THE COOPER UNION
Albert Nerken School of Engineering
Soil Mechanics Laboratory
Experiment No. 2 - Specific Gravity Determination
To determine the compressive strength of a cohesive soil sample.

 

1) "Soil Testing for Engineers" by T. W. Lambe - Chapter II.

2) "Engineering Properties of Soils and Their Measurements" 4th edition by Joseph E. Bowles; Experiment No. 7. 

3) A.S.T.M. Standards, 1978, Part 19; Designation D854-58. 

 

1) Volumetric flask (500 ml.).

2) Triple-beam balance (sensitive to 0.1 gm.).

3) Thermometer (sensitive to 0.10C.).

4) Electric oven.

5) Evaporating dish (250 ml.).

6) Vacuum pump.

7) Miscellaneous apparatus and reagents - spatulas, funnels, beakers, watch glasses, dessicator, acetone, ether, deaired - distilled water, etc.

 

A. GENERAL :

  1) Record number and weight of volumetric flask on data sheet. (If a magnetic stirrer is used, include the weight of the stirring bar). 

2) Thoroughly clean the flask inside and outside using a brush and soap and water if necessary. 

3) Dry the outside of the flask with a paper towel. 

4) Dry the inside of the flask in the following manner: 

 

a) Shake out as much water as possible. 

b) Rinse with acetone to dissolve remaining water. 

c) Shake out as much acetone as possible. 

d) Rinse with ether to dissolve remaining acetone and hold flask with neck down for approximately 10 minutes to allow ether vapor, which is heavier than air, to escape. 

  5) Carefully fill the flask with deaired-distilled water (If a magnetic stirrer is to be used, at this time, place the stirring bar in the flask with the water ), up to approximately 1 inch of the mark on the neck of the flask. 

6) Add the additional water with a pipette, carefully bringing the bottom of the meniscus, up to the calibration mark. 

7) Weigh the stopper, flask, water (and stirring bar) on a triplebeam balance to 0.10 gm. Make certain the outside of the flask is dry and there is no water above the mark on the inside of the neck. 

8) Record this weight on data sheet as Wfw

9) Insert the thermometer in the flask to the depth at which the thermometer is designed to be read. 

10) Record this temperature on the data sheet as T1

11) The procedure to be followed to determine the specific gravity of a soil sample will vary depending on whether the soil is granular (cohesionless) or cohesive. Section B is the procedure reccommended for granular or cohesionless soils and Section C is the procedure recommended for cohesive soils. 

 

B. For GRANULAR SOILS (COHESIONLESS) :

  1) Place an evaportating dish containing a sample of approximately 150 gm. in the electric oven, which has been set at 110oC., and dry to a constant weight. This may require from one to five or, six hours depending on a sample size, initial moisture content, and grain size distribution. 

2) Remove sample and cool to room temperature in a dessicator. 

3) Weigh this sample and dish immediately to 0.1 gm on the triplebeam balance, and record the weight on the data sheet. 

4) Add approximately 100 cc of deaired, distilled water (and stirring bar) to the volumetric flask. 

5) Using a wide mouth powder funnel and spatula, add the weighed soil sample to the volumetric flask. Perform this addition slowly, a spatula-full at a time, gently shaking the soil off the spatula and into the funnel.

 

6) Add additional distilled water to fill approximately 3/4 of the base of the flask. The 100 cc (approximately) of water in the flask in step B4 and the slow addition of the soil of step B5 procedures are intended to permit the soil grains to settle,more or less, individually and so minimize the amount of air brought into the water in the soil voids. If, on the other hand, the dry soil sample had been poured into a dry flask and water added subsequently, a considerable amount of air would be entrapped in the soil voids. 

7) Since a certain small amount of entrapped air will probably still exist in the soil voids, a procedure must be adopted to remove it. 

8) This entrapped air will be removed by boiling, produced by evacuating the flask using a high vacuum pump. 

9) Attach the vacuum line to the volumetric flask; open the valve on the vacuum line slowly, to prevent a sudden rise of the soil and water level above the calibration mark on the neck of the flask or possibly into the vacuum line, resulting in a loss of part of the weighed soil sample. This rise of the water surface is caused by the boiling and the increased volume of the entrapped air in this pressure-reduced atmosphere. Continue to apply the full vacuum for ten minutes. 

10) Roll the flask gently during the application of the vacuum in order to aid in the elimination of the entrapped air.  

Note: Step 10 is not needed if a magnetic stirrer is used. 

  11) To test the completeness of the air removal, gently disconnect the vacuum line and mark the position of the water level on the flask with a wax pencil. 

12) Reapply the full vacuum as explained in step B9. 

13) Note if a rise of the water sur occurs; if it does, entrapped air is still present, boiling must be continued, and steps Bll and B12 repeated. 

14) When evacuation of the entrapped air is complete, add sufficient deaired-distilled water to bring the water to within an inch of the calibration mark on the neck of the flask. 

15) Re-apply the vacuum as in step B9. This is done primarily as a check on steps B11 - B13. It will be quite a good check since the cross-sectional area of the neck is much smal@er than the portion of the base the water level occupied in step B11 - B13 so that any surface rise will be exaggerated in this small cross-sectional area. If a surface rise, occurs repeat steps B9 - B12, but this time only apply the vacuum for 5 minutes. 

16) Add sufficient distilled water with a pipette to bring the bottom of the meniscus up to the calibrated mark. Be certain to observe the warning step of General-7. 

17) Weigh the flask, stopper, soil, water (and stirring bar) to 0.1 gm. on the triple-beam balance. 

18) Record this weight on the data sheet as Wfws

19) Insert the thermometer in the flask and determine the temperature of soil and water mixture to 0.1oC. 

20) Record this temperature on data sheet at Tx

 @/TD>

C. For COHESIVE SOILS :

  1) Secure a sample of the soil, which, regardless of its present moisture content, will contain approximately 50-75 grams of oven-dry soil grains. 

2) Place the soil in an evaporating dish and add 100-150 cc. of distilled water to work the soil into a thin slurry with a spatula.  [/P>

3) Transfer this soil-water mixture to the volumetric flask by means of a funnel. Use a wash bottle or syringe to clean the final particles from the evaporating dish to the funnel and from the funnel to the volumetric flask.  

4) Add sufficient distilled water to fill approximately 3/4 of the base of the flask and the stirring bar. 

5) Attach the volumetric flask to the vacuum line and evacuate the entrapped air for at least 10 minutes. Observe the precaution of Step B-9. 

6) Steps B-10 through B-20. 

7) Clean and weigh a 1000 ml. beaker and watch glass on t/e triplebeam balance to 0.1 gm. 

8) Record this weight on the data sheet. 

9) Transfer all of the contents of the flask to the beaker being careful not to lose a single drop. 

10)Use a wash bottle or syringe to wash the remaining soil grains from the flask and add this wash water and soil to the water and soil already in the beaker. Work with a minimum amount of water since every bit used must be evaporated in he next step. 

Note: Remove stirring bar from beaker before placing it in the oven, if a magnetic stirrer was used. 

  COMPUTATIONS:
 

1) If Aemperature T1 of weight Wfw, from Step 10 General is not equal to temperature Tx of weight Wfws, then Wfw must be converted to a@ equivalent weight at temperature Tx

2) Compute this equivalent weight by using Formula No. 1 on the data sheet and a table of unit weights of water. 

3) Using Formula No. 2 compute the specific gravity of the soil at temperature Tx.enbsp;

4) Using Formulas No. 3 & 4 compute the specific gravity of the soil at 20oC and at 4oC. 

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