Troxler nuclear density testing on a slope

[bgervais]

What are the specifications to conducting density testing on a slope? Is it required to cut out a "notch" so that the gauge is level in reference to the horizon line? Or can you directly test on a slope as long as the surface is flat?

 

[civilperson]

Flat, the volume represented will be a cone with the tip of the probe at the apex. As long as the probe is at right angles to the surface the readings are valid. The specifications call for level lifts for the contractor, not slanted with uniform thickness. Level is considered less than 5% grade for fill purposes.

 

[TDAA]

civil person has it right, but perhaps with one exception:

The specifications call for level lifts for the contractor, not slanted with uniform thickness. Level is considered less than 5% grade for fill purposes.

This depends on the fill. I have done extensive landfill work, where the fill for the clay line is place on the slope in 6 inch lifts, not level as indicated here (so many short lift interfaces would be bad, and very hard to construct).

So, just get it flat, unless they should be placing it level. Then, it is just the pain in the but of walking and testing on the slope that will be a pain.

 

[civilperson]

TDAA,
How steep was the slope for the clay line that was filled?

 

[brbarkmj]

ASTM D 2922 (nuclear-density in place soil-aggregate) Sec 9.5 appears to require a "smooth horizontal surface".

However, I too have performed clay-lined landfill construction where the testing was performed on slope. Our drive cylinders always came back from the lab within 2% of the gauge readings, indicating a valid test by our specs.

Any idea why ASTM requires horizontal?

 

[TDAA]

Liners and covers are "normally" designed at about 3H:1V. I have done some up to 2.57:1.

With some of the synthetic caps, the slope has decreased to 4:1 to allow for veneer stability at the liner/cover soil interface.

As you can calculate, the horizontal thickness of a 2' liner on a 3:1 is around 6.5'. To use normal equipment, this would need to be double to do a horizontal lift, and then be cut off (or left). This gets to be impractical, cost prohibitive, and a waste of clay resouces, and in my experience (many, many landfills from many design firms), it is never done.

 

[civilperson]

Normal fill techniques require compactive effort to achieve the specified density. The machines and rollers used are mainly heavy impact type,(sheepsfoot, steel wheels, rubber tires, etc.), and are most efficient when acting with gravity at the normal with the surface. Compacting on steep slopes is inefficient since the effort is not at right angles to the surface. Benching and level lifts are required in most DOT specs for building embankments with 3:1 side slopes for this reason. Liners in land fills will negate the use of benching.

 

[dirtsqueezer]

The problem there is not testing on a slope, but compacting on a slope. What I've run into is contractors that want to place their fill at an angle. If the contractor is placing against a slope, they should start at the bottom using horizontal lifts and place up, not place sideways laterally from the slope surface. Soil compacts better when there's a hard suface to compact against(down), not an angled surface that the lift can slide on. I've only been on one job where the contractor tried to build this way, and it made a big difference as far as densities were concerned.

 

[TDAA]

Sure it is inefficient, and not the standard for structural fill placement, but my point was only that there is a place and time for testing on the slope, and that it is possible.

I’m not sure if you know just how inefficient it can be, until you see it done. The compactor looses some compactive effort due to the slope, but I can’t count the number of times I have seen a D6 push an 815 compactor up a slope, blade to blade. This takes a lot of extra time. I have even seen pictures of compators being pulled up and down on cables. Then there is the need to water the material. Definitely interesting on a slope. Sure it can be processed in the pit, but with a tight moisture spec, inevitably there is the need to do it in-place.