Specific Gravity of Specific Gravity of SoilsSoils

Specific GravitySpecific Gravity

• This number indicates how much This number indicates how much heavier/lighter a material is than heavier/lighter a material is than water.water.

• In soils, SG refers to the mass of solid In soils, SG refers to the mass of solid matter of a given soil sample as matter of a given soil sample as compared to an equal volume of compared to an equal volume of water.water.

Specific GravitySpecific Gravity

• For example: A material with SG of 2 is twice as For example: A material with SG of 2 is twice as heavy as water (2x 62.4 lbs/ftheavy as water (2x 62.4 lbs/ft3 3 ) = 124.8 lbs/ft) = 124.8 lbs/ft33

• Equation Form: SG = MEquation Form: SG = Mss/V/VssΥΥwaterwater

• We use the SG of soils to calculate other We use the SG of soils to calculate other engineering properties like the volume of solids in engineering properties like the volume of solids in a sample….a sample….

• This leads to the phase diagram (like last class) This leads to the phase diagram (like last class) and…and…– S, S, nn, , ee

Specific GravitySpecific Gravity

1 ft3

Soil Solids Water

W = 187.2 lbs W= 62.4 lbs

SG= 187.2/62.4 = 3.0

1 ft3

General Ranges of SG General Ranges of SG For SoilsFor Soils

• SandSand 2.63 – 2.672.63 – 2.67• SiltSilt 2.65-2.72.65-2.7• Clay & Silty ClayClay & Silty Clay 2.67-2.92.67-2.9• Organic SoilsOrganic Soils <2.0<2.0

Procedures For Specific Procedures For Specific Gravity LabGravity LabASTM D 854ASTM D 854

See Chapter 3, Page 55 For Your Data SheetSee Chapter 3, Page 55 For Your Data Sheet

APPARATUS:APPARATUS:

500 ml flask500 ml flask

Ice Ice

Heating PlateHeating Plate

Thermometer CThermometer C

Scale (readability .1g)Scale (readability .1g)

Evaporating DishEvaporating Dish

Distilled WaterDistilled Water

Procedures (Method B)Procedures (Method B)

1.1. Dry specimens to constant mass in oven at 110 Dry specimens to constant mass in oven at 110 C.C.

2.2. Select a 500 ml flask and record mass (g)Select a 500 ml flask and record mass (g)

3.3. Fill with distilled water to 500 ml line and Fill with distilled water to 500 ml line and record mass (g)record mass (g)

4.4. Record temperature of water in degrees Record temperature of water in degrees Celsius (TCelsius (T11).).

5.5. Pour 2/3 of water back into distilled containerPour 2/3 of water back into distilled container

8.8. Weigh out 100g of sandy soil and transfer to flask Weigh out 100g of sandy soil and transfer to flask

9.9. Add distilled to 2/3 full and boil gently for 10 minutesAdd distilled to 2/3 full and boil gently for 10 minutes

10.10. Bring temperature back to TBring temperature back to T1 1 using cooling bucket using cooling bucket w/ice.w/ice.

11.11. Add distilled to 500 ml line and record mass (g)Add distilled to 500 ml line and record mass (g)

12.12. Record mass of evaporating dish (g)Record mass of evaporating dish (g)

13.13. Pour ALL sample into dish and dry to constant weight.Pour ALL sample into dish and dry to constant weight.

14.14. Record mass of oven dried dish/sample.Record mass of oven dried dish/sample.

15.15. Complete calculations on data sheet, including Complete calculations on data sheet, including correction for temperature …. SG is always reported correction for temperature …. SG is always reported at 20 C.at 20 C.

16.16. See page 44 for correction factors.See page 44 for correction factors.