|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.
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:
|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 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.
|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
12) Reapply the full vacuum as explained in step B9.
13) Note if a rise of the water surface 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 smaller than the portion of the base the water level occupied in step B11 - B13 so that any surface rise will be exaggerated in this samll crosssectional area. If a surface rise occurs repeat steps B9 - B12, but this time only apply 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.
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
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.
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 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 B-9.
6) Steps B-10 through B-20.
7) Clean and weigh a 1000 ml. beaker and watch glass on the 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 the next step.
|11) Place the beaker in the oven
at 110oC; cover with the watch glass and dry
to constant weight. The reason for the watch glass is to
prevent the loss of some of the soil as the last few
drops of water in the beaker splatter about while
12) Remove the beaker from the oven and cool to room temperature in a dessicator.
13) Weigh the beaker, watch glass, and soil to 0.1 gm. on the triple beam balance. Make this weighing immediately upon removal from the dessicator so that no moisture is absorbed from the atmosphere.
14) Record this weight on the data sheet.
15) Compute the weight of the oven-dry soil and record on data sheet at Ws.