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.

Here is the link to the video showing pumping due to overcompaction: http://www.youtube.com/watch?v=TFPKDpIBWXc

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?