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Compacting Backfill and Engineering Insights

1:57
20:43
174.1K views

At 1:57 in

WHY Retaining wall Engineers ARE ALL WRONG!!

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What happens here

The presenter demonstrates the use of a plate compactor in a narrow trench behind the retaining wall. He explains the critical importance of using short lifts, specifically 2.5 to 3 inches, for effective compaction with a 250-pound plate compactor. He clarifies that using larger lifts would only compact the top few inches, leaving the lower layers unstable. An expert in an inset video emphasizes that while technical regulations might advise against compacting within 3 feet of a retaining wall, compacting the 2-foot zone directly behind the 12-inch drainage area is essential to prevent future problems. Workers are shown actively spreading and compacting gravel using the plate compactor, with a mini excavator periodically dumping fresh gravel.

Goal: Properly compact backfill and understand related engineering principles.

Tools and materials

  • Gravel — Backfilling and providing drainage behind the wall
  • Mini Excavator Bobcat — Moving and dumping gravel into the backfill area
  • Plate Compactor — Compacting gravel and soil layers behind the retaining wall
  • Rake — Spreading gravel evenly
  • Retaining Wall Blocks — Constructing the visible part of the retaining wall
  • Shovel — Moving and spreading soil/gravel

What they say

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gotta remember so here's a fun one that even the engineers can't explain to me you're technically not supposed to compact within three feet of the back side of a retaining wall except your drainage zone is only supposed to be 12 inches behind the retaining wall so that means technically you're supposed to have two feet of uncontrolled fill going in behind your retaining wall no way if you don't pack that two foot that goes behind the drainage zone you're going to have problems and so we always compact it and when i've questioned the engineers they've never yet come up with a good solution and speaking of engineers if you are going to build an engineered retaining wall you can't just get any old civil engineer i'm going to recommend you get somebody that not only understands retaining wall construction but also has specialty programs designed to help you build that retaining wall meaning that there is cad aided designs that will allow you to allow an engineer to design the specific grid lengths for the retaining wall here's where it gets interesting even though you got a six foot let's say you got a six foot retaining wall not all of your grid lengths behind that retaining wall are going to be equal distance or equal length behind the retaining wall it'll depend on the surcharge and the surcharge means the load that is placed behind the retaining wall and typically the surcharge is going to come from two different forms or functions one is going to be a hill the other one is going to be a structure and then the grid lengths are dependent on the le the height of the retaining wall the type of soil that is going behind the retaining well that's a critical element to make sure you have a soil sample and then the surcharge that the retaining wall is going to experience all of these three things tie together to actually make a properly engineered retaining wall and that's why i back up to say you don't want just any old civil engineer you want to make sure you get somebody that understands retaining wall construction because you as the installer no matter what happens if you screw that wall up you're liable for it for eight years that's right if they find a fault in you don't even have to give a warranty if there's if it's legally you find a fault in your retaining wall because the installer pay that bill for eight years so you best do it right [Music]

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