How to check compaction is achieved or not

[SYED SHEERAZ AHMED]

Hey there,

I have some queries. I have a geotechnical report recommends for foundations placement and it recommends to place 250mm thick layer of Structural Fill material. The material should have a size of 3-4 inches and the compaction value shall not be less than 99%.

Now after compaction how to confirm that required compaction is achieved. FDT is not working on 3-4 inches of particle size and we are also unable to find proctor values.

Can any body confirm about this? Which test should I perform for this?

 

[geotechguy1]

What are you building? A rockfill dam? A footing? The sequence described in the image makes it sounds more like you are putting open-graded drainage rock wrapped in geotextile at the base of an excavation expected to be wet and then putting normal well-graded gravel on it. It reads very poorly.

The image you linked instructs you to determine compaction using the Bertram GE 1973 method which is a section in the 1973 book 'Embankment Dam Engineering - Casagrande Volume' and is about testing of compacted rockfills for dams. Print copies of that book are commonly held by university libraries. Also there are PDF versions floating around the internet. I have the book and basically it's just doing a large-diameter in-situ compaction test. However if what you're doing is putting open-graded drainage rock in a geotextile at the base of a trench it will be a waste of time and it seems like an overzealous spec.

If what you're doing is actually the Bertram reference, basically (it's probably slightly more complicated than this in practice):

1. Steel ring say 4-6 times the diameter of the max particle size (The Betram section of that text uses a 6 foot diameter ring)
2. Excavate a circular hole within the steel ring through your lift thickness (or maybe more)
3. Measure the weight of what you dig out.
4. Line the hole with a plastic sheet, fill it with water (and measure how much water you put in)

You now know the in-situ density

There's also this:

https://apps.dtic.mil/sti/tr/pdf/ADA035981.pdf

You may find these geoengineer articles useful:

https://www.geoengineer.org/educati...ent-compaction-guidelines-for-mine-structures

https://www.geoengineer.org/educati...test-fills#test-fill-placement-and-compaction

https://www.geoengineer.org/educati...ensity-gradation-tests-in-compacted-rockfills

 

[EireChch]

To be honest the degree of compaction beneath a slab is somewhat irrelevant. Do a PLT and check the stiffness

 

[geotechguy1]

I don't get the UK obsession with PLTs...most problems have scale effects that make PLTs very misleading / useless. Are the soil conditions there largely homogenous such that the top 500mm is representative of all the soil influenced by the foundation?

 

[iandig]

Being based in the UK, I have to admit that the level of reliance on plate load testing is not always matched by an understanding on what the plate load test is actually measuring, let alone test laboratories not following the instructed procedure. However, if undertaken to an appropriate methodology, a plate test can be used to assess the 'adequacy' of the compaction. This is generally following the DIN 18134 standard, where dual cycle tests are undertaken following a strict procedure (using the DIN equipment which differs from other plate tests with a hydraulic ram in the center of a circular plate). The vertical stiffness modulus (Ev)for the first (Ev1) and second cycle (Ev2) are calculated and the ratio of Ev2/Ev1 determined. This can then be used as a measure of 'adequacy' of compaction *(this is the terminology used in the DIN). For highway fill, a ratio of better than 2.4 is recommended and selected fill, this reduces to better (less) than 2.0

 

[geotechguy1]

@iandig - interesting approach. I suppose in that context as a compaction test it's not really any different than doing an NDM and being limited to ~300mm depth testing

 

[PEinc]

How does anyone expect to get 99% compaction for a 10-inch layer of 4-inch clean(?) gravel?

http://www.PeirceEngineering.com