Compacting Till on 3:1 Slope

[NewNorthernGeotech]

Here's a good one! (I think so anyways)

New project for me, weekend and no senior advice around, so I turn to the internet... GOD HELP ME!

We're constructing a containment area with 3:1 slopes on the inside berms. Nicely compacted rock fill as the base and beautiful till material being placed. However, we've removed oversized material for our key trench for permiability reasons, but left all oversize in it for the slopes because we will us a liner.

The issue! I'm QC and QA now wants to develop a method spec for the placement. Test strips are the plan with varying lift thicknesses, levels of compaction, yada yada yada.

Boulders visually range up to 600 mm and oversize content (larger then 20 mm) has to be up around 70 to 85%! Soil matrix is great, well graded with 25 to 30% silts/clays.

QUESTION 1: Density testing with nuclear device has been decided on and I personally question the usefullness based on the quantity of larger particles. I'll take an obscene amounts of readings and see if anything sensical comes out of it, but IS THERE A BETTER WAY!

QUESTION 2: Does the "Nuke" have to be flat? Or can I place it right on the 3:1 slope and get good readings. I'm headed out there shortly and plan to satisfy myself by spending some time, but am interested to see what sort of responses I get here!

QUESTION 3: ALSO! QA seems to be pressuring me to develope the procedure for this testing, since I don't believe it's the best solution and have to senior advice I'm reluctant. Monday is coming, but shouldn't QA be supplying me with the plan and I simply impliment and give out results??

THANKS!!

 

[civilperson]

Flat is required for nuclear probe plate, (level is not required). Why the the worry of compaction on the slopes? line up the over sized boulders in a row and fill on either side with finer material. Compact with thin lifts and keep the moisture at optimum or above for the fines.

 

[RWF7437]

For liability reasons, consider a performance specification; rather than a prescriptive specification. If you tell the Contractor in great detail how to do the job you may be accepting responsibilty for the result. Why not specify the result you want, prohibit any method that would clearly not achieve that result and let the Contractor decide how to do it?

As for QA ( does he/she have enough experience in this to be specifying anything ? or ( is he/she the responsible Engineer of Record ?).

What are the consequences of failure ?

good luck

 

[Stego1]

It sounds like you're doing a landfill or similar, and in this case if permeability of the mineral element of the side-slope is not a major issue then you're going for strength and stability.
When I worked on landfill construction we would always do a number of test pads to see which method best suited the material used for construction however we were concerned with both strength and permeability.
For good results I found that lifts of 250mm to 500mm were normal, with 300mm being most common. If this is the case I would imagine that 600mm boulders would cause you problems, the process of compaction would cause punching voids/shear within the clay matrix leaving potential zones of weakness or a path for water movement which is likely to soften clays and more so if its silty.
In your case I would suggest removing particles larger than say 250mm if at all possible and maybe use them elsewhere in the job, possibly as core for bunds or something.