CEEN 341 - Lecture 6 - Soil Compaction

This lecture describes what soil compaction is and why it is beneficial to civil engineers. The theory and mechanics behind Proctor tests are covered. An explanation is provided for overcompaction or "pumping" of fine-grained soils. Benefits of being wet or dry of optimum are discussed. Methods to measure dry unit weight and moisture content in the field are discussed, including the sand cone test and the nuclear density gauge.

Critical Questions to Consider:
1) What is the purpose of soil compaction? Why is it useful?
2) Why does a compaction curve go up and then back down with increasing moisture content?
3) How does the location of the compaction curve in density/moisture content space change with increasing energy? Why?
4) Why do we engineers provide specifications (i.e., relative compaction limits and allowable moisture contents) to contractors? What is the usual consequence for not compacting the soil in accordance with the specifications?
5) Which method is more accurate: the sand cone or the nuclear density gauge? Why?

[United_ArenaUSA]

Dr Franke breaks it down to pieces! He's so gifted at explaining the seemingly hard things to look so easy.I will recommend his videos anytime.

[georgebakirtzis]

Internet is a great tool. Thank you very much sir, watching all your lectures on soil mechanics as we are getting closer to the end of the sememster and they really help a lot! :)

[tom]

I'm a homeowner and retired software engineer with nothing to do with mechanical engineering. HOWEVER I am putting in a patio and I'm compacting the soil/gravel base/sand. I stumbled onto your video and I'm fascinated. The proctor test and compaction curve help me understand exactly what's going on under my feet. I had no idea that if you compact soil too much it can become viscous. Good to know, though I doubt if I'd be able to get to that point! Thanks for the great video. Much more fun watching it than going outside and working on the patio!

[tedchuparkoff]

Really good stuff! Explained very well. This guy knows his stuff. Worth watching.

[mikewarner]

Great videos! I am a geologist learning soil mechanics for my job at a geotechnical company, your videos are some of the best content I can find online by a long shot!

One question, you mention that the best water content is -1% and +3% of optimum, why is the error on the wet side greater if the increase in moisture makes the soils less strong and give potential for swelling and pumping?

[martyp]

Recently started a position as a Field Tech and this video helped my understanding greatly. Thanks for your effort.

[musoodkarim]

Really well explained. The theory reminded me about the soil mechanics lectures around 1985 at Aston University and later at City University, London. Musood Karim.

[ahmedkamla]

I cant thank you enough for the excellent explanation.

[NK-iyif]

God bless you! Your explanation is very precise and clear! Thank you so much for posting those videos they are extremely helpful!

[WG-fttz]

Dr. Franke - thank you for the content. How are the results of the modified proctor actually applied in the field, for situations where the soil won't be disturbed, say at the base of a spread footing. Suppose the optimum moisture is determined, how is a contractor actually increasing or decreasing the moisture % in the field, and to what depth? The layer beneath said depth won't be tested or compacted, isn't the compaction only as good as that beneath layer?

[sumitmaskey]

Being a field engineer, my question would be HOW CAN WE SAY IF THE MOISTURE IS INSIDE THE SPEC LIMITS say, +-3% of OMC by feel before giving the Green sign to the earthwork contractor? As per the experience, they say, Nuke doesn't reflect the exact moisture. Therefore, need to feel the moisture and relay to the contractor. Also, the dummy test is performed. However, by the time of completion of the dummy test, the contractor would have placed the layer.

Your expertise shall be highly appreciated.

Sumit

[ruymenezes]

Modified proctor test in Brazil are 55 blows per layer(55/5) 10lbs hammer and cylinder volume 2080 g/cm³

[khaliqhussainnazirahmed]

Thanks for very informative lecture.. I revised my old knowledge, , Nice Job Sir..

[josephchungu]

Well explained and to the point, I LIKE IT!!

[picajoool]

Is there any correlation between the Proctor test and the CRB test?

[ahmedobidat]

In 7:06 you say we can get the unit weight by weighing the moist sample and dividing it by the known volume (volume of the container), then we dry it in the oven and can obtain the dry unit weight by weighing it and then dividing by the same volume. Then using the following formula, we can calculate the moisture content: moisture content = (moist unit weight - dry unit weight)/dry unit weight. I don't see where the specific gravity of soil solids (Gs) comes into play?

[rossh]

How do contractors know how much moisture to add to base materials to achieve optimum compaction ?

[prakharpatankar]

How do the contractor add proper amount of water and equal energy to get the maximum dry density?

[patrickcummins]

Thank you. I just started at a geotech firm.

[israrullah]

you explain in such a nice way. can't we use core cutter method to find dry density?