, cracking sounds were heard, but only the existing edge cracks were visible.
- The concrete block's face showed no signs of cracking propagation.
- The geogrid stretching being centered, indicated that the load was concentrated in the middle of the geogrid.
- The cracks that formed were near the edge of the geogrid.
Conclusion:
- The geogrid withstood the ultimate long-term load (42.4 kN) for the required 15 minutes, with only minor concrete cracking.
- The geogrid showed significant stretching before ultimate failure, indicating that the failure mode was primarily geogrid stretching.
- The concrete cracks were localized to the geogrid edges, suggesting a concentrated pull-out force.
