THE COOPER UNION
Albert Nerken School of Engineering
Soil Mechanics Laboratory
Experiment No. 5 - Compaction Test
To determine the relationships between moisture contents and soil densities under a standard method of compaction and also the effects of these moisture contents on the ability of the soil to resist penetration.

 

REFERENCES:

1) 'Soil Testing for Engineers' by T. W. Lambe; Chapter V.

2) "Engineering Properties of Soils and Their Measurements", 4th ed. by Joseph E. Bowles; Experiment No. 9.

3) A.S.T.M. Standards, 1978, Part 19; Designation D698-70, D1557-70.

APPARATUS AND REAGENTS:
 

1) Compaction mold of 1/30 cu. ft. volume and collar.

2) 5-1/2 pound hammer with 12" drop.

3) Electronic top loading balance sensitive to 0.01 gm.

4) Balance sensitive to 0.1 gm. and with a capacity of 10,000 gm.

5) Electric oven.

6) 1.375" diameter loading block.

7) Testing machine of 5000 pound capacity with a rate of strain controlled to 0.06"/min.

8) Dial indicator with 0.001" sensitivity.

9) Watch glasses, straightedge, U. S. #4 sieve, micrometer, water sprayer, compressed air supply and mixing pan.

EXPERIMENTAL PROCEDURE
  1) Take a sample of approximately 3000 gm. of air dry soil passing the U.S. No. 4 sieve and place in a mixing pan.

2) Weigh the empty compaction mold and base to 1.0 gm.

3) Record this weight in Table 1 and Table 2.

4) Deposit a two-to-three inch layer of the soil in the mold.

5) Place the mold on the surface of the compacting box.

6) Compact the layer of soil in the mold by applying the compacting hammer, using twenty-five free falls uniformly distributed over the surface area.

Note: Record weight of hammer, height of fall of hammer, number of layers and number of blows per layer in Table 1.

  7) Repeat the procedure for a second and third layer. Be certain that sufficient soil is used for the third layer so that when compaction is completed the soil surface extends slightly above the rim of the mold. Also, each compacted layer should be the same thickness.

8) Force a spatula between the inside face of the collar and the soil and work the spatula around the circumference of the collar, separating the soil from the collar.

9) Remove the collar from the mold by, first, rotating the collar to break any remaining bond between collar and soil and, then, lifting the collar.

10) Trim the soil extending above the rim of the mold by applying the straightedge in a series of short, scraping operations, beginning at the vertical axis of the mold and moving to the outer rim.

11) Brush all loose soil particles from the outside of the mold, weigh the mold and soil to 1.0 gm., and record this weight in Table 2.

12) Center the 1.375 inch diameter loading block on the surface of the soil.

13) Place the mold in the compression loading zone of the testing machine.

14) Set the dial indicator to measure the penetration of the loading block.

15) Apply the load to the loading block at a rate of strain of 0.06 in/min.

16) Record in Table 3, the loads in pounds at penetrations of 0.025, 0.050, 0.075, 0.100, 0.200, 0.300, 0.400 and 0.500 inches.

17) Extrude the soil from the mold using the hydraulic sample extruder and, from the center of the soil, obtain a moisture content sample and place in a weighed crystallizing dish and watch glass.

18) Weigh soil and container to 0.01 gm., record in Table 2 and. place in the electric oven for drying.

19) Steps 4-18 constitute one trial. Additional trials, possibly four or five, will be necessary to secure sufficent data to properly establish the desired relationships.

20) To perform each new trial, break up the remaining soil from the mold so that it passes the U. S. No. 4 sieve and mix it with the original soil in the mixing pan. Increase the moisture content of the soil by two-to-three per cent by uniformly spraying water on the soil and mixing with a trowel, and repeat steps 4 to 18.

21) The last trial will have been completed when the total weight of mold, soil, and water, which has been increasing in each successive trial, first exhibits a decrease.

22) Remove the dried samples (step 18) from the oven, weigh to 0.01 gm. and record in Table 2.

COMPUTATIONS:
 

1) From the data of steps 18 and 22 compute the moisture contents for each trial and record in Table 2.

2) Using the loads recorded in step 16 and the contact area of the loading block compute the contact stresses in p.s.i. and record them in Table 3.

3) Compute the total and dry unit weights for each of the trials performed, and record them in Table 2.

4) Compute the porosity for each of the trials performed using Formula 1 and the dry unit weights of the previous step, and record the values in Table 2.

5) Compute the theoretical dry unit weights, using Formula 2 for each of the moisture contents of Computations - 1, for a saturation of 100% and for a saturation of 80%.

GRAPHS:
 

1) Orient a sheet of Cartesian coordinate paper with the 17"-side, vertical, use approximately nine inches for the plots of 2,3 and 4. Use the lower eight inches for the plot of 6.

2) Plot the total and dry unit weights (Computations-3) as ordinate vs. moisture contents (Computations-1) as abscissa.

3) Plot the porosity (Computations-4) as ordinate vs. moisture content as abscissa.

4) Plot the theoretical dry unit weights for both 100% saturation and 80% saturation (Computations-5) as ordinate, using the same scales as used for Graphs-2, vs. moisture content, as abscissa.

5) Plot on another sheet of Cartesian coordinate paper, the contact stresses (Computations-2) for each trial as ordinate vs.the penetration in inches as abscissa. If these curves overlap to the extent that confusion occurs, then plot the curves of no more than one or two trials on a single sheet. Perform the following graphical construction on each curve.

 

a) If the curve exhibits a curve of continually decreasing slope, i.e., convex upward, select the value of stress at 0.100 in. and 0.200 in. penetration.

b) Divide the stress for 0.100 in. by 1000 and divide the stress for 0.200 in. by 1500 and multiply both by 100. These two values are California Bearing Ratios (CBR's) and should be in agreement by about 5% of CBR units. If the agreement is not good, this run should be repeated. If the agreement is good, then the CBR for the 0.100 in. penetration is selected as the CBR for this run.

c) If the curve exhibits a reverse character beginning with an increasing slope, passing through a contraflexure point, and then into a decreasing slope, i.e., beginning convex downward and changing, through a contraflexure point, to convex upward, then the following procedure must be followed:

 

Select the contraflexture point and draw a tangent through it extending back through the zero ordinate (stress) line. This point becomes the Corrected Zero.

 

d) Using this Corrected Zero, lay off penetration of 0.100 in. and 0.200 in. and repeat above using these "corrected Penetrations".

 

6) Plot CBR values as ordinate vs. moisture content as abscissa.

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