Proctor Compaction Test Procedure and Equipment

Proctor Compaction Test

1. Obtain air-dry soil on which the compaction test is to be conducted.

2. Sieve the soil.

3. Add enough water.

4. Determine the weight of the Proctor mold + base plate.

5. Attach the extension to the top of the mold.

6. Pour the moist soil into the mold in three equal layers.

7. Remove the top attachment from the mold.

8. Using a straight edge, trim the excess soil above the mold.

9. Determine the weight of the mold + base plate +- compacted moist soil in the mold, W2 (lb).

10. Remove the base plate from the mold. Using a jack, extrude the compacted soil cylinder from the mold.

11. Take a moisture can and determine its mass, W3 (g).

12. From the moist soil extruded in Step 10, collect a moisture sample in the moisture can (Step II) and determine the mass of the can + moist soil, W4 (g).

13. Place the moisture can with the moist soil in the oven to dry to a constant weight.

14. Break the rest of the compacted soil (to No.4 size) by hand and mix it with the leftover moist soil in the pan. Add more water and mix it to raise the moisture content by about 2%.

15. Repeat Steps 6 through 12. In this process, until at least two successive down readings are obtained.

16. The next day, determine the mass of the moisture cans + soil samples, W5 (g) (from Step 13).

Objective

For construction of highways, airports, and other structures, it is often necessary to compact soil to improve its strength. Proctor developed a laboratory compaction test procedure to determine the maximum dry unit weight of compaction of soils.

Equipment

• Compaction mold
• No.4 U.S. sieve
• Standard Proctor hammer (5.5lb)
• Balance sensitive up to 0.01 lb
• Balance sensitive up to 0.1 g
• Large flat pan
• Jack
• Steel straight edge
• Moisture cans
• Drying oven
• Plastic squeeze bottle with water

Consolidation Stress

Consolidation stress is the process of time-dependent settlement of saturated clayey soil when subjected to an increased loading.

Preconsolidation Pressure

Preconsolidation pressure is the maximum effective vertical overburden stress that a particular soil sample has sustained in the past.

Compression Index

The compression index is used to find the settlement in the normally consolidated clay.

Recompression Index

Recompression index is used to find the consolidation settlement for over consolidated clay.

Plastic Limit

Plastic limit is defined as the moisture content, in percent, at which a cohesive soil will change from a plastic state to a semisolid state.

Equipment

• Porcelain evaporating dish
• Spatula
• Plastic squeeze bottle with water
• Moisture can
• Ground glass plate

Procedure

1. Put approximately 20 grams of a representative soil.
2. Add water from the plastic squeeze bottle to the soil.
3. Determine the mass of moisture can in grams.
4. From the moist soil prepared in Step 2, prepare several ellipsoidal-shaped soil masses by squeezing the soil with your fingers.
5. Take one of the ellipsoidal-shaped soil masses (Step 4) and roll it on a ground glass plate.
6. When the thread is being rolled in Step 5 reaches 1/8-in. (3.18 mm) in diameter, break it.
7. Repeat Steps 5 and 6 until the thread crumbles into several pieces.
8. Collect the small crumbled pieces in the moisture can put the cover on the can.
9. Take the other ellipsoidal soil masses formed in Step 4 and repeat Steps 5 through 8.
10. Determine the mass of the moisture can plus the wet soil (W2) in grams. Remove the cap from the top of the can and place the can in the oven.
11. After about 24 hours, remove the can from the oven and determine the mass of the can plus the dry soil (W3) in grams.

Liquid Limit of the Soil

Liquid limit of the soil is the moisture content (in percent) at which the cohesive soil will pass from a liquid state to a plastic state.