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> I helped build earthen structures with sharper slopes than 25 degrees 30 some years ago that are still holding back ponds today. I think you may be mistaken

> I helped build earthen structures with sharper slopes than 25 degrees 30 some years ago that are still holding back ponds today. I think you may be mistaken - note that a "25 degree slope" is just a different way to say a 2 to 1 slope (2 feet across, 1 foot up). I've seen 2:1 slopes used for highway embankments, but earth fill usually specified as a 3:1 slope (18 degrees) - eg when I worked with an earth fill dam (holding back water, same as yours). I've only seen anything steeper (1:1, 45 deg) used a as a temporary (during construction) condition. Sheepsfoot rollers are good for packing very fine material (silt, clay) but not very good for packing larger granular material (i.e. crushed stone/gravel). Silt and clay are very water sensitive materials: each has a very specific moisture content where it can be packed properly, if your material is outside of this narrow range it will not get to maximum compaction (and therefore it will eventually settle). Water moves very slowly through clay so if it is too wet or too dry it's very difficult to get it back into the proper moisture range, and if there's a bit too much sun or some rain between excavation and placement it will not get packed well. The only reason I've seen clay-ey earth intentionally used is for inhibiting water movement, IE an earth fill dam - and even there, it was a secondary barrier if anything happened to leak through the barrier membrane. Crushed stone is (relatively) very easy to get to maximum compaction, and if it sits out for a while and gets too dry you can just hit it with a water truck before placing. It packs quickly and easily, and is stable at the ssame side slopes as earth fill

h2odragon 5y ago
Yes my experience is dated and my memory none too good, thank you for expanding. My experience is all with "perfect" high clay soils and I'm sure many of our jobs were "under-engineered" to put it politely. We had some crazy operators who would do things like chaining the dozer to a trackhoe at the top of the hill so it would not roll over, to do the final grade of the slope. There's more laws now, and/or fewer fools with earth moving equipment.
- SECProto 5y ago
  > Yes my experience is dated and my memory none too good, thank you for expanding No worries, when I heard 25 degrees my gut reaction was "that can't be right". Then I did the calculation and saw that the common ratios used are a lot fewer degrees than I expected :) I was thinking of grades in percentage (rise divided by run expressed as a percentage - so 50% for a 2:1 slope, 33% for a 3:1, etc) > There's more laws now, and/or fewer fools with earth moving equipment I think stricter rules (or enforcement thereof) has led to the proliferation of long-reach excavators.
  - jaclaz 5y ago
    In my experience "normal" slopes (without using any kind of reoinforced earth) are 1:1 (base/height i.e. 50 % slope degrees) for excavation and 3:2 (base/height i.e. 66% slope), with reinforced earth (depending on types, soils, etc.) you can usually go to 1:3 or 1:4 or even 1:5.
    - SECProto 5y ago
      Yeah, I acknowledged 1:1 for excavation in a comment up a couple levels. That said, where are you that 3:2 is a standard slope for unreinforced permanent slopes? That's 34deg, which is outside the angle of repose for many materials, and doesn't leave much factor of safety even for a crushed stone. Reinforced earth is a different beast altogether for sure.
      - jaclaz 5y ago
        Yep, it is the the typical slope for earth moving, Italy here, thousands of km of roads are made with this slope, exceptionally it is lowered up to 4:1, a reference: https://www.manualihoepli.it/media/doc/pr141.pdf https://www.manualihoepli.it/media/doc/pr141.pdf What I mean by 3:2 (base divided by height) is often referred to as 2/3 (height divided by base) and is roughly the "natural" angle of repose of - say - gravel.
        h2odragon 5y ago
        I towed my sheepsfoot roller around with a big Italian Same tractor in the 1980's, in West TN. We had those for the ground speed PTOs but they climb things like mountain goats, unique to the market at the time, which enabled some of the stupid tricks we built. By comparison to their source, our hills are pleasant soft sandcastles, all rubbery clays with veins of sand or gravel and never any excuse for explosives.
        SECProto 5y ago
        Thanks for the reference. It's interesting that they work that close to the stability limits without just adding some slope reinforcement. It doesn't leave much room for error (execution error, erosion over time, unexpected surcharge load, stability changes with soil saturation, or earthquake).

h2odragon 5y ago

Yes my experience is dated and my memory none too good, thank you for expanding. My experience is all with "perfect" high clay soils and I'm sure many of our jobs were "under-engineered" to put it politely. We had some crazy operators who would do things like chaining the dozer to a trackhoe at the top of the hill so it would not roll over, to do the final grade of the slope. There's more laws now, and/or fewer fools with earth moving equipment.

SECProto 5y ago
> Yes my experience is dated and my memory none too good, thank you for expanding No worries, when I heard 25 degrees my gut reaction was "that can't be right". Then I did the calculation and saw that the common ratios used are a lot fewer degrees than I expected :) I was thinking of grades in percentage (rise divided by run expressed as a percentage - so 50% for a 2:1 slope, 33% for a 3:1, etc) > There's more laws now, and/or fewer fools with earth moving equipment I think stricter rules (or enforcement thereof) has led to the proliferation of long-reach excavators.
- jaclaz 5y ago
  In my experience "normal" slopes (without using any kind of reoinforced earth) are 1:1 (base/height i.e. 50 % slope degrees) for excavation and 3:2 (base/height i.e. 66% slope), with reinforced earth (depending on types, soils, etc.) you can usually go to 1:3 or 1:4 or even 1:5.
  - SECProto 5y ago
    Yeah, I acknowledged 1:1 for excavation in a comment up a couple levels. That said, where are you that 3:2 is a standard slope for unreinforced permanent slopes? That's 34deg, which is outside the angle of repose for many materials, and doesn't leave much factor of safety even for a crushed stone. Reinforced earth is a different beast altogether for sure.
    - jaclaz 5y ago
      Yep, it is the the typical slope for earth moving, Italy here, thousands of km of roads are made with this slope, exceptionally it is lowered up to 4:1, a reference: https://www.manualihoepli.it/media/doc/pr141.pdf https://www.manualihoepli.it/media/doc/pr141.pdf What I mean by 3:2 (base divided by height) is often referred to as 2/3 (height divided by base) and is roughly the "natural" angle of repose of - say - gravel.
      - h2odragon 5y ago
        I towed my sheepsfoot roller around with a big Italian Same tractor in the 1980's, in West TN. We had those for the ground speed PTOs but they climb things like mountain goats, unique to the market at the time, which enabled some of the stupid tricks we built. By comparison to their source, our hills are pleasant soft sandcastles, all rubbery clays with veins of sand or gravel and never any excuse for explosives.
      - SECProto 5y ago
        Thanks for the reference. It's interesting that they work that close to the stability limits without just adding some slope reinforcement. It doesn't leave much room for error (execution error, erosion over time, unexpected surcharge load, stability changes with soil saturation, or earthquake).