Published on October 31, 2016
1. COMPACTION TEST OF SOIL Soil Mechanics Standardization : ASTM 698
2. PREAMBLE Compaction is the process of densification of soil by reducing air voids by mechanical energy. The degree of compaction of a soil is measured in terms of its dry unit weight. When water is added to the soil during compaction, it acts as a softening agent. The dry unit weight after compaction first increases with moisture content. Beyond a certain moisture content dry unit weight reduces with any increase of moisture content. The moisture content at which the maximum dry unit weight attained is called Optimum Moisture Content. Compaction test is now called Proctor Test.
3. Soil compaction is needed for five reasons: a) To increase shear strength b) To increase in unit weight c) To decrease future settlement d) To decrease permeability e) To decrease in compressibility The laboratory tests indicate optimum mixing water contents which are lower than the actual field tests.
4. • FACTOR AFFECTING COMPACTION: Moisture content Soil type Compaction effort (energy per unit volume) There are two types of compaction test: i. Standard ii.Modified
5. Standard proctor ASTM 698 Modified proctor ASTM 1557 Method A Method B Method C Method A Method B Method C Material ≤ 20% Retained On No. 4 Sieve > 20% Retained On No. 4 Sieve ≤ 20% Retained On 3 8 " Sieve > 20% Retained On 3 8 " Sieve < 30% Retained On 3 4 " Sieve ≤ 20% Retained On No. 4 Sieve > 20% Retained On No. 4 Sieve ≤ 20% Retained On 3 8 " Sieve > 20% Retained On 3 8 " Sieve < 30% Retained On 3 4 " Sieve For test sample , Soil passing Sieve No. 4 3 8 " Sieve 3 4 " Sieve Sieve No. 4 3 8 " Sieve 3 4 " Sieve Mold 4"Dia 4"Dia 6"Dia 4"Dia 4"Dia 6"Dia No. of layers 3 3 3 5 5 5 Blows per no. of layer 25 25 56 25 25 56
6. OBJECTIVE To determine the proper amount of mixing water to use when compacting the soil in the field and the resulting degree of denseness which can be expected from compaction at this optimum water content.
7. SCOPE OF THE TEST Most engineering properties such as stiffness, strength, resistance to shrinkage and imperviousness of soil will improve by increasing of soil density. Mechanical compaction is one of the common and cost effective means of stabilizing soils. Design specifications mostly state the required density ( as a percentage of the maximum density measured in standard laboratory test) and the water content.
8. EQUIPMENT For standard proctor 1 30 ft3 mold 5.5lb hammer 12" drop 3 layers of soil 25 blows per layer For modified proctor 1 30 ft3 mold 10lb hammer 18" drop 5 layers of soil 25 blows per layer
9. PROCEDURE: (STANDARD PROCTOR COMPACTION TEST) Take approximately 10lb of soil sample. Pulverize the soil and run it through the #4 sieve. Determine the weight of the soil sample as well as the weight of the compaction mold with its base (without the collar). Compute the amount of initial water to add. Measure out the water, add it to the soil and then mix it thoroughly into the soil. Assemble the compaction mold to the base, place some soil in the mold and compact the soil in the three layers with 25 blows each layer. The drops should be applied at a uniform rate not exceeding around 1.5 seconds per drop. The soil should completely fill the cylinder and the last compacted layer must extend slightly above the collar joint. Carefully remove the collar and trim off the compacted soil. Weigh the compacted soil while it’s in the mold and to base. Remove the soil from the mold using a mechanical extruder and take soil moisture content samples from the top and bottom of the specimen.
11. CALCULATION Calculate the moisture content of each compacted soil specimen by using the average of the two water contents Compute the wet density of the compacted soil sample by dividing the wet mass by the volume of the mold used. Compute the dry density using the following formula: