COMPACTION TEST OF SOIL

Soil MechanicsStandardization : ASTM 698

PREAMBLECompaction 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.

Soil compaction is needed for five reasons: a) To increase shear strengthb) To increase in unit weightc) To decrease future settlementd) To decrease permeabilitye) To decrease in compressibility

The laboratory tests indicate optimum mixing water contents which are lower than the actual field tests.

•FACTOR AFFECTING COMPACTION: Moisture content Soil type Compaction effort (energy per unit volume)

There are two types of compaction test:i. Standard ii.Modified

 Standard proctor

ASTM 698Modified proctor

ASTM 1557Method A Method B Method C Method A Method B Method C

Material Retained On No. 4 Sieve

Retained On No. 4 Sieve

Retained On Sieve

Retained On Sieve

Retained On Sieve

Retained On No. 4 Sieve

Retained On No. 4 Sieve

Retained On Sieve

Retained On Sieve

Retained On Sieve

For test sample ,

Soil passing

Sieve No. 4 Sieve Sieve Sieve No. 4 Sieve Sieve

Mold Dia Dia Dia Dia Dia DiaNo. of layers

3 3 3 5 5 5

Blows per no. of layer

25 25 56 25 25 56

OBJECTIVETo 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.

SCOPE OF THE TESTMost 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.

EQUIPMENT

For standard proctor

For modified proctor

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.

PROCEDURE

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:

Plot the dry density values on the y-axis and the moisture contents on the x-axis. On the same graph draw a curve of complete (100%) saturation or “zero air voids curve”. it is theoretical dry

density which is maximum limit of compaction at any water content.

Calculate percent compaction or relative compaction, …

Sl.no.

Can no. Wt. of can

(gm)

Wt. of can + wet soil

(gm)

Wt. of can +

dry soil(gm)

Wt. of dry soil

(gm)

Wt. of moistu

re(gm)

Moisture

Content

%

Wt. of

mold (gm)

Wt. of mold + compa

cted soil

(gm)

Wt. of compacted soil

(gm)

Wet Unit Wt. ( /)

Dry Unit

Wt. ( /)

  839 10.2 42.2 40 29.8 2.2 7.38 4190 5280 1630 16.94 15.7

  794 6 28.7 26.96 20.96 1.74 8.3

  835 7.1 38.2 35.53 28.43 2.67 9.39 4290 6070 1780 18.49 16.92

  861 7.4 32.3 30.2 22.8 2.1 9.21

  2170 10.4 37.2 34.48 24.08 2.78 11.29 4210 6040 1830 19.02 16.99

  2338 10.5 42.5 38.92 28.42 3.58 12.59

  824 7.3 28.7 25.97 18.67 2.78 14.89 4200 6130 1930 20.06 17.4

  864 10.7 30.3 27.64 16.94 2.66 15.7

  183 7.3 38 33.58 26.28 4.42 16.82 4200 6060 1860 19.33 16.498

  869 11.3 41.5 37 25.7 2.5 17.51

  2059 7.3 53.7 46.1 38.8 7.6 19.59 4200 6030 1830 19.02 15.83

  2060 7.2 61.5 52.2 44.9 9.3 20.71

DATA SHEETSpecific gravity:2.75

SAMPLE CALCULATIONWeight of can no. 2059 : 7.3 gm

Weight of can + wet soil =53.7gm

Weight of can + dry soil =46.1gm

Weight of moisture =7.6gm

Moisture content =19.59%

Average moisture content = %

Weight of mold = 4200gm

Weight of mold + compacted soil =6030gm

Weight of compacted soil =1830gm

Wet Unit Weight =

Dry Unit Weight =

6 8 10 12 14 16 18 20 2215

15.516

16.517

17.518

18.519

19.520

20.521

21.522

22.523

Unit Weight Vs Moisture Content

Dry Unit WeightZero Air Void

Moisture Content , w (%)

Dry

Unit

Wei

ght,

( )

(/

^3 )

𝛾𝑑𝑘𝑁

𝑚

DISCUSSION

i. From data obtained we have got the dry unit weight of soil for corresponding moisture content.

ii. By this data set we have plotted a graph showing dry unit weight vs moisture content, which gives a curvilinear relationship between dry unit weight and moisture content.

iii. In the graph it is clearly seen that the highest dry unit weight is 17.4 kN/which means the corresponding water content (15.295%) is the optimum water/moisture content.

iv. Again, we plotted unit weight (without any void) vs water content. This gives almost a linear line and that line is above the previous curve. This line is known as zero air void line.

v. This means that the presence of any void decrease the unit weight of any soil sample of same specific gravity.

vi. Again, this graph tells us that unit weight increases with a certain limit of increasing water content and then gradually decreases with increasing water/moisture content.