Objective - To determine the optimum moisture content and dry density of a compacted soil sample.
Procedure (The same as the Standard except you use a 10 lb hammer, 18" drop, 5 layers)
1. Obtain 2500g of oven dry (air dry will work, but not as well) soil passed through the #4 sieve.
2. Weigh 3 "bread pan" moisture content containers individually and record weights on the data sheet in your manual.
3. Weigh a 4 inch diameter compaction mold. (V = 1/30 of a cubic foot)
4. Add enough water to your sample to obtain a 12% moisture content (300 grams of water).
5. Compact the soil into the mold in FIVE layers using a 10 pound hammer and 25 blows per layer. Make sure that on the last layer, your compacted sample is just above (1/4" or so) the top of the mold so it can be trimmed and weighed.
6. Weigh the mold and the sample (in pounds) and record on your data sheet.
7. Take a representative sample of the soil (about half of it evenly distributed from the entire sample) and place in a "bread pan" moisture content container. Weigh the sample, record the data, and place in the oven. Work quickly because water is being lost as time progresses.
8. Repeat steps 1 through 7 twice, increasing the moisture content to 15% for the 2nd point and then 18% for the third point.
9. Obtain all weights the following day and plot moisture content vs. dry unit weight to scale on graph paper and indicate optimum moisture and maximum dry unit weight.
Next Lab - Review your plot and perform additional points using the above process to fill in missing or faulty data so that a smooth curve that peaks is obtained.