SOIL MECH 3 Specific Gravity

Laboratory Exercise No. 3 Determination of the Specific Gravity of Soil

Introduction: Applicable ASTM Standard ASTM D854: Standard Test Method for Specific Gravity of Soils Purpose of Measurement Specific Gravity of solid soils is used for performing weight – volume calculations in soils. Definition and Theory Specific gravity of soil solids, GS, is the mass density of mineral solids in soil normalizes relative to the mass density of water. Alternatively, it can be viewed as the mass of a given volume of soil solids normalizes relative mass of an equivalent volume of water. Specific gravity is typically expressed using three significant figures. For sands, GS is often assumed to be 2.65 because this is the specific gravity of quartz. Since the mineralogy of clay is more variable, G S for clay is more variable, and is often assumed to be somewhere between 2.70 and 2.80 depending on mineralogy. Equipment and Materials: The following equipment and materials are required for specific gravity of soil solids measurement:        

Oven – dried soil sample Scale (capable of measuring to the nearest 0.01 grams) Pycnometer or Volumetric flask Distilled or demineralized water Squeeze bottle Thermometer (capable of reading to the nearest 0.5°C) Funnel Stopper and tubing for connecting flask to vacuum supply



Vacuum supply (capable of achieving a gauge vacuum of 660 mm Hg or 12.8 psi.)

Procedure: The procedure presented herein is consisted with ASTM D854 Test Method A, where an oven- dried specimen of soil is used. The specific gravity calculation is based on three measurements. 1.) Mass of the flask filled with distilled water to the etch mark, Ma; 2.) Mass of the flask filled with water and soil to the etch mark, Mb; 3.) Mass of the dry soil, Mo. Specific gravity of foil solids, Gs, is calculated based on these three parameters. _________________________ Since the density of water is temperature–dependent, a temperature correction factor, K, may be applied to report GS at a standard temperature of 20

° C. The temperature-corrected G , G S s20

is expressed as:

Temperature Correction Factor, K, for reporting Gs20 Temperature

Correction Factor

(°C) 17 18 19 20 21 22

K 1.0006 1.0004 1.0002 1.0000 0.9998 0.9996

23 24

0.9993 0.9991

The procedure for performing the specific gravity measurement is as follows: 1) 2) 3) 4) 5)

Weigh approximately 60 grams of dry soil to obtain Mo. Fill the flask to the etch line with distilled or demineralized water to obtain Ma. Pour half of the water out of the flask and place the soil in the flask with a funnel. Was the soil down the inside neck of the flask. Connect the flask to the vacuum source with a hose and stopper and apply vacuum for

30 minutes, occasionally agitating the mixture. 6) Fill the flask to the etch with distilled water and weigh to obtain Mb. 7) Record the water temperature in the flask and use Table to obtain K.

Figures:

Figure 3.1 Obtaining of the oven-dried soil sample.

Figure 3.2 Weighing of the can.

Figure 3.4 Sieving of the crushed and fragmented soil sample.

Figure 3.5 Pouring of water to the pycnometer.

Figure 3.3 Weighing of the pycnometer.

Figure 1.6 Weighing of the pycnometer with water and soil sample.

Data:

TABLE 3.1 Determination no. Weight of pycnometer & water + soil, (W1, g) Temperature ˚C

A1

A2

A3

354.25

359.78

358.17

28

28

28

Weight of pycnometer + water (W2, g)

339.83

339.83

339.83

Weight of Dish + Dry soil, g Weight of Dish, g

121.96 93.44

127.16 93.44

123.83 93.44

Weight of dry soil, Ws g Specific gravity of water at T, Gt Specific gravity of soil, Gs

28.52 0.99802741 7 2.01870510 2

33.72 0.9980274 2 2.4439712 8

30.39 0.9980274 2 2.5170168 6

Computations:

Results and Discussion:

From the experiment, the computed specific gravities for trials A1, A2 and A3 are 2.02, 2.44 and 2.52, respectively.